Open Loop Op-Amp Configurations

When connected in open-loop configuration,the op-amp functions as a high gain amplifier.These are three open loop op-amp configurations.

1. Differential Amplifier
2. Inverting Amplifier
3. Non-Inverting Amplifier

These configurations are classed according to the number of inputs used and the terminal to which the input is applied when a single input is used.

Disadvantages of open loop configurations

1. The open loop of the op-amp is very high.Therefore only the smaller signals having low frequency may be amplified accurately without distortion.
2. Open loop Voltage gain of the op-amp is not a constant voltage gain varies with changes in temperature and power supply as well as mass production techniques.This makes op-amp unsuitable for many linear applications
3. Bandwidth of most open loop op-amps is negligibly small or almost zero therefore op-amp is impractical in ac applications.

For these reasons,the open loop op-amp is generally not used in linear applications.In certain applications,the open loop op-amp is purposely used as a non -linear device;that is a square wave output is obtained by applying a relatively large input signal.

We can select as well as control the gain of the op-amp if we introduce a modification in the basic circuit.This modification involves the use of feedback ie an output signal is fed back to the input either directly or via another network.If the signal fed back is of opposite polarity or out of phase of 180 degree.with respect to the input signal,the feedback is called negative feedback.Negative feedback is also known as degenerative feedback.

If the signal fed back is of the same polarity or in the phase with the input signal,the feed back is called positive feed back.In positive feedback,the feedback signal is aid the input signal.It is also known as regenerative feedback.

When used in amplifiers,negative feedback stabilizes the gain,increases the bandwidth and changes the input and output resistance.Other benefits include a decrease in harmonic or non-linear distortion and reduction in the effect of input offset voltage at the output.It is also reduces the effect of variations in the temperature and supply voltages on the output of the op-amp.

Written by arjun on October 14th, 2008 with 2 comments.
Read more articles on Linear Integrated Circuits and op-amp and Open and closed loop configurations.

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