An amplifier, in electronics and telecommunications, is a device capable of varying the amplitude of a signal of a multiplication factor commonly referred to as gain (A), usually expressed in dB.
It is an active (powered) device, that is, it absorbs energy to achieve the aforementioned amplification functionality, which in fact means increasing the energy of the signal. More specifically, a generic amplifier (linear) has an input to which the signal to be amplified is applied and an output from which the amplified signal is taken, of amplitude equal to Sometimes the original signal. If the gain of the amplifier is not constant, but varies according to certain characteristics of the signal, it is referred to as a nonlinear amplifier. Their use is often necessary to cope with excessive signal attenuation along the communication channel or in general in the system in which it transits.