Static Test Compaction Using Independent Suffixes of a Transparent-Scan Sequence

Transparent-scan enhances test compaction by allowing scan shift and functional capture cycles to be interleaved in arbitrary ways, and using both types of clock cycles for detecting faults. An initial transparent-scan sequence T can be obtained by translating every clock cycle of a compact scan-based test set C into a test vector of T. This sequence can then be compacted to achieve a lower number of clock cycles than that required for C. A bottleneck in the compaction of T is the need to perform repeated sequential fault simulation. This article makes the new observation that a transparent-scan sequence contains independent subsequences, where fault detection is not influenced by and does not influence the rest of the sequence. The article focuses on independent subsequences at the end of T, referred to as independent suffixes. The test compaction procedure described in this article identifies the shortest independent suffix, compacts it without considering the rest of the sequence, and moves it to the beginning of the sequence. This is repeated as long as new independent suffixes are obtained. Experimental results for benchmark circuits demonstrate the effectiveness of this approach.