Common mode feedback circuit with backgate control
AssigneeAnalog Devices, Inc.
InventorsDaniel F. KELLY, Franklin M. MURDEN, Daniel REY-LOSADA
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Abstract
A common mode feedback (CMFB) loop for a differential amplifier sense an output common mode of a differential circuit and provides feedback to the gates of tail current transistors. Many CMFB loops cannot easily adjust the output common mode voltage and the output common mode may vary over process, voltage, and temperature. An improved CMFB circuit adds a control circuit to control backgates of tail current transistor device(s) of the differential circuit such that the output common mode voltage can be made adjustable.
Claims20
A differential amplifier having common mode feedback and backgate control, comprising:
- differential pair of transistors whose gates receive a differential input voltage;
- tail current transistors whose drains are connected to respective sources of the differential pair of transistors and gates are coupled to differential output nodes of the differential amplifier;
- and
- a control circuit controlling backgates of the tail current transistors.
A method for common mode feedback and backgate control for a differential amplifier, the method comprising:
- receiving common mode feedback of differential output nodes of the differential amplifier;
- and
- driving one or more backgates of one or more tail current transistors of the differential amplifier based on the common mode feedback and a target output common mode voltage.
An apparatus comprising:
- a differential amplifier;
- means for generating common mode feedback from differential output nodes of the differential amplifier;
- and
- control means coupled to backgates of tail current transistors for varying an output common mode voltage of the differential amplifier based on the common mode feedback.
Dependencies are inferred from the claim text.