A two-phase fault simulation scheme for sequential circuits

A two-phase fault simulation scheme for sequential circuits is proposed. In this fault simulation, the input sequence is divided into two parts. In the first phase, fault free simulation is performed with the first sequence of patterns. In the second phase, fault simulation is performed with the rest of the patterns. Five cases of faults which result from two-phase fault simulation are discussed in detail. Significant speedup in simulation time can be obtained because this fault simulation approach can quickly drop Case 1 faults, which are time-consuming faults and would be considered undetectable in the traditional three-value fault simulation but are actually detected in exact fault simulation. Almost "exact" results can be obtained for detected faults except for a small percentage of over-detected-faults (ODFs) and under-detected-faults (UDFs).