A scattering parameter based method for the transient analysis of lossy, coupled, nonlinearly terminated transmission line systems in high-speed microelectronic circuits.

Abstract

The problem of accurate and efficient calculation of transient signal waveforms microelectronic circuits consisting of arbitrarily connected systems of multiple, coupled transmission lines and nonlinear devices such as transistors and diodes has been considered. Both non-dispersive and dispersive transmission lines can be handled. For the dispersive case, the dispersion is due to geometric or material nonuniformity as well as dielectric and conductor losses which may also exhibit frequency dependence. A general approach has been formulated which enables the simulation of arbitrarily connected linear networks, described in the frequency domain in terms their scattering parameters, and nonlinear networks with models described in the time domain. The inverse fast Fourier transform is used to obtain the impulse response for the frequency-dependent networks, and subsequently combined with the nonlinear models using convolution techniques to carry out the simulation in the time domain in a time-marching fashion. A technique has been developed that enables the reduction of large linear networks described in terms of scattering parameters into a smaller, compact description. This makes repeated simulations very economical in terms of computational time. In addition, the above procedure enables the simulation of transmission line systems with varying cross-section. The scattering parameters for the linear elements can be derived from a TEM or quasi-TEM field approximation for dominant TEM structures, a full-wave analysis for highly dispersive structures and discontinuities, or from measurements performed on the actual structures. A Fortran program has been developed that can simulate arbitrarily connected lossless or lossy transmission line systems and standard SPICE2G.6 devices (such as bipolar, MOS, junction field effect transistors etc.) Several applications of the program showed that losses and nonuniformities in the cross-sectional dimensions of the transmission lines may add significantly to the degradation of the signals propagated. Therefore, the simulator developed here is an indispensible tool for the analysis of such circuits.