Design of a 92 dB Fully-Integrated Low Voltage Folded Cascode OTA with Class AB Output Buffer and gain-enhancement in 55 nm CMOS Technology

This paper presents a design of folded cascode operational transconductance (OTA)amplifier with class AB output buffer and a gain-enhancement circuit. The proposed circuit is suitable for low-voltage operation in applications with limited power and high gain bandwidth product (GBW). All MOSFETs in the proposed architecture conduct 16 µA of current under equilibrium conditions. The speed of the op-amp is increased by a fully-integrated biased circuit that is designed to boost the currents and overdrive voltages of the MOSFETs. By adjusting the drain of the cascode current sources to increase the output resistance, a class AB output buffer is placed at the folded cascode OTA's output node. Differential amplifier circuits with sourcefollower level shifters are added to the folded-cascode architecture for gainenhancement. This scheme enhances the gain which is necessary for precision amplification. The overall circuit simulation results using industry-standard CMOS 55-nm technology reveal improved performance as compared to state of the art. The proposed folded cascode OTA with class AB output buffer and gain-enhancement scheme operates on a supply of 1 V and offers a DC gain of 92 dB, phase margin of 750 and a gain bandwidth (GBW) of 30 MHz.