Fault coverage estimation by test vector sampling

We have developed a new statistical technique for estimating delay fault coverage in combinational circuits. True value simulation is performed for a sample of vector pairs chosen randomly from the test set. Transition probabilities and observabilities are estimated from the simulation data. These allow us to estimate fault detection probabilities per vector pair. Fault models considered are the transition faults, path delay faults, and the longest path delay faults. We analyze the vector sampling error and find a high-confidence lower bound for the detection probability that is used to compute the fault coverage for the entire vector set. Experimental results show that vector sampling can provide a close approximation to other methods. It requires reduced computing resources compared to other statistical methods. The savings over fault simulation is even greater.<
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