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doc. Ing. Josef Dobeš, CSc.

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Efficient Time-Domain Analysis of Complicated RF Circuits with the Use of Higher Interpolation Orders

  • Authors: doc. Ing. Josef Dobeš, CSc.,
  • Publication: 2023 IEEE Radio and Antenna Days of the Indian Ocean (RADIO). Institute of Electrical and Electronics Engineers Inc., 2023. p. 1-2. ISBN 9798350347913.
  • Year: 2023
  • DOI: 10.1109/RADIO58424.2023.10146104
  • Link: https://doi.org/10.1109/RADIO58424.2023.10146104
  • Department: Department of Radioelectronics
  • Annotation:
    Nowadays, practically all the circuit simulators have the implemented algorithms for numerical solving differential-algebraic equations constrained by the maximum order of used interpolation polynomials of six. In the paper, it is suggested that a usage of higher interpolation orders can improve the resulting efficiency of the algorithm considerably without endangering its numerical stability. Using the orders of interpolation polynomials up to ten is demonstrated on a sophisticated distributed microwave oscillator.

Parallelized A Posteriori Multiobjective Optimization in RF Design

  • DOI: 10.3390/electronics12102343
  • Link: https://doi.org/10.3390/electronics12102343
  • Department: Department of Radioelectronics
  • Annotation:
    A posteriori multiobjective optimization relies on a series of mutually independent single-objective optimization subproblems, which can be run in parallel, thus making full use of a multiprocessor (or multicore) computer. This paper presents a parallel process launching scheme, such that practically no computing capacity gets wasted. This is achieved using standard Windows API kernel objects for process synchronization of the semaphore and mutex types. The algorithm used was further modified to inherently generate the desired Pareto front in the convenient form of a contour plot.

Comparing the L&S and L-Band Antenna Low-Noise Amplifiers Designed by Multi-Objective Optimization

  • Authors: doc. Ing. Josef Dobeš, CSc., Míchal, J.
  • Publication: Proceedings of 2022 IEEE International Conference on IC Design and Technology. Institute of Electrical and Electronics Engineers Inc., 2022. p. 65-68. ISSN 2691-0462. ISBN 9781665459013.
  • Year: 2022
  • DOI: 10.1109/ICICDT56182.2022.9933072
  • Link: https://doi.org/10.1109/ICICDT56182.2022.9933072
  • Department: Department of Radioelectronics
  • Annotation:
    In the paper, it is demonstrated that the optimal properties of low-noise amplifiers in radio-frequency design can be achieved by the multi-objective optimization, which enables a suitable trade-off between the transducer power gain and noise figure in the form obtained on Pareto front. First, a modification of a classical multi-objective method is suggested that enables asymptotically uniform coverage of the Pareto front. Second, an application of the modified method is demonstrated in the design of the antenna low-noise amplifier for a satellite-navigation receiver. The efficiency of the algorithm is proved on its use for L- and L&S-band low-noise amplifiers, where the resulting amplification and noise-figure correspond to expected optima.

Deep Learning Neural Network Algorithm for Computation of SPICE Transient Simulation of Nonlinear Time Dependent Circuits

  • DOI: 10.3390/electronics11010015
  • Link: https://doi.org/10.3390/electronics11010015
  • Department: Department of Radioelectronics
  • Annotation:
    In this paper, a special method based on the neural network is presented, which is conveniently used to precompute the steps of numerical integration. This method approximates the behaviour of the numerical integrator with respect to the local truncation error. In other words, it allows the precomputation of the individual steps in such a way that they do not need to be estimated by an algorithm but can be directly estimated by a neural network. Experimental tests were performed on a series of electrical circuits with different component parameters. The method was tested for two integration methods implemented in the simulation program SPICE (Trapez and Gear). For each type of circuit, a custom network was trained. Experimental simulations showed that for well-defined problems with a sufficiently trained network, {the method allows in most cases reducing} the total number of iteration steps performed by the algorithm during the simulation computation. Applications of this method, drawbacks, and possible further optimizations are also discussed.

Design of Dual-Band Antenna Low-Noise Preamplifiers by Multi-Objective Optimization and Its Verification with More Precise Measurement Method

  • Authors: doc. Ing. Josef Dobeš, CSc., Míchal, J.
  • Publication: 2022 Asia-Pacific Microwave Conference Proceedings. Tokyo: IEICE, Institute of Electronics, Information and Communication Engineers, 2022. p. 743-745. ISBN 978-4-902339-56-7.
  • Year: 2022
  • Department: Department of Radioelectronics
  • Annotation:
    The paper demonstrates a practical application of multi-objective optimization in radio-frequency design to achieve a suitable trade-off between the noise figure and transducer power gain of low-noise amplifiers. A variation of the standard optimization method providing asymptotically uniform coverage of the Pareto front is presented. Its usefulness is demonstrated in the design of a dual-band antenna low-noise preamplifier for satellite navigation. Obtained design goals have been verified by measurement. The precision of standard noise factor measurement method (Y-factor method with calibration stage) has been improved by partial correction of the dependence of transducer gain on output impedance of noise source.

Quantifying Measurement Uncertainty of Microwave Amplifiers with Very Low Noise Figures Designed by Multi-Objective Optimization

  • Authors: doc. Ing. Josef Dobeš, CSc.,
  • Publication: International Conference on Electronics, Information, and Communication 2022. Piscataway (New Jersey): IEEE, 2022. p. 597-600. ISSN 2767-7699. ISBN 978-1-6654-0934-6.
  • Year: 2022
  • DOI: 10.1109/ICEIC54506.2022.9748767
  • Link: https://doi.org/10.1109/ICEIC54506.2022.9748767
  • Department: Department of Radioelectronics
  • Annotation:
    Best properties of low noise amplifiers in RF design can only be achieved by the multi-objective optimization, which enables a compromise between the transducer power gain and noise figure in some shape of Pareto front. However, as the final circuit constructed in this way is not fully matched at the output, measuring the amplifier - unmatched neither to transducer power gain nor to noise figure - is quite complicated, especially in the case of the very low noise figures. Although we have recently suggested a measurement method for such circuits, it can be principally affected by the tolerances of the equipment. In this paper, we propose quite accurate estimation of these tolerances.

An Accurate and Efficient Computation of Poles and Zeros of Transfer Functions for Large Scale Analog Circuits and Digital Filters

  • DOI: 10.1007/978-981-15-9209-6_8
  • Link: https://doi.org/10.1007/978-981-15-9209-6_8
  • Department: Department of Radioelectronics
  • Annotation:
    The poles and zeros of a circuit transfer function can be efficiently computed solving the generalized eigenvalue problem, which could be transformed into the standard eigenvalue problem to be solved by a suitably modified QR algorithm. In this way, the poles and zeros can be obtained for any linear circuit or a nonlinear circuit linearized at an operating point (using the Laplace transform), or for any digital filter (using the Z transform). Both the reduction of the generalized eigenvalue problem to the standard form and the iterative procedures of the QR algorithm are very sensitive to the numerical precision of all calculations. The numerical accuracy is especially critical for the two kinds of circuits: the microwave circuits characterized by huge differences among the magnitudes of the poles and zeros, and the large scale circuits, where the errors of poles and zeros are increased by the extreme number of arithmetic operations and frequent multiplicity of the poles and zeros as well. In this chapter, two illustrative examples of the reduction of the general eigenvalue problem (the first for analog and the second for digital circuit) and using the QR algorithm are shown first. After that, four circuits of various sizes are analyzed: simpler microwave low noise amplifier, larger power operational amplifier, more complex example with a 272 integrated operational amplifier, and the most difficult analysis of a distributed oscillator. A meticulous comparison of the obtained results shows that a usage of newly implemented 128-bit arithmetics in GNU Fortran or C compilers with partial pivoting can assure both efficient and enough accurate procedures for computing the poles and zeros of the circuit transfer function.

An Algorithm to Solve Systems of Nonlinear Differential-Algebraic Equations With Extraordinary Efficiency Even at High Demanded Precisions

  • Authors: doc. Ing. Josef Dobeš, CSc., Černý, D.
  • Publication: Proc. of the 2021 International Conference on Computational Science and Computational Intelligence (CSCI’21). Los Alamitos: IEEE Computer Society, 2021. p. 1-5. ISBN 978-1-60132-515-0.
  • Year: 2021
  • Department: Department of Radioelectronics
  • Annotation:
    There are many situations when systems of nonlinear differential algebraic equations need to be solved with extraordinary precision. A steady-state analysis (determining the steady-state period of a system after a transient) is a typical case because a vector of unknown variables should be exactly the same after a numerical integration on the period-long interval. Therefore, we need to develop such kinds of numerical algorithms that are computationally effective, even at very high requirements on the accuracy of the results. In the paper, an efficient and reliable algorithm for solving systems of algebraic-differential nonlinear equations is characterized first. Unlike in other cases, the procedure is based on a sophisticated arrangement of the Newton interpolation polynomial (i.e., not the Lagrange one). This feature provides greater flexibility in rapidly changing interpolation step sizes and orders during numerical integration. At the end of the paper, two complicated examples are presented to demonstrate that the algorithm's computational requirement is quite low, even at very high demands on the accuracy of results.

Algorithm for Estimating Error of Symbolic Simplification

  • Authors: Kolka, Z., Biolkova, V., doc. Ing. Josef Dobeš, CSc., Horak, M.
  • Publication: 2020 2nd International Conference on Computer Science, Communication and Network Security (CSCNS2020). MATEC, 2020. p. 1-5. 2. ISSN 2261-236X.
  • Year: 2020
  • DOI: 10.1051/matecconf/202133606023
  • Link: https://doi.org/10.1051/matecconf/202133606023
  • Department: Department of Radioelectronics
  • Annotation:
    The paper deals with an improved algorithm for estimating errors during approximate symbolic analysis. A linear system can be solved symbolically. However, the size of the resulting formula grows exponentially with the matrix size. The approximate symbolic analysis omits insignificant terms of the exact formula to decrease its size, which, on the other hand, limits the validity of the approximate result. The proposed algorithm estimates, in a computationally feasible way, the approximation error over a region of system parameters. This makes it possible to maintain the validity of the results even if the tolerances of the system parameters are defined. The method is based on the first-order approximation of error functions. The algorithm is demonstrated using the SNAP symbolic analyzer, which has been developed by the authors.

Analysis and Measurement of IM3 Anomalies in Single- and Double-Band Low-Noise Amplifiers

  • DOI: 10.1109/RFM50841.2020.9344764
  • Link: https://doi.org/10.1109/RFM50841.2020.9344764
  • Department: Department of Radioelectronics
  • Annotation:
    In the paper, a theoretical background of the unexpected third-order intermodulation power decrease at some levels of input power is discussed first. This anomaly can be partially explained by various physical phenomena, RF stress, e.g., as shown in the state-of-the-art review in the paper. Then a simulation of the IM3 dependency is performed, including a comparison between the computed and measured IP3 points. Finally the single- and double-band low-noise amplifiers designed by multi-objective optimization are measured from this point of view, and a frequency dependence of the IM3 anomalies is demonstrated. An improved optimization method is defined too.

GPU Accelerated Nonlinear Electronic Circuits Solver for Transient Simulation of Systems with Large Number of Components

  • DOI: 10.3390/electronics9111819
  • Link: https://doi.org/10.3390/electronics9111819
  • Department: Department of Radioelectronics
  • Annotation:
    GPU cards have been used for scientific calculations for many years. Despite their ever-increasing performance, there are cases where they may still have problems. This article addresses possible performance and memory issues and their solutions that may occur during GPU calculations of iterative algorithms. Specifically, the article focuses on the optimization of transient simulation of extra-large highly nonlinear time-dependent circuits in SPICE-like electronic circuit simulator core enhanced with NVIDIA/CUDA (Compute Unified Device Architecture) interface and iterative Krylov Subspace methods with emphasis on improved accuracy. The article presents procedures for solving problems that may occur during this integration and negatively affect either the simulation speed or the accuracy of the calculation. Finally, a comparison of the implementation of an iterative calculation procedure with the use of GPU cards, calculation by the direct method and calculation on the CPU only is presented.

An Accurate and Efficient Computation of Zeros and Poles of Transfer Function for Large Scale Circuits

  • Department: Department of Radioelectronics
  • Annotation:
    The zeros and poles of a circuit transfer function are computed solving a general eigenvalue problem, which could be transformed to a standard eigenvalue task to be solved by a suitably modified QR algorithm. Both reduction of the general eigenvalue problem to the standard form and the iterative procedures of the QR algorithm are very sensitive to the numerical precision of all calculations. The numerical accuracy is especially critical for two kinds of circuits: the microwave ones characterized by huge differences among magnitudes of the zeros and poles, and the large scale circuits, where the errors of the zeros and poles are increased by an extreme number of arithmetic operations. In the paper, an illustrative example of the reduction of the general eigenvalue problem and using the QR algorithm is shown first. After that, three circuits of various sizes are analyzed: simpler microwave low noise amplifier, larger power operational amplifier, and the most complex example with a 272 integrated operational amplifier. A meticulous comparison of obtained results shows that a usage of newly implemented 128-bit arithmetics in GNU Fortran or C compilers with partial pivoting can assure both efficient and enough accurate procedures for computing the zeros and poles.

Chua’s Table as a Tool for Constructing Dual Networks

  • Authors: Biolek, D., Vavra, J., Biolek, Z., Kolka, Z., Biolkova, V., doc. Ing. Josef Dobeš, CSc.,
  • Publication: Proceedings of the 2019 IEEE Asia Pacific Conference on Circuits and Systems. Piscataway, NJ: IEEE, 2019. p. 145-148. ISBN 978-1-7281-2940-2.
  • Year: 2019
  • Department: Department of Radioelectronics
  • Annotation:
    Chua’s table is presented as a tool for transforming circuits, compounded from nonlinear higher-order elements, into their dual mutations. The transformation is carried out via three assorted operations in Chua’s table, denoted as FLIP, SHIFT, and MOVE. It is shown that their combination can yield dual circuits with interesting parameters, and that the dual circuits can be used for efficient modeling or hardware emulation of the original circuits, for example the circuits containing memristors.

Improved MESFET/pHEMT Models and Their Comprehensive Comparison With Standard Ones

  • Authors: doc. Ing. Josef Dobeš, CSc., Grábner, M., Biolková, V.
  • Publication: Proceedings of the 2019 IEEE Asia Pacific Conference on Circuits and Systems. Piscataway, NJ: IEEE, 2019. p. 149-152. ISBN 978-1-7281-2940-2.
  • Year: 2019
  • Department: Department of Radioelectronics
  • Annotation:
    In the paper, we suggest several new updates to the equations that ordinarily describe the MESFETs and pHEMTs in both DC and time domains. We have composed some novel forms of the equations that are especially convenient for accurate describing transconductance voltage dependences, which is important for realistic modeling the low noise amplifiers with pHEMTs including calculations of their IP3 points. In other words, the attention is not only directed to the precision of the equation themselves, but also to the accuracy of the derivatives of them with respect to both gate-source and gate-drain voltages (up to the third order). The paper contains comprehensive comparisons of our recently updated models with our previous one and many others; two pHEMTs have been used for comparisons: the first working from 1 GHz up to 18 GHz, and the second operating at the frequencies greater than 100 GHz. Both DC characteristics and high-frequency s-parameters have been compared, and the comparisons show that the precision of our model modifications is at least comparable with the model like TriQuint ones. (And they seem even better in modeling input reflection coefficient, e.g.)

A Novel L-Probe Proximity Fed Patch Antenna with Parasitic Patch and Its Utilization in Antenna Arrays

  • DOI: 10.1088/1757-899X/321/1/012010
  • Link: https://doi.org/10.1088/1757-899X/321/1/012010
  • Department: Department of Radioelectronics
  • Annotation:
    An analysis of the L-probe fed patch antenna with an extraordinary parasitic patch is described. The element of the antenna is fed by the L-probe partially implemented in PCB. An excellent impedance matching is obtained (<-26 dB in the design frequency band 4.4-5 GHz). The radiation characteristics are also very good (gain > 10 dBi). For the numerical analyses, the Full Wave-CST Microwave Studio software was used in both frequency and time domains, and a very good agreement between the Time Domain Solver (TDS) and Frequency Domain Solver (FDS) was obtained. Real antenna samples have been created and measured as well as eight-element antenna arrays designed by the Dolph-Chebyshev method.

Accurate diode behavioral model with reverse recovery

  • Authors: Banáš, S., Divín, J., doc. Ing. Josef Dobeš, CSc., Paňko, V.
  • Publication: Solid-State Electronics. 2018, 139 31-38. ISSN 0038-1101.
  • Year: 2018
  • DOI: 10.1016/j.sse.2017.10.034
  • Link: https://doi.org/10.1016/j.sse.2017.10.034
  • Department: Department of Radioelectronics
  • Annotation:
    This paper deals with the comprehensive behavioral model of p-n junction diode containing reverse recovery effect, applicable to all standard SPICE simulators supporting Verilog-A language. The model has been successfully used in several production designs, which require its full complexity, robustness and set of tuning parameters comparable with standard compact SPICE diode model. The model is like standard compact model scalable with area and temperature and can be used as a stand-alone diode or as a part of more complex device macro-model, e.g. LDMOS, JFET, bipolar transistor. The paper briefly presents the state of the art followed by the chapter describing the model development and achieved solutions. During precise model verification some of them were found non-robust or poorly converging and replaced by more robust solutions, demonstrated in the paper. The measurement results of different technologies and different devices compared with a simulation using the new behavioral model are presented as the model validation. The comparison of model validation in time and frequency domains demonstrates that the implemented reverse recovery effect with correctly extracted parameters improves the model simulation results not only in switching from ON to OFF state, which is often published, but also its impedance/admittance frequency dependency in GHz range. Finally the model parameter extraction and the comparison with SPICE compact models containing reverse recovery effect is presented.

