This brief deals with soft-fault diagnosis of analog circuits. Both ac and dc linear circuits, as well as dc nonlinear circuits with limited number of test points are considered and the presence of component tolerances is taken into account. An approach using the linear-programming concept and the simplex method is developed. Contrary to the other methods which use optimization techniques for diagnosis, no optimization process for evaluating the parameters deviations is performed. In fact, only phase 1 of the simplex method is applied to check the existence of a feasible solution. It enables us to state whether the actual parameters are within tolerance ranges or some components are faulty. Identification of the faulty elements is achieved using a similar idea. Three numerical examples illustrate this approach.

This paper deals, for the first time, with catastrophic fault diagnosis of nonlinear analog circuits containing bipolar and MOS transistors having multiple operating points (DC solutions). The faults are cuts of some connecting paths and short-circuits of some pairs of points. Simulation-before-test approach is applied for detection and identification of a single catastrophic fault. To build a fault dictionary, a diagnostic test is arranged based on DC analysis. In the discussed circuits having multiple DC solutions, the tested output voltage may assume different values for fixed value of the input voltage. This fact considerably complicates the fault diagnosis. The crucial point of the proposed approach is tracing large number of nonlinear multivalued input-output characteristics at different values of circuit parameters within their tolerance ranges. For this purpose an efficient and fast algorithm is developed, based on the theory known under the name a linear complementarity problem. To illustrate the proposed approach and show its efficiency, four numerical examples are given.

This paper deals with multiple soft fault diagnosis of nonlinear analog circuits and offers a method that allows locating the faulty parameters and evaluating their values. The method works with a system of nonlinear algebraic test equations, which are not given in explicit analytical form, and actually may possess multiple solutions. The solutions are specified by one or several sets of the diagnostic parameter values that meet the test. To find the multiple solutions, an extended systematic search method has been developed. The diagnostic algorithm proposed in this paper exploits this method and brings a new concept for finding the actual solution. As a result, the diagnostic process is considerably improved. It can be applied to bipolar junction transistor and CMOS circuits manufactured in micrometer and nanometer technologies. In the last case, however, the transistors are characterized by intricate models (PSP 103 or BSIM 4). In consequence, the CPU time increases due to very complex sensitivity analyses of the circuits required by the diagnostic method. In such a case, the proposed approach is useful at the preproduction stage, where the CPU time is offline and not crucial. For illustration, two numerical examples are given. Index Terms-Analog circuits, bipolar and CMOS circuits, fault diagnosis, multiple soft faults, nonlinearity.0018-9456