If a circuit has been found to be faulty during design characterization before it is in high volume production, it may be useful to diagnose the cause of the failure. If faults are identified and located, a circuit can then be redesigned to be less sensitive to common failure mechanisms. Fault diagnosability analysis is an approach to enhancing the diagnosabilty of a circuit. Whereas the design for diagnosability ensures that the test points are properly selected and the generation of tests is considerably simplified, diagnosability analysis is used to locate sections of a circuit having poor diagnosability. The information allows estimation of a circuit's diagnosability before the fault diagnosis is attempted. Hence any potential problem can be located early on the design phase, allowing modifications to be introduced to improve the final diagnosability of the circuit. This paper presents a simple diagnosability analysis process in which the diagnosability of a circuit is measured from a graph that describes the circuit topology and a given set of test points, and no circuit simulation is needed. Since the graphical description of a circuit topology is not unique, the developed diagnosability analysis will find a graph with the maximum diagnosability that the circuit can possibly achieve, and identify the components/sub-circuits with poor diagnosability. (C) 1998 John Wiley Sons, Ltd. References: 18
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