Analog amplifier having DC offset cancellation circuit and method of offset cancellation for analog amplifiers
AssigneeAgere Systems Inc.
InventorsJinghong Chen, Gregory W. Sheets, Joseph Anidjar, Robert J. Kapuschinsky, Lane A. Smith
Life of this patent
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Abstract
An amplifier having DC offset compensation includes at least one input node and a pair of differential output nodes, a biasing circuit coupled to the input node; and a plurality of current sources. Selected ones of said current sources are coupled to the input node to adjust a DC voltage at the input node to provide DC offset compensation for the amplifier
Claims16
An apparatus comprising:
- an amplifier (e.g., 110) having a pair of differential input nodes (e.g., INP, INN) and a pair of differential output nodes (e.g., VON, VOP);
- first and second biasing circuits (e.g., Rbias, Rcm, ibias) coupled to first and second input nodes of the pair of differential input nodes, respectively;
- and
- a first group of two or more selectable current sources (e.g., 116) coupled to the first input node, wherein the first group selectably adjusts DC voltage at the first input node to compensate for DC offset between the pair of differential output nodes;
- and
- a second group of one or more selectable current sources (e.g., 116), different from the first group, coupled to the second input node, wherein the second group selectably adjusts DC voltage at the second input node to compensate for the DC offset between the pair of differential output nodes.
A method for compensating DC offset at a pair of differential output nodes of an amplifier, the method comprising:
- (a) monitoring outputs at the pair of differential output nodes to characterize DC offset corresponding to a configuration of a plurality of selectable current sources, the plurality of selectable current sources comprising:
- a first group of two or more selectable current sources coupled to a first differential input node of the amplifier;
- and
- a second group of one or more selectable current sources, different from the first group, coupled to a second differential input node of the amplifier;
- and
- (b) adjusting, based on the characterization in step (a), the configuration of the plurality of selectable current sources to reduce the DC offset.
A calibration system for a decision circuit comprising an amplifier having DC offset compensation, the amplifier comprising at least one input node, a pair of differential output nodes, and a DC offset compensation circuit responsive to a control signal to adjust a DC voltage at the input node to provide the DC offset compensation for the amplifier, wherein the offset compensation adjustment circuit comprises a plurality of selectable current sources, selected ones of the current sources being selected for coupling to the input node of the amplifier by the control signal to adjust the DC voltage at the input node to provide the DC offset compensation for the amplifier, the system comprising:
- an offset detection module having a pair of inputs corresponding to the output nodes, the offset detection module providing an offset detection output representative of the DC offset;
- and
- an offset compensation control module for providing the control signal to the offset compensation adjustment circuit for adjusting the DC offset, wherein the amplifier is formed in an integrated circuit and the offset compensation control module is external to the integrated circuit, wherein the control signal programs the DC offset into the integrated circuit.
Dependencies are inferred from the claim text.