Non-Ideal Op-Amp Circuit Analysis

Abstract

Op-amps are commonly used by instrumentation engineers. In the ideal case, the open-loop gain of an op-amp is regarded as infinite, the input impedance as infinite, and the output impedance as zero. In many cases, however, it is necessary to estimate the performance of an op-amp circuit with consideration of non-ideal parameters, and therefore it is necessary to analyse the non-ideal characteristics of the op-amp circuit. This paper discusses the effect on circuit performance of non-ideal parameters, i.e. finite open-loop gain, finite input impedance and non-zero output impedance of op-amps. A concept ‘loop gain’ is introduced and the dynamic behaviour, i.e. the frequency response, is analysed based on a first-order dynamic model.