Vector replacement to improve static-test compaction for synchronous sequential circuits

Static-test compaction procedures for synchronous sequential circuits may saturate and be unable to further reduce the test-sequence length before the test length reaches its minimum value, resulting in test sequences that may be longer than necessary. We propose a method to take a static-compaction procedure out of saturation and allow it to continue reducing the test-sequence length. The proposed method is based on the replacement of test vectors in the test sequence every time the compaction procedure reaches saturation. Test-vector replacement is done such that the fault coverage of the sequence is maintained. Experimental results using an effective static-compaction procedure demonstrate that reductions in test length can be obtained by the proposed vector replacement method.