This paper deals with soft fault diagnosis of linear analog circuits and concentrates on the circuits including second generation current conveyors. Properties of these circuits are taken into account and an appropriate realistic conveyor model is put forward. The fault diagnosis includes fault detection, locating faulty elements from among all circuit elements, and estimating their values. The diagnostic method developed in this paper exploits a measurement test in an AC state and uses the nonlinear programming as a mathematical tool. Values of the faulty parameters may belong to wide ranges around their nominal values. For illustration a real-life current conveyor circuit is laboratorily and numerically tested. Proposed method efficiently diagnoses different faults giving correct results in short time. Although the method is dedicated to single fault diagnosis, it can be generalized to double and triple faults either. However, in the case of multiple faults it is less effective.

Introduction

Fault diagnosis of analog circuits has been an active research topic for the past decades, e.g. [2,3,6,10,11,21,25,26]. It helps in reducing the overall cost of devices due to imperfect manufacturing process [21]. Soft fault diagnosis includes fault detecting, locating faulty elements and estimating their values. Most reported works are focused on the diagnosis of a single fault, e.g. [8,28,30] because the single fault case is the most frequent. Some methods in this area are based on a measurement test leading to a set of nonlinear equations with variables being the circuit parameters. The more variables, the more complex and time consuming the process of solving the test equations is. To simplify the diagnostic process a fault verification approach can be applied, e.g. [16,22– ۲۴]. It is based on the hypothesis that only some of the parameters are potentially faulty and the others are fault-free. In this manner the number of the variables is reduced, but a drawback of this approach is the need for selecting the possibly faulty elements. Unlike the verification approach the goal of the diagnosis method proposed in this paper is to find faulty elements (and evaluate their values) from among all the circuit elements. Although huge number of research works have been reported in the past decades there is no all-purpose procedure for soft fault diagnosis of a broad class of circuits. The diagnosis procedure developed in this paper can be applied to linear circuits including passive and active devices with the special attention paid to the current conveyor circuits. It takes into account specific properties of this class of circuits and inherent limitations.