Constant-gm techniques for rail-to-rail CMOS amplifier input stages: a comparative study

This paper presents a comparative study of a number of constant-transconductance (g_m) techniques for CMOS amplifier input stages. The pros and cons of each technique are discussed. Theoretical analysis along with simulation results are discussed to demonstrate the performance of each constant-g_m technique. Finally, we propose a novel technique which achieves within ±3% g_m variation over the full input common-mode voltage range. The new technique exhibits improvement over other existing techniques.