On Computing Optimized Input Probabilities for Random Tests

Self testing of integrated circuits by random patterns has several technical and economical advantages. But there exists a large number of circuits which cannot be randomly tested, since the fault coverage achieved that way would be too low. In this paper we show that this problem can be solved by unequiprobable random patterns, and an efficient procedure is presented computing the specific optimal probability for each primary input of a combinational network. Those optimized random patterns can be produced on the chip during self test or off the chip in order to accelerate fault simulation and test pattern generation.