Show an OP-Amp with Negative Feedback

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- An OP-amp is almost always operated with negative feedback i.e., a part of the output is fed back in phase opposition to the input (See Fig. 7.45).

- The reason is simple. The open-loop voltage gain of an OP-amp is very high (usually greater than 100,000).
- Therefore, an extremely small input voltage drives the OP-amp into its saturated output stage. For example, assume v_in = 1mV and A_OL = 100,000. Then, v_out = A_OL v_in = (100,000) × (1 mV) = 100 V
- Since the output level of an OP-amp can never reach 100 V, it is driven deep into saturation and the device becomes non-linear. With negative feedback, the voltage gain (A_CL) can be reduced and controlled so that OP-amp can function as a linear amplifier. In addition to providing a controlled and stable gain, negative feedback also provides for control of the input and output impedances and amplifier bandwidth. The table below shows the general effects of negative feedback on the performance of OP-amps.

Wilfykil answered the question on August 16, 2019 at 09:17

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