Patent ID: 6867643

Claim:
A rail-to-rail operational amplifier circuit to extract a true mean of two signals, comprising: an n-type buffer input stage that receives the two signals and produces a first offset common mode output signal therefrom; an n-type amplifier input stage that receives both the first offset common mode output signal and a first feedback signal, and produces a first differential error signal therefrom; a p-type buffer input stage that receives the two signals and produces a second offset common mode signal therefrom; a p-type amplifier input stage that receives both the second offset common mode output signal and a second feedback signal, and produces a second differential error signal therefrom; a differential input high-gain amplifier output stage that receives the first and second differential error signals and produces a true common mode output signal that is substantially equal to the true mean of the two signals; a feedback stage that receives the true common mode output signal and produces the first and second feedback signals therefrom; and a transitioning stage that controls how much the first differential error signal from the n-type amplifier input stage and the second differential signal from the p-type amplifier input stage contribute to the differential input of the high-gain amplifier output stage.