Class-D amplifiers switch high voltages and currents at high frequencies and hence produce electromagnetic interference (EMI). This work presents a technique to reduce the high frequency ripple, which is still present after the output filter. A Class-A ripple reduction amplifier is put in parallel to the output of the Class-D amplifier, each having their own feedback loop with digital filters. High ripple reduction loop gain is achieved at the PWM frequency by using a resonator as digital loop filter. Dissipation in the Class-A amplifier is reduced by using a low common-mode signaling technique. Common-mode and differential-mode switching components at the PWM frequency are reduced by 27 dB and 18 dB respectively. Total system efficiency is 79% at 40 W output power.

中文翻译：

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通过主动降低 PWM 纹波降低 D 类放大器的 EMI

D 类放大器以高频切换高电压和电流，因此会产生电磁干扰 (EMI)。这项工作提出了一种减少高频纹波的技术，该纹波在输出滤波器之后仍然存在。A 类纹波降低放大器与 D 类放大器的输出并联，每个放大器都有自己的带有数字滤波器的反馈回路。通过使用谐振器作为数字环路滤波器，在 PWM 频率下实现了高纹波降低环路增益。通过使用低共模信号技术降低了 A 类放大器的功耗。PWM 频率下的共模和差模开关组件分别降低了 27 dB 和 18 dB。在 40 W 输出功率下，总系统效率为 79%。