Patent ID: 7576610
Filing Date: 2009-08-18
Classification: H03F

Abstract:
1. A class AB operational amplifier comprising: a first input transistor coupled between a first internal node and a first common node, and having a control terminal coupled to a first differential input terminal; a second input transistor coupled between a second internal node and the first common node, and having a control terminal coupled to a second differential input terminal; a first input stage load transistor diode connected and coupled between a first voltage reference and the first internal node; a second input stage load transistor diode connected and coupled between the first voltage reference and the second internal node; first and second output transistors coupled in series between the first voltage reference and a second voltage reference, an interconnection node of the first and second output transistors being an output terminal of the operational amplifier, and the first output transistor having a control terminal connected to a control terminal of the second input stage load transistor; a tail current generator coupled between the first common node and the second voltage reference; an adaptive bias block coupled between the first and second voltage references, the adaptive bias block being coupled to the first common node; and a positive feedback network coupled between the first voltage reference and the first and second internal nodes, wherein the adaptive bias block comprises one or more circuits that each include a current subtractor that determines a difference between a current at the first internal node and a current at the second internal node and generates a boost current that is proportional to this difference.