Common-mode response shaping in rail-to-rail op-amp input stages

Low-voltage rail-to-rail (r-t-r) operational amplifiers (op-amps) suffer from large deviations in their small-signal and large signal behaviors, as a function of the input common-mode (CM) voltage. This paper introduces the concept of the CM response shaping as an effective technique for maintaining roughly constant op-amp behaviors over the full input range. This is achieved by means of two input variable floating voltage sources. Experimental results obtained from a 0.8-/spl mu/m standard CMOS 3-V input/output r-t-r op-amp are shown.