A pre-simulation measure of d.c. design-for-testability fault diagnosis quality

Equivalent faults inhibit fault diagnosis by producing indistinguishable test metric measurements. Removal of conditions causing the equivalence in response exhibited by such faults is necessary, if fault diagnosis quality is to be improved. As Design for-Testability (DFT) methodology aims to deliver a degree of fault diagnosis substantially greater than that obtainable testing unassisted by on-chip test specific hardware, designing a DFT scheme with minimal fault equivalence is an issue to be addressed. Presented is a set of simple and inexpensive tests, applied pre-simulation, for identifying catastrophic resistive component faults that cause numerical equivalent d.c. test model responses. Using a biquadratic notch filter modified with a novel DFT scheme, we demonstrate that equivalent fault information is a useful initial measure for assessing the potential increase in fault diagnosis quality obtainable with a DFT scheme.