A fault model for function and delay testing

Existing gate-level fault models are not well suited to test generation for circuits that contain modules whose logic implementation and timing behavior are unspecified. A high-level fault model called the coupling fault (CF) model is presented which aims to cover both functional and timing faults in an integrated manner. Intuitively, a (single) CF denoted xi|zj exists between input xi and output zj of a module if xi|zj blocks any dynamic effect of xi on zj The set of test vectors CTS_xi|zj that detect xi|zj is represented by the boolean difference of zj with respect to xi. A pair of adjacent vectors in CTS_xi|zj, constitutes a coupling delay test. This article studies the basic properties of coupling faults and test sets, focusing on the relationship between coupling tests and other high-level tests. A coupling test set provides powerjhl, realization-independent coverage of stuck-at faults. Coupling delay tests can detect all robust path delay faults in any realization of afunction.