Design of low voltage low noise folded cascode CMOS op-amp with class AB output stage

• Main Author: Ang, Kok Wai
• Other Authors: Siek Liter
• Format: Final Year Project
• Language: English
• Published: Nanyang Technological University 2021
• Subjects: Engineering::Electrical and electronic engineering
• Online Access: https://hdl.handle.net/10356/149810
• Institution: Nanyang Technological University

The market size of IoT devices is expanding rapidly as artificial intelligence and 5G technology are maturing. These smart portable devices require low power performance and a small chip area. The goal of this project is to design a 1.2V supply voltage rail-to-rail input and output operational amplifier with low noise performance. The technology node used in this project is GF 55nm CMOS process. The design in this project is a two-stage op-amp, which comprises a differential folded cascode amplifier with complementary input pair and a feedforward Class-AB output stage. A constant gm bias circuit with start-up circuitry is included in this project to provide the reference current to the op-amp. The challenges of this op-amp design are the undesired variation of input transconductance and the quiescent current of output transistors. The op-amp in this project has achieved a 9% input gm variation over the rail-to-rail common-mode input voltage using hex-pair input structure. The current consumption of op-amp in unity configuration with load (10kOhm and 10pF) is 148.3µA when input common-mode voltage is 0.6V. The input-referred noise voltage of the op-amp is 141.9nV/√Hz at 1 kHz frequency. The design also achieved a 77.9dB open-loop gain with a 77.2° phase margin at the unity-gain bandwidth of 3.10MHz. The open-loop gain is slightly low as the transistors have a large channel modulation index in this process.