A 0.4-mA-Quiescent-Current, 0.00091%-THD +N Class-D Audio Amplifier With Low-Complexity Frequency Equalization for PWM-Residual- Aliasing Reduction Yi-Zhi Qiu , Shih-Hsiung Chien

Abstract

This article proposes a low-complexity frequency equalization technique for pulsewidth modulation (PWM)- residual-aliasing reduction in closed-loop Class-D audio ampli- fiers to achieve both low total harmonic distortion plus noise (THD+N) and low quiescent current. Based on the comprehen- sive analysis on the phase shift delay between the audio input and the loop filter’s output for the prior PWM-residual-aliasing reduction technique, the proposed technique minimizes the non-idealities via a frequency-equalization path to enhance the cancellation ability of high-frequency PWM switching com- ponents. In this way, the PWM-residual-aliasing distortion is greatly suppressed, thereby permitting Class-D audio amplifiers to achieve a further-reduced THD +N for the entire audio band while operating at a low switching frequency ( f SW ), leading to less quiescent current consumption. Moreover, due to the minimized phase shift delay, the required bias current of the loop filter’s first operational amplifier for the target THD +N can be reduced, resulting in even lower quiescent current. Compared with other state of the arts, this work’s high-fidelity second-order Class-D audio amplifier, fabricated with cost-efficient 0.5- µmC M O S technology, not only achieves a competitive minimal THD +N of 0.00091% for a 1-kHz i nput as well as the lowest maximal THD+N of 0.0027% over the entire audio band while operating at a low f SW of 168 kHz but also features both the highest figure of merit (FOM) of 2