During built-in self-test (BIST), the set of patterns generated by a pseudo-random pattern generator may not provide a sufficiently high fault coverage. This paper presents a new technique for synthesizing combinational mapping logic to transform the set of patterns that are generated. The goal is to satisfy test length and fault coverage requirements while minimizing area overhead. For a given pseudo-random pattern generator and circuit under test, there are many possible mapping functions that will provide a desired fault coverage for a given test length. This paper formulates the problem of finding a mapping function that can be implemented with a small number of gates as a one of finding a minimum rectangle cover in a binate matrix. A procedure is described for selecting a mapping function and synthesizing mapping logic to implement it. Experimental results for the procedure are compared with published results for other methods. It is shown that by performing iterative global operations, the procedure described in this paper generates mapping logic that requires less hardware overhead to achieve the same fault coverage for the same test length.
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