Design Procedures for a Fully Differential Telescopic Cascode Two-Stage CMOS Operational Amplifier

In this paper, a fully differential telescopic operational amplifier design is presented which achieve both high dc gain and high unity-gain frequency. Trade-offs among such factors as bandwidth, gain, phase, margin, bias current, signal swing, slew rate, and power are made evidently. The characteristic of this kind of two-stage operational amplifier is investigated theoretically, in this paper. The results indicate that proposed two-stage operational amplifier achieves broader unity bandwidth, increases the DC gain. Simulation results show that, at 5 V power supply, the output swing is ±4.3 V, settling time is 167.4 ns. Based on the two-stage operational amplifier structure, the operational amplifier with 2.5 V output common voltage shows a DC gain greater than 87 dB, Gain Bandwidth over 39 MHz (5pF load) and a phase margin larger than 84° with power dissipation of 3mW. These good results could be used in Σ-△ modulation and A/D conversion etc.