A low-power 900 mV rail-to-rail class-AB operational amplifier

In this paper, we proposed a novel rail-to-rail CMOS opamp that uses a native NMOS input stage to replace conventional PMOS pair. A simple current regulation circuit, which takes advantage of weak inversion mode, is proposed to obtain constant Gm in the entire common mode range. In addition, a class-AB output buffer, which consists of two float current sources, is employed to obtain a wide output range. The designed opamp is dedicated to low frequency 900 mV applications. It features with a DC gain of 84 dB and bandwidth of 122 kHz, while consumes power only 2.2 μW. The dynamic range of opamp is from 50 mV to 850 mV. The simulation result also shows that the proposed opamp is able to work under a voltage as low as 600 mV.