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Basic OP AMP (Operational Amplifier) Circuits | Working of Inverting Amplifier

2,577 views · Published 9 December 2017 · 3:23 · Indexed 28 September 2026

Channel: Physics4students · 2017 · Education

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This section concentrates on the principles involved with basic OP-AMP circuit. 

(i) Working of Inverting amplifier
The basic OP-AMP inverting amplifier is shown in visual. The input voltage V, in is applied to the inverting input through the input resistor R in. The non inverting input is grounded. The feedback resistor Rf is connected between the output and the inverting input. 

Since the input impedance of an op-amp is considered very high, no current can flow into or out of the input terminals. Therefore i, in must flow through Rf and is indicated by If (the feedback current). Since R, in and Rf are in series, then i, in is equal to i, f. The voltage between inverting and non-inverting inputs is essentially equal to zero volts. Therefore, the inverting input terminal is also at zero volt. For this reason the inverting input is said to be at virtual
ground. The output voltage (V, out) is taken across Rf.

It can be proved that
i, F is equal to minus V out by RF

Since i in is equal to i F, then

V in by R in, is equal to minus V out by RF.

Rearranging the equation, we obtain

minus V out by V in is equal to RF by R in.

Therefore, the voltage gain of an inverting amplifier can be expressed as
AV is equal to minus RF by R in.

The amplifier gain is the ratio of RF to R in.
Finally, the output voltage can be found by

V out is equal to minus RF by R in into V in.

The output voltage is out of phase with the input voltage.

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