Testing fully differential amplifiers using common mode feedback circuit: A case study

This paper presents a simple and low-cost test methodology applied to fully differential amplifiers (FDAs). This kind of amplifier needs a common mode feedback (CMFB) circuit to keep the output common mode tightly controlled. In this work we propose the reuse of the CMFB circuit of FDAs as an embedded checker to ease the test of the whole amplifier, increasing the observability of faults occurring either in the amplifier or in the CMFB block. Catastrophic faults are injected into these two circuits by means of SPICE simulations, considering a 0.18µm FDA as case study. Transient and DC (Direct Current) tests are performed and the fault coverage is evaluated. Simulation results point to high fault coverage, while only the common mode feedback signal needs to be monitored. This way, a low-cost and low area overhead test methodology is achieved with affordable test time.