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A single-chip of Class-D audio amplifier with high-power efficiency is presented. It includes a rectangular wave delta modulator (RWDM) and bridge-tied load output gate-drivers. The RWDM has a multiple inputs floating-gate hysteresis comparator and a feedback integrator formed by the external L-R low-pass filter. This monolithic Class-D audio amplifier with a maximum power efficiency of 92% has a flat frequency response with ±0.3 dB up to 20 kHz, and is capable of delivering up to 0.45 W of continuous average power into an 8-Ω load at less than 0.5% total harmonic distortion plus noise from a 2.5-V power supply in the high fidelity range (20 Hz-20 kHz).