Derivation of signal flow for switch-level simulation

This paper presents a new algorithm for deriving the direction of signal flow in MOS circuits. The algorithm detects so-called unidirectional transistors. In a unidirectional transistor, signal flow is restricted to one direction during switch-level simulation, without compromising the simulation results. The algorithm uses a static analysis of the switch-level characteristics of the circuit, such as the transistor strengths and node capacitor sizes. It was implemented and used in the simulation of a large, commercial microprocessor. For this processor, 98.5% of the transistors were determined to be unidirectional by the algorithm. The simulation time for this processor decreased significantly when unidirectional transistors were detected