Enhanced multivariate steady-state time-domain method

Highly nonlinear circuits are very demanding to simulate, especially when they are excited with two separate frequencies as is the case with, e.g., RF circuits and SC filters. Frequency-domain methods, e.g. harmonic balance (HB), that can handle two-tone signals are more suitable for sine wave excitations and weakly nonlinear circuits. Multivariate steady-state time-domain (MSSTD) analysis is efficient also for signals with sharp edges and strongly nonlinear circuits. The computation of this method has been improved to make the MSSTD analysis faster than before. New features are initial guess, i.e. quick MSSTD (QMSSTD), and new preconditioners for the generalized minimum residual (GMRES) method of the MSSTD analysis, both of which are implemented into the APLAC circuit simulator achieving remarkable speed-up.