Application of group delay equalisation in testing fully-balanced OTA-C filters

This paper proposes a new BIST structural testing methodology for fully-balanced OTA-C filters. The methodology is based on using a simple group-delay equaliser to emulate the filter function; any discrepancies resulting from comparing the filter and equaliser outputs indicates a faulty circuit. The test circuitry is designed using detailed analysis of the possible faults and their effects on the filter output. This ensures a high fault coverage and minimisation of test accuracy dependence on manufacturing process variations. Furthermore, the equaliser circuitry requires only a single low-precision capacitor and the test stimulus frequency does not need to be exact. Simulation, has shown that up to 99% fault coverage is possible when the proposed methodology is applied to a 4.5 MHz Chebyshev low pass filter. From actual layout, the estimated test circuitry area overhead is 20% which compares well with recently reported results.