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A prefilter equalizer for pulse width modulation

Authors
Journal
Signal Processing
0165-1684
Publisher
Elsevier
Volume
92
Issue
10
Identifiers
DOI: 10.1016/j.sigpro.2012.03.006
Keywords
  • Pulse Width Modulation
  • Digital Audio Amplifier
  • Precompensation
  • Volterra Prefilter
Disciplines
  • Musicology

Abstract

Abstract This article demonstrates the feasibility of pulse-width-modulation (PWM) of discrete time signals in a digital audio amplifier without inducing the nonlinear distortion usually associated with straightforward PWM. This is achieved by prefiltering the signal prior to the PWM mapping in such a manner that the overall result is distortion-free. All processing is done in the discrete time domain and relies on the interpretation of PWM as a Volterra filter. Computer simulations on CD music signals were performed. With no upsampling the distortion due to PWM gave a signal-to-noise-ratio (SNR) of approximately 45–50dB. Using the prefiltering scheme developed in this work, dramatic improvements of the reconstructed signal quality was demonstrated. The 9th order prefilter gave an SNR of well above 90dB for the music signals tested. Experiments using the same signals upsampled with N=8 showed that a 3rd order prefilter was sufficient for removing PWM-induced distortion.

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