Junji Kawata

Analysis of Chua's circuit with transmission line

The purpose of this brief is that, by an application of the method of characteristics, we analyze chaotic phenomena in Chuas circuit with lossy transmission line. The transmission line is replaced by the equivalent lumped circuit and a time-delayed element so that it can be solved efficiently by the Runge-Kutta method. It is found from numerical experiments that the circuit has complicated and interesting chaotic attractors.

On synchronization phenomena in chaotic systems coupled by transmission line

In this study, synchronization phenomena in chaotic oscillators coupled by a transmission line are investigated. In particular investigation using real circuits is done for the first time. We report the very interesting results.

Envelope analysis of nonlinear electronic circuits based on harmonic balance method

We propose here a Spice-oriented envelope analysis based on the HB (harmonic balance) method, where Fourier coefficients are assumed to be slowly varying. The Fourier expansions of nonlinear devices are executed by MATLAB in the symbolic forms. In this time, the nonlinearities need to be approximated by the polynomial functions. The determining equation of the HB method is formulated as Sine–Cosine circuit in the form of schematic diagram using ABMs (analog behavior models) of Spice. Each sub-circuit corresponding to the higher harmonic component is almost the same circuit topology as the original one and has dynamic elements such as capacitors and inductors. The Sine–Cosine circuit can be solved by the transient analysis of Spice. Thus, our method is rather a symbolic approach in the meaning that the HB determining equation is given by the schematic diagram of Spice. Our method can be easily applied to the analysis of middle order of nonlinear communication circuits such as mixers and amplitude modulators and to the analysis of interesting phenomena in the nonlinear oscillations. After many simulation experiments, the results show that our envelope analysis is about 50 times faster than the direct transient analysis. Copyright

Spice-Oriented Frequency-Domain Analysis of Nonlinear Electronic Circuits

Distortion analysis of nonlinear circuits is very important for designing analog integrated circuits and communication systems. In this letter, we propose an efficient frequency-domain approach for calculating frequency response curves, which is based on HB (harmonic balance) method combining with ABMs (Analog Behavior Models) of Spice. Firstly, nonlinear devices such as bipolar transistors and MOSFETs are transformed into the HB device modules executing the Fourier transformations. Using these modules, the determining equation of the HB method is formed by the equivalent sine-cosine circuit in the schematic form or net-list. It consists of the coupled resistive circuits, so that it can be efficiently solved by the DC analysis of Spice. In our algorithm, we need not to derive any troublesome circuit equations, and any kinds of the transformations.

Asymptotic analysis of nonlinear electronic circuits

It is very important to analyze mixers and modulators for designing communication circuits. They are driven by multiple frequencies, one of which is usually very high carrier frequency compared to the other. To know the transient behaviors, we need to calculate many carrier waveforms, so that the transient analysis is very time-consuming. Hence, we propose an efficient envelope analysis for calculating the asymptotic behaviors of the amplitudes, which is based on the harmonic balance (HB) method with the slowly varying coefficients. In order to develop the Spice-oriented simulators, the Fourier expansions of nonlinear devices such as bipolar transistors are executed with MATLAB, and the Fourier modules should be stored in our computer library. Thus, we can easily formulate the determining equations of HB method called sine-cosine circuit. We found from many examples that the envelope method is several ten times faster than the transient analysis.

Sensitivity Analysis and Optimization Algorithm —– Based on Nonlinear Programming —–

We propose here a fully Spice-oriented design algorithm of op-amps for attaining the maximum gains under low power consumptions and assigned slew-rates. Our optimization algorithm is based on a well-known steepest descent method combining with nonlinear programming. The algorithm is realized by equivalent RC circuits with ABMs (analog behavior models) of Spice. The gradient direction is decided by the analysis of sensitivity circuits. The optimum parameters can be found at the equilibrium point in the transient response of the RC circuit. Although the optimization time is much faster than the other design tools, the results might be rough because of the simple transistor models. If much better parameter values are required, they can be improved with Spice simulator and/or other tools.

A new Spice-oriented frequency-domain optimization technique

There are many kinds of optimization techniques for designing high-performance RF circuits. In this paper, we propose a new frequency-domain Spice-oriented optimization algorithm using the steepest descent method. We have developed a simulator executing the frequency-domain analysis based on the harmonic balance (HB) method, where all the nonlinear devices such bipolar transistors and MOSFETs are replaced by the equivalent HB modules. The objective functions in the optimization are estimated by the DC analysis of the modified HB circuits. On the other hand, our steepest descent algorithm is realized by equivalent circuit model. Thus, the optimum solution is stably found by the transient analysis of Spice. We show the formulation of HB circuits in section II, the Spice-oriented optimization algorithm in section III and the interesting examples in section IV

BER performance of a chaos communication system including modulation-demodulation circuits

In this article, estimation of bit error rate (BER) performance in a general chaos communication system including modulation-demodulation circuits is investigated. We observe influences of modulation-demodulation circuits by both computer simulation and SPICE simulation. BER is calculated by computer simulation. We confirm that nonlinearity of modulation-demodulation and several circuits influence chaos synchronization and also communication quality.

Spice-Oriented Intermodulation Analysis Combining with MATLAB

It is very important to analyze the mixer and modulator circuits which are driven by multiple input frequencies. Volterra series methods are widely used for the frequency-domain analysis of nonlinear circuits, which can be applied to relatively strong nonlinear circuits. We compare properties of the above two methods using illustrative examples. In this paper, we propose a Spice-oriented HB method combining with MATLAB. Firstly, for the circuits containing nonlinear devices characterized by the special function, they are approximated by the Taylor series. Then, the Fourier coefficients can be calculated by MATLAB in the symbolic forms. Thus, the determining equations of HB method can be formulated by net-list in Spice simulator. It can be efficiently solved by the DC analysis of Spice, and the frequency-domain solutions are obtained. We found from examples that, although Volterra series method can be efficiently applied to weakly nonlinear circuits, it becomes erroneous to strong nonlinear circuits.

Bifurcation and complex phenomena in chaotic systems coupled by transmission line

In this study, bifurcation and complex phenomena in synchronizing chaotic oscillators coupled by a lossless transmission line are investigated. The period-doubling bifurcation with varying the time delay is observed in our circuit model. Further the voltage distribution of transmission line is simulated in order to investigate whether the current flowing through the transmission line is constant or not. It is found that the subsystems synchronize although the current through the transmission line keeps on varying.