Mehmet Ali Tan

Pole-zero computation in microwave circuits using multipoint Pade approximation

A new method is proposed for dominant pole-zero (or pole-residue) analysis of large linear microwave circuits containing both lumped and distributed elements. The method is based on a multipoint Pade approximation. It finds a reduced-order rational s-domain transfer function using a data set obtained by solving the circuit at only a few frequency points. We propose two techniques in order to obtain the coefficients of the transfer function from the data set. The proposed method provides a more efficient computation of both transient and frequency domain responses than conventional simulators and more accurate results than the techniques based on single-point Pade approximation such as asymptotic waveform evaluation. >

Biquadratic transconductance switched-capacitor filters

A new type of sampled data filter consisting of transconductance elements, switches and capacitors, and called a transconductor switched-capacitor (TSC) filter is presented. Transconductance elements do not degrade their performance within a wide frequency range and tunable ones are available. The synthesis of TSC filters is explained on the basis of a signal flow graph realizing the general z-domain biquadratic transfer function. The transconductance elements employed as active devices are readily available in various technologies and are easily implemented and more suitable than operational amplifiers in a CMOS technology. Because the building blocks are not involved in any continuous feedback, frequency compensation is not necessary for stability purposes. The filter coefficients are determined by the clock pulse width and the transconductances, both of which can be tuned, and the integrator capacitors. This method can be easily generalized to the higher order filters. >

Piecewise linear asymptotic waveform evaluation for transient simulation of electronic circuits

A general purpose circuit simulation program, PL-AWE (piecewise linear asymptotic waveform evaluator) is developed especially for the analysis of VLSI circuits. PL-AWE uses the asymptotic waveform evaluation (AWE) technique, which is a new method to analyze linear(ized) circuits, and piecewise-linear (PL) models to represent nonlinear elements. AWE employs a form of Pade approximation rather than numerical integration to approximate the behavior of linear(ized) circuits in either the time or the frequency domain. The authors discuss the internal workings of the program, and indicate its effectiveness in terms of several illustrative examples.<<ETX>>

Analog CMOS implementation of cellular neural networks

The analog CMOS circuit realization of cellular neural networks with transconductance elements is presented. This realization can be easily adapted to various types of applications in image processing just by choosing the appropriate transconductance parameters according to the predetermined coefficients. The effectiveness of the designed circuits for connected component detection is shown by HSPICE simulations. For fixed function cellular neural network circuits, the number of transistors is reduced further by using multi-input transconductance elements. >

A reduction in the number of active components used in transconductance grounded capacitor filters

The number of active components in transconductance grounded capacitor filters is reduced. This reduction is possible in the case where capacitor loops and/or inductor cutsets exist in the LC-ladder prototype. A more significant reduction is obtained in the OTA-C (operational transductance amplifier-capacitor version). The number of OTAs is reduced to seven from 13 while the total capacitance value remains intact. It is also important to note that all transconductance elements or OTAs are identical except possibly one. The only drawback of this reduction is implementation of some floating capacitors instead of all grounded capacitors.<<ETX>>

Transient analysis of nonlinear circuits by combining asymptotic waveform evaluation with Volterra series

A new method is proposed for the transient analysis of circuits with large number of linear lumped elements and lossy coupled transmission lines, and with few mildly nonlinear terminations. The method combines the Volterra-series technique with Asymptotic Waveform Evaluation approach and corresponds to recursive analysis of a linear equivalent circuit. >

A new method for the steady-state analysis of periodically excited nonlinear circuits

We propose a new method for the steady state analysis of periodically excited nonlinear microwave circuits. It is a modified and more efficient form of Newton-Raphson iteration based harmonic balance (HB) technique. It solves the convergence problems of the HB technique at high drive levels. The proposed method makes use of the parametric dependence of the circuit responses on the excitation level. It first computes the derivatives of the complex amplitudes of the harmonics with respect to the excitation level efficiently and then finds the Pade approximants for the amplitudes of the harmonics using these derivatives.

Synthesis of artificial neural networks by transconductors only

Hardware implementation of artificial neural networks has been attracting great attention recently. In this work, the analog VLSI implementation of artificial neural networks by using only transconductors is presented. The signal flow graph approach is used in synthesis. The neural flow graph is defined. Synthesis of various neural network configurations by means of neural flow graph is described. The approach presented in this work is technology independent. This approach can be applied to new neural network topologies to be proposed or used with transconductors designed in future technologies.

A new method for nonlinear circuit simulation in time domain: NOWE

A new method for the time-domain solution of general nonlinear dynamic circuits is presented. In this method, the solutions of the state variables are computed by using their time derivatives up to some order at the initial time instant. The computation of the higher order derivatives is equivalent to solving the same linear circuit for various sets of dc excitations. Once the time derivatives of the state variables are obtained, an approximation to the solution can be found as a polynomial rational function of time. The time derivatives of the approximation at the initial time instant are matched to those of the exact solution. This method is promising in terms of execution speed, since it can achieve the same accuracy as the trapezoidal approximation with much smaller number of matrix inversions.

A novel algorithm for DC analysis of piecewise-linear circuits: popcorn

A fast and convergent iteration method for piecewise-linear analysis of nonlinear resistive circuits is presented. Most of the existing algorithms are applicable only to a limited class of circuits. In general, they are either not convergent or too slow for large circuits. The new algorithm presented in the paper is much more efficient than the existing ones and can be applied to any piecewise-linear circuit. It is based on the piecewise-linear version of the Newton-Raphson algorithm. As opposed to the Newton-Raphson method, the new algorithm is globally convergent from an arbitrary starting point. It is simple to understand and it can be easily programmed. Some numerical examples are given in order to demonstrate the effectiveness of the proposed algorithm in terms of the amount of computation. >