Patent ID: 7411451

Claim:
An operational amplifier circuit comprising: (a) an input stage including first and second input transistors coupled to a first tail current source and to first and second load devices, respectively; (b) a folded cascode circuit including i. first and second cascode transistors each having a first electrode, a second electrode, and a control electrode, the first electrode of the first cascode transistor being coupled by a first conductor to the first input transistor and the first load device, the first electrode of the second cascode transistor being coupled by a second conductor to the second input transistor and the second load device, the control electrodes being coupled to a first bias voltage, ii. a first controlled current source coupled between the first electrode of the first cascode transistor and a first reference voltage, a second controlled current source coupled between the first electrode of the second cascode transistor and the first reference voltage, a third controlled current source coupled between the second electrode of the first cascode transistor and a second reference voltage, and a fourth controlled current source coupled between the second electrode of the second cascode transistor and the second reference voltage; (c) a second stage having first and second inputs coupled to the second electrodes of the first and second cascode transistors, respectively, an output conductor for conducting an output signal, and a tail current conductor coupled to a second tail current source, the tail current conductor having a node at which a voltage representative of a common mode input voltage of the second stage is established, and first and second compensation capacitors coupled to the first and second inputs, respectively, of the output stage; and (d) a bias circuit, coupled to the second stage node, for biasing control terminals of the first, second, third, and fourth controlled current sources in response to the common mode input voltage established at the tail current conductor.