Enumeration of test sequences in increasing chronological order to improve the levels of compaction achieved by vector omission

We describe a method to improve the levels of compaction achievable by static compaction procedures based on vector omission. Such procedures are used to reduce the lengths of test sequences for synchronous sequential circuits without reducing the fault coverage. The proposed procedure enumerates, in increasing chronological order, test sequences consisting of subsets of the vectors included in a given test sequence that needs to be compacted. The unique feature of this approach is that test vectors omitted from the test sequence at an earlier iteration can be reintroduced at a later iteration. This results in a less greedy procedure and helps reduce the compacted test sequence length beyond the length that can be achieved if vectors are omitted permanently as in earlier procedures.