Inverting Amplifier using Op-Amp

From the different modes of operational amplifier series, this article will stress on the concept of inverting amplifier using operational amplifier

Operational Amplifier can be used as inverting amplifer with controlled amount of voltage gain by connecting the op-amp as shown below.

inverter amplifier using op amp


This is a peculiar case in which input signal is applied to the inverting input (-) through a resistor Rin. And output is feedback to the same input through a resistor Rf.

As a non-intuitive case non-inverting input (+) is grounded. From the ideal op-amp characteristics, the concept of infinite input impedence is of greater use because infinite input impedence results in zero current at the inverting input. The result of having zero current at the inverting input is we get a no voltage drop between our inverting (-) and non-inverting (+) inputs, because the positive input, which is the non-inverting (+) is grounded, the voltage at the negative input that is the inverting (-) input is zero.

This zero voltage at the inverting input terminal is referred as VIRTUAL GROUND.

Since, there is no current at the inverting input, the current flowing through our resistor Rf and Rin are equal

Iin = If;

The voltage across Rin equals Vin because the resistor is connected to the inverting input of the op-amp which may be termed at virtual ground

Iin = (Vin/Rin)

Rearranging, we get

Vout = – Rf

Vin      Rin

From this we conclude the overall gain (A) of the amplifier is A= (-Rf/Ri)

It is clearly evident that the output received through the op-amp is of opposite polarity.

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Author: JAY

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