Effect of open-loop gain on an inverting amplifier

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Note that as you make the open-loop gain larger and larger, the differential input voltage V_diff and the differential input current I_d get smaller and smaller. Also, the actual closed-look gain becomes closer and closer to the nominal gain given by the ratio of R₂ to R₁. Real operational amplifiers have open loop gains that are so high (50,000 or more) that is a good approximation to assume that it is infinite, and therefore that the differential input voltage V_diff and the differential input current I_d are both zero. This is not exactly true, of course, but the accuracty of this approximation is better that the accuracy of the resistors (even of precision resistors).

In this simulation you can change the values of R₁, R₂ and the differential input resistance (typically 1 to 100 Megohm).

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