Accurate Semisymbolic Analysis With Usage of 128-bit Arithmetics

  • Authors: doc. Ing. Josef Dobeš, CSc., Míchal, J., Banáš, S.
  • Publication: Conference Proceedings of 2018 IEEE Radio and Antenna Days of the Indian Ocean (RADIO). New Jersey: IEEE, 2018. ISBN 978-99949-0-470-9.
  • Year: 2018
  • DOI: 10.23919/RADIO.2018.8572443
  • Link: https://doi.org/10.23919/RADIO.2018.8572443
  • Department: Department of Radioelectronics
  • Annotation:
    The semisymbolic analysis generally requires meticulous algorithms from the point of view of accuracy of resulting poles and zeros, especially in the case of huge differences among their absolute values. In the paper, an optimal pivoting strategy is suggested for the algorithm which reduces general eigenvalue problem to the standard one in the case of both full- and sparse-matrix procedures. Using the pivoting, the precision of the poles and zeros increases considerably. However, it is still insufficient for a number of tasks, especially for radio frequency circuits where the poles and zeros are spread over many decades of magnitudes. As contemporary compilers of C++ and Fortran languages have built-in quad precision libraries, it is possible to further enhance the semisymbolic-analysis accuracy using this 128-bit arithmetics.

Anomalous Phenomena in Ultra High Voltage JFET Channel Pinching

  • Authors: Banáš, S., doc. Ing. Josef Dobeš, CSc., Paňko, V.
  • Publication: 2018 28th International Conference Radioelektronika. IEEE (Institute of Electrical and Electronics Engineers), 2018. p. 1-4. ISBN 978-1-5386-2485-2.
  • Year: 2018
  • DOI: 10.1109/RADIOELEK.2018.8376349
  • Link: https://doi.org/10.1109/RADIOELEK.2018.8376349
  • Department: Department of Radioelectronics
  • Annotation:
    The paper deals with challenges in the modeling of high voltage JFET. As the most important, the effect of pinch-off voltage and related issues are discussed here. The pinch-off voltage in the traditional SPICE compact JFET model is only considered as a drop in the drain-source current, while other phenomena, such as capacitance sharp drop, or punch-through between gate and substrate are completely ignored. The traditional compact JFET model does not even consider the gate as isolated from substrate. In this paper, an implementation of a dual-gate JFET model is discussed with a special emphasis on pinch-off voltage and related effects.

Composing Scalable Solver for Simulation of Electronic Circuits in SPICE

  • Authors: Černý, D., doc. Ing. Josef Dobeš, CSc.,
  • Publication: Proceedings of the 2018 International Conference on Intelligent & Innovative Computing Applications (ICONIC). New Jersey: IEEE, 2018. p. 420-424. ISBN 978-1-5386-6477-3.
  • Year: 2018
  • DOI: 10.1109/ICONIC.2018.8601234
  • Link: https://doi.org/10.1109/ICONIC.2018.8601234
  • Department: Department of Radioelectronics
  • Annotation:
    The most efficient solvers use composite procedures that adaptively rearrange computation algorithms to maximize simulation performance. A similar concept can be integrated into a process of electronic circuit analysis, where the combination of different algorithms allows scalability of simulation performance. In this paper, we propose a new adaptive internal solver based on Biconjugate gradient stabilized method for the iterative solution of nonsymmetric linear systems supplemented with incomplete LU factorization as an efficient replacement for the direct solver implemented in program Spice for solving large-scale circuits. We describe basic concepts of a simulation of electronic circuits with nonlinear time dependent devices and present implementation examples of the proposed methods. Optimal setting of the method and its application in program Spice is shown in comparison to other modern iterative solvers for nonsymmetric linear systems.

Efficient Procedure Improving Precision of High Conditioned Matrices in Electronic Circuits Analysis

  • Authors: Černý, D., doc. Ing. Josef Dobeš, CSc., Banáš, S.
  • Publication: Radioengineering. 2018, 27(4), 1100-1111. ISSN 1210-2512.
  • Year: 2018
  • DOI: 10.13164/re.2018.1100
  • Link: https://doi.org/10.13164/re.2018.1100
  • Department: Department of Radioelectronics
  • Annotation:
    In this article, we propose several improvements that could be done to SPICE simulator. The first is based on a functional implementation of device models. The advantages of functional implementation are demonstrated on basic Shichman-Hodges model of MOS transistor. It starts with a description of primary algorithms used in SPICE simulator for the solution of circuits with nonlinear devices and identify the problems that can occur during simulations. Main part of the article is devoted to improved factorization procedure for simulation of the nonlinear electronic circuits. The primary intention of the proposed method is to increase final precision of the result in a case of high condition linear systems. The procedure is based on a use of the iterative methods for solution of nonlinear and linear equations. Utilizing those methods for one iterative process helps to reduce memory consumption during simulation computation, and it can significantly improve simulation precision. The procedure allows to use enumeration with definable precision in a very efficient way.

Novel Method for Noise Figure Measurement of Antenna Low Noise Amplifiers Optimized for a Trade-Off Between Gain and Noise Properties

  • DOI: 10.1109/APCAP.2018.8538100
  • Link: https://doi.org/10.1109/APCAP.2018.8538100
  • Department: Department of Radioelectronics
  • Annotation:
    The best properties of antenna low noise preamplifiers can be achieved by the multi-objective optimization which generates a trade-off between the transducer power gain and noise figure in the form of Pareto front. However, as the resultant circuit designed in this way is not fully matched at the output, measuring the amplifier - unmatched neither to gain nor to noise figure - is quite difficult, especially in the case of very low noise figures. In this paper, a more accurate two-stage measurement method is presented, where both calibration and measurement stages contain improvements to end the device with standard impedances and increase needed overall measurement sensitivity.

A new assessment method of pHEMT models by comparing relative errors of drain current and its derivatives up to the third order

  • DOI: 10.1088/1757-899X/198/1/012004
  • Link: https://doi.org/10.1088/1757-899X/198/1/012004
  • Department: Department of Radioelectronics
  • Annotation:
    Nowadays, there exist relatively precise pHEMT models available for computer-aided design, and they are frequently compared to each other. However, such comparisons are mostly based on absolute errors of drain-current equations and their derivatives. In the paper, a novel method is suggested based on relative root-mean-square errors of both drain current and its derivatives up to the third order. Moreover, the relative errors are subsequently relativized to the best model in each category to further clarify obtained accuracies of both drain current and its derivatives. Furthermore, one our older and two newly suggested models are also included in comparison with the traditionally precise Ahmed, TOM-2 and Materka ones. The assessment is performed using measured characteristics of a pHEMT operating up to 110 GHz. Finally, a usability of the proposed models including the higher-order derivatives is illustrated using s-parameters analysis and measurement at more operating points as well as computation and measurement of IP3 points of a low-noise amplifier of a multi-constellation satellite navigation receiver with ATF-54143 pHEMT.

Analysis of L-Probe Proximity Fed Patch Antenna With Parasitic Patch

  • DOI: 10.23919/RADIO.2017.8242219
  • Link: https://doi.org/10.23919/RADIO.2017.8242219
  • Department: Department of Radioelectronics
  • Annotation:
    In this paper, an analysis of the Fat Patch Antenna with the extraordinary parasitic patch is described. For the numerical simulations, the Full Wave-CST Microwave Studio software is used. The element of the antenna is fed by the L-probe partially implemented in PCB. An excellent impedance matching is obtained (< 26 dB in the design frequency band 4.4-5 GHz). The radiation characteristics are also very good (gain > 10 dBi). A very good agreement between the Time Domain Solver (TS) and Frequency Domain Solver (FS) has also been obtained. Real antenna samples have been created and measured as well as eight-element antenna arrays designed by Dolph-Chebyshev method.

Functional chaining mechanism allowing definable models of electronic devices

  • DOI: 10.1109/ECCTD.2017.8093250
  • Link: https://doi.org/10.1109/ECCTD.2017.8093250
  • Department: Department of Radioelectronics
  • Annotation:
    Fast and stable processing optimized for given simulation problem is essential for any modern simulator. It is characteristic for electronic circuit analysis that complexity of simulation is given by circuit size and used device models. Implementation of electronic device models in program SPICE uses traditional functional paradigm allowing fast computation but further modification of model can be questionable. In this article, we propose modification of standard procedure inserting functional computation layer into the process. It allows on-the-fly modification of standard models and own functional definition during circuit definition without a loss in computational performance. It also gives a possibility of functional chaining mechanism and improves mapping performance of circuit variables to device models.

Implementation of Bi-modal Statistical Distribution into SPICE Models

  • Authors: Banáš, S., Brzobohatý, M., doc. Ing. Josef Dobeš, CSc.,
  • Publication: Proceedings of the 39th PIERS in Singapore. Cambridge, MA: The Electromagnetics Academy, 2017. p. 1-7. ISBN 978-1-5386-1211-8.
  • Year: 2017
  • DOI: 10.1109/PIERS-FALL.2017.8293630
  • Link: https://doi.org/10.1109/PIERS-FALL.2017.8293630
  • Department: Department of Radioelectronics
  • Annotation:
    This paper deals with the technique of bi-modal statistical distribution modeling applicable to all standard SPICE simulators. Bi-modal statistical distribution can have several reasons, however only some of them should be implemented to the SPICE models. The paper presents some examples of bi-modal statistical distributions and the way, how to implement it to the SPICE model. The detailed model equations as well as the plots representing the simulated results are presented.

A new assessment of pHEMT models by comparing relative errors of drain current and its derivatives up to the third order

  • DOI: 10.1109/RADIO.2016.7772016
  • Link: https://doi.org/10.1109/RADIO.2016.7772016
  • Department: Department of Radioelectronics
  • Annotation:
    At present, there are relatively more precise pHEMT models available for computer-aided design, and they are frequently compared to each other. However, such comparisons are mostly based on absolute errors of drain-current equations and their derivatives. In the paper, a novel method is suggested based on relative root-mean-square errors of both drain current and its derivatives up to the third order. Moreover, the relative errors are then relativized to the best model in each category to further clarify obtained accuracies of the drain current and its derivatives. Furthermore, one our older and two newly suggested models are also included in the comparison with the traditionally accurate Ahmed, TOM2 and Materka ones. The assessment is performed using measured characteristics of a 110 GHz pHEMT. Finally, a usability of the models of the higher-order derivatives is illustrated using an IP3 computation/measurement of a multi-constellation receiver for a satellite navigation with ATF-54143.

A New Criterion for Stability Assessment of the Microwave pHEMT-based Low-Noise Amplifiers

  • DOI: 10.1109/IMFEDK.2016.7521697
  • Link: https://doi.org/10.1109/IMFEDK.2016.7521697
  • Department: Department of Radioelectronics
  • Annotation:
    At present, the foremost low-noise amplifiers are based on usage of the pseudomorphic high-electron-mobility transistors (pHEMTs). However, in many cases, the amplifiers are often constructed at the limits of absolute stability or even in the region of potential instability because only such solutions give requested circuit properties as a trade-off between the transducer power gain and noise figure. The stability properties are mostly checked by the classical criteria such as the Rollett conditions, mu-factor etc. In the paper, a novel additional very efficient criterion is proposed, finding the most critical couple of poles and evaluating the ratio of imaginary and real part. The efficiency of the method is demonstrated on a low-noise antenna preamplifier for a multi-constellation satellite-navigation receiver based on an ATF-54143 pHEMT.

An Efficient Procedure for Transient Analysis of Electronic Circuits with Increased Precision

  • Authors: Černý, D., doc. Ing. Josef Dobeš, CSc.,
  • Publication: 20th International Conference on Circuits, Systems, Communications and Computers (CSCC). Les Ulis: EDP Sciences, 2016. p. 1-4. vol. Bulucea. ISSN 2261-236X.
  • Year: 2016
  • DOI: 10.1051/matecconf/20167601007
  • Link: https://doi.org/10.1051/matecconf/20167601007
  • Department: Department of Radioelectronics
  • Annotation:
    This article presents an efficient procedure allowing to increase the final accuracy of the electronic circuits simulation. To obtain Transient Analysis of a nonlinear circuit the simulator needs to perform various algorithms, from an evaluation of initial DC state through a nonlinear iterative algorithm, to a numerical integration. These complex computations have to be implemented effectively with regards to memory and processor usage. Direct implementation of arbitrary precision types can directly lead to increased simulation accuracy but also significantly decrease simulation performance. As a compromise, we suggest using an additional algorithm based on Newton Iteration method for the solution of matrix inversion. The method was modified to be comparable to direct LUF solver.

Analog Emulator of Genuinely Floating Memcapacitor with Piece-Wise-Linear Constitutive Relation

  • Authors: Biolek, D., Biolková, V., Kolka, Z., doc. Ing. Josef Dobeš, CSc.,
  • Publication: Circuits, Systems, and Signal Processing. 2016, 35(1), 43-62. ISSN 0278-081X.
  • Year: 2016
  • DOI: 10.1007/s00034-015-0067-8
  • Link: https://doi.org/10.1007/s00034-015-0067-8
  • Department: Department of Radioelectronics
  • Annotation:
    The paper presents a method for emulating floating memcapacitors with piece-wise -linear constitutive relations between timedomain integrals of voltage and charge. The emulation is based on multiple-state floating capacitor, implemented via the switched-capacitor technique. The states of internal switches are derived from the memcapacitor memory, which stores the history of the terminal voltage. The procedure is demonstrated on a two-state memcapacitor. Computer simulations are compared with measurements on the manufactured specimen.

Comprehensive behavioral model of dual-gate high voltage JFET and pinch resistor

  • Authors: Banáš, S., Paňko, V., doc. Ing. Josef Dobeš, CSc., Hanyš, P., Divín, J.
  • Publication: Solid-State Electronics. 2016, 123(9), 133-142. ISSN 0038-1101.
  • Year: 2016
  • DOI: 10.1016/j.sse.2016.05.001
  • Link: https://doi.org/10.1016/j.sse.2016.05.001
  • Department: Department of Radioelectronics
  • Annotation:
    Many analog technologies operate in large voltage range and therefore include at least one or more high voltage devices built from low doped layers. Such devices exhibit effects not covered by standard compact models, namely pinching (depletion) effects, in high voltage FETs often called quasisaturation. For example, the conventional compact JFET model is insufficient and oversimplified. Its scalability is controlled by the area factor, which only multiplies currents and capacitances but does not take into account existing 3-D effects. Also the optional second independent gate is missing. Therefore, the customized four terminal (4T) model written in Verilog-A (FitzPatrick and Miller, 2007; Sagdeo, 2007) was developed. It converges very well, its simulation speed is comparable with conventional compact models, and contains all required phenomena, including parasitic effects as, for example, impact ionization. This model has universal usage for many types of devices in various high voltage technologies such as stand-alone voltage dependent resistor, pinch resistor, drift area of power FET, part of special high side or start-up devices, and dual-gate JFET.

Techniques of JFET Gate Capacitance Modeling

  • Authors: Banáš, S., doc. Ing. Josef Dobeš, CSc., Paňko, V.
  • Publication: World Congress on Engineering and Computer Science 2016. Hong Kong: Newswood Limited - International Association of Engineers, 2016. p. 771-775. vol. II. ISSN 2078-0958. ISBN 978-988-14048-2-4.
  • Year: 2016
  • Department: Department of Radioelectronics
  • Annotation:
    This paper presents various techniques and principles of modeling JFET gate capacitance. Various layout concepts as well as their gate capacitance measurements and modeling techniques are presented. Experience with potential modeling or measurement challenges is shared. The paper also deals with an often-omitted tight interaction between C-V and DC models, necessary for the well-fitting compact model. Good agreement has been achieved between measured silicon data and SPICE simulations for all discussed layout variants. Plots of various layouts and various tests from real production models are also presented.

Adaptive sparse matrix indexing technique for simulation of electronic circuits based on λ-calculus

  • Authors: Černý, D., doc. Ing. Josef Dobeš, CSc.,
  • Publication: 2015 European Conference on Circuit Theory and Design. Piscataway: IEEE, 2015. pp. 1-4. ISBN 978-1-4799-9877-7.
  • Year: 2015
  • DOI: 10.1109/ECCTD.2015.7300054
  • Link: https://doi.org/10.1109/ECCTD.2015.7300054
  • Department: Department of Radioelectronics
  • Annotation:
    In this paper, a fundamentally new approach to computer-aided design and simulation of electrical circuits based on a use of λ-calculus for circuit device model representation and dynamic sizeable containers for sparse matrix simulation indexation indices is presented. This approach differs from traditional procedure where the entire simulation was performed over the matrix or matrix system assembled by modified nodal analysis (MNA). Turning device model definitions using λ-calculus to functionals allowed to reduce an effort required for their specification and opened new possibilities for simulation evaluation. Considering MNA matrix as second-order tensor system holding the functional definition of original sparse matrix entries allows to imagine these dependencies as chains with respect to a model definition and global dependencies between their defining inner functions. In this particular case, standard indexing methods would be a waste of memory during a computation, this problem occurs when huge sparse matrices enter the simulation. Therefore, new optimized indexing technique for non-zero matrix entries and variable size container types for those indexation vectors is proposed.

Comparing the Steady-State Procedures Based on Epsilon-Algorithm and Sensitivity Analysis

  • DOI: 10.1109/ICECS.2015.7440388
  • Link: https://doi.org/10.1109/ICECS.2015.7440388
  • Department: Department of Radioelectronics
  • Annotation:
    Although many programs have built-in various methods for finding the steady state nowadays, their actual implementations are often quite unsatisfactory regarding algorithm efficiency and reliability. We improved and checked procedures built on both epsilon-algorithm and sensitivity analysis in time domain. First of all, it was clearly demonstrated that increasing demands on the overall numerical accuracy do not lead to an excessive number of necessary integration steps and therefore LU factorizations correspondingly. This feature is especially significant for the suggested procedure based on the epsilon-algorithm. Furthermore, the practical experiments confirmed that a proposed arrangement of the extrapolation method is greatly insensitive to its order, which is even more important because a program user is unable to estimate the appropriate order for complicated circuits well. The properties of the methods are demonstrated using rectifier, C-class amplifier, and LNA for which exceptional attention was given to checking the insensitivity of the extrapolation to its order.

