Dictionary of Electrical Engineering

Commonly used terms in the Electrical industry.

feedback
(1) signal or data that is sent back to a commanding unit from a control process output for use as input in subsequent operations. In a closed-loop system, it is the part of the system that brings back information on the process condition under control.

(2) the provision of a path from the output to the input of a system, such that the output may be made a function of both the input and the previous outputs of the system.

(3) the technique of sampling the output of an amplifier and using that information to modify the amplifier input signal. A portion of the output is "fed back" to the input. Positive feedback occurs when the output is added to the input; negative feedback occurs when the output is subtracted from the input. Negative feedback, invented by communications engineer Harold Black in 1928, usually results in a gain - bandwidth tradeoff: decreasing and stabilizing the amplifier gain, while increasing the bandwidth. According to Norbert Wiener, feedback is a method of controlling a system by reinserting into it the results of its past performance.
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