Fast and accurate estimation of gain and unity-gain bandwidth of an OpAmp

Checking the compliance of the specifications is a key issue in the post-production process of analog circuits. Thus, in analog test, where it is fundamental to be able to measure the actual value of OpAmps performance parameters, it can be very interesting to be able to get a fast and accurate estimation of these values. One of the most popular estimation techniques is the oscillation-based test, where the analog circuit is mapped into an oscillator, and the oscillation frequency is used to get an estimation of some key value. When OBT is applied to OpAmps, the main problem is that it is very difficult, if not impossible, to get an actual circuit to behave outside the saturation region. In this paper we present a technique that allows direct calculation of an OpAmp unity-gain bandwidth and the gain using the oscillation frequency of slightly saturated oscillators. Results show that we can estimate the actual values with errors less than 10%, using only two frequency measurements.