Simulation techniques for mixed analog/digital circuits

The techniques used in the iSPLICE3 simulator for the analysis of mixed analog/digital (A/D) circuits are described. iSPLICE3 combines circuit, switch-level timing, and logic simulation modes and uses event driven selective-trace techniques. It also uses a hierarchical schematic capture package called iSPI (Simulation Program Interface) for design entry, circuit partitioning, and simulation control. The contributions here include a new DC solution method, a mixed-mode interface modeling technique, and an automatic partitioning approach for MOS logic circuits. The details of these three methods are provided, along with the architecture and transient simulation algorithms used in iSPLICE3. The results of circuit simulations and mixed-mode simulations of a CMOS static RAM, two A/D converters, and a phase-locked loop are presented. These results indicate that iSPLICE3 is between one and two orders of magnitude faster than SPICE2 with negligible loss in accuracy.