Testing the Fleischer-Laker switched-capacitor biquad using the diagnosis-after-test procedure

This paper demonstrates an efficient diagnosis-after-test (DAT) procedure for testing the Fleischer-Laker SC biquad based on the static linear behavior (SLB) analog fault model. For typical switched-capacitor (SC) filter design, the transfer functions are mainly determined by capacitor ratios. Therefore, the practical capacitor ratios are important parameters for designers to diagnose their designs. The DAT procedure can not only test for the real transfer function of the SC biquad for making reliable pass/fail decision without conducting many tests, but also diagnose the capacitor ratios of the SC biquad. With the diagnosis results, designers can find out which capacitors cause the failure and revise the design for a better yield. Mathematical analysis shows that the entire DAT procedure requires only a three-tone test, which implies a very short test time. A second-order low-pass filter adopting the E-circuit of the Fleischer-Laker SC biquad is taken as a test example. Simulation results show the DAT procedure can provide good test accuracy with the three-tone test data. In addition, the test achieves a 100% parametric fault coverage of the capacitor ratios defined by the SLB fault model for the Fleischer-Laker SC biquad.