Operational amplifier is an integral part of analog circuits. With the advent of portable device technology, power consumption has become an area of concern.To reduce power consumption and improve battery life performance, supply voltages are scaled. This leads to a reduced input common mode range for an operational amplifier. A rail-to-rail amplifier composed of complementary CMOS differential pairs is employed to obtain a wider input common mode range. However, the complementary differential pairs, when operated in parallel lead to a large variation in the total transconductance thereby making the circuit highly unstable. A simple and novel technique to remedy this is to use a diode connected NMOS to shift the transition region of the NMOS differential pair. This circuit is simple and consumes less power.
XFAB 0.35µm process technology is used in the design of the circuit. Cadence SPECTRE simulator is used for all the simulations.