A New Method for Improving Path Delay Fault Coverage

In the test of a circuit for faults it is very desirable to have the minimum paths that are to be tested for a complete circuit test. At first, the best test vectors are chosen and then these pairs of vectors are applied to the circuit. Each of these pair of vectors is able to detect a certain number of the faults and the path delay fault coverage for each and all of them may be calculated. Suitable choice of a path may result in the coverage of the whole circuit and increases detected faults. In this paper, a new method for choosing the minimum suitable paths is introduced. Decreasing the number of test paths causes an increase in the number of detectable faults by a certain number of test vector pairs, hence giving a better fault coverage. In the presented method, a test path would be selected, if and only if, there exists at least one "two-piece" segment in that path which has not been tested before in the previously tested paths. If the chosen path has at least one "three-piece" (or "more-piece") segment the method will become more complicated. The method is applied to some ISCAS89 benchmarks circuits. Keywords– Sequential circuit, path delay fault, fault coverage