Abstract: A one-chip integrated circuit of class D audio amplifier with high efficiency and high fidelity is presented in this paper.The continuous-time sigma-delta modulation (CT-SDM) technique with noise-shaping effect is utilized in this design.A self-oscillating modulator which occupies smaller chip area is obtained based on CT-SDM.A low noise wide bandwidth OTA is also designed to decrease output noise.The amplifier is implemented in a 0.6μm BCD process and occupies 1.67×2.5mm².With 4Ω load, the efficiency can reach 96% @120W output power, while the THD+N is 0.005% @60W output power with 1kHz input signal.