STAFAN: An Alternative to Fault Simulation

STAtistical Fault ANalysis (STAFAN) is proposed as an alternative to fault simulation of digital circuits. In this analysis, controllabilities and observabilities of circuit nodes are defined as probabilities which are estimated from signal statistics obtained from fault-free simulation. Special procedures are developed for dealing with these quantities at fanout nodes and at feedback nodes. The computed probabilities are used to derive unbiased estimates of fault detection probabilities and overall fault coverage for the given set of input vectors. Fault coverage and the undetected fault data obtained from STAFAN for actual circuits are shown to agree favorably with the fault simulator results. The computational complexity added to a fault-free simulator by STAFAN grows only linearly with the number of circuit nodes.