A high PSRR Class-D audio amplifier IC based on a self-adjusting voltage reference

In a wide range of applications, audio amplifiers require a large Power Supply Rejection Ratio (PSRR) that the current Class-D architecture cannot reach. This paper proposes a self-adjusting internal voltage reference scheme that sets the bias voltages of the amplifier without losing on output dynamics. This solution relaxes the constraints on gain and feedback resistors matching that were previously the limiting factor for the PSRR. Theory of operation, design and IC evaluation in a Class-D amplifier in CMOS 0.25µm will be shown in this paper. The use of this voltage reference increased the amplifier's PSRR by 15dB, with only a 140µA increase in current consumption.