On the Pedagogy of Feedback Systems

The undergraduate student contacts feedback ideas from two distinct points of view, each with its own nomenclature and symbolism: electronics on one hand, and control systems on the other. In the typical electronics or communications book treating feedback at an undergraduate level, the analysis is constrained to the steady-state sinusoidal situation. Nyquist's criterion is merely presented without proof or justification. The student finds this theorem, when presented so briefly, a rather mysterious and vague concept. On the other hand, the author of the control systems or servo-mechanism text gives space in his book for a more thorough treatment of the feedback system but usually he uses terms and symbols that to the student seem to be unrelated to those terms and symbols used in the electronics "brand" of feedback. In recent years, the pole-zero concept has become a part of the undergraduate student's background in circuits. Pedagogically, the root-locus approach to the feedback system follows with ease. In contrast, Nyquist's criterion definitely becomes the more difficult concept. Furthermore, the root-locus approach is broader in scope. From three to fifteen lectures are needed to bridge the gap between the pole-zero concepts of circuits to a basic understanding of the feedback system.