Application of Predictive Oscillation-Based Test to a CMOS OpAmp

A predictive oscillation-based test (POBT) strategy, combined with supply current monitoring, is proposed as an alternative to the specification-based test of analog circuits. According to our simulation results, the combination of both techniques is excellent in predicting the main performance parameters of a CMOS operational amplifier (OpAmp) (dc gain, bandwidth, and slew rate) from test observables such as oscillation frequency and variations on the supply current. Considering tolerances in the fabrication process, a set of mapping functions has been found by circuit simulation, giving correlation coefficients higher than 0.999 and RMS prediction errors below 1.5%. A set of 19 fabricated circuits has been measured in both normal and test modes. The correlation between performance parameters and test observables, which are both measured, gives RMS errors of 0.65% for the dc gain, 11.30% for the bandwidth, and 4.12% for the slew rate.