Simple Op Amp Measurements

When testing op amps, their high open-loop gain makes it hard to avoid small voltage errors due to pick-up, stray currents, or the Seebeck effect. The measurement process can be simplified by using a servo loop to force a null at the input, thus allowing the amplifier to measure its own errors. This article describes a versatile circuit that employs an auxiliary op amp as an integrator to establish a stable loop with very high dc open-loop gain.