Synaptics Incorporated
Operational amplifier with reduced input capacitance

Abstract:

An operational amplifier includes a first transistor, a second transistor, a third transistor, a first constant current source, an output state, a first switch, and a second switch. The first transistor has a first gate configured to receive an output voltage from an output node. The second transistor has a second gate. The third transistor has a third gate configured to receive an input voltage. The first constant current source is coupled to sources of the first transistor, the second transistor, and the third transistor. The output stage is configured to drive the output voltage on the output node based on a first current through the first transistor, a second current through the second transistor, and a third current through the third transistor. The first switch is coupled between the second gate of the second transistor and the third gate of the third transistor; and the second switch is coupled between the output node and the second gate of the second transistor.