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US 8,618,882 B2Granted
Variable gain amplifier
AssigneeTexas Instruments Incorporated
InventorsBrett Forejt, Jeff Berwick, David J. Baldwin
Life of this patent
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Abstract
An apparatus and method are provided. Generally, an input signal is applied across a main path (through an input network) and across a cancellation path (through a cancellation circuit). The cancellation circuit subtracts a cancellation current from the main path as part of the control mechanism, where the magnitude of the cancellation current is based on a gain control signal (that has been linearized to follow a control voltage).
Claims19
An apparatus comprising:
- a transconductance circuit having a positive input terminal and a negative input terminal, the transconductance circuit including:
- a level shifter;
- an output stage coupled to the level shifter;
- a first input stage coupled to the output stage
- a second input stage coupled to the output stage,
- the first and second input stage each comprising a first and second darlington pair,
- wherein the level shifter is a digital signal level shifter that generates a logic high signal at pump a voltage.
4 more elements
An apparatus comprising:
- a positive input terminal for the apparatus;
- a negative input terminal for the apparatus, wherein the positive and negative input terminals for the apparatus receive positive and negative portions of an input signal, respectively;
- a first resistor that is coupled to the positive input terminal for the apparatus;
- a second resistor that is coupled to the negative input terminal for the apparatus;
- a cancellation circuit having:
- a third resistor that is coupled to the positive input terminal for the apparatus;
- a fourth resistor that is coupled to the negative input terminal for the apparatus;
- a plurality of shunt switches that are coupled between the third resistor and the forth resistor;
- a fifth resistor that is coupled to the third resistor;
- and
- a sixth resistor that is coupled to the fourth resistor;
- a control circuit that generates a gain control signal that follows a control voltage and that is coupled to provide the gain control signal to each of the shunt switches;
- and
- a transconductance circuit having a positive input terminal and a negative input terminal, wherein the negative input terminal of the transconductance circuit is coupled to the second and sixth resistors, and wherein the positive input terminal of the transconductance circuit is coupled to the third and fifth resistors,
- the transconductance circuit including:
- a level shifter;
- an output stage coupled to the level shifter;
- a first input stage coupled to the output stage
- a second input stage coupled to the output stage,
- the first and second input stage each comprising a first and second darlington pair.
17 more elements
A transconductance circuit having a positive input terminal and a negative input terminal, the transconductance circuit including:
- a level shifter;
- an output stage coupled to the level shifter;
- a first input stage coupled to the output stage
- a second input stage coupled to the output stage,
- the first and second input stage each comprising a first and second darlington pair,
- wherein the transconductance amplifier further includes a current bias network coupled to the first and second input stages, and
- wherein a differential input pair of the transconductance circuit operates in conjunction with a plurality of transistors as a folded cascode amplifier,
- wherein the transconductance circuit is further coupled to:
- an input network that is coupled to the positive and negative input terminals of the transconductance circuit and that receives an input signal;
- a control circuit that generates a gain control signal;
- and
- a cancellation circuit that is coupled to the positive and negative input terminals of the transconductance circuit, that is coupled to the gain control circuit, and that receives the input signal, wherein the cancellation circuit subtracts a cancellation current from the positive and negative input terminals of the transconductance circuit, and wherein the magnitude of the cancellation current is based at least in part on the gain control signal.
9 more elements
Dependencies are inferred from the claim text.