Extremely simple constant-gm technique for low voltage rail-to-rail amplifier input stage

In this paper we present a novel, extremely simple constant transconductance (gm) technique for a rail-to-rail CMOS amplifier input stage. While the level shifting technique is one of the most popular conventional methods to achieve constant-gm ([1], [6]), in [1], two PMOS source followers, totalling 4 PMOS transistors, are used for level shifting. But in this paper, only one diode connected NMOS transistor is used and similar results to the conventional level shifting method have been achieved. Rail-to-rail input stage with 1.6V supply voltage is proposed and simulated by Cadence SPECTRE with TSMC 0.25-μm CMOS technology.