In the early years of radio circuits, fading (defined as slow variations in the amplitude of the received signals) required continuing adjustments in the receiver’s gain in order to maintain a relative constant output signal. Such situation led to the design of circuits, which primary ideal function was to maintain a constant signal level at the output, regardless of the signal’s variations at the input of the system. Originally, those circuits were described as automatic volume control circuits, a few years later they were generalized under the name of Automatic Gain Control (AGC) circuits [1,2].