Why feedback amplifier is used?

Answer 1

transitors amplify signals in a very non-linear fashion. somehow (i don't know how), adding in the negative output of the transistor (negative feedback loop) makes the output much more linearmostly for stabilization, but there can be other reasons in specific cases.

Answer 2

A negative feedback amplifier (or more commonly simply a feedback amplifier) is an amplifier a fraction of the output of which is combined with the input so that a negative feedback opposes the original signal. The applied negative feedback improves performance (gain stability, linearity, frequency response, step response) and reduces sensitivity to parameter variations due to manufacturing or environment. Because of these advantages, negative feedback is used in this way in many amplifiers and control systems.[1]

Answer 3

Transistors have large variations in their "beta" values - the amount they can amplify a signal. As an example, for two transistors of the same model, this beta value may be 100 in one transistor, 1000 in another. The manufacturer merely guarantees that it is within a certain range, but as you can see, this range can be quite large. The basic purpose of using negative feedback is to stabilize the circuit against such large changes (when replacing one transistor by another of the same model), at the cost of part of the amplification. In other words, such a stabilized circuit will no longer amplify at a factor of 100 or more, but there won't be large variations in the amplification factor if you replace the transistor.