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本文提出一种采用PWM共模控制的全差分D类音频放大器，通过稳定共模环路增益克服反馈电阻匹配限制，实现了118dB的电源抑制比和0.00067%的总谐波失真加噪声，输出功率达3.1W，适用于电池供电的移动设备。
A high power-supply rejection ratio (PSRR) and high-linearity Class-D audio amplifier (CDA) becomes important as the CDA is directly connected to a battery supply for efficiency considerations in mobile phone applications. Several closed-loop pulse-width-modulation (PWM) CDAs with high PSRR (>90dB) have been published recently. In conventional PWM fully differential CDAs [1,2], these designs are focused on increasing differential loop gain to improve PSRR. However, the PSRR is mainly limited by feedback gain-matching, that is, resistor matching of the feedback network; hence, it is difficult to achieve PSRR >80dB for yield >99%. In [3], a pseudo-differential structure composed of two singleended opamps is adopted to achieve PSRR >90dB. Nevertheless, it suffers from 3dB noise increase as compared to the fully differential counterpart. Moreover, unity-gain bandwidth (GBW) of single-ended opamps is usually smaller than that
Wen-Chieh Wang, Yu-Hsin Lin
MediaTek, Hsinchu, Taiwan