Analysis of the class AD audio amplifier including hysteresis effects

Combinations of analog and switching techniques have led to the development of audio power amplifiers capable of producing low distortion with high efficiency. The high efficiency is achieved with a combination of an inverter and an analog amplifier, where the inverter provides the power, and the analog amplifier acts as an active filter to correct distortion. In this paper, a full analysis of the system is presented using the hysteresis describing function approach to model the inverter. The set of equations obtained allows the description of the nonlinear behavior of the system, such as the limit cycle of the output voltage and its dependency on the hysteresis. The theoretical development also provides the relation between the switching frequency and the system parameters. The derived equations are verified and compared using PSpice simulations.