Bang–Bang Control Class-D Amplifiers: Power-Supply Noise

In this paper, the bang-bang control class-D amplifiers (bang-bang amp) is suggested as an alternative to the incumbent pulsewidth-modulation class-D amp for low voltage power-critical applications, including hearing aids. The effects of power supply noise, qualified by power-supply rejection ratio (PSRR), on two bang-bang amps, bang-bang type-I and type-II, are investigated for low signal bandwidth hearing aid applications and for the usual full audio bandwidth applications. By deriving analytical expressions for PSRR of these amps, the important parameters related to PSRR are analyzed. The analyses are verified by means of HSPICE simulations and by measurements on practical circuits. The relationships derived herein provide good practical insight to the design of bang-bang amps, including how various parameters may be varied/optimized to meet a given PSRR specification.