On Undetectable Faults and Fault Diagnosis
Irith Pomeranz, Sudhakar M. Reddy · IEEE Transactions on Computer-Aided Design of Integrated Circuits and Systems · 2010
The presence of an undetectable faultuimay modify the response of a detectable faultdjto a test set used for fault diagnosis. This may impact the accuracy of fault diagnosis based on the responses of single faults. Many state-of-the-art diagnosis processes are based on the responses of single stuck-at faults even though their goal is to diagnose defects (including multiple defects) that are different from stuck-at faults. Therefore, we study the effects of undetectable single stuck- at faults on the accuracy of fault diagnosis based on the responses of single stuck-at faults. For this purpose, we consider the cases where the response of a double stuck-at faultui&dj, which consists of an undetectable faultuiand a detectable faultdj, is different from the response of the single faultdj. We show that there are significant, yet manageable, numbers of such faults in benchmark circuits under test sets used for fault diagnosis. In all these cases, a fault diagnosis process based on single stuck-at faults may not identify the locations ofdjanduias candidate defect sites if a defect affects the sites ofdjandui. We conclude that it is important to considerui&djduring fault diagnosis in order not to preclude the sites ofdjanduias candidate defect sites.