Accumulator-based compaction of test responses

An accumulator-based compaction (ABC) scheme for parallel compaction of test responses is introduced. The asymptotic and transient coverage drop introduced by accumulators with binary and 1´s complement adders is studied using Markov chain models. It is proven that the asymptotic coverage drop in ABC with binary adders is 2^-k, where k is the number of bits in the adder that the fault can reach. In ABC with 1´s complement adders, the asymptotic coverage drop for a fairly general class of faults is (2n-1)^-1, where n is the total number of bits. The analysis of transient behavior relates the coverage drop with the probability of fault injection, the size of the accumulator, and the length of the test experiment. The process is characterized by damping factors derived for various values of these parameters