Efficient BDD-based Fault Simulation in Presence of Unknown Values

Unknown (X) values, originating from memories, clock domain boundaries or A/D interfaces, may compromise test signatures and fault coverage. Classical logic and fault simulation algorithms are pessimistic w.r.t. the propagation of X values in the circuit. This work proposes efficient hybrid logic and stuck-at fault simulation algorithms which combine heuristics and local BDDs to increase simulation accuracy. Experimental results on benchmark and large industrial circuits show significantly increased fault coverage and low runtime. The achieved simulation precision is quantified for the first time.