An open-loop class-D audio amplifier with increased low-distortion output power and PVT-insensitive EMI reduction

An open-loop class-D audio amplifier with the proposed adaptive-coefficient delta-sigma modulator (ACDSM) and low-EMI control method is implemented in a 0.18μm BCD process. Compared with conventional DSMs, the ACDSM simultaneously achieves a wide stable input range and high in-band noise suppression, resulting in a 20% increase of low-distortion output power for open-loop class-D amplifiers without boosting the supply voltage or degrading the THD+N at small output power. Moreover, the proposed low-EMI control method realized by a simple finite state machine eases the PVT-sensitive issues of common-mode EMI reduction.