Patent ID: 6828855
Filing Date: 2004-12-07
Classification: H03F

Abstract:
A class AB amplifier comprising:(a) a differential input stage including first and second input transistors each having a gate coupled to a first input and a third input transistor having a gate coupled to a second input, sources of the first, second, and third input transistors being coupled to a current source, drains of the first, second, and third input transistors being coupled to first, second and third conductors; (b) a first class AB output stage including a first output transistor having a gate coupled to a first gate drive conductor and a drain coupled to a first output conductor and a second output transistor having a gate coupled to a second gate drive conductor and a drain coupled to the first output conductor; (c) a first split folded cascode stage including i. first and second cascode transistors each having a gate coupled to a reference signal conductor, the first and second cascode transistors having drains coupled to the first and second gate drive conductors, respectively, and sources coupled to the first and second conductors, respectively; ii. a first current source transistor coupled between the source of the first cascode transistor and a first reference voltage conductor, and a second current source transistor coupled between the source of the second cascode transistor and the first reference voltage conductor; and (d) first class AB control circuitry including a first input coupled to receive a signal representative of a current in the first output transistor, a second input coupled to receive a signal representative of a current in the second output transistor, and a first output coupled to the first conductor, wherein the drains of the first and second cascode transistors present high output impedances to the first and second gate drive conductors resulting in high loop gain and consequently resulting in precise control of a first quiescent bias current in the first and second output transistors.