On the Effect of Time Delays in Negative Feedback Amplifiers

Abstract

Abstract-Time delays are intrinsic to all existing devices and circuits. For the majority of applications, time delays are so small that their effects can be disregarded. However, when considering feedback amplifiers, depending on open-loop poles and loop gain, the effect of a small time delay inside the feedback path may turn to be of considerable importance. This paper analyzes the frequency response effects associated with time delays in feedback amplifiers, exploiting these effects to achieve bandwidth enhancements. An illustration of this effect is presented using a TL082 in series-shunt configuration, attaining 100% bandwidth extension, when associated with a 36m length RG58 coaxial cable as delay element.

General Model for Delayed Feedback and its Application to Transimpedance Amplifier's Bandwidth Optimization

“…It was also observed that for the 2 nd order approximation, the bandwidth gain reduction was more pronounced. This agrees with the bandwidth gain reduction effect observed in second order delayed feedback systems, as reported previously in [1,2].…”

“…The best scenario is a frequency response exhibiting peaking behaviors near the cut-off frequency region. However, depending on the amount of the delay, it is also possible to violate the stability restrictions [1]. On the first two scenarios it is possible to optimize bandwidth adding a delay element in the loop.…”

“…However, there are applications [3] where high-gain, high-bandwidth requirements together with these delays, lead to instability. Recent developments [1,2] reported the usage of delayed feedback as a means of achieving significant bandwidth improvements (thus allowing significant gain-bandwidth improvements). Using a small delay inside the feedback loop of a feedback amplifier enables almost 110% bandwidth improvement without losing frequency response performance that is; maintaining flatness and linear phase decay inside the sought bandwidth.…”

A time‐delay technique to improve GBW on negative feedback amplifiers

“…Only recently has Nowack [2] rediscovered the problem of a delay-induced instability phenomenon in highgain high-bandwidth transimpedance amplifiers. Nevertheless, the usage of small delays inside the feedback path of feedback amplifiers as a means of achieving larger GBW was not ever covered [6,7]. Figure 1(b) shows an NDFA comprising a delay element inside the feedback loop (having a delay value of seconds).…”