Effect of carrier topologies on PSRR and PS-IMD of open-loop Class D amplifiers for hearing aids

Open-Loop Pulse Width Modulation (PWM) Class D amplifiers are attractive for power critical applications including hearing aids due to their simple hardware and high power-efficiency. Nevertheless, a drawback of open-loop Class D amplifiers is their susceptibility to supply noise, quantified by power supply rejection ratio (PSRR) and power supply induced intermodulation distortion (PS-IMD). In this paper, PSRR and PS-IMD of a commonly-used carrier generation method are investigated and compared against other common carrier generation methods. The analyses are verified by means of HSPICE simulations. The analyses and comparisons provide designers useful insight to the design of power critical Class D amplifiers.