Impedance matched variable gain low noise amplifier using shunt feed-back
AssigneeBroadcom Corporation
InventorDanilo Manstretta
Life of this patent
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Abstract
The variable gain amplifier includes a forward path that provides the amplifier variable gain, and a feedback path. The feedback path uses a switch that is turned on at low gain levels. The switch taps into the feedback resistor, shunting it to signal-ground and eliminating the feedback mechanism. This ensures that the input impedance seen at the input port does not grow excessively, using part of the feedback resistor as a passive termination at low gain levels. In this way variable gain ranges in excess of 30 dB can be achieved.
Claims20
An amplifier, comprising:
- a forward amplifier having an input and an output;
- a feedback path coupled across said input and output, including,
- a feedback amplifier and a resistor connected in series;
- and
- means for shunting a signal output of said feedback amplifier to ground for low gain applications.
A variable gain differential amplifier, comprising:
- a differential forward amplifier having a differential input and a differential output;
- and
- a differential feedback path coupled across said differential input and said differential output, including,
- a differential feedback amplifier;
- a first differential resistor coupled to an output of said differential feedback amplifier;
- means for shorting a first terminal of said first differential resistor to a second terminal of said first differential resistor;
- and
- a second differential resistor coupled said first differential resistor and to said differential input.
A method of amplifying an input signal, comprising:
- receiving an input signal at an input terminal;
- variably amplifying the input signal to produce an amplified signal at an output;
- feeding back a portion of the amplified signal through a resistive feedback path that is coupled to the input terminal to produce a feedback signal;
- and
- shunting the feedback signal to ground prior to the input terminal for low gain applications.
A method of variably amplifying a differential input signal, comprising:
- receiving a differential input signal at an input terminal;
- variably amplifying the differential input signal to produce a differential amplified signal at an output;
- feeding back a portion of the differential amplified signal through a resistive feedback path that is coupled to the input terminal to produce a differential feedback signal, the resistive feedback path having a differential resistor having first and second resistor components;
- and
- operating a switch across the first and second resistor components of the differential resistor based on a desired gain of said differential amplifier.
Dependencies are inferred from the claim text.