Invalid state identification for sequential circuit test generation

For sequential circuit test pattern generation, the information on invalid states will help greatly on backward justification to reduce the test generation time. This paper proposes three algorithms to find invalid states for sequential circuit test generation. The first two algorithms search the complete set of invalid states by exploring all valid states and reachable states respectively. The first algorithm is efficient for circuits having more invalid states than valid states while the second algorithm is efficient for circuits having more valid states than invalid states. The third algorithm searches only the invalid states that are required for test generation to stop justification early. Experimental results on ISCAS benchmark circuits show that the algorithm can identify invalid states in short time and can help improve test generation significantly in the fault coverage, detection efficiency, and generation time.