Transition Fault Testing for Sequential Circuits

This paper addresses the problem of simulating and generating tests for transition faults in nonscan and partial scan synchronous sequential circuits. A transition fault model for sequential circuits is first proposed. In this fault model, a transition fault is characterized by the fault site, the fault type, and the fault size. The fault type is either slow-to-rise or slow-to-fall. The fault size is specified in units of clock cycles. Fault simulation and test generation algorithms for this fault model are presented. The fault simulation algorithm is a modification of PROOFS, a parallel, differential fault simulation algorithm for stuck faults. Experimental results show that neither a comprehensive functional verification sequence nor a test sequence generated by a sequential circuit test generator for stuck faults produces a high fault coverage for transition faults. Deterministic test generation for transition faults is required to raise the coverage to a reasonable level. With the use of a novel fault injection technique, tests for transition faults can be generated by using a stuck fault test generation algorithm with some modifications. Experimental results for ISCAS-89 benchmark circuits and some AT&T designs are presented. For partial scan circuits, we first describe a test application scheme for detecting transition faults. Modifications to test generation and fault simulation algorithms required for partial scan circuits are presented. Experimental results on large benchmark circuits show that a high transition fault coverage can be achieved for the partial scan circuits designed using the cycle breaking technique [1].