Efficient implication-based untestable bridge fault identifier

This paper presents a novel, low cost technique based on implications to identify untestable bridging faults in sequential circuits. Sequential symbolic simulation is first performed, as a preprocessing step, to identify nets which are uncontrollable to a specific logic value. Then, an implication-based analysis is carried out for each fault to determine if a particular fault is testable or not. We also use information about the untestable stuck-at faults to filter out some bridges early in the analysis process. The application of our technique to ISCAS '89 sequential benchmark circuits and a few industrial circuits showed that a large number of untestable bridges could be identified at a low cost, both in terms of memory and execution time.