The effective input
resistance R_{in} 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 V_{in} and the input current is simply the
differential input current I_{d}. Thus R_{in}
is equal to V_{in}/I_{d} and is
very large because of the vanishingly small value of I_{d}. In fact, the
effective input resistance is even larger than
the differential input resistance between the
inputs, R_{d}. Algebraically, R_{in} can be shown to be A*R_{d}.

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 R_{1} and R_{2} and the differential
input resistance (typically 1 to 100 Megohm), depending on the type of op amp.

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 toh@umd.edu.
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