Design of GaAs operational amplifiers for analog sampled data applications

High-grain operational amplifiers for implementation in GaAs technology are an essential component for analog GaAs signal processing systems using switched-capacitor circuit techniques. The requirement for high voltage gains and fast settling times in the context of the inherent technological disadvantages of GaAs (MESFET) devices leads to the development of a whole range of novel circuit techniques. For optimum performance, single-stage designs with single-ended input are considered initially. A description is given of a differential-to-single-ended converter stage that can be combined with these high gain stages to yield differential input amplifiers. A new procedure for characterizing amplifiers in terms of settling time is presented. It reveals the ultimate speed limitation for a given amplifier design and allows the MESFET gatewidths to be scaled in order to obtain optimum settling behavior for any given capacitive load. Ideas are pursued for a new generation of amplifiers with very fast settling times approaching 200 ps, intended for future switched-capacitor systems with 1-GHz switching frequencies. Considerable emphasis is placed throughout on the minimization of chip area and power consumption. The application of one of the amplifier designs in an integrated switched capacitor filter chip is presented, along with encouraging preliminary measurement