Common-mode feedback for differential amplifier

A method, comprising:

• detecting a common-mode output voltage at a first output terminal and a second output terminal of an operational amplifier;
• attenuating the common-mode output voltage according to a voltage division to produce an attenuated common-mode output voltage;
• generating a control signal based on a comparison of the attenuated common-mode output voltage with a reference voltage generated according to the voltage division;
• and
• providing the control signal to the operational amplifier, wherein the operational amplifier is configured to vary the common-mode output voltage based on the control signal, wherein the operation amplifier comprises a high-gain fully differential stage and a low-gain fully differential stage, wherein the high-gain fully differential stage comprises an inverting output and a non-inverting output, wherein the low-gain fully differential stage comprises a non-inverting input and an inverting input, wherein the inverting output of the high-gain fully differential stage is tied to the non-inverting input of the low-gain fully differential stage without intervening circuitry, and wherein the non-inverting output of the high-gain fully differential stage is tied to the inverting input of the low-gain fully differential stage without intervening circuitry.

A circuit, comprising:

• a differential amplifier having a first output terminal and a second output terminal, the differential amplifier having a first stage configured to receive an input voltage, and a second stage configured to amplify an output of the first stage and generate an output signal at the first output terminal and the second output terminal of the differential amplifier;
• a common-mode detector coupled between the first output terminal and the second output terminal, the common-mode detector configured to detect a common-mode output voltage of the output signal at a first pair of input terminals of the common-mode detector;
• an impedance element coupled between an output node of the common-mode detector and a supply voltage;
• and
• an error amplifier having a first terminal coupled to the output node of the common-mode detector, the error amplifier configured to receive a reference voltage at a second terminal of the error amplifier, wherein the error amplifier is further configured to provide a control signal to the first stage of the differential amplifier based on a difference between the reference voltage and a voltage at the output node of the common-mode detector, wherein the first stage of the differential amplifier comprises an inverting output and a non-inverting output, wherein the second stage of the differential amplifier comprises a non-inverting input and an inverting input, wherein the inverting output of the first stage of the differential amplifier is tied to the non-inverting input of the second stage of the differential amplifier without intervening circuitry, and wherein the non-inverting output of the first stage of the differential amplifier is tied to the inverting input of the second stage of the differential amplifier without intervening circuitry.