Probabilistic measures of fault equivalence in mixed-signal systems

A study of fault equivalence in mixed analogue-digital circuits and systems is presented, emphasizing both the theoretical analysis of the equivalence concept as well as experimental results from three classes of circuits: sample-and-hold, digital-to-analog converter, and analog-to-digital converter. While fault equivalence is well understood in digital fault models, the concept is still quite new for analog fault models. The concept is also valid within the context of mixed-signal fault models, but the equivalence has to be defined in the frequency domain and in some cases, has to be approached from a probabilistic perspective. The experimental results include fault effects due to the classic digital stuck-at-fault models as well as analog faults such as out-of-specification performance, nonlinearity, etc. For each class of circuit, extensive simulation is conducted to study the fault behavior and experimental measurements are carried out to verify these behaviors as well as to confirm the validity of equivalence definition. The major application of this study is in test generation and fault diagnosis, similar to the application of digital equivalent faults in defining test vectors for equivalence classes.<>