Testable design of multiple-stage OTA-C filters

This paper presents a novel design and test methodology to increase the testability of multistage operational transconductance amplifier and grounded capacitor (OTA-C) filters. As assumed herein, a fault can cause the value of a passive circuit component to deviate from its normal value in order to detect such faults. This deviation causes open-circuit and/or short-circuit effects or changes the operating characteristics of the active components. That is, the catastrophic and parameter deviation faults are considered in this paper. The proposed methodology is also effective in detecting single and multiple faults. Simulation results for the faulty and fault-free circuits are compared to verify the feasibility of our design-for-testability (DFT) structure. The physical layout of a third-order Butterworth OTA-C filter is implemented by the TANNER layout tool. The extra hardware overhead to make the OTA-C filters testable is less than 9%, which is quite a reasonable value for analogue circuits.