In a class-D amplifier, the input signal is compared with a carrier signal to generate a basic PWM signal, the PWM signal is then sent to a pulse processing unit, and by comparing with a basic periodic signal, half-width of the output PWM signal is extracted. Then, in the pulse processing unit, the half-width PWM pulse signal is used to generate a complete pulse whose width equals to the output PWM signal. The output power of the class-D amplifier can be kept as large as that by using differential input signals although the input signal is single-end and the entire signal processing path is kept single-ended.