A Theory of Testability with Application to Fault Coverage Analysis

When test vectors are applied to a circuit, the fault coverage increases with the number of vectors. The rate of increase, however, is circuit-dependent. In fact, the actual rise of fault coverage also depends on the characteristics of the vectors. This paper shows that the average fault coverage can be computed from circuit testability. A relationship between fault coverage and circuit testability is derived. The mathematical formulation allows computation of coverage for both deterministic and random vectors. Applications of this analysis include: Determination of circuit testability from fault simulation, coverage prediction from testability analysis, prediction of test length, and test generation by fault sampling.