Editing Amplifier (section)

==Negative feedback==
{{Unreferenced section|date=December 2024}}
[[Negative feedback]] is a technique used in most modern amplifiers to increase bandwidth, reduce distortion, and control gain.  In a negative feedback amplifier part of the output is fed back and added to the input in the opposite phase, subtracting from the input.   The main effect is to reduce the overall gain of the system. However, any unwanted signals introduced by the amplifier, such as distortion are also fed back.  Since they are not part of the original input, they are added to the input in opposite phase, subtracting them from the input. In this way, negative feedback also reduces nonlinearity, distortion and other errors introduced by the amplifier. Large amounts of negative feedback can reduce errors to the point that the response of the amplifier itself becomes almost irrelevant as long as it has a large gain, and the output performance of the system (the "closed [[loop performance]]") is defined entirely by the components in the feedback loop.  This technique is used particularly with [[operational amplifier]]s (op-amps).

Non-feedback amplifiers can achieve only about 1% distortion for audio-frequency signals. With [[Negative-feedback amplifier|negative feedback]], distortion can typically be reduced to 0.001%.  Noise, even crossover distortion, can be practically eliminated.  Negative feedback also compensates for changing temperatures, and degrading or nonlinear components in the gain stage, but any change or nonlinearity in the components in the feedback loop will affect the output. Indeed, the ability of the feedback loop to define the output is used to make [[active filter|active filter circuits]].

Another advantage of negative feedback is that it extends the [[bandwidth (signal processing)|bandwidth]] of the amplifier.    The concept of feedback is used in [[operational amplifier]]s to precisely define gain, bandwidth, and other parameters entirely based on the components in the feedback loop.

Negative feedback can be applied at each stage of an amplifier to stabilize the [[operating point]] of active devices against minor changes in power-supply voltage or device characteristics.

Some feedback, positive or negative, is unavoidable and often undesirable—introduced, for example, by [[parasitic element (electrical networks)|parasitic elements]], such as inherent capacitance between input and output of devices such as transistors, and capacitive coupling of external wiring. Excessive frequency-dependent positive feedback can produce [[parasitic oscillation]] and turn an amplifier into an [[oscillator]].