Patent ID: 7545214
Filing Date: 2009-06-09
Classification: H03F

Abstract:
1. An operational amplifier comprising: an input terminal; an input stage coupled to the input terminal of the operational amplifier, wherein the input stage is configured to couple to a control circuit and to a rail-to-rail output stage of the operational amplifier, wherein the input stage includes: wherein, when the input terminal is at one of a positive voltage rail or a negative voltage rail of the operational amplifier, one of the first or second differential input circuits is activated and the other differential input circuit is deactivated; wherein, in response to activating one of the first or second differential input circuits, the first current mirror is configured to provide a current of a predetermined value to input terminals of the control circuit, and to nodes coupled to the rail-to-rail output stage of the operational amplifier; wherein the input stage is configured to maintain the current provided to the input terminals of the control circuit and to the nodes coupled to the rail-to-rail output stage constant over the full input voltage range from the negative voltage rail to the positive voltage rail.