Constant-gm low-power rail-to-rail operational amplifier

A low-power rail-to-rail operational amplifier (Op-amp) was realized in SMIC 0.18 ¿m CMOS process. Under a 1.8 V supply voltage, a constant transconductance (within 5.4% of maximum variation) is ensured for the whole common-mode input range. The class AB output stage also has a full voltage swing. The circuit provides a gain bandwidth of 17.3-MHz and a DC gain of 99.6 dB. The input transistors operate in weak inversion, which have big g_m/I_d value, so the power consumption is reduced to only 89.02 ¿W (C_load = 5pf).