Circuits and methods for variable gain amplifiers
AssigneeAltera Corporation
InventorVishal Giridharan
Life of this patent
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Abstract
A variable gain amplifier circuit includes a differential pair of transistors and a variable current source circuit. The differential pair of transistors generates an output signal based on an input signal. The variable current source circuit is coupled to the differential pair of transistors. A gain of the output signal relative to the input signal varies in response to variations in a bias current through the variable current source circuit. The variable gain amplifier circuit maintains a common mode voltage of the output signal substantially constant in response to the variations in the bias current through the variable current source circuit.
Claims20
A variable gain amplifier circuit comprising:
- a differential pair of transistors to generate an output signal based on an input signal;
- a variable current source circuit coupled to the differential pair of transistors, wherein a gain of the output signal relative to the input signal varies in response to variations in a bias current through the variable current source circuit, and
- wherein the variable gain amplifier circuit maintains a common mode voltage of the output signal substantially constant in response to the variations in the bias current through the variable current source circuit;
- and
- an operational amplifier circuit to generate a supply voltage for the variable gain amplifier circuit based on a reference voltage and the common mode voltage of the output signal.
A variable gain amplifier circuit comprising:
- a differential pair of transistors to generate an output signal based on an input signal;
- a variable current source circuit coupled to the differential pair of transistors, wherein a gain of the output signal relative to the input signal varies in response to variations in a bias current through the variable current source circuit;
- and
- a feedback amplifier circuit to maintain a common mode voltage of the output signal substantially constant in response to the variations in the bias current through the variable current source circuit.
A decision feedback equalizer circuit comprising:
- a variable gain amplifier circuit comprising a differential pair of transistors to generate an output signal based on an input signal, wherein the variable gain amplifier circuit further comprises a variable current source circuit coupled to the differential pair of transistors, wherein a gain of the output signal relative to the input signal varies in response to variations in a bias current through the variable current source circuit, and wherein the variable gain amplifier circuit maintains a common mode voltage of the output signal substantially constant over the variations in the bias current;
- a combiner circuit to generate a combined signal based at least in part on the output signal of the variable gain amplifier circuit;
- and
- an adaptation circuit to generate control signals for varying the bias current through the variable current source circuit based on the combined signal.
A method comprising:
- generating an output signal based on an input signal using a differential pair of transistors in an amplifier circuit;
- varying a gain of the output signal relative to the input signal in response to variations in a bias current through a variable current source circuit in the amplifier circuit;
- and
- generating a supply voltage for the amplifier circuit using an operational amplifier circuit to maintain a common mode voltage of the output signal substantially constant in response to the variations in the bias current through the variable current source circuit.
A method comprising:
- generating an output signal based on an input signal using a differential pair of transistors in an amplifier circuit;
- varying a gain of the output signal relative to the input signal in response to variations in a bias current through a variable current source circuit in the amplifier circuit;
- and
- maintaining a common mode voltage of the output signal substantially constant in response to the variations in the bias current through the variable current source circuit by maintaining the common mode voltage of the output signal near a reference voltage using a feedback amplifier circuit.
Dependencies are inferred from the claim text.