A Low Power Class-AB Audio Power Amplifier With Dynamic Transconductance Compensation in 55 nm CMOS Process

This paper presents a Class-AB audio power amplifier with state-of-the-art power efficiency and performance. In this work, the second stage transconductance of the three-stage power amplifier can be dynamically compensated, in order to automatically adjust the amplifier pole according to the operating condition of the output stage. Working with a current sensing module, the proposed dynamic transconductance compensation scheme is more power-efficient to allocate the frequency of non-dominant-pole under a specified stability requirement. A prototype chip is designed and fabricated using 55 nm CMOS process. The measured static current consumption of the core circuit is 0.35 mA with a 1.8 V supply voltage. -85 dB THD+N, 106 dB signal dynamic range and 55 mW output power are verified in silicon under a wide range of load capacitance from 5 pF to 20 nF. Measurement result shows the proposed transconductance compensation technique is effective in both constant voltage supply mode and dynamic supply (Class-G) mode.