BETSY: synthesizing circuits for a specified BIST environment

This paper presents a logic synthesis tool called BETSY (BIST Environment Testable SYnthesis) for synthesizing circuits that achieve complete (100%) fault coverage in a user specified BIST environment. Instead of optimizing the circuit for a generic pseudo-random test pattern generator (by maximizing its random pattern testability), the circuit is optimized for a specific test pattern generator, e.g., an LFSR with a specific characteristic polynomial and initial seed. This solves the problem of having to estimate fault detection probabilities during synthesis and guarantees that the resulting circuit achieves 100% fault coverage. BETSY considers the exact set of patterns that will be applied to the circuit during BIST and applies various transformations to generate an implementation that is fully tested by those patterns. When needed, BETSY inserts test points early in the synthesis process in an optimal way and accounts for them in satisfying timing constraints and other synthesis criteria. Experimental results are shown which demonstrate the benefits of optimizing a circuit for a particular test pattern generator.