Differential amplifier with modified common mode rejection, and to a circuit with an improved common mode rejection ratio
AssigneeAnalog Devices Global
InventorJonathan Ephraim David Hurwitz
Life of this patent
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Abstract
An amplifier circuit having improved common mode rejection is provided. This can be achieved by estimating the common mode value of an input signal and using this to adjust a target common mode voltage at the output of the amplifier. This can help avoid the differential gain becoming modified by the common mode voltage.
Claims20
A fedback defined differential amplifier comprising:
- an impedance network coupled to a gain block, wherein a gain of the differential amplifier is set by the impedance network coupled to the gain block;
- and
- a target output common mode voltage input node of the gain block configured to receive, via a feed forward path, an input signal to set a target common mode output voltage of the differential amplifier, wherein the gain block is configured to generate a common mode voltage at an output of the differential amplifier as a function of the received input signal that represents a common mode signal at differential inputs of the differential amplifier, and wherein the target common mode output voltage is configured to track changes in the common mode signal at the differential inputs.
A method of improving the common mode rejection performance of a feedback defined differential amplifier having an impedance network coupled to a gain block and having a control node for controlling a target common mode output voltage of a differential output of the differential amplifier, wherein a gain of the differential amplifier is set by the impedance network coupled to the gain block, the method comprising:
- feeding forward a control signal to the target common mode voltage control node of the gain block to set the target common mode output voltage of the differential amplifier;
- and
- generating a common mode voltage at the output of the differential amplifier as a function of the control signal that represents a common mode signal at differential inputs of the differential amplifier,
- wherein the target common mode output voltage is configured to track changes in the common mode signal at the differential inputs.
A feedback defined differential amplifier comprising:
- an impedance network coupled to a gain block, wherein a gain of the differential amplifier is set by the impedance network coupled to the gain block;
- and
- a target output common mode voltage input node of the gain block configured to receive, via a feed forward path, an input signal to set a target common mode output voltage of the differential amplifier;
- and
- means for generating a common mode voltage an output of the differential amplifier as a function of the received input signal that represents a common mode signal at differential inputs of the differential amplifier,
- wherein the target common mode voltage is configured to track changes in the common mode signal at the differential inputs.
Dependencies are inferred from the claim text.