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Input resistance of a non-inverting amplifier

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The effective input resistance Rin of a non-inverting amplifier configuration is much greater than for the inverting amplifier configuration. The input resistance is defined as the ratio of the input voltage to the input current. The input voltage is Vin and the input current is simply the differential input current Id. Thus Rin is equal to Vin/Id and is very large because of the vanishingly small value of Id. In fact, the effective input resistance is even larger than the differential input resistance between the inputs, Rd. Algebraically, Rin can be shown to be A*Rd.

You can vary the open loop gain in this simulation by using the slider on the right. Note that for any reasonably large value of open-loop gain, the actual closed-look gain is very close to the nominal gain and that the differential input voltage is very small compared to the other voltages.

You can also change the values of R1 and R2 and the differential input resistance (typically 1 to 100 Megohm), depending on the type of op amp.

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This page is maintained by Prof. T. C. O'Haver , Department of Chemistry and Biochemistry, The University of Maryland at College Park. Comments, suggestions and questions should be directed to Prof. O'Haver at
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