Test compaction for at-speed testing of scan circuits based on nonscan test. sequences and removal of transfer sequences

Proposes a procedure for generating compact test sets with enhanced at-speed testing capabilities for scan circuits. Compaction refers here to a reduction in the test application time, while at-speed testing refers to the application of primary input sequences that contribute to the detection. of delay defects. The proposed procedure generates an initial test set that has a low test application time and consists of long sequences of primary input vectors applied consecutively. To construct this test set, the proposed procedure transforms a test sequence T_o for the nonscan circuit into a scan-based test by selecting an appropriate scan-in state and removing primary input vectors from T_o if they do not contribute to the fault coverage. If T_o contains long transfer sequences, several scan-based tests with long primary input sequences may be obtained by replacing transfer sequences in T_o with scan operations. This helps reduce the test application time further. We demonstrate through experimental results the advantages of this approach over earlier ones as a method for generating test sets with minimal test application time and long primary input sequences