Abstract: A rail-to-rail operational amplifier with low-voltage low-offset and constant transconductance is designed in TSMC 0.18 μm CMOS process.The operational amplifier has a rail-to-rail folded cascode input stages, which ensures a constant transconductance over the available common-mode input range and all input transistors operate in sub-threshold region.A class-AB output stage with folded mesh feedback is used to achieve the rail-to-rail output range.The chopper stabilization technique is exploited to reduce the input referred offset and noise.The circuit is simulated in Cadence Spectre with a single 1 V supply.The simulation results show that the dc gain is 119dB and the GBW is 5.6 MHz.Montecarlo simulations demonstrate an offset distribution with 14 μV standard deviation.The input noise spectral density is 18.19 nV/√Hz