CLASS AB OPERATIONAL AMPLIFIER WITH SPLIT FOLDED-CASCODE STRUCTURE AND METHOD

摘要

Bias current in output transistors of a class AB output stage is controlled by providing equal amplification to both an output of an input stage (2) of an amplifier and an output (17,18) of a class AB control circuit (46). A split input transistor circuit structure for a first side of the differential input stage (2) includes first (15) and second (16) input transistors with gates coupled to a first input (Vin+). A third input transistor (10) of the input stage has a gate coupled to a second input (Vin−). A split folded common gate cascode circuit includes first (25) and second (30) cascode transistors having their drains coupled to gates of the output transistors, respectively, and a third cascode transistor has a source coupled to a drain of the third input transistor. The bias current is sensed and compared with a reference current to produce an error signal that is amplified to produce a differential error current a signal which is introduced applied to sources of the first and second cascode transistors.