AES San Francisco 2008
Audio Product Design Event T17
Sunday, October 5, 2:30 pm — 4:30 pm
T17 - An Introduction to Digital Pulse Width Modulation for Audio Amplification
, Freescale Semiconductor Inc. - Austin, TX, USA
Digital PWM is highly suitable for audio amplification. Digital audio sources can be readily converted to digital PWM using digital signal processing. The mathematical nonlinearity associated with PWM can be corrected with extremely high accuracy. Natural sampling and other techniques will be discussed that convert a PCM signal to a digital PWM signal. Due to limitations of digital clock speeds and jitter, the duty ratio of the PWM signal has to be quantized to a small number of bits. The noise due to quantization can be effectively shaped to fall outside the audio band. PWM specific noise shaping techniques will be explained in detail. Further, there is a need for sample rate conversion for a digital PWM modulator to work with a digital PCM signal that is generated using a different clock. The mathematics of an asynchronous sample rate converters will also be discussed. Digital PWM signals are amplified by a power stage that introduces nonlinearity and mixes in noise from the power supply. This mechanism will be examined and ways to correct for it will be discussed.