A high-swing 2 V CMOS operational amplifier with gain enhancement using a replica amplifier

An open-loop gain enhancement circuit in 1.2- mu m CMOS that does not require cascode or long-channel transistors, thus maximizing output swing and input common-mode range, is described. Since gain enhancement is not achieved by increasing output resistance, but by matching main and replica amplifiers, high effective open-loop gain is maintained even with resistive loads. This circuit can be used with any transconductance amplifier circuit. A basic two-stage amplifier circuit demonstrates gain enhancement for low-voltage applications. The effective DC gain is increased by a factor of approximately 18 with no load resistor, and by a factor of 58 with a 1-k Omega load.<>