On the use of counters for reproducing deterministic test sets

We propose a very simple and fast CAD tool to check whether a binary counter can reproduce a predetermined set of test patterns in a reasonable time. Given a test matrix T, the tool uses column merging, complementation, and permutation so that the distance between the starting and the finishing vector of the corresponding counter is minimized. The hardware overhead of the proposed approach is by far lower than that of any other existing approach. Although it is computationally difficult (NP-hard) to obtain the absolute minimum distance, we present an algorithm which in the absence of don´t cares in the test matrix, finds an appropriate column merging, complementation, and permutation that guarantees the distance is never more than twice as large as the best possible. In the presence of don´t cares, the latter algorithm forms the basis of a powerful heuristic. Experiments on various test sets on benchmark circuits show that the exact number of clock cycles needed for a binary counter to reproduce all the patterns for the hard-to-detect faults compares favorably with the expected number yielded by existing Weighted Random LFSR-based approaches which have significantly higher hardware overhead