Digital control of a class-D audio amplifier

Abstract

Modern technologies have led to extensive digital music reproduction and distribution. It is fitting then that digital audio be amplified directly from its source rather than being converted to an analogue waveform before amplification. The benefits of using a digital controller for audio processing include being able to easily reconfigure the system and to add additional functions at a later stage. Digital audio is primarily stored as Pulse Code Modulation (PCM) while Pulse Width Modulation (PWM) is the most popular scheme used to drive a class-D amplifier. The class-D amplifier is selected in many applications due to its very high energy efficiency. Conventional PCM to PWM conversion is inherently nonlinear. Various interpolation schemes are presented in this research project which help to address the nonlinearity. Digitally generated PWM has a limited resolution which is constrained by the system clock. This thesis presents noise shaping techniques which increase the effective resolution of the PWM process without having to use an excessively high system clock. Noise shaping allows a low resolution modulator to be used to reproduce high resolution audio.