RTL DFT techniques to enhance defect coverage for functional test sequences

Functional test sequences are often used in manufacturing testing to target defects that are not detected by structural test. However, they suffer from low defect coverage since they are mostly derived in practice from existing design-verification test sequences. Therefore, there is a need to increase their effectiveness using design-for-testablity (DFT) techniques. We present a DFT method that uses the register-transfer level (RTL) output deviations metric to select observation points for an RTL design and a given functional test sequences. Simulation results for six ITC´99 circuits show that the proposed method outperforms two baseline methods for two gate-level coverage metrics, namely bridging and gate-equivalent fault coverage. Moreover, by inserting a small subset of all possible observation points using the proposed method, significant fault coverage increase is obtained for all benchmark circuits.