Open AccessDigital removal of pulse‐width‐modulation‐induced distortion in class‐D audio amplifiers
Author(s) -
Aase Sven Ole
Publication year - 2014
Publication title -
iet signal processing
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.384
H-Index - 42
ISSN - 1751-9683
DOI - 10.1049/iet-spr.2013.0383
Subject(s) - upsampling , pulse width modulation , computer science , reconstruction filter , low pass filter , digital filter , amplifier , filter (signal processing) , speech recognition , root raised cosine filter , electronic engineering , mathematics , bandwidth (computing) , artificial intelligence , telecommunications , computer vision , engineering , electrical engineering , voltage , image (mathematics)
In an all‐digital, class‐D audio amplifier, pulse‐width‐modulation (PWM) of a digital signal source is usually followed by a low‐order analog low‐pass filter to construct the analog audio waveform. This study shows how to remove the non‐linear distortion usually associated with PWM, by prefiltering the digital signal prior to the PWM mapping in such a manner that the overall result is distortion‐free. The prefiltering is done using computationally effective infinite‐impulse‐response filters combined with short‐kernel anticausal finite‐impulse‐response filters, and relies on the interpretation of PWM as a Volterra filter. A case study is presented where a second‐order Butterworth analog low‐pass filter is used for reconstruction of the analog audio signal. A complete amplifier system is modelled, including upsampling, Volterra prefiltering and noise feedback coding. Computer simulations on CD music signals were performed. Using a third‐order prefilter, a signal‐to‐noise ratio of 97–102 dB was obtained for the music signals tested. All necessary filter data needed for realisation of the prefilter are given in the Appendix.