Amplifier with common mode loop and chop

A fully differential amplifier circuit comprising:

• a class D amplifier configured to receive an input differential mode voltage and output an output differential mode voltage based on an input common mode voltage;
• a first feedback resistor connected between a positive output of the class D amplifier and a negative input of the class D amplifier;
• a second feedback resistor connected between a negative output of the class D amplifier and a positive input of the class D amplifier;
• a first input resistor connected to the first feedback resistor and the negative input of the class D amplifier;
• and
• a second input resistor connected to the second feedback resistor and the positive input of the class D amplifier, a local feedback loop forcing a common mode voltage at the positive input and the negative input of the class D amplifier to be equal to a constant voltage that is independent of a power supply voltage of the fully differential amplifier circuit, the output differential mode voltage being based on a mismatch between the first feedback resistor and the second feedback resistor.

A method comprising:

• receiving, by an amplifier including a positive input and a negative input, an input differential mode voltage based on an input common mode voltage;
• controlling, by a local feedback loop, the input differential mode voltage, the controlling including:
• switching, by chopper switches, a higher value current between the positive input and the negative input;
• and
• based on the switching, equalizing a current flow into the positive input of the amplifier to a current flow into the negative input of the amplifier;
• and
• based on the controlling of the input differential mode voltage received by the amplifier, outputting, by the amplifier, an output differential mode voltage that is independent of a power supply voltage for the amplifier.

A system comprising:

• a fully differential amplifier circuit including a class D amplifier, a first feedback path, and a second feedback path, the first feedback path providing a feedback path from a positive output of the class D amplifier to a negative input of the class D amplifier and the second feedback path providing a feedback path from a negative output of the class D amplifier to a positive input of the class D amplifier;
• a chopper clock circuit configured to output a chopper clock signal at a variable duty cycle;
• first chopper switches configured to receive the chopper clock signal, the first chopper switches:
• being coupled with the positive input of the class D amplifier and the negative input of the class D amplifier;
• and
• based on the chopper clock signal, filtering respective signals applied to the positive input of the class D amplifier and the negative input of the class D amplifier;
• and
• second chopper switches configured to receive the chopper clock signal, the second chopper switches:
• being coupled with the positive output of the class D amplifier and the negative output of the class D amplifier;
• and
• based on the chopper clock signal, control respective polarities of an output signal of positive output of the class D amplifier and the negative output of the class D amplifier.