A digital Class-D audio amplifier is presented in this paper. This amplifier uses a sixth-order PWM modulator to generate the driver signal of the output stage of the amplifier. The transformation of pulse-amplitude-modulation (PAM) signal to pulse-width-modulation (PWM) signal is moved into the closed sigma-delta modulator loop that the noise and distortion generated during the transformation of PAM signal to PWM signal is suppressed by the high gain of the forward loop of the sigma-delta modulator. Therefore, at the output of the digital modulator, a very clean PWM signal is generated to drive the power stage of the class-D amplifier. This class-D amplifier achieves 110dB dynamic range (DR), 100dB signal to noise rate (SNR) and 0.005% total harmonic distortion plus noise (THD+N).