BITSIM—A General Purpose Circuit Simulator

Abstract

In this paper we describe a general purpose circuit simulator, BITSIM, based on a new hybrid equation formulation technique. The formulation technique uses graph decomposition and exploits the good structural properties of the topological constraints imposed by KVL and KCL. Given any arbitrary network N and a partition of its branches into sets A and B, we decompose it into two networks N^AL and N^BK. The simultaneous solution of N^AL and N^BL under matching boundary conditions is equivalent to the solution of N. We use efficient graph theoretic algorithms (0(|E|); E=set of edges of N) to generate and N^BK This needs to be done only once per simulation run. Equation formulation for N^AL is of the NODAL ADMITTANCE type while for N^BK it is of the LOOP IMPEDANCE type. The resulting system matrix has good computational properties such as NEAR POSITIVE DEFINITENESS. To exploit them BITSIM's linear equation solver is based on an iterative method (GENERALISED CONJUGATE RESIDUAL).

Indexing terms:

• Circuit simulator
• Linear equation solver