A class D headphone amplifier with DC coupled outputs and 1.2mA quiescent current

This paper shows the design of a headphone amplifier using Pulse Width Modulation (PWM) to improve its power efficiency compared to existing Class AB and Class G structures. A numerical optimization of the switching frequency and output transistors size, combined with the use of a soft switching scheme, brought the current consumption down to 1.2mA at idle for the complete stereo amplifier. The outputs are DC coupled, with no common mode voltage, thanks to the use of a Negative Charge Pump (NCP). Theory of operation, optimization, and the design in a 0.25μm CMOS process will be explained.