Analysis of noninverting amplifiers' gain error patterns by MathCAD

Abstract

Based on deducing the gain error's formula of noninverting amplifier, MathCAD was used to analyze the influences of real opamp's nonideal parameters. Result shows: For the modern opamps whose open-loop gain is larger than 120dB, the optimal value of feedback resistance Rf can be settled in a very wide range which is 3–5 orders of magnitude, but Rf shouldn't be too large and had better not smaller than 500 ohms. Opamp's input resistance and output resistance have minor influence on the gain error, while the open-loop gain is the main factor, the larger the open-loop gain is, the smaller the gain error is. The gain error is smaller when the target gain is smaller. The values of Rf that keep minimum gain error settles in a narrower range when target gain and/or open-loop gain is smaller.