Influence of Oscillator Topology on Fault Sensitivity in Oscillation Based Testing (OBT) of OTAs

Oscillation based testing (OBT) of operational transimpedance amplifiers (OTAs) has previously been shown sensitive to variation in oscillator component values, with significant influence on the OBT circuit's ability to discriminate between faulty and non-faulty circuits. Here, we extend on prior analyses by comparing the fault discrimination in eight different oscillator topologies for OTAs designed in 0.5 μm CMOS. It is found that the appropriate choice of oscillator circuit can increase the sensitivity of the OBT circuit to an injected fault by up to 4.86 times for f_osc detection and more than 52 times for V_pp detection. We further demonstrate a new figure-of-merit (FOM) for OBT, as an extension on the traditional fault coverage measure, that includes statistical distribution in measured OBT outputs to quantify the fault sensitivity of a specific OBT circuit. This enables comparison of OBT circuits despite process variation.