Extension of the asymptotic waveform evaluation technique with the method of characteristics

Abstract

A problem inherent in methods for simulating distributed elements with the asymptotic waveform evaluation (AWE) technique is that they use complex exponentials to approximate pure delays in the time responses of transmission lines. The aproximation can lead to spurious ringing in the simulation results. This problem can be overcome within the context of a SPICE-based simulator. The generalized method of characteristics is used to derive an equivalent circuit model for a system of coupled lines. This allows the pure delay to be factored out; AWE can then be used to approximate the characteristic admittance, as well as the propagation functions of the lines. The AWE approximation can be simulated efficiently within a modified version of SPICE. Examples are presented to demonstrate that this technique is both accurate and faster than other methods.