A 2.4 mA Quiescent Current, 1 W Output Power Class-D Audio Amplifier with Feed-Forward PWM-Intermodulated-Distortion Reduction

This work proposes a feed-forward PWM-intermodulated-distortion reduction (FFPIDR) technique for closed-loop class-D audio amplifiers. The proposed FFPIDR technique overcomes the trade-off between out-of-band loop attenuation and in-band loop gain to reduce the PWM-intermodulated distortion while maintaining a high in-band distortion suppression capability without increasing the switching frequency. This results in a high-fidelity and low-quiescent-current audio amplifier suitable for mobile devices. This work is implemented in a 0.5μm CMOS technology, and the measurement result with a 4.2 V supply voltage shows that the proposed FFPIDR technique improves the THD + N by 12 dB when an output power of 340 mW is delivered to an 8-Ω load. Compared with other state of the arts, the proposed class-D amplifier achieves 0.0037% THD + N with a quiescent current of 2.4 mA and the smallest chip area of 0.86mm² and the measured peak efficiency reaches 92%.