1927: Negative Feedback

Photo: Harold Black. In 1927, Harold Black proposed a novel technique for correcting instability and distortion in the process of amplifying communications signals. Called "negative feedback," the technique requires that part of the signal coming out of the amplifier be fed back and compared with the input signal. Distortions introduced by the amplifier are thus precorrected and largely eliminated. As a result, the amplifier can be made almost distortionless, despite fluctuations in the power supply and performance of electronic components.