Advances on CMOS Folded-Cascode Operational Transconductance

In this paper, a tutorial review on several structural improvements of the CMOS folded-cascode Operational Transconductance Amplifier (OTA) is presented. After a brief discussion on the structure and operation of the conventional Folded-Cascode Amplifier, its several architectural improvements are reviewed. These improvements include advances on class A and class AB Folded-Cascode Amplifier s and recycling Folded-Cascode Amplifier. Afterwards, several improved class A and class AB recycling folded-cascode Operational Transconductance Amplifiers are discussed, and finally some two-stage Operational Transconductance Amplifiers based on the current recycling technique are reviewed. As it can be seen, many architectural innovations have been proposed to improve both small-signal parameters, including DC gain, unity-gain bandwidth, phase margin, and large-signal operation, which is usually characterized by slew rate in the proposed OTAs compared to the basic Folded-Cascode Amplifier. Current recycling, shunt current sources, cross-coupled transistors to realize local positive feedback paths, local Common-Mode Feedback, Flipped Voltage Follower cells to realize class AB operation, active current mirrors, and several other techniques have been utilized in the structural improvements of the basic folded-cascode Operational Transconductance Amplifier. The achieved results are more promising and demonstrate substantial achievements in the design of Operational Transconductance Amplifiers in low-voltage and more scaled nano-meter CMOS processes.