Fault diagnosis and fault model aliasing

During fault diagnosis, the existence of equivalent faults, or faults that are not distinguished by the test set applied to the circuit, can create ambiguity as to the location of a defect. This happens if the circuit-under-test produces a response that matches the circuit response in the presence of two faults in different locations of the circuit. Equivalence between faults of different models, or a test set that does not distinguish two such faults, can increase the ambiguity as to the defect location as well as its type. We refer to this phenomenon as fault model aliasing. We study the extent to which fault model aliasing can be expected to occur under various test sets. We also describe a test generation procedure that can reduce it.