Comparison of iterative methods for AC analysis in PISCES-IIB

This letter describes the implementation of an improved small-signal ac simulation capability in the general-purpose device simulator PISCES-IIB. The preconditioned generalized conjugate algorithm has been implemented, which allows ac simulations to be performed up to any frequency without convergence problems, although at great computational expense. The current implementation of PISCES-IIB uses the block successive overrelaxation algorithm for ac simulations. This algorithm fails at high frequencies, thus making it impossible to determine accurately the cutoff frequency and switching speed of high-frequency devices. The preconditioned GCR algorithm has been implemented using two different preconditioners. A comparison of the three methods shows that they are most efficient at different frequency ranges, which allows programming of an automatic switching algorithm which chooses the most efficient simulation method.