US 7,471,150 B2Granted

Class AB folded cascode stage and method for low noise, low power, low-offset operational amplifier

AssigneeTexas Instruments Incorporated

InventorsSergey V. Alenin, Henry Surtihadi

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Abstract

A class AB folded cascode circuit includes a differential current follower having first and second cascode transistors with emitters connected to first and second input conductors. An input of a first current mirror is coupled to the first input conductor, and an input of a second current mirror is coupled to the second input conductor. Outputs of the second and first current mirrors are coupled to collectors of the first and second cascode transistors, respectively, and also to first and second outputs, respectively, of the differential current follower. A third current mirror converts a differential output current in the first and second output conductors to a corresponding single-ended output voltage on the second output conductor.

Claims16

Dependent claims

A class AB folded cascode circuit comprising:

(a) a differential current follower circuit including
i. first and second cascode transistors each having a first electrode, a second electrode, and a control electrode, the control electrodes being coupled to a bias voltage source;
the differential current follower circuit having a first input conductor coupled to the first electrode of the first cascode transistor, a second input conductor coupled to the first electrode of the second cascode transistor, a first output conductor coupled to the second electrode of the first cascode transistor, and a second output conductor coupled to the second electrode of the second cascode transistor;
ii. a first current mirror circuit having an input coupled to the first input conductor and an output coupled to the second output conductor;
and
iii. a second current mirror circuit having an input coupled to the second input conductor and an output coupled to the first output conductor;
the differential current follower circuit producing a differential output current at the first and second output conductors which follows a differential input current applied at the first and second input conductors;
and
(b) a third current mirror circuit for performing a conversion of differential output current in the first and second output conductors to a corresponding single-ended output voltage on the second output conductor;
wherein the output of the first current mirror circuit is coupled to the second output conductor by means of a third cascode transistor having a first electrode coupled to the output of the first current mirror circuit, a second electrode coupled to the second output conductor, and a control electrode coupled to the bias voltage source;
and
wherein the output of the second current mirror circuit is coupled to the first output conductor by means of a fourth cascode transistor having a first electrode coupled to the output of the second current mirror circuit, a second electrode coupled to the first output conductor, and a control electrode coupled to the bias voltage source.

9 more elements

A class AB folded cascode circuit comprising:

(a) a differential current follower circuit including
i. first and second cascode transistors each having a first electrode, a second electrode, and a control electrode, the control electrodes being coupled to a bias voltage source;
the differential current follower circuit having a first input conductor coupled to the first electrode of the first cascode transistor, a second input conductor coupled to the first electrode of the second cascode transistor, a first output conductor coupled to the second electrode of the first cascode transistor, and a second output conductor coupled to the second electrode of the second cascode transistor;
ii. a first current mirror circuit having an input coupled to the first input conductor and an output coupled to the second output conductor;
and
iii. a second current mirror circuit having an input coupled to the second input conductor and an output coupled to the first output conductor;
the differential current follower circuit producing a differential output current at the first and second output conductors which follows a differential input current applied at the first and second input conductors;
and
(b) a third current mirror circuit for performing a conversion of differential output current in the first and second output conductors to a corresponding single-ended output voltage on the second output conductor;
wherein the first current mirror circuit includes a first current mirror input transistor having a first electrode coupled to a first reference voltage and a control electrodes and a second electrode coupled to the first input conductor;
and a first current mirror output transistor having a first electrode coupled to the first reference voltage, a control electrode coupled to the control electrode of the first current mirror input transistor, and a second electrode coupled to the second output conductor;
and
wherein the second current mirror circuit includes a second current mirror input transistor having a first electrode coupled to the first reference voltage and a control electrode and a second electrode coupled to the second input conductor;
and a second current mirror output transistor having a first electrode coupled to the first reference voltage, a control electrode coupled to the control electrode of the second current mirror input transistor, and a second electrode coupled to the first output conductor.

11 more elements

An operational amplifier circuit comprising:

(a) an input stage including first and second input transistors coupled to a tail current source and to first and second load devices, respectively;
(b) a class AB folded cascode circuit including
1) a differential current follower circuit including
i. first and second cascode transistors each having a first electrode, a second electrode, and a control electrode, the control electrodes being coupled to a bias voltage source;
the differential current follower circuit having a first input conductor coupled to the first electrode of the first cascode transistor, a second input conductor coupled to the first electrode of the second cascode transistor, a first output conductor coupled to the second electrode of the first cascode transistor, and a second output conductor coupled to the second electrode of the second cascode transistor;
ii. a first current mirror circuit having an input coupled to the first input conductor and an output coupled to the second output conductor;
and
iii. a second current mirror circuit having an input coupled to the second input conductor and an output coupled to the first input conductor;
the differential current follower circuit producing a differential output current at the first and second conductors which follows a differential input current applied at the first and second input conductors;
and
2) a third current mirror circuit for performing a conversion of differential output current in the first and second output conductors to a corresponding single-ended output voltage on the second output conductor;
and
(c) an output stage having an input coupled to one of the first and second output conductors.

10 more elements

Dependencies are inferred from the claim text.

Facts

Application: 11/279,416Filed 12 Apr 2006
Published: US 2007/0241818 A118 Oct 2007
Granted: 30 Dec 2008
Term ends: Not estimatedThe source records don’t support an estimate.

Classification11 codes

H03F 3/45291
Long tailed pairs: folded cascode stages
H03F 1/26
Details of amplifiers with only discharge tubes, only semiconductor devices or only unspecified devices as amplifying elements: modifications of…
H03F 3/3066
Single-ended push-pull [SEPP] amplifiers ; Phase-splitters therefor: the collectors of complementary power transistors being connected to the output
H03F 3/45094
Long tailed pairs: folded cascode stages