On the Switching Activity in Faulty Circuits During Test Application

An excessive switching activity during the functional capture cycles of scan-based tests can lead to overtesting of delay faults. Low-power test generation procedures that address this issue consider the switching activity of the fault-free circuit. This paper observes that an excessive switching activity in a faulty circuit can also affect the test application process. In particular, we show that a fault effect may disappear if a signal-transition is delayed because of an excessive switching activity in the faulty circuit. Thus, excessive switching activity in the faulty circuit can result in test escapes. Using functional broadside tests for benchmark circuits, we study the extent to which the switching activity of a faulty circuit may exceed the switching activity that is possible during functional operation. We also consider the effects of eliminating tests with excessive switching activity in faulty circuits.