Title :
THD of Closed-Loop Analog PWM Class-D Amplifiers
Author :
Shu, Wei ; Chang, Joseph S.
Author_Institution :
Sch. of Electr. & Electron. Eng., Nanyang Technol. Univ., Singapore
fDate :
7/1/2008 12:00:00 AM
Abstract :
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+1 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 ( > 3 kHz), 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.
Keywords :
Fourier series; analogue circuits; feedback amplifiers; harmonic distortion; pulse width modulation; Fourier series analysis; THD; closed-loop analog PWM amplifiers; double-feedback class-D amplifiers; duty cycle error; harmonic components; single-feedback class-D amplifiers; total harmonic distortion; Class D amplifier; Class-D amplifier (CDA); Total Harmonic Distortion; duty cycle error; phase error; total harmonic distortion (THD);
Journal_Title :
Circuits and Systems I: Regular Papers, IEEE Transactions on
DOI :
10.1109/TCSI.2008.918000