A class-D amplifier configured to adjust at least one input signal to at least one output signal. The class-D amplifier comprises: a loop filter, configured to receive the input signal; a PWM circuit, configured to generate at least one PWM signal; a summing circuit, coupled between an output of the loop filter and an input of the PWM circuit; an output circuit operating at a supply voltage, configured to generate the output signal responding to the PWM signal; and a supply voltage filter, configured to monitor the supply voltage to generate a filtered signal to the summing circuit. The summing circuit is configured to sum the output of the loop filter and the filtered signal to adjust a common-mode level of the input of the PWM circuit.