An Adaptive Biased Single-Stage CMOS Operational Amplifier with a Novel Rail-to-Rail Constant-gm Input Stage

Abstract

Using rail-to-rail (R-R) swing analog circuits has become almost mandatory in the design of low supply voltage circuits. In this paper, a new architecture for constant-gm rail-to-rail input stages is presented. The design features a less than 5% deviation in gm over the entire range of the input common-mode voltage. Furthermore, a new structure for folded cascode amplifier based on the use of a floating current source is presented. By employing these techniques, a low-power operational amplifier (op-amp) with 100 MHz unity-gain bandwidth, 106 dB gain, 60? phase margin, 2.65 V swing, and 6.4 nV/?Hz input-referred noise with rail-to-rail input common-mode range is realized in a 0.8 ? m CMOS technology. This amplifier dissipates 10 mW from a 3 V power supply.