Reducing the cost of circular built-in self-test by selective flip-flop replacement

The cost of self-testing and diagnosing VLSI circuits which use Circular Built-In Self-Test (BIST) is reduced through the selective replacement of existing flip-flops with Circular BIST flip-flops. We find that maximal fault coverage can be maintained while only replacing approximately 60% of the existing flip-flops in the VLSI circuit as opposed to the 80% to 100% replacement performed in most applications. On the other hand, we find that the optimal fault coverage vs. area overhead is obtained with approximately 30% replacement.