A 0.5-V 85-nW rail-to-rail operational amplifier with a cross-coupled output stage

A 0.5-V rail-to-rail operational amplifier (op-amp) with a large common-mode input range is proposed. It has a two-stage structure which consists of a complementary input stage and a novel cross-coupled output stage. The cross-coupled output stage increases the transconductances of MOSFETs of the output stage without increasing the chip area. And hence, it increases the drivability for a capacitive load. Using HSPICE simulations, it is verified that the proposed circuit has a DC gain of more than 80 dB for common-mode input voltages from 40 mV to 400 mV with a supply voltage of 0.5 V. Unity-gain frequency is 8.2 kHz with a capacitive load of 40 pF and the power consumption is 85nW including all bias circuits.