Enhanced Model of Nonlinear Spiral High Voltage Divider

  • Authors: Paňko, V., Banáš, S., Burton, R., Ptáček, K., Divín, J., doc. Ing. Josef Dobeš, CSc.,
  • Publication: Radioengineering. 2015, 24(1), 130-136. ISSN 1210-2512.
  • Year: 2015
  • DOI: 10.13164/re.2015.0130
  • Link: https://doi.org/10.13164/re.2015.0130
  • Department: Department of Radioelectronics
  • Annotation:
    This paper deals with the enhanced accurate DC and RF model of nonlinear spiral polysilicon voltage divider. The high resistance polysilicon divider is a sensing part of the high voltage start-up MOSFET transistor that can operate up to 700 V. This paper presents the structure of a proposed model, implemented voltage, frequency and temperature dependency, and scalability. A special attention is paid to the ability of the created model to cover the mismatch and influence of a variation of process parameters on the device characteristics. Finally, the comparison of measured data vs. simulation is presented in order to confirm the model validity and a typical application is demonstrated.

Lumped RF Model of MOSFET Gate Resistance for GHz+ Frequencies Enhancement of Compact BSIM MOSFET Model

  • Authors: Banáš, S., Hoggatt, Ch., Paňko, V., doc. Ing. Josef Dobeš, CSc., Divín, J.
  • Publication: The Third International Conference on Advances in Information Processing and Communication Technology - IPCT 2015. Santa Barbara: Institute of Research Engineers and Doctor, 2015. pp. 75-79. ISBN 978-1-63248-077-4.
  • Year: 2015
  • DOI: 10.15224/978-1-63248-077-4-22
  • Link: https://doi.org/10.15224/978-1-63248-077-4-22
  • Department: Department of Radioelectronics
  • Annotation:
    This paper presents a lumped RF model of high voltage FET applicable for the frequency up to GHz range. Unlike the compact MOSFET model, the proposed solution contains not only parasitic capacitances and resistances but also parasitic inductance. The signal delay caused by relatively large device area including the parasitic resonance modeled by distributed RLC network is considered. The model is applicable in commercial SPICE simulators, e.g. Eldo, Spectre or HSpice.

Multi-Objective Optimization of a Low-Noise Antenna Amplifier for Multi-Constellation Satellite-Navigation Receivers

  • Authors: doc. Ing. Josef Dobeš, CSc., Míchal, J., Popp, J., Grábner, M., prof. Ing. František Vejražka, CSc., Kákona, J.
  • Publication: Proceedings of the 28th IEEE International System on Chip Conference (SOCC). Monterey: IEEE Circuits and Systems Society, 2015. p. 88-93. ISSN 2164-1706. ISBN 978-1-4673-9093-4.
  • Year: 2015
  • DOI: 10.1109/SOCC.2015.7406919
  • Link: https://doi.org/10.1109/SOCC.2015.7406919
  • Department: Department of Radioelectronics
  • Annotation:
    Although the major parts of function blocks for the satellite navigation receivers are fully integrated in a CMOS chip in most cases, it is convenient to create an antenna preamplifier as a separate circuit based on a low-noise pHEMT. Such an RF front end can be strongly optimized to attain a trade-off between the noise figure and transducer power gain. Furthermore, as all the principal navigation systems (GPS, GLONASS, Galileo, and Compass) work in similar frequency band (roughly from 1.1 to 1.7 GHz), it is reasonable to create this low-noise preamplifier for all of them. In the paper, a sophisticated method of the amplifier design is suggested based on multi-objective optimization. First, an extraction of pHEMT model parameters was performed, including comparisons among several models. The extraction was carried out by our original three-step robust identification procedure based on a combination of meta-heuristic and direct optimization methods. Second, a substantial improvement of a standard method for the multi-objective optimization is outlined. Third, the equations of passive elements of the circuit (including transmission lines and T splitters) were carefully defined using frequency dispersion of their parameters as Q, ESR, etc. Fourth, an optimal selection of the amplifier operating point and essential passive elements was performed using the previously improved goal attainment method. Finally, the s-parameters and noise figure of the proposed preamplifier were measured, and the third-order intermodulation products were also checked.

Precise Characterization and Multiobjective Optimization of Low Noise Amplifiers

  • DOI: 10.13164/re.2015.0670
  • Link: https://doi.org/10.13164/re.2015.0670
  • Department: Department of Radioelectronics
  • Annotation:
    Although practically all function blocks of the satellite navigation receivers are realized using the CMOS digital integrated circuits, it is appropriate to create a separate low noise antenna preamplifier based on a low noise pHEMT. Such an RF front end can be strongly optimized to attain a suitable tradeoff between the noise figure and transducer power gain. Further, as all the four principal navigation systems (GPS, GLONASS, Galileo, and COMPASS) work in similar frequency bands (roughly from 1.1 to 1.7 GHz), it is reasonable to create the low noise preamplifier for all of them. In the paper, a sophisticated method of the amplifier design is suggested based on multiobjective optimization. A substantial improvement of a standard optimization method is also outlined to satisfy a uniform coverage of Pareto front. Moreover, for enhancing efficiency of many times repeated solutions of large linear systems during the optimization, a new modification of the Markowitz criterion is suggested compatible with fast modes of the LU factorization. Extraordinary attention was also given to the accuracy of modeling. First, an extraction of pHEMT model parameters was performed including its noise part, and several models were compared. The extraction was carried out by an original identification procedure based on a combination of metaheuristic and direct methods. Second, the equations of the passive elements (including transmission lines and T-splitters) were carefully defined using frequency dispersion of their parameters as Q, ESR, etc. Third, an optimal selection of the operating point and essential passive elements was performed using the improved optimization method. Finally, the s-parameters and noise figure of the amplifier were measured, and stability and third-order intermodulation products were also checked.

Functional Programming Languages in Computer Simulation of Electronics Circuits

  • Authors: Černý, D., doc. Ing. Josef Dobeš, CSc.,
  • Publication: PROCEEDINGS OF THE 2014 INTERNATIONAL CONFERENCE ON COMPUTATIONAL SCIENCE & COMPUTATIONAL INTELLIGENCE. Los Alamitos: IEEE Computer Society, 2014. p. 229-234. ISBN 978-1-4799-3009-8.
  • Year: 2014
  • DOI: 10.1109/CSCI.2014.46
  • Link: https://doi.org/10.1109/CSCI.2014.46
  • Department: Department of Radioelectronics
  • Annotation:
    Increasing significance of functional languages could be observed in programming and software development. Many new tools and development frameworks starting to provide in standard structural and object oriented environment also new functional style of programming or even turning all programming paradigm to functional style. Many simulation programs especially for computer simulation of electronics devices as SPICE simulator, were developed more than 30 years ago. It is clear that continue in development is very almost not possible and it is very difficult to fulfill customer requirements. This paper makes a brief introduction to basic of this problem and it proposes new principles for developing new modern simulator of electronics circuit and devices. Main part presents new ordering techniques for sparse matrices systems which are given by modified nodal analysis. The comparison of performance of standard matrix storages and novel sparse matrix ordering techniques is summarized at the end of this article. It is demonstrated on LU factorization and also on several types of solvers of nonlinear equations. Article includes definition of two basic devices in functional language: simple diode and voltage source.

Multiobjective Optimization of Input Low Noise Amplifier for Common GPS/Galileo/GLONASS/Compass Satellite Navigation System Receiver

  • DOI: 10.1109/ISOCC.2014.7087575
  • Link: https://doi.org/10.1109/ISOCC.2014.7087575
  • Department: Department of Radioelectronics
  • Annotation:
    As all the four main navigation systems (GPS, Galileo, GLONASS, and Compass) work in similar frequency bands, it is reasonable to create a common input low noise amplifier for all of them. Although the whole chip including a lot of correlators and other digital circuits is quite complicated, a common low noise antenna preamplifier operating at the frequencies from 1.1 to 1.7 GHz could be quite simple and efficient. We have proposed finding a compromise between the amplifier’s amplification and noise figure under several natural constrains by multiobjective optimization. Moreover, we have utilized our enhancement of known optimization algorithm (the goal attainment method) to improve its efficiency, which led to finding a very good design tradeoff for the amplifier.

Universal behavioral model for accurate modeling of high voltage devices

  • Authors: Banáš, S., Paňko, V., Stejskal, V., Slezák, V., doc. Ing. Josef Dobeš, CSc.,
  • Publication: Proceedings of the 2014 International Conference on Communication Technology and Application (CTA 2014). Southampton: WIT Press, Ashurst Lodge, 2014. p. 545-551. ISSN 1743-3517. ISBN 978-1-84564-930-2.
  • Year: 2014
  • DOI: 10.2495/CTA140671
  • Link: https://doi.org/10.2495/CTA140671
  • Department: Department of Radioelectronics
  • Annotation:
    This paper presents the universal behavioral model applicable in Spice simulators for the simulation of high voltage components containing pinch effect and related phenomena, e.g., HV LDMOS, startup FET, dual gate JFET or pinch resistor. Unlike standard compact models focused typically to the submicron technologies operating in voltages <<100 V the presented model is in HV applications more accurate and contains all phenomena typical for devices operating in hundred volts, including parasitic effects.

Using the Sensitivity Analysis of the Noise Spectral Density and the Sensitivity Analysis of the Noise Figure for Practical Circuit Design

  • DOI: 10.1109/ISCAS.2014.6865475
  • Link: https://doi.org/10.1109/ISCAS.2014.6865475
  • Department: Department of Radioelectronics
  • Annotation:
    Although the sensitivity analysis is implemented in contemporary software tools for computer-aided design, kinds of available sensitivities are limited. For example, Spice or Micro-Cap calculate DC or small-signal AC sensitivities, and SpectreRF contains a periodic noise analysis or a parametric sensitivity analysis that can be efficiently used for determining the phase noise. In this paper, some novel types of the noise sensitivity analysis are described, which are not implemented in the usually applied circuit simulators. First, a procedure for determining the sensitivities of the noise figure was suggested. Second, an improvement of the algorithm for computing the noise figure was described, which incorporates circuit matching and eliminates necessary subtraction of the output noise generated by the load resistance at each frequency. Third, a new formula was derived for a computation of the sensitivities of the noise figure. The sensitivity analysis of the noise spectral density is demonstrated by means of an analytically solved example. The application of the sensitivity analysis of the noise figure for improving the noise properties of a microwave integrated circuit is described in a detailed way as well. Finally, using a sophisticated multi-objective optimization is suggested for a better selection of the operating point instead of classical circuit matching. This method was utilized for a practical design of an antenna preamplifier for a GPS/Galileo/GLONASS/Compass receiver.

A Flexible Algorithm for Solving Systems of Circuit Differential-Algebraic Equations With Integrated Fortran 95 Compiler for Modeling

  • Authors: doc. Ing. Josef Dobeš, CSc., Paňko, V., Černý, D., Divín, J.
  • Publication: IEEE AFRICON 2013. Piscataway: IEEE, 2013. pp. 1-5. ISSN 2153-0025. ISBN 978-1-4673-5943-6.
  • Year: 2013
  • DOI: 10.1109/AFRCON.2013.6757802
  • Link: https://doi.org/10.1109/AFRCON.2013.6757802
  • Department: Department of Radioelectronics
  • Annotation:
    Although many simulation tools contain advanced algorithms for the solution of the systems of differential-algebraic nonlinear equations, some classes of circuits still cause serious problems. In the paper, a very flexible and reliable algorithm for solving the circuit differential-algebraic equations is characterized first, which is based on a sophisticated arrangement of the Newton interpolation polynomial. After that, a reliable method is introduced for improving the convergence with four possible criteria. Unlike the similar algorithms focused on an operating point analysis only, the proposed method also works in a transient analysis. Moreover, for an ability of the procedure to model practically arbitrary electronic device, a subset of the Fortran 95 programming language was integrated to the circuit simulator with a power to differentiate functions symbolically.

A Reliable Algorithm for a pHEMT Nonlinear Model Identification Using a Set of Multibias s-parameters

  • Authors: doc. Ing. Josef Dobeš, CSc., Grábner, M.
  • Publication: International Semiconductor Device Research Symposium 2013. Piscataway: IEEE, 2013. pp. 1-2. ISBN 978-1-63173-156-3.
  • Year: 2013
  • Department: Department of Radioelectronics
  • Annotation:
    The nonlinear models of MESFETs implemented in the contemporary CAD tools can well serve to perform various both time- and frequency-domain simulations of microwave circuits with pHEMTs, and the s-parameters measured at different bias points provide valuable information needed to extract the parameters of such nonlinear models. Regarding the model accuracy, a comprehensive comparison has been created for the Curtice, Statz, TOM, TOM2, Materka, Ahmed, and Dobes models. However, creating a reliable optimization procedure for the nonlinear model parameters' extraction from the s-parameters is a complicated task. After a lot of tests, we have suggested a robust combination of a meta-heuristics (Simulated Annealing selected) and a direct method (Levenberg-Marquardt one selected). We have checked the algorithm on two practical examples. First, for a development of a low-noise amplifier intended as a common input unit for a GPS/Galileo/GLONASS/Compass receiver, an accurate nonlinear model of ATF-54143 is necessary. Therefore, we have utilized a set of multibias s-parameters, and we have extracted all the parameters for both our Dobes model (which is further used for a multiobjective optimization) and Statz one (which is necessary for standard simulators like Micro-Cap, e.g.). Second, we have extracted model parameters for a 110 GHz GaAs pHEMT with a gate length 0.25 um. The DC characteristics and s-parameters for this pHEMT are shownfor the frequencies from 4 to 90 GHz.

An Improved Model of High-Voltage Power LDMOSFET and Its Usage in Multi-Objective Optimization of Radio-Frequency Amplifiers

  • Authors: doc. Ing. Josef Dobeš, CSc., Paňko, V., Banáš, S., Černý, D.
  • Publication: The 14th IEEE Workshop on Control and Modeling for Power Electronics (COMPEL). Piscataway: IEEE, 2013. pp. 1-5. ISSN 2151-0997. ISBN 978-1-4673-4916-1.
  • Year: 2013
  • DOI: 10.1109/COMPEL.2013.6626472
  • Link: https://doi.org/10.1109/COMPEL.2013.6626472
  • Department: Department of Radioelectronics
  • Annotation:
    In the paper, a set of improvements of the semiempirical MOSFET model is suggested to ensure required accuracy for simulating power electronic circuits. The enhancement of the precision was arranged by incorporating the more accurate Grove-Frohman equations into the semiempirical model because the contemporary short-channel-oriented models BSIM and EKV are inappropriate for characterizing the power transistors. The ability of the modified model to characterize power devices was confirmed by successful processes of extracting its parameters for medium- and high-power transistors, and a demonstration of this process for an SIPMOS power transistor is also shown in the paper. Finally, a multi-objective optimization of a C-class radio-frequency power amplifier with LDMOSFET is demonstrated as well as an analogous procedure for a low-noise preamplifier. In the two examples in time and frequency domains, resulting three- and two-dimensional Pareto fronts are presented in convenient graphic forms for a comfortable selection of a tradeoff by a user.

MOSFET gate dimension dependent drain and source leakage modeling by standard SPICE models

  • Authors: Paňko, V., Banáš, S., Prejda, D., doc. Ing. Josef Dobeš, CSc.,
  • Publication: Solid-State Electronics. 2013, 81(3), 144-150. ISSN 0038-1101.
  • Year: 2013
  • DOI: 10.1016/j.sse.2013.01.001
  • Link: https://doi.org/10.1016/j.sse.2013.01.001
  • Department: Department of Radioelectronics
  • Annotation:
    The leakage current in standard MOSFET models (BSIM3/BSIM4) is typically modeled by drain–bulk and source–bulk diodes. This modeling method does not consider the impact of several parasitic bipolar devices. For the accurate modeling the impact of the following bipolar transistors has to be considered: a lateral bipolar transistor drain–bulk–source, a vertical bipolar transistor drain–bulk-substrate (only in isolated structures), and a vertical bipolar transistor source–bulk-substrate (only in isolated structures). For example, the drain or source leakage as a function of gate length cannot be modeled without the scalable parasitic bipolar devices. This contribution demonstrates the structure of a proposed macro model, implemented scalability (in most cases nonlinear), developed scaling equations, and physical explanation of this scaling. Finally, the comparison of measured data vs. simulation is presented in order to confirm the model validity. This model improvement solves not only leakage current scaling, but it also accounts for additional parasitic bipolar effects, such as current injection to the substrate.

Multiobjective Optimization for Electronic Circuit Design in Time and Frequency Domains

  • Authors: doc. Ing. Josef Dobeš, CSc., Míchal, J., Biolková, V.
  • Publication: Radioengineering. 2013, 22(1), 136-152. ISSN 1210-2512.
  • Year: 2013
  • Department: Department of Radioelectronics
  • Annotation:
    The multiobjective optimization provides an extraordinary opportunity for the finest design of electronic circuits because it allows to mathematically balance contradictory requirements together with possible constraints. In this paper, an original and substantial improvement of an existing method for the multiobjective optimization known as GAM (Goal Attainment Method) is suggested. In our proposal, the GAM algorithm itself is combined with a procedure that automatically provides a set of parameters for which the method generates noninferior solutions uniformly spread over an appropriately selected part of the Pareto front. Moreover, the resulting set of obtained solutions is then presented in a suitable graphic form so that the solution representing the most satisfactory tradeoff can be easily chosen by the designer. Our system generates various types of plots that conveniently characterize results of up to four-dimensional problems. Technically, the procedures of the multiobjective optimization were created as a software add-on to the CIA (Circuit Interactive Analyzer) program. This way enabled us to utilize many powerful features of this program, including the sensitivity analyses in time and frequency domains. As a result, the system is also able to perform the multiobjective optimization in the time domain and even highly nonlinear circuits can be significantly improved by our program. As a demonstration of this feature, a multiobjective optimization of a C-class power amplifier in the time domain is thoroughly described in the paper. Further, a four-dimensional optimization of a video amplifier is demonstrated with an original graphic representation of the Pareto front. As an example of improving noise properties, a multiobjective optimization of a low-noise amplifier is performed, and the results in the frequency domain are shown. Finally, a necessity of a use of metaheuristic methods at least with a combination with the classical ones is demonstrated.

