Influence of passive oscillator component variation on OBT sensitivity in OTAs

Abstract

Oscillation based testing (OBT) relies on converting the Circuit Under Test (CUT) into an oscillator during the test phase by adding a feedback loop in order to provoke self-sustained oscillation which is monitored at an output. The monitored output frequency and amplitude has previously been shown found sensitive to variation in the OBT's passive feedback circuit, while the choice of oscillator topology was shown to influence the discrimination between faulty and non-faulty circuits in idealized circuits. In this work, we evaluate the influence of this variation on fault discrimination in three different OBT oscillator configurations for an operational transimpedance amplifier (OTA). It is found that a 100% variation in passive component value can effect variation in the discrimination of below 29%, or as much as 2900%, depending on the oscillator topology under nominal operation. We further subject a typical test case to Monte Carlo analysis, which indicates that fault discrimination is maintained despite process variation.