Using a WLFSR to embed test pattern pairs in minimum time

We propose a methodology for reducing the number of test cycles needed by a Weighted LFSR (WLFSR) to reproduce a 2P × W test matrix T of P pattern pairs. The methodology introduces a very small number of extra cells into the WLFSR and uses appropriate combinational mapping logic in order to make the time E_P,W+δ·2 ^δ, where E_P,W+δ is the time to generate vectors containing the W bits of the first pattern for each pair plus the δ extra bits. We present an algorithm that makes the value of δ less than or equal to [log₂ λ], where λ is the size of the maximum subset of pairs in T with identical first patterns. This is a significant improvement over the time E_P,W·P required by a trivial approach that uses a WLFSR with W cells to generate the first patterns of the pairs and a P × W ROM to store the second patterns of the pairs. Experimental results on the application of the methodology to the embedding of test matrices for path delay faults are particularly encouraging, even for very large numbers of test pattern pairs that are necessary for provably high fault coverage