An Accurate DC and RF Modeling of Nonlinear Spiral Polysilicon Voltage Divider in High Voltage MOSFET Transistor

  • Authors: Paňko, V., Banáš, S., Ptacek, K., Burton, R., doc. Ing. Josef Dobeš, CSc.,
  • Publication: 2012 IEEE 11th International Conference on Solid-State and Integrated Circuit Technology. Piscataway: IEEE, 2012. pp. 538-540. ISBN 978-1-4673-2472-4.
  • Year: 2012
  • DOI: 10.1109/ICSICT.2012.6467635
  • Link: https://doi.org/10.1109/ICSICT.2012.6467635
  • Department: Department of Radioelectronics
  • Annotation:
    This paper presents an accurate DC and RF modeling of nonlinear spiral high resistance polysilicon divider. The spiral divider is a sensing part of the high voltage start-up MOSFET transistor operating up to 700 V. The strong electric field in low doped drain drift area located under the low doped polysilicon spiral divider results in parasitic effects that have a significant influence on DC and RF device characteristics and makes divider ratio voltage and frequency dependent. This paper demonstrates the structure of a proposed macro model, implemented voltage and frequency dependency, and physical explanation of these phenomena. Finally, the comparison of measured data vs. simulation is presented in order to confirm the model validity.

Characterization of Electronic Circuit Elements by Exclusive and Corrective Artificial Neural Networks

  • Authors: Pospíšil, L., doc. Ing. Josef Dobeš, CSc., Yadav, A.
  • Publication: International Journal of Mathematics and Computers in Simulation. 2012, 6(1), 136-143. ISSN 1998-0159.
  • Year: 2012
  • Department: Department of Radioelectronics
  • Annotation:
    At present, there are many novel electronic circuit elements for which their nonlinear models for CAD are necessary, especially for microwave ones. However, in the PSpice-family programs, only a class of several classic types of the MESFET model is available for the microwave area. In the paper, a novel reliable way is suggested for modeling various electronic structures by exclusive neural networks, or by corrective neural networks working attached to a modified analytic model. The accuracy of the proposed modification of the analytic model is assessed by extracting the model parameters of GaAs MESFET, AlGaAs/InGaAs/GaAs pHEMT, and GaAs microwave varactors. First, a precise approximation of the pHEMT output characteristics is carried out by means of both exclusive and corrective artificial neural networks; and second, an approximation of the capacitance (C-V) function of the SACM InGaAs/InP avalanche photodiode is performed by the exclusive neural network. Further, the Pt-TiO_(2-x)-Pt memristor characteristic with an extraordinary (but typical) hysteresis is approximated by a set of cooperative artificial neural networks, because a single network is unable to characterize this especial element. Last, a sequence of systematic experiments is performed, which shows that the optimal structure of the network can be found relatively easily, and it should not be too complicated.

Multi-Objective Optimization of Radio-Frequency Front-Ends

  • Authors: doc. Ing. Josef Dobeš, CSc., Míchal, J., Biolková, V.
  • Publication: IEEE International SOC Conference. Monterey: IEEE Circuits and Systems Society, 2012. pp. 192-197. ISSN 2164-1706. ISBN 978-1-4673-1295-0.
  • Year: 2012
  • Department: Department of Radioelectronics
  • Annotation:
    This paper proposes an enhancement of a standard method for the multi-objective optimization known as GAM (Goal Attainment Method). In our modification, the GAM algorithm is combined with a procedure that automatically provides a set of parameters (weights, coordinates of the reference point) for which the method generates non-inferior solutions uniformly spread over a suitably selected part of the Pareto front. The resulting set of the solutions is then presented in a convenient graphic form so that the solution representing the most satisfactory trade-off can easily be chosen. The whole algorithm was implemented as a program and tested on various circuit design examples. A typical one was a four-dimensional multi-objective optimization of an RF video front-end. Therefore, this task is thoroughly described in the paper as a representative demonstration of the capability of the program, including a sophisticated quasi four-dimensional graphic for selecting the trade-off. Moreover, a comparison of our modification with WSM (Weighted Sum Method) is also performed.

Multiobjective Optimization of Nonlinear Circuits

  • Authors: doc. Ing. Josef Dobeš, CSc., Míchal, J., Paňko, V.
  • Publication: The 2012 International Conference on Scientific Computing. Las Vegas: CSREA Press, 2012. pp. 20-26. ISBN 1-60132-207-0.
  • Year: 2012
  • Department: Department of Radioelectronics
  • Annotation:
    This paper suggests an enhancement of an existing method for the multiobjective optimization known as GAM (goal attainment method). In our proposal, the GAM algorithm is combined with a mechanism that automatically provides a set of parameters (weights, coordinates of the reference point) for which the method generates noninferior solutions uniformly spread over a suitably selected part of the Pareto front. The resulting set of solutions is then presented in a suitable graphic form so that the solution representing the most satisfactory tradeoff can be easily chosen. The whole algorithm was implemented as a program and tested on various design examples. The most difficult one was a multiobjective optimization of a C-class power amplifier in the time domain. Therefore, this task is thoroughly described in the paper as a demonstration of the program capability.

New Sparse Matrix Ordering Techniques for Computer Simulation Of Electronics Circuits

  • Authors: Černý, D., doc. Ing. Josef Dobeš, CSc.,
  • Publication: 3rd European Conference of Circuit Technology and Devices. NY: North Atlantic University Union, 2012. pp. 247-251. ISBN 978-1-61804-138-8.
  • Year: 2012
  • Department: Department of Radioelectronics
  • Annotation:
    Engineers and technicians rely on many computer tools, which help them in the development of new devices. Especially in the electronic circuit design, there is required advantageous and complex equipment. This paper makes a brief introduction to the basic problematic of electronic circuit's simulation. It proposes the key principles for developing modern simulators and possible further steps in computer simulation and circuit design. Main part of the article presents a novel sparse matrix ordering techniques specially developed for solving LU factorization. LU factorization is critical part of any electronic circuit simulation. This paper also presents complete description of backward and forward conversion of the new sparse matrix ordering techniques. The comparison of performance of standard matrix storages and novel sparse matrix ordering techniques is summarized at the end of this article.

Precise Characterization of Memristive Systems by Cooperative Artificial Neural Networks

  • Authors: doc. Ing. Josef Dobeš, CSc., Pospíšil, L., Yadav, A.
  • Publication: The 6th International Conference on Soft Computing and Intelligent Systems, and The 13th International Symposium on Advanced Intelligent Systems. Piscataway: IEEE, 2012. pp. 2130-2133. ISSN 1880-3741. ISBN 978-1-4673-2742-8.
  • Year: 2012
  • DOI: 10.1109/SCIS-ISIS.2012.6505343
  • Link: https://doi.org/10.1109/SCIS-ISIS.2012.6505343
  • Department: Department of Radioelectronics
  • Annotation:
    Nowadays, there are many emerging electronic structures for which their nonlinear models for CAD are necessary, especially for the ones from the area of nanoelectronics. However, for such structures, sufficiently accurate analytic models are mostly unavailable. This is partially caused by the fact that the physical principles of the element operation are sometimes not fully clear (especially for quantum devices), and also by bizarre characteristics of some elements (typically with irregularities and a hysteresis in parts of characteristics). In such cases, models based on artificial neural networks are necessary and useful for these elements. Majority of the elements can be characterized with a single artificial neural network. However, for certain kinds of elements, a cooperation of more artificial networks is necessary. This case is described in the paper, where the Pt - TiO_(2-x) - Pt memristor characteristic with an extraordinary (but typical) hysteresis is approximated by a set of cooperative artificial neural networks, as a single network is unable to characterize this unconventional element. Moreover, a semiautomatic selection of an optimal structure of the networks (both numbers of hidden layers and the numbers of the elements in the layers) is suggested in the paper.

Precise Modeling of Emerging Electronic Structures by Artificial Neural Networks

  • Authors: doc. Ing. Josef Dobeš, CSc., Pospíšil, L., Yadav, A.
  • Publication: World Congress on Engineering and Computer Science 2012. Hong Kong: The International Association of Engineers IAENG, 2012. p. 847-850. ISSN 2078-0958. ISBN 978-988-19252-4-4.
  • Year: 2012
  • Department: Department of Radioelectronics
  • Annotation:
    Nowadays, there are many emerging electronic structures for which their nonlinear models for computeraided design are necessary, especially for the ones from the areas of nanoelectronics and microwave techniques. However, for such structures, sufficiently accurate analytic models are mostly unavailable. This is partially caused by the fact that the physical principles of the element operation are sometimes not fully clear (especially for quantum devices), and also by bizarre characteristics of some of the elements (typically with irregularities and a hysteresis in parts of characteristics, or by negative differential conductances that are typical for the microwave transistors). In such cases, models based on artificial neural networks are necessary and useful for these elements. Majority of the elements can be characterized with a single artificial neural network. However, for certain kinds of elements, a cooperation of more artificial neural networks is necessary. This case is described in the paper first, where the Pt-TiO2-x-Pt memristor characteristic with an extraordinary (but typical) hysteresis is approximated by a set of cooperative artificial neural networks, as a single network is unable to characterize this unconventional element. Second, an ability of the artificial neural networks for modeling the negative differential conductance is demonstrated by characterizing the 110GHz pseudomorphic high electron mobility transistor (pHEMT). Moreover, a semiautomatic selection of an optimal structure of the networks (both numbers of hidden layers and the numbers of the elements in the layers) is also suggested.

Reliable and Efficient Procedure for Steady-State Analysis of Nonautonomous and Autonomous Systems

  • Department: Department of Radioelectronics
  • Annotation:
    The majority of contemporary design tools do not still contain steady-state algorithms, especially for the autonomous systems. This is mainly caused by insufficient accuracy of the algorithm for numerical integration, but also by unreliable steady-state algorithms themselves. Therefore, in the paper, a very stable and efficient procedure for the numerical integration of the nonlinear differential-algebraic systems is defined first. Afterwards, two improved methods are defined for finding the steady state, which use this integration algorithm in their iteration loops. The first is based on the idea of extrapolation, and the second utilizes nonstandard time-domain sensitivity analysis. The two steady-state algorithms are compared by analyses of a rectifier and a C-class amplifier, and the extrapolation algorithm is primarily selected as a more reliable alternative. Finally, the method based on the extrapolation naturally cooperating with the algorithm for solving the differential-algebraic systems is thoroughly tested on various electronic circuits: Van der Pol and Colpitts oscillators, fragment of a large bipolar logical circuit, feedback and distributed microwave oscillators, and power amplifier. The results confirm that the extrapolation method is faster than a classical plain numerical integration, especially for larger circuits with complicated transients.

A more efficient arrangement of the sparse LU factorization for the large-scale circuit analysis

  • Authors: doc. Ing. Josef Dobeš, CSc., Černý, D., Yadav, A.
  • Publication: 2011 IEEE/IFIP 19th International Conference on VLSI and System-on-Chip. Piscataway: IEEE, 2011. p. 416-421. ISBN 978-1-4577-0170-2.
  • Year: 2011
  • DOI: 10.1109/VLSISoC.2011.6081619
  • Link: https://doi.org/10.1109/VLSISoC.2011.6081619
  • Department: Department of Radioelectronics
  • Annotation:
    In the paper, an efficient and reliable algorithm for solving the circuit nonlinear algebraic-differential equations based on a sophisticated arrangement of Newton interpolation polynomial is characterized first. After that, a novel method is introduced for improving the convergence with four suggested criteria that are being compared. For enhancing the efficiency of repeated solutions of linear systems necessary in the Newton-Raphson method, a novel modification of the Markowitz criterion is suggested, which is compatible with the fast modes of the LU factorization. The modified criterion consists in an estimation of probabilities of the fill-in enlargement. The probabilities are determined for all columns of the system matrix before the LU factorization, where the column probability is calculated as the average value of the probabilities for all the column elements. Finally, the columns are reordered so that first and last should be those with the minimum and maximum probabilities.

Accurate Modeling of Unusual Electronic Circuit Elements with Artificial Neural Networks

  • Authors: Pospíšil, L., doc. Ing. Josef Dobeš, CSc., Yadav, A.
  • Publication: Proceedings of 2nd Conference on Circuits, Systems, Control, Signals. Athens: World Scientific and Engineering Academy and Society, 2011. pp. 150-155. ISBN 978-1-61804-035-0.
  • Year: 2011
  • Department: Department of Radioelectronics
  • Annotation:
    Nowadays, there are many electronic structures for which their models are necessary. However, in the recent PSpice programs, only a class of five types of the MESFET model is available. In the paper, a new method is suggested for modeling electronic structures by exclusive neural networks, or by corrective neural networks working attached to a modified analytic model. The accuracy the analytic model is assessed by extracting the model parameters of MESFET, pHEMT, and microwave varactors. The accuracy of procedures that use the neural networks is assessed by extracting model parameters in static and dynamic domains. First, an approximation of the pHEMT output characteristics is carried out by means of both exclusive and corrective networks; and second, an approximation of the C-V function of an avalanche photodiode is performed by the exclusive network. Last, the memristor characteristic with an extraordinary hysteresis is approximated by a set of cooperative artificial neural networks.

Accurate Procedures of the Sparse-Matrix Deflation for Circuit Pole-Zero Analysis

  • Authors: doc. Ing. Josef Dobeš, CSc., Černý, D., Kolka, Z., Biolková, V., Míchal, J.
  • Publication: IEEE Africon 2011. Piscataway: IEEE, 2011. pp. 1-6. ISSN 2153-0025. ISBN 978-1-61284-993-5.
  • Year: 2011
  • Department: Department of Radioelectronics
  • Annotation:
    The pole-zero analysis is generally known to be very sensitive to the numerical precision of the computer arithmetic. In the paper, various methods are suggested for solving that problem. First, an optimal pivoting strategy of the algorithm that reduces the general eigenvalue problem to the standard one is presented for both full- and sparse-matrix procedures. The algorithm increases the precision of the semisymbolic analysis. A new technique has also been incorporated recognizing multiple poles or zeros, which are often computed inaccurately by the standard algorithms. A novel type of this procedure called secondary root polishing is described in a detailed way. The accuracy is further increased using longer numerical data. First, the long double precision is utilized. Furthermore, a novel application of a suitable multiple-precision arithmetic library is suggested. Finally, using the longer numerical data to eliminate possible imprecision of the multiple eigenvalues is evaluated.

An implementation of the circuit multiobjective optimization with the weighted sum strategy and goal attainment method

  • Authors: doc. Ing. Josef Dobeš, CSc., Míchal, J.
  • Publication: 2011 IEEE International Symposium on Circuits and Systems. Piscataway: IEEE, 2011. pp. 1728-1731. ISSN 0271-4302. ISBN 978-1-4244-9474-3.
  • Year: 2011
  • DOI: 10.1109/ISCAS.2011.5937916
  • Link: https://doi.org/10.1109/ISCAS.2011.5937916
  • Department: Department of Radioelectronics
  • Annotation:
    A robust implementation of the weighted sum strategy and goal attainment method is described, and a comparison of both methods is performed. While the weighted sum strategy is preferable if the problem is known to be convex, or if a smaller number of controlling parameters is advantageous, the goal attainment method provides a better control over accessed parts of the Pareto front, but only at the cost of higher demands on the designer as well as on the used computational power. The robustness is increased by means of a two-stage modified singleobjective method. The use of both methods is demonstrated on a practical example of a video amplifier design involving a four-dimensional optimization. Obtained results are evaluated and discussed regarding average correlation and inferiority. Furthermore, an interpolative approach to generating graphical output suitable for multidimensional problems is suggested and used for the four-dimensional objective space of the optimized circuit.

Common LISP as Simulation Program (CLASP) of Electronic Circuits

  • Department: Department of Radioelectronics
  • Annotation:
    In this paper, an unusual and efficient usage of functional programming language Common LISP as simulation program (CLASP) for electronic circuits is proposed. The principle of automatic self-modifying program has enabled complete freedom in definition of methods for optimized solution of any problem and speeding up the entire process of simulation. A new approach to program structure in electronic circuit simulator CLASP is described. The definition of simple electronic devices as resistor, voltage source and diode is given all together with description of their memory management in program CLASP. Other circuit elements can be easily defined in the same way. Simulation methods for electronic circuits as linear and nonlinear direct current analysis (DC) are suggested. A comparison of performances of two different linear solvers (an original and the standard GNU GSL) for circuit equations is demonstrated by an algorithm for automatic generation of huge circuits.

Efficient algorithm for solving systems of circuit differential-algebraic equations with reliable divergence suppression in DC and time domains

  • Authors: doc. Ing. Josef Dobeš, CSc., Yadav, A., Černý, D.
  • Publication: 2011 IEEE 54th International Midwest Symposium on Circuits and Systems. Piscataway: IEEE, 2011. pp. 1-4. ISSN 1548-3746. ISBN 978-1-61284-857-0.
  • Year: 2011
  • DOI: 10.1109/MWSCAS.2011.6026589
  • Link: https://doi.org/10.1109/MWSCAS.2011.6026589
  • Department: Department of Radioelectronics
  • Annotation:
    Although many simulation tools contain advanced algorithms for the solution of the systems of differential-algebraic nonlinear equations, some classes of circuits still cause serious problems. These are typically the circuits with strong negative feedbacks, flip-flop circuits, the blocks that are characterized by macromodels with unusual elements, and large distributed amplifiers and oscillators. In the paper, a very efficient and reliable algorithm for solving the circuit differential-algebraic equations is characterized first. After that, a novel method is introduced for improving the convergence with four suggested criteria that are being compared. Unlike the similar algorithms focused on an operating point analysis only, the proposed method also works in a transient analysis. All the four criteria are thoroughly tested. The results confirm extraordinary robustness of the proposed method, even circuits with a large memelement hysteresis can be solved.

