  In this manuscript, we discuss the use of describing functions as a
systematic approach to the analysis and design of oscillators. Describing
functions are traditionally used to study the stability of nonlinear control
systems, and have been adapted for analyzing LC oscillators. We show that they
can be applied to other categories of oscillators too, including relaxation and
ring oscillators. With the help of several examples of oscillators from various
physical domains, we illustrate the techniques involved, and also demonstrate
the effectiveness and limitations of describing functions for oscillator
analysis.
