On the usage of delayed-feedback in amplifiers

Time delays are intrinsic to all electronic circuits and feedback amplifiers are no exception. The effect of a small time delay inside the feedback path may turn to be of considerable importance. Depending on the open-loop poles, the loop-gain and the time delay, the closed-loop response may be unstable. This paper shows that it is possible to explore the presence of time delays in feedback amplifiers in order to achieve significant bandwidth enhancements, without losing stability. A practical demonstration of these concepts is presented. The delayed feedback concept is then applied to the case of cascade association of amplifiers, showing the possibility of associating a large number of stages without the inherent bandwidth loss.