BiCMOS variable-gain transconductance amplifier
AssigneeSequoia Communications
InventorsDamian Costa, John B. Groe, Michael Farias
Life of this patent
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Abstract
A variable-gain BiCMOS transconductance amplifier (VGA). An NMOS differential pair amplifier with bipolar cascoding provides continuous gain control by adjustment of drain-source voltage to shift the NMOS differential pair from a saturation region operation and high gain to a triode operation and low gain. A simple control circuit is used in order to generate the desired exponential gain to linear control voltage characteristic that is stable over temperature and process. The shift from saturation to triode operation of the input NMOS differential pair simultaneously increases the input linearity as the gain is reduced.
Claims15
A variable-gain amplifier that amplifies an input signal to produce an amplified output signal and wherein the amplifier provides an exponential gain to linear control voltage characteristic, the amplifier comprising:
- a control voltage generator that generates a first control signal in response to a second control signal;
- an input transconductance stage that receives the input signal and provides the second control signal at a signal terminal that is coupled to the control voltage generator;
- a cascode transistor pair that is coupled to the input transconductance stage, the cascode transistor pair receives the first control signal and generates the amplified output signal;
- and
- an output load coupled to the amplified output signal.
A method for amplifying an input signal to produce an amplified output signal, wherein the method provides an exponential gain to linear control voltage characteristic, the method comprising steps of:
- receiving the input signal at a transconductance stage that is coupled to a cascode transistor pair;
- generating a first control signal that is input to the cascode transistor pair in response to a second control signal that is provided at a signal terminal of the transconductance stage that is also coupled to a current source;
- generating the amplified output signal at an output of the cascode transistor pair;
- and
- providing a load that is coupled to the amplified output signal.
In a radio receiver that receives and processes radio frequency (RF) transmissions, a variable-gain amplifier that amplifies an input signal derived from the RF transmissions to produce an amplified output signal, and wherein the amplifier provides an exponential gain to linear control voltage characteristic, the amplifier comprising:
- a control voltage generator that generates a first control signal in response to a second control signal;
- an input transconductance stage that receives the input signal and provides the second control signal at a signal terminal that is coupled to the control voltage generator;
- a cascode transistor pair that is coupled to the input transconductance stage, the cascode transistor pair receives the first control signal and generates the amplified output signal;
- and
- an output load coupled to the amplified output signal.
Dependencies are inferred from the claim text.