Jiri Vlach

Time-domain analysis of networks with internally controlled switches

A computer-oriented method for the time-domain analysis of networks with internally controlled ideal switches is presented. No assumptions are made about the continuity of the circuit response at the switching instants; even Dirac impulses are permitted. In fact, it is shown that Dirac impulses must be considered for the analysis of some switched networks, even though they may only be present for intermediate steps of the analysis. Several topological changes may be needed at each switching instant to ensure that the topology after switching is valid. The theories have been implemented in a computer program, SWANN. The network equations are generated with a two-graph modified nodal analysis technique, rather than the state equation formulation. Various internally controlled switches are permitted, such as the ideal diode, thyristor, and voltage- and current-controlled switches. Numerical results show the generality and accuracy of the method on three switched networks. >

Switched-capacitor circuits with reduced sensitivity to amplifier gain

A new technique for reducing the effect of finite amplifier gain in switched-capacitor circuits is described. The principle is to perform a preliminary charge transfer operation preceding every desired charge transfer operation, thus obtaining a close approximation of the finite gain error which is stored and subsequently used for correction. This provides excellent suppression of the finite gain effect, independent of the relationship between the clock rate and the signal frequencies. The technique is quite general in nature and can be applied in a wide variety of switchedcapacitor circuits. Its major applications will be in precision analog signal processing circuits like precision amplifiers, A/D and D/A converters, and analog arithmetic building blocks. Simulation studies indicate that this technique has the potential to reduce the amplifier gain requirements in such circuits by one to two orders of magnitude. This would simplify amplifier design and increase the high-frequency capability of these circuits.

Analysis of nonlinear networks with inconsistent initial conditions

Inconsistent initial conditions and/or Dirac impulses can appear in networks with ideal switches, and in such cases simulators may give wrong results. To avoid errors, many simulators do not allow ideal switching. This paper presents simple CAD methods which can handle correctly, and automatically, inconsistent initial conditions of linear as well as nonlinear networks. For easy understanding, all explanations are done on simple examples, with the minimum of mathematics. >

Computation of time domain response by numerical inversion of the Laplace transform

Abstract A new method for the calculation of time responses of lumped time invariant networks is presented. It is based on the numerical inversion of the Laplace transform and involves the computation of the frequency domain function at pre-assigned complex points and forming a weighted sum. The method exactly inverts a certain number of terms of the Taylor expansion of the time response and is thus equivalent to the methods used for the integration of differential equations. This equivalence is established on two examples. The order of integration can be changed between 1 and 46 without any difficulty. Additional properties resulting from the application of the numerical Laplace transform inversion are also discussed and some novel applications indicated.

Analysis and sensitivity of periodically switched linear networks

A completely general computer-oriented method for exact frequency-domain analysis of multiphase periodically switched linear networks is presented. Input signals can be either continuous or sample-and-held. The theory is valid even for cases where the network variables are discontinuous during switching. An algorithm to compute sensitivity of the response to element changes is also given. The method unifies analysis of general switched linear networks and ideal switched capacitor networks to a single algorithm. Equation formulation is based on the two-graph modified nodal analysis. The theoretical results presented are compared to previously published results. The theories have been implemented in a computer program. Numerical results of the analysis of three networks are given. They show the usefulness of the program in the analysis and design of switched networks. >

Symbolic analysis of analog and digital circuits

An efficient computer method for symbolic analysis of linear analog and digital circuits is described. The tableau formulation is used in the derivations but the mixed nodal tableau method is used in actual computations of analog circuits. One triangular factorization of the system matrix, followed by m + 1 forward and back substitutions, is sufficient to generate all partial derivatives of the numerator and denominator of the immitance function in terms of m variable elements. In the case of frequency dependent elements, the fast Fourier transform algorithm is used to obtain the polynomial coefficients. The computational cost is discussed and compared with that of other well-known symbolic analysis algorithms. Difficult programming sections are given. Little software is needed beyond that if a program for frequency analysis is available.

RC models of a constant phase element

SUMMARY The paper describes models of a constant-phase element consisting of passive R and C components. The models offer any input impedance argument (phase) between −90° and 0° over a selectable frequency band covering several decades. The design procedure makes it possible to choose values of average phase, phase ripple, frequency bandwidth, and total number of R and C elements. The model can cover three frequency decades with as few as five resistors and five capacitors. The models can be used for practical realization of fractional analog differentiators and integrators, fractional oscillators, chaotic networks or for analog simulation of fractional control systems. Copyright

Ellipsoidal method for design centering and yield estimation

A method for constraint region approximation, design centering and yield estimation is introduced. Extreme points of the constraint region are identified by inscribing into it the largest possible ellipsoid. Ellipsoid center is the point that centers the design. Ellipsoidal, polytope and second order Taylor series approximation schemes to the constraint region are discussed. Accuracy and implementation of the method are outlined. Two examples testing the method are included and applications to centering, tolerancing and yield estimation are shown. >

A new floating resistor for CMOS technology

A new floating resistor consisting entirely of MOS devices in saturation has been developed. Linearity within +or-0.04% is achieved through nonlinearity cancellation via current mirrors over an applied voltage range of +or-1 V. The frequency response exceeds 10 MHz, and the resistors are expected to be useful in implementing integrated circuit active RC filters. >

A unified approach to statistical design centering of integrated circuits with correlated parameters

This paper presents a general method for statistical design centering of integrated circuits with correlated parameters. It unifies worst-case design, nominal design and tolerance design in a single framework by selecting appropriate norms to measure the distances from the nominal values. The method uses an advanced first-order second moment technique as an alternative to the simplicial algorithm. Yield estimation is calculated in the original space and no transformation to uncorrelated variables is required. The solution algorithms are based on the recently developed interior-point methods for semi-definite programming. One tutorial and one practical example explain the application.