On invalidation mechanisms for non-robust delay tests

In most of the delay fault testing literature there is a widespread belief that a non-robust test for a path delay fault can be invalidated only through the existence of another path delay fault. In this paper the author presents an analysis of conditions that can invalidate a non-robust test, and gives four different invalidation mechanisms. Three of these mechanisms, in addition to pulse dampening, do not require the existence of another path delay fault in a circuit. He also defines pseudo-VNR tests, and shows that this is the most common interpretation of validatable-non-robust tests in the literature. Uncovering the invalidation mechanisms for non-robust tests is quite important given the fact that a large number of paths in a circuit usually do not have any robust tests.