It is difficult to analyze the harmonic distortion of a self-oscillating power amplifier (SOPA), because the SOPA is a hard nonlinear system without an external clock. The single or multiple sinusoidal inputs describing function (DF) method is commonly used to linearize a nonlinear element, but this method considers only the components at the same frequencies as the input signals (i.e., fundamental components) at the nonlinear element’s output. In this paper, besides the fundamental components, the third harmonic components are also calculated at the output of a comparator with three sinusoidal inputs, to create a linearized model of the comparator, and thus of the SOPA. The third harmonic distortion of the SOPA is calculated. The models of the zeroth and the first order SOPA are verified by behavioral simulation using MATLAB.

关键词： Describing function (DF),  Comparator,  Self-oscillating power amplifier (SOPA),  Third harmonic distortion