Feedback amplifier
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A feedback amplifier, also known as negative feedback amplifier is an amplifier which uses a feedback network, generally for improving performance (gain stability, linearity, frequency response etc.). Feedback can be negative or positive, but must be negative for overall stability of the system.
Negative feedback (NFB) in an electronic amplifier was invented by Harold Stephen Black (US patent 2,102,671 (issued in 1937) http://eepatents.com/patents/2102671.pdf ). The idea of this invention is simple: if the loop gain is large, overall response of the whole system can be very close to inverted feedback network response. As feedback network can be simple a passive, high degree of stability and linearity can be obtained. The most widely-known realisation of this principle in electronics are circuits, based on operational amplifiers.
One way to model negative feedback amplifiers is the asymptotic gain model.