Abstract:

A novel constant transconductance rail-to-rail CMOS operational amplifier is proposed in this paper.Its rail-to-rail input stage consists of four MOSFETS as dummy differential pairs to limit the current of the differential pair to provide a constant transconductance value within the ranges for the operating region.A front-feed class AB output stage is used to ensure that the output swing achieves rail-to-rail.The simulation results show that the input common-mode range reaches rail-to-rail with a variation of the gm of only 3%;the Op Amp performs an open-loop gain of 108.5 dB,the unity gain bandwidth is 26.7 MHz,and the phase margin 76.3°when the circuit driving a output load of 10 pF∥10 kΩ under 5 V power supply.

Key words: rail ro rail;constant transconductance;class AB output stage;CMOS operational amplifier