Spectral Signature Testing of Multiple Stuck-at Faults in Irredundant Combinational Networks

Earlier spectral signature testing methods are extended to the multiple stuck-at fault model. The testability condition for multiple- input faults is established and a minimal spanning signature (MSS) is defined to cover all these faults. It is then shown that an MSS, which in most cases contains a single spectral coefficient, will detect over 99 percent of all input and internal multiple faults. An approach is described to obtain a complete signature for all multiple faults in any irredundant combinational network with comparatively small numbers of fan-outs. Tree networks that include XOR/XNOR gates are shown to be easily tested. Internally fan-out-free and general irredundant networks are also considered. A design approach is proposed to enable a network to be tested for all single and most multiple faults using a single coefficient, with the possible overhead being an extra control input.