Study and hardware demonstration of the self-oscillating class D amplifier circuit for hearing aids

Abstract

Class D amplifiers are conventionally designed by feeding the modulated pulse signal at the output stage while leaving the low pass filter as an open-loop structure. But it’s demonstrated that the low pass filter due to the lack of compensation, contributes a significant amount of non-linearity and noise. In this report, we discuss and study a high fidelity Class D amplifier based on a self-oscillating approach with a single loop complete feedback network (feedback from the low-pass filter instead of the output stage). After that, a breadboard hardware demonstration of the mentioned self-oscillating class D amplifier circuit and its dual-rail configuration (two resemblant circuits sharing inputs, reference voltage and supply voltage) is also implemented and the observation of the switching frequency versus output performance and the interference phenomenon is discussed.