Abstract
This paper presents a load-adaptive Class-G headphone amplifier to improve the power efficiency for different headphone impedances. For an impedance value, the amplifier utilizes two techniques, voltage rails selection and Class-G switching activity control, to reduce the power dissipation of the amplifier and the power loss of a Class-G power generator, respectively. In addition, a supply-rejection bandwidth enhancement technique for the Class-AB output stage is proposed to suppress the out-of-band noise by the Class-G supply rails switching. Compared with the conventional fixed 2-level Class-G amplifier, the integrated $0.18~\mu \text {m}$ CMOS amplifier improves the total-path efficiency to 37% from 31% (1.45 mA current can be saved from a 1.8 V supply) while delivering 5 mW into a $16~\Omega $ . The PSRR of the amplifier is 130 dB at 217 Hz and is still larger than 100 dB up to 20 kHz. Finally, the decoder and amplifier together achieve 108 dB DR and 95 dB SNDR with a $16~\Omega $ headphone load.
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