Pseudo-exhaustive built-in TPG for sequential circuits

Abstract

We address the issue of pseudo-exhaustive test pattern generation (TPG) for the built-in self-test (BIST) of sequential circuits. Let d be the sequential depth, and w be the input dependency limit. We use an LFSR/SR Test Pattern Generator and a small additional hardware overhead to automatically generate d/spl middot/2/sup w/ test patterns to test the circuit pseudo exhaustively or, alternatively, pseudo-randomly with less hardware overhead and extremely high fault coverage. Our scheme uses novel retiming algorithms and transforms the circuit to an equivalent (for test purposes) one by scanning a subset of flip-flops for breaking its cyclic structure, bounding the sequential depth, forcing the input dependency limit, balancing the circuit, and maintaining the clock period. We present the first polynomial time algorithm to bound the sequential depth of a circuit by retiming with minimum number of flip-flops and subject to a clock period bound. We also give a retiming-based polynomial time algorithm to balance a circuit by inserting a minimum number of bypass delay cells. Experimental results on the ISCAS'89 benchmarks indicate that our method outperforms a previously proposed approach, which not only does not provide for on-chip test pattern generation but also requires O(q/spl middot/f/spl middot/2/sup w/) test patterns, where q is the total number of primary or pseudo-primary outputs in the circuit and f is the total number of flip-flops.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>