Abstract
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 $0.5\;\upmu\text{m}$ 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 $8\text{-}\Omega$ 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 $0.86\;\text{mm}^2$ , and the measured peak efficiency reaches 92%.
Published Version
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