A High-PSRR Reconfigurable Class-AB/D Audio Amplifier Driving a Hands-Free/Receiver 2-in-1 Loudspeaker

A high-power-supply-rejection-ratio (PSRR), reconfigurable class-AB/D audio power amplifier is designed for direct battery hookup in portable applications. The proposed design employs the on-chip battery voltage tracking common-mode reference (BAVTCMR) generator and the pseudo-differential topology to achieve the high SNR requirement in a hands-free/receiver 2-in-1 loudspeaker. This amplifier can achieve 106 dB/100 dB PSRR at 217 Hz and 1 kHz, respectively. In receiver mode, this design can drive 46 mW into an 8- Ω load. A true 100-dB SNR is also achieved when a global system for mobile communications (GSM) is generating ripple noise on the system power lines. Reconfiguration is implemented by employing the low-noise operational amplifier (opamp) and capacitors in the class-D integrator as the first gain stage and the compensation capacitors, respectively, in a class-AB amplifier. Hence, the hardware redundancy and the design complexity are both minimized. Fabricated with 0.153-μm CMOS technology, 74-dB/76-dB THD are achieved for class-AB and class-D, respectively. More than 90% efficiency is achieved in class-D mode operation. The maximum output power at 1% THD is 1.23 W. The active area of the prototype class-AB/D amplifier is 0.5 mm².