Efficient Procedure for Solving Circuit Algebraic-Differential Equations with Modified Sparse LU Factorization Improving Fill-In Suppression

  • Authors: doc. Ing. Josef Dobeš, CSc., Černý, D., Biolek, D.
  • Publication: 2011 20th European Conference on Circuit Theory and Design (ECCTD). Piscataway: IEEE, 2011. pp. 689-692. ISBN 978-1-4577-0618-9.
  • Year: 2011
  • DOI: 10.1109/ECCTD.2011.6043637
  • Link: https://doi.org/10.1109/ECCTD.2011.6043637
  • Department: Department of Radioelectronics
  • Annotation:
    In the paper, an efficient and reliable algorithm for solving the circuit algebraic-differential equations is characterized first, which is based on a sophisticated arrangement of the Newton interpolation polynomial. For enhancing the efficiency of repeated solutions of linear systems necessary in the Newton-Raphson method, a novel modification of the Markowitz criterion is suggested, which is compatible with the fast modes of the LU factorization. The modified criterion consists in an estimation of probabilities of the fill-in enlargement. The probabilities are determined for all columns of the system matrix before the LU factorization, where the column probability is calculated as the average value of the probabilities for all the column elements. Finally, the columns are reordered so that first and last should be those with the minimum and maximum probabilities, respectively. As a verification of the proposed algorithm, a comprehensive set of numerical tests has been performed.

Methods for Improving Efficiency in High Frequency Circuit Simulation

  • Authors: Černý, D., doc. Ing. Josef Dobeš, CSc.,
  • Publication: Workshop 2011,CTU Student Grant Competition in 2010 (SGS 2010). Praha: ČVTVS, 2011. pp. 1-4.
  • Year: 2011
  • Department: Department of Radioelectronics
  • Annotation:
    There is no doubt that the SPICE has become the most widely used program for computer simulation of electrical circuits. The key to success of SPICE lies in various kind of analysis such as operating point, sensitivity, transient analysis and many others, which SPICE program can perform. The algorithms used for evaluation of simulation are based on iterative chain of numerical operations, which mostly involve solving of nonlinear differential equations, numerical integration and LU transformation. This paper gives simple overview about weak points of the simulation chain and introduces implementation of new algorithms to improve accuracy and efficiency of the simulation.

Novel HEMT Models with Improved Higher-Order Derivatives and Extracting Their Parameters Using Multibias S-Parameters

  • Authors: doc. Ing. Josef Dobeš, CSc., Grábner, M.
  • Publication: 2011 IEEE Compound Semiconductor Integrated Circuit Symposium. Piscataway: IEEE, 2011. p. 189-192. ISSN 1550-8781. ISBN 978-1-61284-712-2.
  • Year: 2011
  • DOI: 10.1109/CSICS.2011.6062468
  • Link: https://doi.org/10.1109/CSICS.2011.6062468
  • Department: Department of Radioelectronics
  • Annotation:
    Novel two HEMT models are suggested in the paper with improved accuracy of higher-order derivatives, which is very important for modeling radio-frequency devices as mixers, etc. The proposed modifications of the models are based on empirical relations for the transconductance dependence on gate-source voltage. Moreover, a way is suggested how to extract the model parameters of various nonlinear HEMT models from a measured multibias s-parameter data set. The proposed extraction procedure is based on a three-step identification procedure that uses robust optimization methods. Finally, various HEMT models -- including the proposed ones -- are compared in terms of the root-mean-square error of DC characteristics and multibias s-parameters.

Precise Algorithms for Pole-Zero Analysis in Electronic Circuit Design

  • Authors: doc. Ing. Josef Dobeš, CSc., Biolek, D., Míchal, J., Černý, D., Sláma, L.
  • Publication: International Journal of Circuits, Systems and Signal Processing. 2011, 5(3), 228-236. ISSN 1998-4464.
  • Year: 2011
  • Department: Department of Radioelectronics
  • Annotation:
    The pole-zero analysis is generally known to be very sensitive to the numerical precision of the arithmetics. Various methods are suggested for solving that problem. First, an optimal pivoting strategy of the algorithm that reduces general eigenvalue problem to the standard one is presented for both full and sparse-matrix procedures. The algorithm increases the precision of the semisymbolic analysis, especially for the large-scale radio frequency circuits. A novel technique is also incorporated recognizing multiple poles or zeros, which are often computed inaccurately by standard algorithms. A new type of this procedure called secondary root polishing is also described. The accuracy is furthermore increased using longer numerical data. First, the long double precision is used. Further, a novel application of a suitable multiple-precision arithmetic library is suggested. Finally, using the longer numerical data to eliminate possible imprecision of the multiple eigenvalues is evaluated.

Tolerance-based Control Mechanism for Approximate Symbolic Analysis

  • Authors: Kolka, Z., Biolek, D., Biolková, V., doc. Ing. Josef Dobeš, CSc.,
  • Publication: IEEE Africon 2011. Piscataway: IEEE, 2011. p. 1-5. ISSN 2153-0025. ISBN 978-1-61284-993-5.
  • Year: 2011
  • DOI: 10.1109/AFRCON.2011.6072093
  • Link: https://doi.org/10.1109/AFRCON.2011.6072093
  • Department: Department of Radioelectronics
  • Annotation:
    The paper deals with an enhanced control mechanism for approximate symbolic analysis of the Simplification-Before- Generation class. A traditional approach consists in the evaluation of errors caused by simplification only for the nominal parameters of network components. The proposed procedure uses sensitivities to estimate the worst-case error due to component tolerances, i.e. the expression validity is checked over the tolerance interval of component parameters. A fast computational algorithm based on the Sherman-Morrison formula is used. The numerical cost is approximately given by two matrix inversions per one control-frequency point and one simplification step.

A Comparison of Steady-State Procedures Based on Epsilon-Algorithm and Sensitivity Analysis

  • Authors: doc. Ing. Josef Dobeš, CSc., Černý, D., Biolková, V., Kolka, Z.
  • Publication: Proceedings of 2010 IEEE Latin American Symposium on Circuits and Systems. Piscataway: IEEE, 2010. pp. 292-295.
  • Year: 2010
  • Department: Department of Radioelectronics
  • Annotation:
    Many software tools of the PSpice class do not contain any steady-state algorithm, especially for autonomous circuits. In paper, two add-ons are described to the algorithm for implicit numerical integration which determine the steady state of both nonautonomous and autonomous circuits by an extrapolation method or sensitivity analysis. The extrapolation procedure is based on scalar epsilon-algorithm which is relatively easy for programing and efficient in terms of number of required iterations. Since the selected algorithm for the implicit numerical integration gives values of derivatives at any time, the determination of unknown periods of autonomous circuits can be performed by modified Newton-Raphson method. The second steady-state procedure efficiently utilizes the outcome of time-domain sensitivity analysis. The efficiency of procedures is demonstrated by the analyses of a feedback microwave oscillator, rectifier, and C-class amplifier.

Controlling Peaks of the Audio Signal by Dynamically Allocated Scale Factor for Lossy Psychoacoustic Encoder

  • Authors: Straňák, P., doc. Ing. Josef Dobeš, CSc.,
  • Publication: Proceedings of the 53rd IEEE International Midwest Symposium on Circuits and Systems. Piscataway: IEEE, 2010. p. 388-391. ISSN 1548-3746. ISBN 978-1-4244-7773-9.
  • Year: 2010
  • DOI: 10.1109/MWSCAS.2010.5548874
  • Link: https://doi.org/10.1109/MWSCAS.2010.5548874
  • Department: Department of Radioelectronics
  • Annotation:
    The paper is aimed at original method of controlling peaks of audio signal by dynamically allocated scale factor. The method is useful in the case of processing audio signal before a psychoacoustic lossy encoder - MPEG1 layer 2 (used in DAB), AAC, HE-AAC v1 (used in DAB+), or HE-AAC v2, for example. Such encoders are very sensitive to a clipping product generated by a conventional clipper. Suggested method eliminates most of unwanted spectral components on the clipper output. Therefore, it produces conditions for optimal function of the psychoacoustic lossy encoders. The paper contains both results of measurements and listening tests which clearly demonstrate the improvements.

Formula Simplification using Two-Graph Method

  • Authors: Kolka, Z., Vlk, M., Biolek, D., Biolkova, V., doc. Ing. Josef Dobeš, CSc.,
  • Publication: Proceedings of 2010 IEEE Latin American Symposium on Circuits and Systems. Piscataway: IEEE, 2010. pp. 260-263.
  • Year: 2010
  • Department: Department of Radioelectronics
  • Annotation:
    The paper deals with a method of graph transformation and its application to approximate symbolic analysis of linearized circuits. Based on the two-graph circuit description the method changes the graph structure in order to decrease the number of common spanning trees, i.e. to decrease the formula complexity. Instead of the simple edge deletion or contraction voltage and current graphs are modified to remove negligible voltages from loops and negligible currents from cuts.

Multiobjective Optimization for RF Low Noise Amplifier Design

  • Authors: Míchal, J., doc. Ing. Josef Dobeš, CSc.,
  • Publication: Proceedings of 2010 IEEE International Conference on Wireless Information Technology and Systems. Piscataway: IEEE, 2010. p. 1-4. ISBN 978-1-4244-7091-4.
  • Year: 2010
  • DOI: 10.1109/ICWITS.2010.5611858
  • Link: https://doi.org/10.1109/ICWITS.2010.5611858
  • Department: Department of Radioelectronics
  • Annotation:
    A modified semiautomatic multiobjective optimization method based on an asymptotically uniform coverage of reference set in combination with goal attainment method was proposed. The method was successfully tested on the multiobjective optimization of an RF low-noise antenna preamplifier.

Multiobjective Optimization With an Asymptotically Uniform Coverage of Pareto Front

  • Authors: Míchal, J., doc. Ing. Josef Dobeš, CSc., Černý, D.
  • Publication: Proceedings of 2010 IEEE International Symposium on Circuits and Systems. Piscataway: IEEE, 2010. pp. 2912-2915. ISSN 0271-4302. ISBN 978-1-4244-5309-2.
  • Year: 2010
  • DOI: 10.1109/ISCAS.2010.5538044
  • Link: https://doi.org/10.1109/ISCAS.2010.5538044
  • Department: Department of Radioelectronics
  • Annotation:
    This paper suggests an enhancement of an existing method for the multiobjective optimization known as GAM (goal attainment method). In our proposal, the GAM algorithm is combined with a mechanism that automatically provides a set of parameters (weights, coordinates of the reference point) for which the method generates noninferior solutions uniformly spread over a suitably selected part of the Pareto front. The resulting set of solutions is then presented in a suitable graphic form so that the solution representing the most satisfactory tradeoff can be easily chosen. The whole algorithm was implemented as a program and tested on several RF design examples (video, low-noise, and power amplifiers), whose optimization results are also presented. For a comparison, the first design example was also solved by another method known as WMM (weighted metrics method).

New Approach for Enhancing Efficiency of Computer Aided Design in Circuit Simulation

  • Authors: Černý, D., doc. Ing. Josef Dobeš, CSc.,
  • Publication: Proceedings of the 17th IEEE International Conference on Electronics, Circuits, and Systems. Piscataway: IEEE, 2010. pp. 641-644. ISBN 978-1-4244-8157-6.
  • Year: 2010
  • Department: Department of Radioelectronics
  • Annotation:
    All versions of SPICE can perform various kinds of analysis such as operating point, sensitivity, and transient analyses, and many others. The algorithms used for computations are based on an iterative numerical solution of nonlinear differential equations. This paper gives a simple overview about these algorithms, their principles, function and disadvantages. It introduces a novel approach and implementation of implicit and explicit algorithms for solving the differential equations in circuit design with the aim to improve the reliability and efficiency of the solution. Furthermore, it presents a comparison between the standard SPICE algorithm and the new developed ones.

New Methods for Improving the Pole-Zero Analysis Accuracy

  • Authors: doc. Ing. Josef Dobeš, CSc., Černý, D., Sláma, L., Biolek, D., Míchal, J.
  • Publication: Mathematical Models for Engineering Science. Berlin: Institute for Environment, Engineering, Economics and Applied Mathematics, 2010. pp. 155-158. ISSN 1792-6734. ISBN 978-960-474-252-3.
  • Year: 2010
  • Department: Department of Radioelectronics
  • Annotation:
    An optimal pivoting strategy of the algorithm that reduces the general eigenvalue problem to the standard one is suggested for both fulland sparse-matrix procedures. The algorithm increases the accuracy of the semisymbolic analysis, especially for resonant and/or large-scale electronic circuits. A novel technique is also incorporated recognizing multiple poles or zeros, which are often computed inaccurately by the standard algorithms. A new type of this procedure called secondary root polishing is described in the paper. The accuracy is further increased using longer numerical data. First, the "long double" precision (available in many C/C++ compilers) is utilized. Second, a novel application of a suitable multiple-precision arithmetic library is suggested. The algorithms were checked on various electronic circuits.

Reliable procedure for electrical characterization of MOS-based devices

  • Authors: doc. Ing. Josef Dobeš, CSc., Míchal, J., Paňko, V., Pospíšil, L.
  • Publication: Solid-State Electronics. 2010, 54(10), 1173-1184. ISSN 0038-1101.
  • Year: 2010
  • DOI: 10.1016/j.sse.2010.05.034
  • Link: https://doi.org/10.1016/j.sse.2010.05.034
  • Department: Department of Radioelectronics
  • Annotation:
    Contemporary models of MOSFET are very complicated, especially the BSIM and EKV ones. Therefore, an identification of many parameters of these models is quite a difficult task from both algorithmic and numeric points of view. Moreover, the complexity of the models makes an optimization of MOS-based functional blocks too difficult. This paper suggests several improvements of both mono-objective and multi-objective optimization methods to enhance the reliability of extraction of the model parameters and to find the most achievable properties of the MOS-based functional blocks.

Selecting an Optimal Structure of Artificial Neural Networks for Characterizing RF Semiconductor Devices

  • Authors: doc. Ing. Josef Dobeš, CSc., Pospíšil, L., Paňko, V.
  • Publication: Proceedings of the 53rd IEEE International Midwest Symposium on Circuits and Systems. Piscataway: IEEE, 2010. pp. 1206-1209. ISSN 1548-3746. ISBN 978-1-4244-7773-9.
  • Year: 2010
  • Department: Department of Radioelectronics
  • Annotation:
    In the paper, a method is suggested for modeling miscellaneous RF semiconductor devices by exclusive neural networks or by corrective neural networks working attached to a modified analytic model. An accuracy of the proposed modification of the analytic model is assessed by extracting model parameters of the AlGaAs/InGaAs/GaAs pHEMT. An accuracy of procedures with neural networks is generally assessed by extracting their parameters in static and dynamic domains. An approximation of the AlGaAs/InGaAs/GaAs pHEMT output characteristics is carried out by means of both exclusive and corrective artificial neural networks. A systematic sequence of analyses is also performed for examining an optimal structure of the artificial neural network from the point of view its structure and complexity. The tests have been performed on both five- and four-layer artificial neural networks that serve for modeling a P-channel JFET and for the AlGaAs/InGaAs/GaAs pHEMT.

A Modified Branin Model of Lossless Transmission Lines

  • Authors: doc. Ing. Josef Dobeš, CSc., Sláma, L.
  • Publication: Proceedings of the 52nd IEEE Midwest Symposium on Circuits and Systems. Piscataway: IEEE, 2009. p. 236-239. ISSN 1548-3746. ISBN 978-1-4244-4479-3.
  • Year: 2009
  • Department: Department of Radioelectronics
  • Annotation:
    Nowadays, absolute majority of circuit simulation programs contains classic Branin model of lossless transmission lines. However, characterizing the four delays (t - TD) incorporated in the model still causes difficulties due to incompatibility with most algorithms for solving algebraic-differential equations. In the paper, a mathematical substitution of the delay is suggested which smoothly cooperates with the circuit algorithms. Moreover, results of the simulation do not contain spurious oscillations that are practically irremovable when an LC model of the line is used. As the model is suitable for RF circuits, its properties are demonstrated by means of an analysis of a microwave oscillator.

Advanced types of the sensitivity analysis in frequency and time domains

  • Authors: doc. Ing. Josef Dobeš, CSc.,
  • Publication: AEU-International Journal of Electronics and Communications. 2009, 63(1), 52-64. ISSN 1434-8411.
  • Year: 2009
  • DOI: 10.1016/j.aeue.2007.10.008
  • Link: https://doi.org/10.1016/j.aeue.2007.10.008
  • Department: Department of Radioelectronics
  • Annotation:
    The majority of standard tools for computer-aided design can perform only limited types of the sensitivity analysis: Spice determines operating-point sensitivities, and SpectreRF contains a parametric sensitivity analysis that can be used for determining the phase noise, for example. In the paper, some new types of the sensitivity analysis in frequency and time domains are described. These types of the analysis are not implemented in the standard circuit simulators.

Improving Convergence of Algorithms for Solving Systems of Circuit Algebraic-Differential Equations

  • Authors: doc. Ing. Josef Dobeš, CSc., Kolka, Z.
  • Publication: ECCTD'09 European Conference on Circuit Theory and Design 2009. Istambul: IEEE, 2009. p. 476-479. ISBN 978-1-4244-3895-2.
  • Year: 2009
  • DOI: 10.1109/ECCTD.2009.5275033
  • Link: https://doi.org/10.1109/ECCTD.2009.5275033
  • Department: Department of Radioelectronics
  • Annotation:
    Nowadays, the majority of circuit simulation programs contain advanced methods for suppressing divergence of algorithms for solving algebraic-differential equations. However, some classes of circuits still cause problems - the circuits with strong feedback, flip-flop circuits, the ones characterized by macro models with unusual elements, and large distributed oscillators. In the paper, a novel method is introduced for improving the convergence with four criteria that are being compared. Unlike similar algorithms focused on an operating point analysis, the method also works in a transient analysis. All the four criteria are thoroughly tested on eight problematic circuits - six of them often diverge in the operating point analysis, and two of them sometimes diverge during the transient analysis.

Parameter Extraction of HEMT Models from Multibias S-Parameters

  • Authors: Grábner, M., doc. Ing. Josef Dobeš, CSc.,
  • Publication: Proceedings of the IEEE International Symposium on Circuits and Systems. Piscataway: IEEE, 2009. p. 2085-2088. ISSN 0271-4302. ISBN 978-1-4244-3827-3.
  • Year: 2009
  • DOI: 10.1109/ISCAS.2009.5118205
  • Link: https://doi.org/10.1109/ISCAS.2009.5118205
  • Department: Department of Radioelectronics
  • Annotation:
    The aim of the paper is to show how to identify the parameters of various nonlinear circuit models of a high electron mobility transistor from the multibias s-parameter dataset measured on a pHEMT device. A three-step identification procedure is described that uses tested optimization methods. Two original model modifications are suggested based on empirical relations for the transconductance dependence on gate-source voltage. Various models including the modified ones are compared in terms of the root-mean-square errors of multibias s-parameters.

