An improved frequency compensation strategy for class AB headphone drivers

Abstract

This paper presents a low-power, highly-linear three-stage Class AB headphone capable of driving a wide load capacitor (C_L) range using an advanced frequency compensation network. A local AC feedback network replaces the classical transconductor-based quality factor control, enabling to reduce the silicon area and quiescent power by implementing the intermediate stage as a simple inverting common-source amplifier. Miller capacitance is split and each portion is coupled to an embedded current buffer, thereby moving non-dominant poles to higher frequencies without requiring new gain stages or bias-dependent elements. The proposed approach combines the wide-range load driving capability and high linearity under reduced power and area, making it suitable for high-fidelity headphone drivers. Post-layout simulation results of a prototype in a standard 65-nm CMOS process demonstrate a robust operation for the capacitive loads from 0 to 22 nF, achieving more than 114 dB DC gain and a minimum phase margin of 45°. It delivers 89.9 mW peak power into a 16 Ω load while consuming 0.52 mW power in 0.22 mm² silicon area. The THD + N of full-scale output is −104.6 dB at 20 KHz.