Analog circuit fault diagnosis based on bandwidth and fuzzy classifier

This paper presents a fault detection algorithm based on SBT (simulation before test) for testing linear analog circuits. In the proposed algorithm the transfer function of the circuit under test (CUT) is derived for nominal value of the circuit components. The frequency response of the CUT is simulated under various fault conditions and the corresponding bandwidth for each fault is obtained. It can be observed that the bandwidth is different for different fault conditions. Therefore using fault dictionary all single and multiple faults in the CUT can be detected. The fuzzy inference system is used to classify the faults effectively. The feasibility of this method is validated through second order Sallen-Key band pass filter and fourth order Leapfrog low pass filter circuits. For faulty conditions the filter parameters are varied to 50 percent of their nominal value. This algorithm is robust to detect all single and multiple faults with encouraging results.