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Class-D audio amplifiers with negative feedback

Cox, Stephen M.; Candy, B. H.


Stephen M. Cox

B. H. Candy


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


Cox, S. M., & Candy, B. H. (2006). Class-D audio amplifiers with negative feedback. SIAM Journal on Applied Mathematics, 66(2),

Journal Article Type Article
Publication Date Jan 1, 2006
Deposit Date May 10, 2007
Publicly Available Date Oct 9, 2007
Journal SIAM Journal on Applied Mathematics
Print ISSN 0036-1399
Publisher Society for Industrial and Applied Mathematics
Peer Reviewed Peer Reviewed
Volume 66
Issue 2
Keywords class-D amplifier; total harmonic distortion; mathematical model
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