A New Design Approach for Feedback Amplifiers

A new design procedure is presented which is based on the root-locus technique. The realization of the following is possible: a) desired closed-loop response bandwidth (or rise time) and gain level (or amount of desensitivity); b) desired response shapes such as flat magnitude or flat delay; and c) desensitivity of both low-frequency and bandedge responses. The key feature of the root-locus technique is the proper use and location of phantom zeros (transmission zeros of the feedback path). To illustrate the technique, a shunt-shunt feedback configuration is used together with the realization of flat-magnitude-type closed-loop responses. The basic amplifier is a three-stage transistor cascade. Typical design examples with experimental results are included.