Reliable Procedure for Electrical Characterization of MOS-Based Devices

  • Authors: doc. Ing. Josef Dobeš, CSc., Paňko, V., Pospíšil, L.
  • Publication: Proceedings of 2009 International Semiconductor Device Research Symposium. Piscataway: IEEE, 2009. pp. 1-2. ISBN 978-1-4244-6031-1.
  • Year: 2009

A Comparison of Distortion Analyses Based on Volterra Series and Steady State Algorithm

  • Department: Department of Radioelectronics
  • Annotation:
    The most accurate way for computing the distortion coefficients is to find a steady state period of the signal, and then to determine spectrum by means of fast Fourier transform. In the paper, main features of a reliable and efficient algorithm for determining the steady state are described. However, even such accelerated method often needs a time-consuming numerical integration over many periods of the faster signal. For this reason, an efficient method for a fast estimation of the main distortion coefficients is also presented which does not contain frequent imperfections in the algorithm implementations. The algorithm uses higher-order Volterra series in a simple multistep algorithm which is compatible with a typical structure of the frequency domain part of software tools. Both methods are compared by analyses of the main intermodulation products of a low-voltage low-power CMOS RF four-quadrant multiplier.

A Comparison of Distortion Analyses Based on Volterra Series and Steady State Algorithm

  • Authors: doc. Ing. Josef Dobeš, CSc.,
  • Publication: Proceedings of PIERS 2008 in Cambridge. Cambridge, MA: The Electromagnetics Academy, 2008. pp. 130-134. ISSN 1559-9450. ISBN 978-1-934142-06-6.
  • Year: 2008
  • Department: Department of Radioelectronics
  • Annotation:
    The most accurate way for computing the distortion coefficients is to find a steady state period of the signal, and then to determine spectrum by means of fast Fourier transform. In the paper, main features of a reliable and efficient algorithm for determining the steady state are described. However, even such accelerated method often needs a time-consuming numerical integration over many periods of the faster signal. For this reason, an efficient method for a fast estimation of the main distortion coefficients is also presented which does not contain frequent imperfections in the algorithm implementations. The algorithm uses higher-order Volterra series in a simple multistep algorithm which is compatible with a typical structure of the frequency domain part of software tools. Both methods are compared by analyses of the main intermodulation products of a low-voltage low-power CMOS RF four-quadrant multiplier.

A Steady-State Add-On to the Algorithm for Implicit Numerical Integration

  • Authors: doc. Ing. Josef Dobeš, CSc.,
  • Publication: 2008 IEEE International 51st Midwest Symposium on Circuits and Systems. Piscataway: IEEE, 2008. pp. 511-514. ISSN 1548-3746. ISBN 978-1-4244-2166-4.
  • Year: 2008
  • Department: Department of Radioelectronics
  • Annotation:
    Many software tools of the PSpice class do not contain an implementation of the steady-state algorithm, especially for autonomous circuits. In the paper, an add-on is described to the algorithm for implicit numerical integration which determines the steady state of both nonautonomous and autonomous circuits by an extrapolation method. The extrapolation procedure is based on scalar epsilon-algorithm which is relatively easy for programing and efficient in terms of number of required iterations. Since the selected algorithm for the implicit numerical integration gives values of derivatives at any time, the determination of unknown periods of autonomous circuits can be performed by modified Newton-Raphson method. The efficiency of the procedure is demonstrated by the steady-state analysis of a tunable distributed microwave oscillator with the results compared with measured data.

An Accurate Gate-Delay Model for High Speed Digital and Analog Circuits

  • Authors: doc. Ing. Josef Dobeš, CSc., Paňko, V., Pospíšil, L.
  • Publication: Proceedings of the 2008 IEEE Dallas Circuits And Systems Workshop. Piscataway: IEEE, 2008. pp. 37-40. ISBN 978-1-4244-2955-4.
  • Year: 2008
  • Department: Department of Radioelectronics
  • Annotation:
    At present, most of simulation programs can characterize gate delays of microwave transistors. However, the delay is mostly approximated by means of a first-order differential equation only. In the paper, a more accurate way is suggested which is based on an appropriate second-order Bessel function. The delay model is implemented to a slightly but efficiently modified classic MESFET model. The proposed model does not create spurious oscillations that are typical for any LC approximations, and the simulation times are comparable with those obtained without the delay model. Properties of the implementation of the second-order Bessel function are demonstrated by an analysis of a tunable distributed microwave oscillator.

Lateral PNP Transistor Modeling with SPICE Models

  • Authors: Paňko, V., Slezák, J., doc. Ing. Josef Dobeš, CSc., Vojkůvka, L.
  • Publication: MOS-AK/ESSDERC/ESSCIRC Workshop. Edinburgh: MOS-AK, 2008. pp. 1.
  • Year: 2008
  • Department: Department of Radioelectronics
  • Annotation:
    Adapted models of vertical NPN transistor are still mostly used for modeling the lateral PNP transistors. It causes inaccurate modeling because the behavior of laterally arranged PN junctions is different than vertically arranged PN junction. This presentation deals with the comparison of the several possible models of a lateral PNP transistor with the MODELLA model developed by Philips company. Differences among models are identified in DC/AC modes. A special attention is paid to the saturation region and models capabilities to describe scattering parameters (S parameters).

Using Volterra Series for an Estimation of Fundamental Intermodulation Products

  • Department: Department of Radioelectronics
  • Annotation:
    The most precise procedure for determining the intermodulation products is to find a steady-state period of the signal first, and then to calculate its spectrum by means of the fast Fourier transform. However, this method needs time-consuming numerical integration over many periods of the faster signal even for enhanced methods for finding the steady state. In the paper, an efficient method for fast estimation of the fundamental intermodulation products is presented. The method uses Volterra series in a simple multistep algorithm which is compatible with a typical structure of the frequency-domain part of circuit simulators. The method is demonstrated by an illustrative testing circuit first, which clearly shows possible incorrect interpretation of the Volterra series. Thereafter, practical usage of the algorithm is demonstrated by fast estimation of the main intermodulation products of a low-voltage low-power RF CMOS fourquadrant multiplier.

Computer Simulation of Continuous-Time and Switched Circuits: Limitations of SPICE-Family Programs and Pending Issues

  • Authors: Biolek, D., doc. Ing. Josef Dobeš, CSc.,
  • Publication: Proceedings of 17th International Conference Radioelektronika 2007. Piscataway: Institute of Electrical and Electronic Engineers, 2007. pp. 15-25. ISBN 1-4244-0821-0.
  • Year: 2007
  • Department: Department of Radioelectronics
  • Annotation:
    The contribution deals with some open problems from the area of Transient and AC analyses of large continuous-time and switched circuits with the focus on switched capacitor circuits and switched DC-DC converters. The discussed weak points of SPICE-like and SPICE-compatible simulation programs consist in the absence of finding effectively the steady-state, in an inefficient integration algorithm for the transient analysis of switching phenomena, and in the absence of a direct AC analysis of switched circuits. The paper also describes some new approaches, which could be helpful in overcoming the above limitations.

Electronic Circuit Design Using Multiobjective Optimization

  • Authors: Míchal, J., doc. Ing. Josef Dobeš, CSc.,
  • Publication: Proceedings of the 50th IEEE International Midwest Symposium on Circuits and Systems. Piscataway: IEEE, 2007. pp. 734-737. ISBN 1-4244-1176-9.
  • Year: 2007
  • Department: Department of Radioelectronics
  • Annotation:
    This paper presents a variation and extension of a previously existing method for multiobjective optimization known as Goal Attainment Method (GAM). The method GAM is in this research combined with a mechanism that automatically provides a set of parameters (weights, coordinates of the reference point) for which the method generates noninferior solutions uniformly spread over a suitably chosen part of the Pareto front. The resulting set of solutions is then presented in a graphic form to the designer so that the solution representing the most satisfactory tradeoff can be easily chosen. The whole algorithm was implemented as a program and tested on two RF design examples (an LNA and a power amplifier), whose optimization results are also presented in the paper.

Enhanced Modes of the Sensitivity Analysis for RF Design

  • Authors: doc. Ing. Josef Dobeš, CSc., Kolka, Z.
  • Publication: Proceedings of the 2007 International Symposium on Signals, Systems and Electronics. Piscataway: IEEE, 2007. pp. 83-86. ISBN 1-4244-1449-0.
  • Year: 2007
  • Department: Department of Radioelectronics
  • Annotation:
    In the paper, some types of the sensitivity analysis in the frequency domain are described which are not present in the standard simulators-especially, a procedure is suggested for determining the sensitivities of noise figure. First, an improvement of the method for computing the noise figure is presented, which incorporates necessary circuit matching and eliminates the subtraction of output noise from load at each frequency. Second, a simple formula is derived for computing the sensitivities of the noise figure. The sensitivity analysis in the frequency domain is generally demonstrated by means of a distributed microwave amplifier first, and then using the sensitivity analysis of the noise figure for improving the noise properties of a monolithic microwave amplifier is described.

Fast Estimation of Main Intermodulation Products Using Volterra Series

  • Authors: doc. Ing. Josef Dobeš, CSc.,
  • Publication: 2007 International Conference on Integrated Circuit Design and Technology. Piscataway: IEEE, 2007. p. 19-22. ISBN 1-4244-0756-7.
  • Year: 2007
  • DOI: 10.1109/ICICDT.2007.4299534
  • Link: https://doi.org/10.1109/ICICDT.2007.4299534
  • Department: Department of Radioelectronics
  • Annotation:
    The most accurate procedure for computing the intermodulation products is to find a steady-state period of the signal, and then to determine the spectrum by means of fast Fourier transform. However, this method needs a time-consuming numerical integration over many periods of the faster signal even for accelerated extrapolation methods for determining the steady state. In the paper, an efficient method for a fast estimation of the main intermodulation products is presented. The method uses higher-order Volterra series in a simple multistep algorithm, which is compatible with a typical structure of the frequency-domain part of software tools. The method is demonstrated by an illustrative example first, which clearly shows possible incorrect interpretation of the Volterra series. Afterwards, the efficiency of the algorithm is demonstrated by a fast estimation of the main intermodulation products of a low-voltage low-power CMOS RF four-quadrant multiplier.

Identifying Model Parameters of Semiconductor Devices Using Optimization Techniques

  • Authors: doc. Ing. Josef Dobeš, CSc., Grábner, M., Hruškovič, Ľ.
  • Publication: Journal of Computing and Information Technology. 2007, 15(4), 331-338. ISSN 1330-1136.
  • Year: 2007
  • DOI: 10.2498/cit.1001141
  • Link: https://doi.org/10.2498/cit.1001141
  • Department: Department of Radioelectronics
  • Annotation:
    The optimization is an indispensable tool for extracting the parameters of any complicated models. Hence, advanced optimization techniques are also necessary for identifying the model parameters of semiconductor devices because their current models are very sophisticated (especially the BJT and MOSFET ones). The equations of such models contain typically one hundred parameters. Therefore, the measurement and particularly identification of the full set of the model parameters is very difficult. In the paper, an optimization method is presented which is applicable for the identifications of very complicated models using a relatively small number of iterations. The algorithm has been implemented into the original software tool C.I.A. (Circuit Interactive Analyzer) to its static and dynamic analysis modes. Therefore, the optimization is able to identify both direct-current and capacitance models of semiconductor devices. The process is demonstrated with various transistors.

Identifying Model Parameters of Semiconductor Devices Using Optimization Techniques

  • Authors: doc. Ing. Josef Dobeš, CSc., Grábner, M., Hruškovič, Ľ.
  • Publication: Proceedings of the ITI 2007 29th International Conference on Information Technology Interfaces. Zagreb: SRCE University of Zagreb, 2007. pp. 603-608. ISSN 1330-1012. ISBN 978-953-7138-09-7.
  • Year: 2007
  • Department: Department of Radioelectronics
  • Annotation:
    The optimization is an indispensable tool for extracting the parameters of any complicated models. Hence, advanced optimization techniques are also necessary for identifying the model parameters of semiconductor devices because their current models are very sophisticated (especially the BJT and MOSFET ones). The equations of such models contain typically one hundred parameters. Therefore, the measurement and particularly identification of the full set of the model parameters is very difficult. In the paper, an optimization method is presented which is applicable for the identifications of very complicated models using a relatively small number of iterations. The algorithm has been implemented into the original software tool C.I.A. (Circuit Interactive Analyzer) to its static and dynamic analysis modes. Therefore, the optimization is able to identify both direct-current and capacitance models of semiconductor devices. The process is demonstrated with various transistors.

Improving the Accuracy of PHEMT Models Using Corrective Artifcial Neural Networks

  • Authors: doc. Ing. Josef Dobeš, CSc., Pospíšil, L.
  • Publication: PIERS 2007 Prague - Proceeding of Progress In Electromagnetics Research Symposium. Cambridge, MA: The Electromagnetics Academy, 2007. pp. 512-515. ISSN 1559-9450. ISBN 978-1-934142-02-8.
  • Year: 2007
  • Department: Department of Radioelectronics
  • Annotation:
    In the recent PSpice-family programs, only a class of five types of the MESFET model is available for a pHEMT representation. In the paper, a way is suggested for modeling pHEMT using a corrective neural network working attached to an updated analytic MESFET model. The accuracy of procedures is assessed by extracting model parameters for a typical TriQuint pHEMT. A sequence of analyses is also performed for determining an optimal structure of the artificial neural network.

Modeling Delays of Microwave Transistors and Transmission Lines by the 2nd-Order Bessel Function

  • Department: Department of Radioelectronics
  • Annotation:
    At present, most of simulation programs can characterize gate delays of microwave transistors. However, the delay is mostly approximated by means of first-order differential equations. In the paper, a more accurate way is suggested which is based on an appropriate second-order differential equation. Concerning the transmission line delay, majority of the simulation programs use both Branin (for lossless lines) and LCRG (for lossy lines) models. However, the first causes extreme simulation times, and the second causes well-known spurious oscillations in the simulation results. In the paper, an unusual way for modeling the transmission line delay is defined, which is also based on the second-order Bessel function. The proposed model does not create the spurious oscillations and the simulation times are comparable with those obtained with the classical models.

Modeling Special High Frequency Devices Using Artificial Neural Networks

  • Authors: doc. Ing. Josef Dobeš, CSc., Pospíšil, L.
  • Publication: Proceedings of the 2007 International Semiconductor Device Research Symposium. Piscataway: IEEE, 2007. ISBN 978-1-4244-1892-3.
  • Year: 2007
  • Department: Department of Radioelectronics
  • Annotation:
    Nowadays, there are miscellaneous types of high frequency devices for which their models for CAD are necessary. However, in the majority of standard programs for RF design, only a class of MESFET models is available. These models are sufficiently accurate for usual devices; however, they are insufficiently accurate for modeling special high frequency devices. In paper, a method is proposed for modeling the special devices using exclusive or corrective artificial neural networks.

Accurate Modeling of the Special Microwave Structures Using Artificial Neural Networks

  • Authors: doc. Ing. Josef Dobeš, CSc., Pospíšil, L.
  • Publication: The 13th IEEE Mediterranean Electrotechnical Conference - MELECON 2006 - Electronic Proceedings. Piscataway: IEEE, 2006. pp. 1-4. ISBN 1-4244-0088-0.
  • Year: 2006
  • Department: Department of Radioelectronics
  • Annotation:
    In the paper, a way is suggested for modeling miscellaneous microwave structures by exclusive neural networks, or corrective neural networks working attached to an updated analytic model. The accuracy of both procedures is assessed by extracting model parameters in static and dynamic domains: first, an approximation of the AlGaAs/InGaAs/GaAs pHEMT output characteristics is carried out by the corrective neural network; and second, an approximation of the capacitance function of the InGaAs/InP avalanche photodiode is performed by the exclusive neural network. A sequence of analyses is also performed for determining optimal structure of the artificial neural network.

Accurate Sparse-Matrix Semisymbolic Analysis of Large-Scale RF Circuits

  • Authors: doc. Ing. Josef Dobeš, CSc., Míchal, J.
  • Publication: Proceedings of the 36th European Microwave Conference. Piscataway: IEEE, 2006. pp. 1598-1601. ISBN 2-9600551-6-0.
  • Year: 2006
  • Department: Department of Radioelectronics
  • Annotation:
    A sophisticated pivoting strategy for the reduction algorithm transforming the general eigenvalue problem to the standard one is presented for both full- and sparse-matrix techniques. The algorithm increases the precision of the semisymbolic analyses especially for the large-scale RF circuits.

An Accurate Sparse-Matrix Semisymbolic Algorithm for Analyzing Distributed Microwave Circuits

  • Authors: doc. Ing. Josef Dobeš, CSc., Biolek, D., Míchal, J.
  • Publication: MWSCAS 2006 Proceedings. Piscataway: IEEE, 2006. pp. 1-5. ISSN 1548-3746. ISBN 1-4244-0173-9.
  • Year: 2006
  • Department: Department of Radioelectronics
  • Annotation:
    An optimal pivoting strategy for the reduction algorithm transforming the general eigenvalue problem to the standard one is presented for both full- and sparse-matrix procedures. The algorithm increases the precision of the semisymbolic analysis especially for the large-scale microwave circuits. The accuracy is furthermore increased using longer numerical data. First, the long double precision is utilized. Further, the application of a suitable multiple-precision arithmetic library is suggested. Finally, using the longer numerical data to eliminate possible imprecision of the multiple eigenvalues is evaluated.

