Patent ID: 7592867

Claim:
A differential amplifier comprising: a differential input transistor pair including first and second input transistors each having a first electrode, a second electrode, and a control electrode; a first folded cascode stage including first, second, third and fourth current source transistors and first and second cascode transistors each having a first electrode, a second electrode, and a control electrode, first and second summing junctions coupled to the second electrodes of the first and second input transistors, respectively, and first and second outputs conducting first and second output signals, respectively, the second electrodes of the first and second current source transistors being coupled by the first and second summing junctions, respectively, to the first electrodes of the first and second cascode transistors, the second electrodes of the first and second cascode transistors being coupled to the first and second outputs, respectively, and the second electrodes of the third and fourth current source transistors being coupled to the first and second outputs, respectively; and common mode feedback circuitry including: a tracking circuit that includes a first section coupled to receive both the first and second output signals for producing the first common mode output signal and a second section coupled to receive both the first and second output signals for producing the second common mode output signal, wherein the first section includes first and second tracking capacitors having first terminals connected to produce the first common mode output signal and a first switch coupled across the first tracking capacitor, a second terminal of the first tracking capacitor being coupled to receive the first output signal, a second terminal of the second tracking capacitor being coupled to receive the second output signal, and wherein the second section includes third and fourth tracking capacitors having first terminals connected to produce the second common mode output signal and a second switch coupled across the third tracking capacitor, a second terminal of the third tracking capacitor being coupled to receive the second output signal, a second terminal of the fourth tracking capacitor being coupled to receive the first output signal; and an auxiliary amplifier stage including a differential input stage including third, fourth and fifth input transistors, gates of the third and fourth input transistors being coupled to receive the first and second common mode output signals, respectively, a gate of the fifth input transistor being coupled to receive a desired common mode voltage, drains of the third and fourth input transistors being coupled to a first input of a secondary amplifying stage having an output, a drain of the fifth input transistor being coupled to a second input of the secondary amplifying stage, the output of the secondary amplifying stage coupling a common mode feedback control signal to bias the control electrodes of the third and fourth current source transistors.