Feedback loop for direct current (DC) offset removal

An apparatus, comprising:

• an input node configured to receive an input signal, wherein the input node comprises a microphone input, and wherein the input signal is an audio input signal;
• an amplifier comprising a first amplifier input node, a second amplifier input node, and an amplifier output node, wherein the first amplifier input node is coupled to the input node;
• a feedback loop coupled to the second amplifier input, wherein the feedback loop is configured to adjust a first common mode of the input signal to control a second common mode of an output signal at the amplifier output node;
• and
• an analog-to-digital converter (ADC) coupled to the amplifier output node, wherein the first common mode is a common mode of the microphone input, and wherein the second common mode is a common mode of the analog-to-digital (ADC) converter,
• wherein the feedback loop comprises a mixed-signal servo loop and wherein the feedback loop is configured to:
• perform digital loop tracking through a digital low-pass filter (LPF) and a digital integrator;
• and
• perform analog loop tracking through the digital low-pass filter (LPF), the digital integrator, a direct current (DC) modulator, and the digital-to-analog converter (DAC).

A method, comprising:

• receiving an input signal at an input node;
• amplifying the input signal to generate an output signal by applying the input signal to a first amplifier input node of an amplifier;
• and
• adjusting a first common mode of the input signal to a second common mode of the output signal during the step of amplifying the input signal, wherein the step of adjusting comprises feeding back a feedback signal through a mixed-signal servo loop from an output of the amplifier to a second amplifier input node of the amplifier, and wherein the step of feeding back comprises:
• performing digital loop tracking through a digital low-pass filter (LPF) and a digital integrator;
• and
• performing analog loop tracking through the digital low-pass filter (LPF), the digital integrator, a direct current (DC) modulator, and a digital-to-analog converter (DAC).