SAT-based fault coverage evaluation in the presence of unknown values

Fault simulation of digital circuits must correctly compute fault coverage to assess test and product quality. In case of unknown values (X-values), fault simulation is pessimistic and underestimates actual fault coverage, resulting in increased test time and data volume, as well as higher overhead for design-for-test. This work proposes a novel algorithm to determine fault coverage with significantly increased accuracy, offering increased fault coverage at no cost, or the reduction of test costs for the targeted coverage. The algorithm is compared to related work and evaluated on benchmark and industrial circuits.