Design of a Fully Differential Gain-Boosted Folded-Cascode Op Amp with Settling Performance Optimization

A single stage fully differential operational amplifier was designed in SMIC 0.25um mix-signal CMOS technology with 2.5V power supply. The designed op amp utilizes gain-boosting technique. The main op amp is a fully differential folded-cascode op amp with switched-capacitor CMFB. Two fully differential folded-cascode op amps with continuous-time CMFBs are used as auxiliary op amps to increase the open-loop gain of the main op amp. In addition, a simulation-based optimization method for the high-speed design of gain-boosted op amp was also presented. The simulation results show that the designed op amp achieves a dc gain of 102dB with a unity-gain frequency of 822 MHz. With the high-speed optimization, the 0.0488% settling time is 3.5ns.