Soft faults of analog circuits are more difficult to diagnose than hard faults because the soft faults are caused by the deviations of component parameters. Node voltages were traditionally used as the testing signals to diagnose analog circuits. With the rapid development of integrated circuits technology, fewer and fewer circuit nodes are accessible. Only the output voltage can be tested in many cases. This cries for other new accessible signal except for the traditional voltage signal. In this paper, the fault features of testing signal in both time-domain and frequency-domain are analysed. The output voltage was acquired firstly. Its fault features were extracted and used for fault diagnosis. The results show that the soft faults of Tow-Thomas filter cannot be uniquely located by using this output voltage only. Then a new accessible signal, which named dynamic power supply current, was acquired and its fault features were analysed. And the results were compared with those using output voltages. The comparing results show the validity of dynamic power supply current. This signal contains information related with the circuits’ topology and can be used for fault diagnosis of analog circuits.
Fault features analysis for soft faults of analog circuits with tolerance
