Fault simulation using small fault samples

This article emphasizes simulation-based sampling techniques for estimating fault coverage that use small fault samples. Although random testing is considered to be the primary area of application of the technique it is also suitable for estimating the fault coverage of nonrandom tests based on specific fault models. Especially for fault coverages exceeding 95%, it is shown that a precise estimate can be obtained using a fault sample of only 500 faults. The estimation is based on a binomial approximation of the probability density of the sample fault coverage. Using Bayes statistics an estimate is obtained whose accuracy is a linear function of the sample size if the fault coverage approaches 100%. The sample size is independent of the circuit size, thus making fault sampling particularly interesting for the fault simulation of ULSI designs due to the resulting reduction of the time complexity of fault simulation from O(N2) to O(N).