Common mode feedback circuit with backgate control
AssigneeAnalog Devices, Inc.
InventorsDaniel F. Kelly, Franklin M. Murden, Daniel Rey-Losada
Life of this patent
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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 to sense an output common mode voltage of the differential amplifier and to control backgates of the tail current transistors based on the sensed output common mode voltage.
A method for common mode feedback and backgate control for a differential amplifier, the method comprising:
- sensing output common mode voltage of differential output nodes of the differential amplifier;
- receiving the sensed output common mode voltage as feedback;
- and
- controlling a backgate of a tail current transistor of the differential amplifier based on the sensed output common mode voltage to drive the sensed output common mode voltage to match a target output common mode voltage.
An apparatus comprising:
- a differential amplifier;
- means for sensing an output common mode voltage of the differential amplifier;
- means for providing the sensed output common mode voltage as feedback to control means;
- and
- the control means coupled to backgates of tail current devices for varying an output common mode voltage of the differential amplifier based on the sensed output common mode voltage.
Dependencies are inferred from the claim text.