A 168 dB high gain folded cascode operational amplifier for Delta-Sigma ADC

Abstract

A fully differential CMOS folded cascode operational amplifier is presented. It uses gain boosting technique on both NMOS and PMOS branch to enhance total gain. New current-sink topology is used to maximally enhance the open-loop gain as well as not to deteriorate the output swing badly. Local small area but good-performance CT-CMFB is adopted in gain-boosted auxiliary amplifier to optimize both area cost and calibration performance. An improved SC-CMFB is used on total amplifier output to stabilize the output common mode node voltage as well as not to impact differential gain performance. Designed in low-cost UMC 110 nm process with a 5V supply voltage, simulation results show DC gain of 164.1 dB and a phase margin of 63 degree at a unity gain bandwidth of 17.09 MHz. The static current is 174 uA along with achieved PSRR of 186.5dB, making it suitable in high-performance Delta-Sigma ADCs.