Class-d amplifier able to reduce power noise

A Class-D amplifier includes a loop filter circuit, a comparator circuitry, an output circuitry, and a common-mode control circuitry. The loop filter circuit generates first and second signals according to input and output signals and adjusts common-mode levels of the first and second signals according to a first common-mode signal. The comparator circuitry respectively compares a ramp signal with the first and second signals to generate pulse signals, and a common-mode level of the ramp signal is set based on a second common-mode signal. The output circuitry is powered by a power supply voltage to generate the output signals according to the pulse signals. The common-mode control circuitry performs an AC-coupling operation on the power supply voltage to generate a noise signal and generate one of the first and second common-mode signals according to the noise signal and another one of the first and second common-mode signals.