An Efficient Steady-State Analysis of Microwave Circuits

  • Authors: doc. Ing. Josef Dobeš, CSc., Biolek, D., Posolda, P.
  • Publication: International Journal of Microwave and Optical Technology. 2006, 1(2), 284-289. ISSN 1553-0396.
  • Year: 2006
  • Department: Department of Radioelectronics
  • Annotation:
    Two methods for determining the steady-state are compared from the point of view of their efficiencyand stability. The first one is based on idea of extrapolation and uses the ε-algorithm as an effective tool; the second one is based on idea of sensitivities and uses the standard sensitivity analyses built in software packages.The comparison is done using a set of typical microwave circuits, especially the nonlinear C-class amplifier. For the autonomous circuits, a reliable detection of unknown period is implemented using derivatives of circuit variables. As a demonstration of solving the autonomous circuits, the steady-state analysis of distributed and feedback oscillators are fulfilled with the results compared using measured data.

Efficient Procedures for Analyzing Large-scale RF Circuits

  • Authors: doc. Ing. Josef Dobeš, CSc.,
  • Publication: Proceedings of the Fifth IEEE Dallas Circuits and Systems Workshop. Piscataway: IEEE, 2006. pp. 63-66.
  • Year: 2006
  • Department: Department of Radioelectronics
  • Annotation:
    The majority of CAD tools have limited modes of the sensitivity analysis: PSPICE only contains a static mode and SPECTRE includes frequency domain and static modes. However, many RF systems use symmetrical structures for enhancing the properties of the circuits. For such systems, the static sensitivities are zero in principle and therefore the time domain sensitivity analysis must be used. In the paper, a new recurrent formula for the time domain sensitivity analysis is derived, which uses by-products of an implicit integration algorithm. Moreover, for a very fast estimation of mixed products, an efficient procedure is described, which is also not implemented in PSPICE. Both methods are demonstrated by analyses of a four-quadrant RF multiplier.

Modeling of Switched DC-DC Converters by Mixed S-Z Description

  • Authors: Biolek, D., Biolková, V., doc. Ing. Josef Dobeš, CSc.,
  • Publication: Proceedings of the 2006 IEEE International Symposium on Circuits and Systems. Piscataway: IEEE, 2006. p. 831-834. ISSN 0277-674X. ISBN 978-0-7803-9389-9.
  • Year: 2006
  • Department: Department of Radioelectronics
  • Annotation:
    The paper explains the basic ideas of how to model the dynamical properties of switched DC-DC converters by means of the so-called generalized transfer functions (GTFs). Switched DC-DC converters exhibit some properties of continuous- and discrete-time characters. These systems can be globally modeled by mixed s-z description, utilizing both the Laplace and z-transform operators. Then the resulting line-to-output and control-to-output transfer functions and the corresponding frequency responses can model some system behavior more faithfully than the classical s-domain zeros/poles location, including special effects above Nyquist's frequency.

Modeling the Arterial Segment as a Non-linear Transmission Line

  • Authors: Jelínek, M., doc. Ing. Josef Dobeš, CSc., Poušek, L.
  • Publication: WSEAS Transactions on Biology and Biomedicine. 2006, 3(1), 7-12. ISSN 1109-9518.
  • Year: 2006
  • Department: Department of Radioelectronics
  • Annotation:
    This primary study is intended to implement a non-invasive pulse wave (PW) measurement of a human arterial system. Measured phonocardiographic signals are used to estimate parameters of arterial segments, above all the arterial compliance. A model of selected parts of the arterial tree was proposed for this purpose. The model is based on electric analogy of the transmission line and the arterial system. The parameters are identified using optimization methods and sensitivity analysis in a time domain in Circuit interactive analyzer (C.I.A.) software.

Modern Radiotechnics

New Criteria Enhancing Robustness and Efficiency of Solving Systems of Circuit Equations

  • Authors: doc. Ing. Josef Dobeš, CSc.,
  • Publication: Proceedings of the 2006 IEEE Asia Pacific Conference on Circuits and Systems. Piscataway: IEEE, 2006. pp. 1-5.
  • Year: 2006
  • Department: Department of Radioelectronics
  • Annotation:
    A new robust algorithm suppressing possible divergence of the Newton-Raphson method for solving the nonlinear circuit equations is proposed in both static and dynamic domains. For enhancing the efficiency of repeated solutions of linear systems necessary in the Newton-Raphson method, a new modification of the Markowitz criterion is suggested which is compatible with the fast modes of the LU factorization. The modified criterion consists in an estimation of probabilities of the fill-in enlargement. The probabilities are determined for all columns of the system matrix before the LU factorization, where the column probability is calculated as the average value of the probabilities for all the column elements. Finally, the columns are reordered so that first and last should be those with the minimum and maximum probabilities, respectively. As a verification of the proposed algorithm, a comprehensive set of numerical tests is described for circuits chosen from various parts of electronics.

A Model of Selected Parts of Human Arterial Tree

  • Authors: Jelínek, M., doc. Ing. Josef Dobeš, CSc., Poušek, L., Schreib, P.
  • Publication: Poster Abstracts of the 27th International Conference on Information Technology interfaces. Zagreb: University of Zagreb, 2005, pp. 29-30. ISSN 1330-1012. ISBN 953-7138-04-6.
  • Year: 2005
  • Department: Department of Radioelectronics
  • Annotation:
    This study deals with an implementation of non-invasive pulse wave measurement in human arterial systém. The arterial systém condition (compliance above all) is estimated using the identification of parameters of designed arterial model.

A Modified Markowitz Criterion for the Fast Modes of the LU Factorization

  • Authors: doc. Ing. Josef Dobeš, CSc.,
  • Publication: Proceedings of the 48th IEEE International Midwest Symposium on Circuits and Systems. Piscataway: IEEE, 2005. pp. 955-959. ISSN 1548-3746. ISBN 0-7803-9197-7.
  • Year: 2005
  • Department: Department of Radioelectronics
  • Annotation:
    A novel modification of the Markowitz criterion is suggested which is compatible with the fast modes of the LU factorization. The modified criterion consists in an estimation of probabilities of the fill-in enlargement. The probabilities are determined for all columns of the system matrix before the LU factorization, where the column probability is calculated as the average value of the probabilities for all the column elements. Finally, the columns are reordered so that first and last should be those with the minimum and maximum probabilities, respectively. As a verification of the proposed algorithm, a comprehensive set of numerical tests is described for circuits chosen from various parts of electronics. Special attention is given to testing the radio frequency and microwave circuits.

Advanced Algorithms for Analysis and Optimization of Electronic Circuits

  • Authors: doc. Ing. Josef Dobeš, CSc.,
  • Publication: WSEAS Transactions on Circuits and Systems. 2005, 10(4), 1443-1448. ISSN 1109-2734.
  • Year: 2005
  • Department: Department of Radioelectronics
  • Annotation:
    The analysis and optimization of electronic circuits are some of the main applications for the art of computer programming. It is mainly caused by problematic convergence of a certain class of the circuits and by extreme differences among the values of the circuit parameters. In the paper, a very flexible algorithm for analyzing the electronic circuits is described with a novel reliable method for suppressing the divergence. Moreover, an efficient algorithm for optimizing the electronic circuits is also characterized with a new method for ensuring the numerical stability using a reliable normalization of the system matrix. The new features of the analysis and optimization algorithms are tested using practical tasks of electronics.

An Alternative Approach to Electronic Circuit Design Based on Multiobjective Optimization

  • Authors: Míchal, J., doc. Ing. Josef Dobeš, CSc.,
  • Publication: WSEAS Transactions on Circuits and Systems. 2005, 10(4), 1355-1362. ISSN 1109-2734.
  • Year: 2005
  • Department: Department of Radioelectronics
  • Annotation:
    Optimization is undoubtedly playing an ever more important role in CAD of electronic circuits. As the complexity of practical designs grows, so does the number of objectives to be optimized simultaneously. Even though a large number of multiobjective optimization methods have been developed in other disciplines like Operations Research, they are still generally unknown to electrical engineers and creators of CAD tools. The present paper provides a brief introduction to multiobjective optimization as such, explains two of the most frequently used methods, and discusses their advantages as well as their drawbacks. Several application guidelines and recommendations based on the authors' experience are proposed. The use of both methods is demonstrated on a practical example of a video amplifier design followed by evaluation and discussion of the obtained results.

An Application of Multiobjective Optimization in Electronic Circuit Design

  • Authors: Míchal, J., doc. Ing. Josef Dobeš, CSc.,
  • Publication: Proceedings of the 5th WSEAS/IASME International Conference on Systems Theory and Scientific Computation. Athens: WSEAS Press, 2005. pp. 213-219. ISBN 960-8457-35-1.
  • Year: 2005
  • Department: Department of Radioelectronics
  • Annotation:
    The present paper provides a brief introduction to multiobjective optimization as such, explains two of the most frequently used methods, and discusses their advantages as well as their drawbacks. Several application guidelines and recommendations based on the authors' experience are proposed. The use of both methods is demonstrated on a practical example of a video amplifier design followed by evaluation and discussion of the obtained results.

An Arterial Segment as a Nonlinear LCRG Transmission Line, Lumped-parameter Model

  • Authors: Jelínek, M., doc. Ing. Josef Dobeš, CSc., Poušek, L.
  • Publication: Proceedings of 2005 WSEAS International Conference on Cellular and Molecular Biology, Biophysics and Bioengineering. Athens: WSEAS Press, 2005. pp. 1-3. ISBN 960-8457-31-9.
  • Year: 2005
  • Department: Department of Radioelectronics
  • Annotation:
    This primary study is intended to implement a non-invasive pulse wave (PW) measurement in a human arterial system. Measured phonocardiographic signals are used to estimate parameters of arterial segments, above all the arterial compliance. A model of selected parts of the arterial tree was proposed for this purpose. The model is based on electric analogy of the RLCG transmission line and the arterial system. The parameters are identified using optimization methods and sensitivity analysis in a time domain in Circuit interactive analyzer (C.I.A.) software.

An Efficient Procedure for the Time-Domain Sensitivity Analysis

  • Department: Department of Radioelectronics
  • Annotation:
    Standard tools for CAD have limited modes of the sensitivity analysis: PSPICE only contains a static mode and SPECTRE includes frequency-domain and static modes. However, many RF systems use symmetrical structures for enhancing the circuit properties. For such systems, the static sensitivities are zero on principle and hence the time-domain sensitivity analysis should be used. In the paper, a novel recurrent formula for the time-domain sensitivity analysis is derived which uses by-products of an efficient implicit integration algorithm. As the selected integration algorithm is more flexible than the Gear's one that is ordinarily used, the sensitivity analysis is more efficient in comparison with the standard CAD tools. An implementation of the method is demonstrated using the analysis of a low-voltage four-quadrant RF multiplier. Nonstandard temperature sensitivity analyses are also tested in the static and dynamic modes.

An Efficient Steady-State Analysis of Microwave Circuits

  • Authors: doc. Ing. Josef Dobeš, CSc., Biolek, D., Posolda, P.
  • Publication: 10th International Symposium on Microwave and Optical Technology. Fukuoka: ISMOT 2005 Organizing Committee, 2005. pp. 463-466. ISBN 4-9902546-1-9.
  • Year: 2005
  • Department: Department of Radioelectronics
  • Annotation:
    Two methods for determining the steady-state are compared from the point of view of their efficiencyand stability. The first one is based on idea of extrapolation and uses the ε-algorithm as an effective tool; thesecond one is based on idea of sensitivities and uses the standard sensitivity analyses built in software packages.The comparison is done using a set of typical microwave circuits, especially the nonlinear C-class amplifier. Forthe autonomous circuits, a reliable detection of unknown period is implemented using derivatives of circuitvariables. As a demonstration of solving the autonomous circuits, the steady-state analysis of tunable microwaveoscillator is fulfilled, and the results are compared with measured data.

Assessing the Pulse Wave Velocity in Human Arterial Tree

  • Authors: Jelínek, M., doc. Ing. Josef Dobeš, CSc., Poušek, L.
  • Publication: Slaboproudý obzor. 2005, 2003(4), 8-12. ISSN 0037-668X.
  • Year: 2005
  • Department: Department of Radioelectronics
  • Annotation:
    This work is aimed to the one method of a time delay estimation of phonocardiographic (PCG) signals. A pulse wave velocity (PWV) is computed us-ing this time delay in a human arterial tree, in its selected segment especially. A non-invasive measuring method is used to a PCG signal scanning. Elec-tronic phonendoscopes (changes in pressure/sound converter) are used as the signal transducers. The time delay assessment is carried out using a correla-tion analysis of the measured PCG signals, square of the PCG signals and the 1st derivation of the PCG signals. The pulse wave velocity in the selected arte-rial segment is then computed from the time delay values obtained. The data processing is realized in MatlabŽ software using a particular ad-hoc applica-tion. A set of examinants was consisted of five young volunteers.

Comparison Between Two Methods to Determine the Pulse Wave Velocity in the Human Arterial Tree

  • Authors: Jelínek, M., doc. Ing. Josef Dobeš, CSc., Poušek, L.
  • Publication: The 3rd European Medical and Biological Engineering Conference - EMBEC´05. Praha: Společnost biomedicínského inženýrství a lékařské informatiky ČLS JEP, 2005, pp. 4311-4314. ISSN 1727-1983.
  • Year: 2005
  • Department: Department of Radioelectronics
  • Annotation:
    In this primary study the sensitivity of the proposed PCG measuring method of pulse wave velocity estimation is verified. As a reference method the commercial measuring system of the pulse wave velocity SphygmoCor (SPH) was used. Both methods are noninvasive. Electronic stethoscopes were used as phonocardiographic signal transducers in the PCG method. The SPH method is intended to measure arterial pressure pulse from the human body surface. Four volunteers were examined in this study, divided in groups of healthy objects and objects with hypertensive disease.

Determination of Condition of Human Arterial Segments

  • Authors: Jelínek, M., doc. Ing. Josef Dobeš, CSc., Poušek, L.
  • Publication: Acta Mechanica Slovaca. 2005, 9(2-A), 247-250. ISSN 1335-2393.
  • Year: 2005
  • Department: Department of Radioelectronics
  • Annotation:
    A condition of human arterial system, a compliance of arterial segment especially, is estimated with application of an electric-analogy arterial model. To identify the non-linear model - a transmission line - of arterial segments a time-domain identification is employed. The model consists of a capacitance which substitutes the arterial wall compliance, a resistance, and an inductance which substitutes an inertia of the arterial segment. Measured phonocardiographic signals (non-invasive measurement) are used as input and output data of the model in themodel identification.

Exclusive and Corrective Artificial Neural Networks for Accurate Modeling the RF Semiconductor Devices

  • Authors: doc. Ing. Josef Dobeš, CSc., Pospíšil, L.
  • Publication: Proceedings of the Third IASTED International Conference on Circuits, Signals, and Systems. Calgary: IASTED / Acta Press, 2005. pp. 286-291. ISBN 0-88986-507-8.
  • Year: 2005
  • Department: Department of Radioelectronics
  • Annotation:
    In the recent PSpice programs, five types of the GaAs FET model have been implemented. However, some of them are too sophisticated and therefore difficult to measure and identify afterwards, especially the realistic model of Parker and Skellern. In the paper, simple enhancements of one of the classical models are proposed first. The resulting modification is usable for reliable modeling of both GaAs FETs and pHEMTs. Moreover, its adjusted capacitance function can effectively serve as a convenient representation of microwave varactors. The accuracy of these models can be strongly enhanced using the artificial neural networks - both using an exclusive neural network without an analytic model and cooperating a corrective neural network with the updated analytic model are discussed.

Measurement and Model Indentification of Semicoductor Devices

  • Authors: doc. Ing. Josef Dobeš, CSc., Grábner, M.
  • Publication: AEE´05 - Proceedings of the 4th WSEAS International Conference on: Applications of Electrical Engineering. Athens: WSEAS Press, 2005. pp. 288-293. ISBN 960-8457-13-0.
  • Year: 2005
  • Department: Department of Radioelectronics
  • Annotation:
    In the paper, an optimization method is presented which is usable for identifications of even very complicated models with a relatively small number of iterations. The algorithm has been implemented into the original software tool called C.I.A. (Circuit Interactive Analyzer) into its static and dynamic analysis modes. Hence, the identification is able to identify both DC and capacitance models of semiconductor devices. The process is demonstrated in the paper using various transistors.

New Features of the Algorithms for Numerical Integration, Steady-State Analysis, and Optimization in the Electronic Circuits Design

  • Department: Department of Radioelectronics
  • Annotation:
    The computer-aided design of electronic circuits is one of the main applications for the art of computer programming. It is caused by problematic convergence of a certain class of the circuits and by extreme differences among the values of the circuit parameters. In the paper, a flexible algorithm for analyzing the electronic circuits is described with a novel reliable method for suppressing the divergence. Moreover, a state-state algorithm is also defined able to analyze autonomous circuits. Finally, an efficient algorithm for optimizing the electronic circuits is characterized with a novel method for ensuring the numerical stability using a robust normalization of the system matrix. The features of the updated algorithms are tested using practical tasks of the electronics design.

Using the Artifical Neural Networks for Accurate RF Devices Modeling

  • Authors: Pospíšil, L., doc. Ing. Josef Dobeš, CSc.,
  • Publication: AEE´05 - Proceedings of the 4th WSEAS International Conference on: Applications of Electrical Engineering. Athens: WSEAS Press, 2005. pp. 139-143. ISBN 960-8457-13-0.
  • Year: 2005
  • Department: Department of Radioelectronics
  • Annotation:
    In the paper, simple enhancements of one of the classical models of GaAs FETs are proposed first. The resulting modification is usable for reliable modeling of both GaAs FETs and pHEMTs. The accuracy of these models can be strongly enhanced using the artificial neural networks. Using an exclusive neural network without an analytic model and co-operating a corrective neural network with the updated analytic model are discussed.

Using The Time Domain Sensitivity Analysis For An Efficient Design Of Symmetric Microwave Circuits

  • Authors: doc. Ing. Josef Dobeš, CSc., Grábner, M.
  • Publication: Proceedings of APMC2005. Santa Monica: IEEE, 2005. pp. 100-104.
  • Year: 2005
  • Department: Department of Radioelectronics
  • Annotation:
    In the paper, a new recurrent formula for the time domain sensitivity analysis is derived, which uses the by-products of an implicit integration algorithm. As the selected integration algorithm is more flexible than the Gear's one used in the PSPICE family, the sensitivity analysis is more efficient in comparison with the standard CAD tools. An implementation of the method is demonstrated using the analysis of a low-voltage four-quadrant CMOS RF multiplier.

