Multiple Time Scales for Simulation and Macromodelling of "Hard" Circuits

Abstract

Circuits like mixers, VCOs and switching converters are hard to analyse using traditional CAD methods, because many cycles of fast waveforms (e.g., a local oscillator signal) must be tracked for the period of much slower waveforms (e.g., an RF input signal). We show how describing such circuits using more than one time scale leads to general and elegant algorithms for solving them, even when they contain strong nonlinearities such as clipping or switching elements. We also describe how multiple time scales are useful for generating small system-level macromodels of communication blocks (like mixers and switched-capacitor filters) automatically, given a detailed description such as an extracted transistor-level SPICE file.