High-speed three-stage operational transconductance amplifiers for switched-capacitor circuits

In this paper, three-stage operational transconductance amplifiers (OTAs) for use in switched-capacitor (SC) circuits using nanometer CMOS technologies are described. Two three-stage OTAs, one with nested-Miller compensation (NMC) as a basic compensation scheme and another with damping factor control frequency compensation (DFCFC) as an advanced compensation scheme are presented. The open-loop small-signal analysis as well as the large signal-analysis for both OTAs are investigated and their speed performance is compared and discussed. Circuit level simulations are carried out using a 90 nm CMOS technology with HSPICE. Simulation results show that the NMC and the DFCFC OTAs achieve a settling time of 17.5 ns and 8.4 ns with 0.02% accuracy, respectively, while consuming 3 mW from a 1.2 V power supply and have the same input-referred thermal noise.