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US 7,009,450 B2Granted
Low distortion and high slew rate output stage for voltage feedback amplifier
AssigneeTexas Instruments Incorporated
InventorsCharles Parkhurst, Muhammad Islam
Life of this patent
Estimating the term…
Abstract
A voltage feedback (“VF”) operational amplifier (“op-amp”) that includes a circuit operable to dynamically bias pre-driver transistors at the op amp output stage. This arrangement provides a dynamic bias from a common base gain stage (302) to the pre-drivers (338, 339) of the output stage (303) so that higher slew rate is achieved with minimal discontinuity in the signal.
Claims17
A circuit for dynamically biasing an output stage of an op amp having a gain stage, comprising:
- a first transistor (Q38), a second transistor (Q39), a third transistor (Q40), a fourth transistor (Q41), a fifth transistor (Q36), and a sixth transistor (Q37);
- the first transistor (Q38) responsively coupled to and driven by current from the fifth transistor (Q36);
- the second transistor (Q39) responsively coupled to and driven by current from the sixth transistor (Q37);
- a seventh transistor (Q42) having a collector coupled to an emitter of the first transistor (Q38) and a base of the third transistor (Q40), and an emitter coupled to a first high impedance node operable to source current from the gain stage;
- and
- an eighth transistor (Q43) having a collector coupled to an emitter of the second transistor (Q39) and a base of the fourth transistor (Q41), and an emitter coupled to a second high impedance node operable to sink current from the gain stage.
3 more elements
An op amp circuit stage, comprising:
- an input stage having at least one input and at least one output:
- a common base gain stage having at least one input, and at least one output coupled to the output of the input stage;
- an output stage including a pre-driver circuit coupled to the output of the common base gain stage;
- and
- a dynamic biasing circuit operable to provide dynamic bias from the common base gain stage to the pre-driver circuit of the output stage,
- wherein the dynamic biasing circuit further comprises:
- a first transistor (Q38), a second transistor (Q39), a third transistor (Q40), a fourth transistor (Q41), a fifth transistor (Q36), and a sixth transistor (Q37);
- the first transistor (Q38) being responsively coupled to and driven by current from the fifth transistor (Q36);
- the second transistor (Q39) being responsively coupled and driven by current from the sixth transistor (Q37);
- a seventh transistor (Q42) having a collector being coupled to an emitter of the first transistor (Q38) and a base of the third transistor (Q40), having an emitter being coupled to a first high impedance node operable to source current from the gain stage;
- and
- an eighth transistor (Q43) having a collector being coupled to an emitter of the second transistor (Q39) and a base of the fourth transistor (Q41), and an emitter being coupled to a second high impedance node operable to sink current from the common base gain stage.
9 more elements
A circuit for biasing pre-drivers of an op-amp output stage, comprising:
- a first transistor (038), a second transistor (Q39), a third transistor (Q40) and a fourth transistor (Q41), a first current source and a second current source;
- an emitter of the first transistor (038) being coupled to a base of the third transistor (Q40);
- an emitter of the second transistor (Q39) being coupled to a base of the fourth transistor (Q41);
- a base of the first transistor (Q38) being responsively coupled to and dynamically driven by current from the first current source;
- and
- a base of the second transistor (Q39) being responsively coupled and dynamically driven by current from the second current source,
- the first current source comprising a fifth transistor (Q36);
- the second current source comprising a sixth transistor (Q37);
- a seventh transistor (Q42) having a collector coupled to an emitter of the first transistor (Q38) and a base of the third transistor (Q40), and an emitter being coupled to a first high impedance node operable to source current from a gain stage of the op amp;
- an eighth transistor (Q43) having a collector coupled to an emitter of the second transistor (Q39) and a base of the fourth transistor (Q41), and an emitter being coupled to a second high impedance node operable to sink current from the gain stage;
- the fifth transistor (Q36), sixth transistor (Q37), seventh transistor (Q42) and eighth transistor (Q43) sharing the same base-emitter connections;
- and
- the fifth transistor (Q36), sixth transistor (Q37), seventh transistor (Q42) and eighth transistor (Q43) being operably coupled to force current from the fifth transistor (Q36) and the seventh transistor (Q42) to substantially match current from the sixth transistor (Q37) and the eighth transistor (Q43) to substantially match, respectively.
10 more elements
Dependencies are inferred from the claim text.