Fast-settling high-gain GaAs operational amplifiers for switched-capacitor applications

The authors are concerned with fast-settling, high-gain GaAs operational amplifiers for high-frequency, switched-capacitor circuit applications. A previous amplifier with a gain of 60 dB is critically assessed from the point of view of settling time, and the device geometries altered to reduce settling time from 450 ps to a minimum of 360 ps. General circuit techniques for obtaining faster settling are developed, and this leads to two designs which have gains still exceeding 60 dB but with minimum settling times now approaching 200 ps.