THD of closed-loop analog PWM class-D amplifiers

• Main Authors: Shu, Wei, Chang, Joseph Sylvester
• Other Authors: School of Electrical and Electronic Engineering
• Format: Article
• Language: English
• Published: 2010
• Subjects: DRNTU::Engineering::Electrical and electronic engineering::Electronic circuits
• Online Access: https://hdl.handle.net/10356/90825; http://hdl.handle.net/10220/6338
• Institution: Nanyang Technological University

This paper presents an analytical modeling of the mechanisms of total harmonic distortion (THD) of second-order based single-feedback and double-feedback Class-D amplifiers (CDAs). We show that the overall THD in these closed-loop CDAs comprises the THD of their open-loop counterparts reduced by the Loop Gain and the THD due to the combined phase and duty cycle error that is due to feedback, hence unique to closed-loop CDAs. We show that the latter THD can be large and is the dominant THD at high input frequencies, and that the mechanisms therein are the phase and duty cycle errors. By means of double Fourier series analysis, analytical expressions for the harmonic components and thereafter a THD expression for closed-loop CDAs are derived. The derived expressions depict the parameters that affect THD, and are insightful to designers to optimize/vary pertinent parameters to reduce THD. The derived THD expression is verified against HSPICE and on the basis of measurements on a prototype CDA IC and other CDAs realized discretely.