Diagnosis of Double Faults Consisting of a Stuck-at Fault and a Transition Fault

Diagnosis is an important process for deducing candidate faults in faulty LSIs. Although most of the diagnosis methods have targeted single stuck-at faults, multiple faults also need to be addressed because methods for diagnosing single stuck-at faults do not cover some of the multiple faults. In this paper, diagnosis methods for a class of multiple faults are proposed, namely double faults consisting of a stuck-at fault and a transition fault. The proposed method first deduces candidate stuck-at faults and candidate transition faults using pass-fail dictionaries. After the candidate faults are reduced, fault simulation is conducted for a faulty circuit assuming that the candidate double fault consists of a candidate stuck-at fault and a transition fault obtained from the reduced lists in the earlier step. Output responses are then compared between the simulation results and the circuit under diagnosis. Furthermore, a design-for-testability technique is applied to observe the compacted output responses on flip-flops and primary outputs during the launch-on-capture test scheme. By observing the compacted output responses, candidate faults are deduced. The effectiveness of the proposed methods is verified by experimental results for benchmark circuits.