An Efficient Time-Domain Sensitivity Analysis for Analog and RF Design

An Electric Analogy of Arterial Segment

  • Authors: Jelínek, M., doc. Ing. Josef Dobeš, CSc., Poušek, L.
  • Publication: Sborník příspěvků konference RADEŠÍN 2004. Brno: FEKT VUT v Brně, 2004. pp. 60. ISBN 80-214-2726-4.
  • Year: 2004

Computer-Aided Design of Electronic Circuit Using SPICE-Class Programs

  • Authors: doc. Ing. Josef Dobeš, CSc., Míchal, J.
  • Publication: Počítačové prostředky pro mikrovlnnou techniku. Praha: Česká elektrotechnická společnost, 2004. pp. 13-16.
  • Year: 2004
  • Department: Department of Radioelectronics
  • Annotation:
    The SPICE-class programs are used in many modifications now. Therefore, it is possible to choice an optimal version for each area of electrotechnical engineering. In the lecture, using appropriate versions of the SPICE program for the analysis and optimization of microwave circuits is demonstrated. Moreover, utilizing free internet tools for CAD of electronic circuits is discussed. The methodology is illustrated by simulation of typical microwave integrated circuit.

Correlation Analysis in a Pulse Wave Velocity Evaluation

  • Authors: Jelínek, M., doc. Ing. Josef Dobeš, CSc., Poušek, L.
  • Publication: Radioengineering. 2004, 13(3), 37-41. ISSN 1210-2512.
  • Year: 2004

Determination of Parameters of Systemic Arterial Tree of Human Body

  • Authors: Jelínek, M., doc. Ing. Josef Dobeš, CSc., Poušek, L., Hána, K.
  • Publication: Proceedings of the Engineering and Physical Sciences in Medicine Conference. Geelong: Deakin University, 2004. p. 192.
  • Year: 2004

Enhancement of the Semisymbolic Analysis Precision Using the Variable-Length Arithmetic

  • Authors: doc. Ing. Josef Dobeš, CSc., Míchal, J.
  • Publication: Proceedings of the 11th IEEE International Conference on Electronics, Circuits and Systems. Piscataway: IEEE, 2004. pp. 387-390. ISBN 0-7803-8715-5.
  • Year: 2004

Enhancing the Accuracy of Microwave Element Models by Artificial Neural Networks

Measurement of the Pulse Wave Velocity in Vivo

  • Authors: Jelínek, M., doc. Ing. Josef Dobeš, CSc., Poušek, L.
  • Publication: Proceedings of Workshop 2004. Praha: České vysoké učení technické v Praze, 2004, pp. 808-809. ISBN 80-01-02945-X.
  • Year: 2004

Time Domain Sensitivity Analysis

  • Authors: doc. Ing. Josef Dobeš, CSc.,
  • Publication: ICSES'04 International Conference on Signals and Electronic Systems. Poznaň: PTETiS, 2004. p. 111-114. ISBN 83-906074-7-6.
  • Year: 2004

Using Modified GaAs FET Model Function for the Accurate Representation of PHEMTs and Varactors

  • Authors: doc. Ing. Josef Dobeš, CSc.,
  • Publication: MELECON 2004 Proceedings. Piscataway: IEEE, 2004. pp. 35-38. ISBN 0-7803-8271-4.
  • Year: 2004
  • Department: Department of Radioelectronics
  • Annotation:
    In the recent PSpice programs, several GaAs FET models of various classes have been implemented. However, some of them are sophisticated and therefore very difficult to measure and identify afterwards, especially the realistic model of Parker and Skellern. In the paper, simple enhancements of one of the standard models are proposed. The resulting modification is usable for the accurate modeling of both GaAs FETs and pHEMTs. Moreover, its updated capacitance function can serve as a precise representation of microwave varactors, which is more important.

An Accuracy Comparsion of the Digital Filter Poles-Zeros Analysis With MATLAB and CIA Algorithms

Enhancing the Efficiency of the Electronic Circuit Analysis by the LU Factorization Arrangement

Evaluation of Phonocardiographic Records in the Pulse Wave Velocity Measurement

  • Authors: Jelínek, M., doc. Ing. Josef Dobeš, CSc., Poušek, L.
  • Publication: Measurement 2003 - Proceedings of the 4th International Conference on Measurement. Bratislava: Slovak Academy of Sciences, Institute of Measurement Science, 2003, pp. 219-221. ISBN 80-967402-6-1.
  • Year: 2003

Expressing the MESFET and Transmission Line Delays Using Bessel Function

  • Authors: doc. Ing. Josef Dobeš, CSc.,
  • Publication: ECCTD'03 Proceedings of the European Conference on Circuit Theory and Design 2003. Monterey: IEEE Circuits and Systems Society, 2003. pp. I-169-I-172. ISBN 83-88309-95-1.
  • Year: 2003

Methodology of Evaluation of Phonocardiograms in Measurement of Pulse Wave Velocity

  • Authors: Jelínek, M., doc. Ing. Josef Dobeš, CSc., Poušek, L.
  • Publication: Proceedings of Workshop 2003. Praha: České vysoké učení technické v Praze, 2003. pp. 906-907. ISBN 80-01-02708-2.
  • Year: 2003

Modeling the PHEMTs and Microwave Varactors by the Modified Functions of the GaAs FET Representation

  • Authors: doc. Ing. Josef Dobeš, CSc.,
  • Publication: COMITE 2003. Praha: IEEE Czechoslovakia Section, 2003. pp. 139-142. ISBN 80-86582-09-4.
  • Year: 2003

Reliable CAD Analyses of CMOS Radio Frequency and Microwave Circuits Using Smoothed Gate Capacitance Models

  • Authors: doc. Ing. Josef Dobeš, CSc.,
  • Publication: AEU-International Journal of Electronics and Communications. 2003, 57(6), 372-380. ISSN 1434-8411.
  • Year: 2003

The Phonocardiography in the Pulse Wave Velocity Measurement

  • Authors: Jelínek, M., doc. Ing. Josef Dobeš, CSc., Poušek, L.
  • Publication: Měřící a řídící technika v biomedicíně. Ostrava: VŠB-TUO, 2003. p. 193-197. ISBN 80-248-0432-8.
  • Year: 2003

Using a Phonocardiography In a Pulse Wave Velocity Measurement

  • Authors: Jelínek, M., doc. Ing. Josef Dobeš, CSc., Poušek, L., Hána, K.
  • Publication: ISSPIT 2003. Darmstadt: IEEE, 2003. pp. 5/TP3. ISBN 0-7803-8293-5.
  • Year: 2003

Using the Variable-Length Arithmetic for an Accurate Poles-Zeros Analysis

An Alternative CAD Model of Transmission Line Suppressing Spurious Oscillations

  • Authors: doc. Ing. Josef Dobeš, CSc.,
  • Publication: MIKON 2002 - 14th International Conference on Microwaves, Radar and Wireless Communications. Warsaw: Telecommunication Research Institute, 2002. pp. 353-356. ISBN 83-906662-5-1.
  • Year: 2002

Analyzing the Steady-State of Microwave Oscillators

  • Department: Department of Radioelectronics
  • Annotation:
    A CAD analysis of the steady-state is proposed for microwave feedback and distributed oscillators. The method is based on an effective combination of the ?-algorithm with a detection of unknown period using derivatives of some output variable. An accuracy of the analyses is increased by a refinement of GaAsFET standard model. The steady-state algorithm and the improved GaAsFET model were implemented and tested by means of author's C.I.A. (Circuit Interactive Analyzer) program using two real microwave oscillators.

Noise Figure Optimization Using CAD

  • Authors: doc. Ing. Josef Dobeš, CSc.,
  • Publication: Proceedings of the 10th EME Conference. ???: International Amateur Radio Moon-Bounce Association, 2002. pp. 8-9.
  • Year: 2002

Nonstandard Sensitivity Analyses in Frequency and Time Domains

  • Authors: doc. Ing. Josef Dobeš, CSc.,
  • Publication: The 9th IEEE International Conference on Electronics, Circuits and Systems. Piscataway: IEEE, 2002. pp. 1119-1122. ISBN 0-7803-7596-3.
  • Year: 2002

Smoothing Gate Capacitance Models for CMOS Radio Frequency and Microwave Integrated Circuits CAD

  • Authors: doc. Ing. Josef Dobeš, CSc.,
  • Publication: IMS 2002 - International Microwave Symposium Digest. Piscataway: IEEE, 2002. pp. 605-608. ISSN 0149-645X. ISBN 0-7803-7239-5.
  • Year: 2002

Smoothing Gate Capacitance Models for CMOS Radio Frequency and Microwave Integrated Circuits CAD

  • Authors: doc. Ing. Josef Dobeš, CSc.,
  • Publication: 2002 IEEE Radio Frequency Integrated Circuits (RFIC) Symposium - Digest of Papers. Piscataway: IEEE, 2002. pp. 495-498. ISSN 1529-2517. ISBN 0-7803-7246-8.
  • Year: 2002

(Semi)symbolic Modeling of Large Linear Systems: Pending Issues

  • Authors: Biolek, D., Biolkova, V., doc. Ing. Josef Dobeš, CSc.,
  • Publication: Proceedings of the ISSSe'01 2001 URSI International Symposium on Signals, Systems, and Electronics. Tokyo: URSI, 2001. pp. 397-399.
  • Year: 2001

A Macromodel Conversion for Programs of Spice Type

  • Authors: Černý, R., doc. Ing. Josef Dobeš, CSc.,
  • Publication: Radioelektronika 2001 - Conference Proceedings. Brno: VUT v Brně, FEI, Ústav radioelektroniky, 2001. pp. 18-21. ISBN 80-214-1861-3.
  • Year: 2001

An Accurate Poles-Zeros Analysis for Large-Scale Analog and Digital Circuits

  • Authors: doc. Ing. Josef Dobeš, CSc.,
  • Publication: ICECS 2001 Proceedings. Piscataway: Institute of Electrical and Electronic Engineers, 2001. pp. 1027-1030. ISBN 0-7803-7057-0.
  • Year: 2001

Digital Signal Processing Application in Radioelectronics

Enhanced Poles-Zeros and Sensitivity Analyses of Microwave Circuits

  • Authors: doc. Ing. Josef Dobeš, CSc.,
  • Publication: MIOP 2001 - The German Wireless Week. Hagenburg: Network, 2001. pp. 388-393. ISBN 3-924651-91-4.
  • Year: 2001

Estimating a Frequency of Oscillations Using Poles Diagram

  • Authors: doc. Ing. Josef Dobeš, CSc.,
  • Publication: COMITE 2001. Praha: IEEE Czechoslovakia Section, 2001. pp. 267-270. ISBN 80-902417-9-4.
  • Year: 2001

A Measurement and Model Identification of Elements of Radioelectronic Circuits

  • Authors: doc. Ing. Josef Dobeš, CSc., Bálek, V., Grábner, M.
  • Publication: Radioelektronika 2000 - Conference Proceedings. Bratislava: STU v Bratislave, FEI, 2000. pp. P-19-P-22. ISBN 80-227-1389-9.
  • Year: 2000

A More Accurate Determining the Noise Figure of Microwave Amplifiers

  • Authors: doc. Ing. Josef Dobeš, CSc.,
  • Publication: MIKON 2000 - XIII International Conference on Microwaves, Radar and Wireless Communications. Warsaw: Telecommunication Research Institute, 2000. pp. 337-339. ISBN 83-906662-0-0.
  • Year: 2000

A Steady-State Analysis of Microwave Oscillators

  • Authors: doc. Ing. Josef Dobeš, CSc.,
  • Publication: 2000 2nd International Conference on Microwave and Millimeter Wave Technology Proceedings. Beijing: Institute of Electrical and Electronics Engineers, 2000. pp. 160-163. ISBN 0-7803-5743-4.
  • Year: 2000

Application of Digital Signal Processing in Radio Engineering

CAD of HF and Microwave Circuits

  • Authors: doc. Ing. Josef Dobeš, CSc.,
  • Publication: Radiokomunikace 2000. Praha: ČVUT FEL, Katedra radioelektroniky, 2000. p. 359-374. ISBN 80-01-02142-4.
  • Year: 2000

CIA - A Comprehensive CAD Tool for Analog, RF, and Microwave IC's

  • Authors: doc. Ing. Josef Dobeš, CSc.,
  • Publication: 8th IEEE International Symposium on High Performance Electron Devices for Microwave and Optoelectronic Applications. Glasgow: University of Glasgow, 2000. p. 212-217. ISBN 0-7803-6550-X.
  • Year: 2000

A Simultaneous Optimization of Gain and Noise Figure of Microwave Amplifiers

  • Authors: doc. Ing. Josef Dobeš, CSc.,
  • Publication: The 10th Conference on Microwave Techniques COMITE 1999. Prague: Czechoslovakia Section IEEE, 1999. pp. 237-240. ISBN 80-902417-3-5.
  • Year: 1999

Analyzing the Nonlinear Static and Dynamic Electronic Circuits

  • Authors: doc. Ing. Josef Dobeš, CSc.,
  • Publication: 1. seminář "Spolupráce vysokých a středních škol". Sborník referátů. Prague: Czechoslovakia Section IEEE, 1999. pp. 13-18. ISBN 80-902417-5-1.
  • Year: 1999

Analyzing the Poles and Zeros for Extensive Analog and Digital Circuits

  • Authors: doc. Ing. Josef Dobeš, CSc.,
  • Publication: Radioelektronika 99. Brno: VUT v Brně, FEI, Ústav radioelektroniky, 1999. pp. 34-37. ISBN 80-214-1327-1.
  • Year: 1999

Modeling the GaAs Nonlinear Microwave Circuits Using the CIA Program

  • Authors: doc. Ing. Josef Dobeš, CSc.,
  • Publication: 1999 European Gallium Arsenide and Related III-V Compounds, Application Symposium (GAAS 99). London: Miller Freeman UK, 1999. pp. 219-224. ISBN 0-86213-142-1.
  • Year: 1999

Steady-State Analysis of Microwave Oscillators

  • Authors: doc. Ing. Josef Dobeš, CSc.,
  • Publication: Workshop CAD&CAE '99. Prague: Czechoslovakia Section IEEE, 1999. pp. 1-4. ISBN 80-902417-4-3.
  • Year: 1999

CAD of HF and Microwave Circuits for Radiocommunication

  • Authors: doc. Ing. Josef Dobeš, CSc.,
  • Publication: Radiokomunikace '98. Praha: ČVUT FEL, Katedra radioelektroniky, 1998. pp. 285-294. ISBN 80-01-01780-X.
  • Year: 1998

Noise Figure Analysis of Microwave Amplifiers by the C.I.A. Program

  • Authors: doc. Ing. Josef Dobeš, CSc.,
  • Publication: Workshop CAD&CAE'98. Praha: ČVUT FEL, Katedra elektromagnetického pole, 1998. pp. 21-24. ISBN 80-902417-2-7.
  • Year: 1998

Optimization of Electronic Circuits

  • Authors: doc. Ing. Josef Dobeš, CSc.,
  • Publication: Radioelektronika 98. Brno: VUT v Brně, 1998. pp. 65-68. ISBN 80-214-0983-5.
  • Year: 1998

Efficient Determination of Intermodulation and Harmonic Components of Circuit Response

  • Authors: doc. Ing. Josef Dobeš, CSc.,
  • Publication: Radioelektronika '97. Bratislava: STU v Bratislave, 1997. pp. 407-410. ISBN 80-227-0943-3.
  • Year: 1997

Modeling the Microwave Transmission Lines without Spurious Oscillations

  • Authors: doc. Ing. Josef Dobeš, CSc.,
  • Publication: COMITE 1997. Pardubice: Univerzita Pardubice, 1997. pp. 255-258. ISBN 80-902417-0-0.
  • Year: 1997

Time and Frequency Sensitivity Analysis for CAD

  • Authors: doc. Ing. Josef Dobeš, CSc.,
  • Publication: Moderní směry výuky elektrotechniky a elektroniky. Brno: Vojenská akademie, 1997. pp. 98-101.
  • Year: 1997

Modeling of Therapeutical Ultrasonic Systems

  • Authors: Kadlec, F., doc. Ing. Josef Dobeš, CSc.,
  • Publication: Workshop 96. Praha: České vysoké učení technické v Praze, 1996. pp. 895-896.
  • Year: 1996

Modelling and Measurement of Medical Ultrasonic Transducers

  • Authors: Kadlec, F., doc. Ing. Josef Dobeš, CSc.,
  • Publication: Proceedings of 14th International Conference on Utilization of Ultrasonic Methods in Condensed Matter. Žilina: VŠDS, 1996. pp. 88-91. ISBN 80-7100-345-X.
  • Year: 1996

Steady-State Analysis of Electronic Circuits

  • Authors: doc. Ing. Josef Dobeš, CSc.,
  • Publication: Radioelektronika '96. Brno: VUT v Brně, 1996. pp. 62-65. ISBN 80-214-0617-8.
  • Year: 1996

Modelling of the GaAs Analog and Digital Microwave Devices with the C.I.A. Program

Modelling the GaAs Microwave Devices with the CIA Program

Modified Mayer's Model of MOSFET Gate Capacitance

A New Stable Algorithm for Reliable Determining the Operating Point of the Nonlinear Electronic Circuits

  • Authors: doc. Ing. Josef Dobeš, CSc.,
  • Publication: Radioelektronika 94 Sborník referátů. Brno: VUT v Brně, FEI, Ústav radioelektroniky, 1994. pp. 42-45.
  • Year: 1994

Analysis and Optimization of Nonlinear Radiofrequency Circuits by the C.I.A. Program

  • Authors: doc. Ing. Josef Dobeš, CSc.,
  • Publication: Workshop CAD & CAE 94. Praha: České vysoké učení technické v Praze, 1994, pp. 20-23.
  • Year: 1994

CAD Analysis and Optimization of Radioelectronic Circuits

Responsible person Ing. Mgr. Radovan Suk