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A new architecture for constant-gm, rail-to-rail(R-R) input stages is presented that has 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. Employing these techniques a low-power operational transconductance amplifier (OTA) 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 R-R input common-mode range is realized in a 0.8 μm CMOS technology. This amplifier dissipates 10 mW from a 3V power supply.