A heuristic approach to the development of frequency response characteristics in the design of feedback amplifiers

One of the most significant benefits in the application of feedback in the design of electronic amplifiers is an increase in the midband frequency bandwidth. Because of the complexity of the mathematics involved in modeling feedback amplifier performance characteristics, several simplifying techniques are typically introduced. Among these in the frequency domain are single-pole approximations and the concept of dominant poles. While these techniques can reasonably approximate many amplifiers, they fail to adequately address some of the significant phenomena invoked when feedback is applied. In addition, it is often difficult for the typical student of electronics to understand the fundamental reasoning behind each approximation and its realm of validity. A unique approach to understanding feedback amplifier frequency response through the use of simple graphical heuristics is introduced. Primary among these is a display of pole migration using a plot of the pole polynomial as a function of the amount of feedback. General pole migration and the formation of pole pairs can easily be seen using this technique. The graphical nature of the approach brings particular significance to understanding pole dominance throughout the possible range of feedback. It can also be seen that the two-pole approximation to multipole feedback amplifiers has a significant region of validity while the validity of single-pole approximations is questionable