Ripple compensation for a class-D amplifier

Cox, Stephen M. and du Toit Mouton, Hendrik (2015) Ripple compensation for a class-D amplifier. SIAM Journal on Applied Mathematics, 75 (4). pp. 1536-1552. ISSN 1095-712X

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Abstract

This paper presents the first detailed mathematical analysis of the ripple compensation technique for reducing audio distortion in a class-D amplifier with negative feedback. The amplifier converts a relatively low-frequency audio signal to a high-frequency train of rectangular pulses whose widths are slowly modulated according to the audio signal (pulse-width modulation, PWM). Distortion manifests itself through unwanted audio-frequency harmonics that arise in the output due to nonlinearities inherent in the design. In this paper, we first develop a small-signal model, which describes the fate of small-amplitude perturbations to a constant input, and demonstrate how this traditional engineering tool may be extended to allow one to infer the most significant contributions to the full output in response to a general audio input. We then compute the audio output of the amplifier through a perturbation expansion based on the ratio between audio and switching frequencies. Our results explicitly demonstrate how the ripple compensation technique significantly linearizes the output, thereby reducing the distortion.

Item Type: Article
Additional Information: First Published in SIAM Journal on Applied Mathematics in volume 75 number 4, 2015, published by the Society of Industrial and Applied Mathematics (SIAM). (c) 2015 Society for Industrial and Applied Mathematics.
Keywords: class-D amplifier, mathematical model, small-signal model, Apostol–Bernoulli functions, pulse-width modulation
Schools/Departments: University of Nottingham, UK > Faculty of Science > School of Mathematical Sciences
Identification Number: https://doi.org/10.1137/140997695
Depositing User: Cox, Stephen
Date Deposited: 12 Nov 2015 11:06
Last Modified: 18 Nov 2016 14:47
URI: http://eprints.nottingham.ac.uk/id/eprint/30737

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