Closed - loop op-amp configuration:
The op-amp can be effectively utilized in linear applications by providing a feedback from the output to the input, either directly or through another network. If the signal feedback is out- of-phase by 1800 with respect to the input, then the feedback is referred to as negative feedback or degenerative feedback. Conversely, if the feedback signal is in phase with that at the input, then the feedback is referred to as positive feedback or regenerative feedback.
An op - amp that uses feedback is called a closed - loop amplifier. The most commonly used closed - loop amplifier configurations are
1. Inverting amplifier (Voltage shunt amplifier)
2. Non-Inverting amplifier (Voltage - series Amplifier)
1. Inverting Amplifier:
The inverting amplifier is shown in figure and its alternate circuit arrangement is shown in figure, with the circuit redrawn in a different way to illustrate how the voltage shunt feedback is achieved. The input signal drives the inverting input of the op - amp through resistor R1 .
The op - amp has an open - loop gain of A, so that the output signal is much larger than the error voltage. Because of the phase inversion, the output signal is 1800 out - of - phase with the input signal. This means that the feedback signal opposes the input signal and the feedback is negative or degenerative.