A low voltage, rail-to-rail, class AB CMOS amplifier with high drive and low output impedance characteristics

This paper describes a CMOS rail-to-rail class AB operational amplifier designed to have extremely low output impedance and large current-drive capability. The amplifier uses an innovative output stage, having both source follower and common source stages working simultaneously throughout the output common-mode range. The source follower ensures low output impedance, which enables it to drive relatively large load capacitors, while the common-source gain stage provides high current drive. Furthermore, the circuit is fully functional with supplies as low as 1.5 V. The amplifier is capable of driving a maximum output current of /spl plusmn/7 mA with only 140 /spl mu/A of total quiescent current, making it power efficient, and thus appropriate for low voltage battery-powered applications.