Class AB CMOS amplifiers
AssigneePotentia Semiconductor, Inc.
InventorRoger Colbeck
Life of this patent
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Abstract
A class AB output stage of a CMOS amplifier has a level-shifting voltage follower constituted by a level-shifting transistor and a current source. A bias circuit replicates the level-shifting voltage follower in a feedback arrangement to produce a variable bias voltage for the current source of both the main and replica level-shifters. The arrangement serves to control the output voltage of the level-shifter such that it provides the amplifier with a relatively constant quiescent current of the output stage over variations of manufacturing process, supply voltage, and temperature. The level shifting function can be facilitated by a resistive on-state of a power-down transistor between the level-shifting and load transistors.
Claims19
A CMOS amplifier having a class AB output stage, the output stage comprising:
- two complementary transistors having source-drain paths coupled in series between two voltage supply rails and providing an output from a junction therebetween;
- a level-shifting transistor and a further transistor having source-drain paths coupled in series between the two voltage supply rails for supplying a signal from a junction therebetween to one of said complementary transistors;
- and
- a signal input to the other of said complementary transistors and to the level-shifting transistor;
- the amplifier further comprising a bias circuit for producing a variable bias voltage for said further transistor, the bias circuit comprising:
- a replica of the level-shifting transistor and a replica of said further transistor coupled in series between the two voltage supply rails in a similar manner to the level-shifting transistor and said further transistor, the replica of said further transistor also being responsive to said variable bias voltage;
- and
- a circuit responsive to a voltage at a junction between the replica of the level-shifting transistor and the replica of said further transistor for producing said variable bias voltage in a manner to reduce variations of a quiescent current of the output stage.
A method of reducing variation, due to manufacturing process, voltage, and/or temperature variations, of a quiescent current of a class AB output stage of a CMOS amplifier including a level-shifting transistor and a further transistor constituting a current source for the level-shifting transistor, comprising the steps of:
- replicating a circuit of the level-shifting and further transistors in a bias circuit;
- in the bias circuit, producing a variable bias voltage dependent upon a voltage of the replicated circuit of the level-shifting and further transistors;
- and
- biasing said further transistor and a replica of said further transistor in the bias circuit in dependence upon said variable bias voltage.
A CMOS amplifier including a level-shifting transistor and a current source transistor for the level-shifting transistor, the amplifier further comprising a bias circuit including a copied level-shifting transistor and a copied current source transistor arranged in a similar manner to the level-shifting transistor and the current source transistor, and a circuit responsive to a level-shifted voltage produced by the copied level-shifting transistor and copied current source transistor for producing a variable bias voltage, the variable bias voltage being supplied to a gate of the current source transistor and to a gate of the copied current source transistor.
Dependencies are inferred from the claim text.