Piecewise Approximate Circuit Simulation

Conventional circuit simulation methods solve a set of coupled, nonlinear, algebraic differential equations by numerical techniques, using analytical models to represent circuit elements. Such methods are very accurate, but slow and inflexible. This paper describes a new simulation methodology for the nonlinear transient analysis of electrical circuits. Equations are formulated on the tree/link basis. All branch and node variables are modeled to be piecewise approximate in time. Electronic devices are represented by empirical table models of I-V characteristics. The table models may be built at various levels of precision and concomitant accuracy levels are reflected in the simulation results. Simulation accuracy may be varied on a branch-by-branch basis or a global basis, thus permitting the user to distribute computer resources in a meaningful manner. The simulation algorithm is event driven and fully exploits temporal sparsity in the underlying circuit equations. Mechanisms for dealing with steady-state situations and stiff circuits have been investigated. A prototype simulator, SPECS, has been developed and tested on large industrial integrated circuits. It has proven to be a reliable and efficient tool in the analysis of digital and mixed circuits. © 1991 IEEE