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

Abstrtict— A general gain-enhancement technique for operational amplifiers using a replica amplifier is described. Unlike conventional techniques such as cascoding, which increases the gain by increasing the output resistance, the replica-amp technique increases the gain by matching the main and the replica amps. Among the advantages of the replica-amp technique are low supply, high swing, and effectiveness with resistive loads. This technique has been demonstrated in a 1.2-pm CMOS two-stage op amp. Operating from + 1-V supplies, the op amp has an effective open-loop dc gain of greater than 10000, while maintaining a high swing of 100 mV from either supply rails. The gain-enhancement circuit is shown to have only a small effect on the settling time experimentally, analytically, and in SPICE simulation.