Class-D audio amplifiers with negative feedback

Cox, Stephen M. and Candy, B. H. (2006) Class-D audio amplifiers with negative feedback. SIAM Journal on Applied Mathematics, 66 (2). pp. 468-488.

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There are many different designs for audio amplifiers. Class-D, or switching, amplifiers generate their output signal in the form of a high-frequency square wave of variable duty cycle (ratio of on time to off time). The square-wave nature of the output allows a particularly efficient output stage, with minimal losses. The output is ultimately filtered to remove components of the spectrum above the audio range. Mathematical models are derived here for a variety of related class-D amplifier designs that use negative feedback. These models use an asymptotic expansion in powers of a small parameter related to the ratio of typical audio frequencies to the switching frequency to develop a power series for the output component in the audio spectrum. These models confirm that there is a form of distortion intrinsic to such amplifier designs. The models also explain why two approaches used commercially succeed in largely eliminating this distortion; a new means of overcoming the intrinsic distortion is revealed by the analysis.

Copyright (2006) Society for Industrial and Applied Mathematics

Item Type: Article
Keywords: class-D amplifier; total harmonic distortion; mathematical model
Schools/Departments: University of Nottingham, UK > Faculty of Science > School of Mathematical Sciences
Depositing User: Cox, Stephen
Date Deposited: 10 May 2007
Last Modified: 04 May 2020 20:29

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