Tutorial T6A: Pedagogy of Negative Feedback Circuits

Abstract

Summary form only given, as follws. This tutorial presents an introduction to negative feedback circuits using an integrator as the central element instead of a high gain amplifier as is normally done. It is shown that it is easier to make a connections to our intuitive notion of negative feedback in the time domain than in the frequency domain. It is also shown that certain aspects of negative feedback systems that they have a nonzero time constant(finite bandwidth), that delay can lead to instability, and that negative feedback systems can be stabilized by slowing them down become immediately clear with this approach. It is also shown that the opamp and the phase locked loop can be synthesized from the prototype negative feedback system using an integrator to continuously drive the output until the error between the desired and actual outputs becomes zero. Realizing such a negative feedback amplifier using real components and striving to improve its performance leads to different opamp topologies. Attempting to realize a frequency multiplier and improving its performance leads to typeI and typeII feedback loops. The synthesis based approach from a common foundation helps one to easily make connections between different negative feedback circuits.