High slew rate micro-power CMOS OTA with class AB input stage

The design of a new single stage class AB operational amplifier is presented. The amplifier incorporates an input differential pair with minimum current selector and common-mode feedback to control the tail current. It shows small-signal behavior of a simple OTA, while class AB feedback provides high slew rate when large input signals are applied. A prototype circuit was manufactured in a 2 μm analog CMOS process. In the quiescent mode it consumes less than 20 μA of supply current. The circuit has a DC gain of 70 dB, slew rate of 2.5 V/μs at 10 pF load and 0.9 V/μs at 100 pF load. THD is better than 90 dB at 0.2 V_p·p input signal and CMRR is 110 dB.