A self-biased high performance folded cascode CMOS op-amp

摘要

Cascode CMOS op-amps use a large number of external bias voltages. This results in numerous drawbacks, namely, an area and power overhead, susceptibility of the bias lines to noise and cross-talk and high sensitivity of the bias point to process variations. In this paper we present a self-biasing technique for folded cascode CMOS op-amps that uses no additional devices and no bias voltages other than the two supply rails. The resulting self-biased op-amps are free from the above mentioned drawbacks and exhibit the same performance as existing folded casode op amps, except for a small reduction in slew rate. This is achieved by following transistor sizing constraints derived through detailed circuit analysis. The technique is applied to an existing high performance op amp. Simulation results show that the high performance is maintained while nine bias voltages are eliminated.