Class-D audio amplifiers with negative feedback

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

Abstract

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

Citation

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
• Public URL: https://nottingham-repository.worktribe.com/output/1018772