Resolving fundamental issues of slowness in envelope simulation methods

Abstract

Fourier-envelope algorithms are an important component of the mixed-signal/RF verification toolbox. In this article the unpredictability and lack of robustness that has been reported for these algorithms is addressed. It is shown that the problem stems from “slow” envelopes that fundamentally feature fast oscillations. We demonstrate that this is related to the fact that the envelope equations are always stiff, whether or not the underlying system is. We show that careful choice of the envelope initial conditions is necessary to obtain useful solutions, and propose two techniques for finding good initial conditions. By applying these techniques and solving the envelope equations with stiffly-stable numerical methods, we obtain a robust and reliable Fourier-envelope method. The new methods are illustrated by a direct-downconversion mixer circuit. © 2005 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2005.