A 1.2V rail to rail output driving amplifier with a folded Class-AB output stage control circuit

A 1.2V rail to rail output driving amplifier used to drive the hearing aid loudspeaker is proposed in this paper. Since the linearity of the cascoded amplifier degrades with the supply voltage decreasing, a three-stage cascaded amplifier is adopted. For the rail to rail output signal with high linearity, a special folded class-AB output stage current control circuit is incorporated in the amplifier. The minimum supply voltage can be reduced to VGS+2|Vdsat|. Fabricated with a 0.18 $\mu \mathrm{m}$ CMOS process, the amplifier with the loading resistance 100ohm achieves -85dB THD while operating from a 1.2V supply and using a 1kHz input sine wave.