Distortion in Feedback Amplifiers

Distortion in feedback amplifiers has previously been studied for the ease where the feedback is independent of frequency. 1 However, in many practical cases, the variation of feedback with frequency produces significant deviations from this simple theory. 2 The present analysis takes into account the magnitude and phase of the feedback at all frequencies in determining the amount of any particular modulation product. This analysis has proved useful in the design of amplifiers for the L3 coaxial carrier system 3 , 4 as well as in the analysis of a number of non-linear circuits. The method is most useful in cases where the distortion products are small compared to the fundamental signals and where the non-linear element can be described by a power series having only a few terms. More complex cases can be treated but the labor involved is appreciably greater. However, many practical feedback amplifiers are adequately described by the analysis and, in addition, some understanding is obtained as to the mechanisms involved. In particular, the dependence of third order distortions on the feedbacks at second order frequencies is demonstrated and formulae are obtained. TIIE PROBLEM