Audio power amplifier using in cellular phone with improved PSRR

A fully differential folded-cascode op-amp is applied into the audio power amplifier successfully. PSRR (power supply rejection ratio) of whole chip is higher than 60 dB between 20 Hz and 20 kHz, especially 82 dB at 217 Hz. Analysis and simulation has shown that PSRR of both op-amp and whole chip are improved. As a result, improved PSRR reduces the effect of noise on power supply lines being picked up and intensified by the audio power amplifier using cellular phone. The chip is manufactured by CSMC 0.6/spl mu/m, 3.3 V/5 V, 2P2M, CMOS process.