Common-mode control for AC-coupled receivers

A receiver circuit, comprising:

• an alternate current (AC)-coupling network coupled to two input nodes, the AC-coupling network configured to filter an input signal and including:
• a resistor-capacitor (RC) network coupled to the two input nodes, the RC network including:
• a first arm connecting a first input node to a first common node, the first arm comprising a first capacitor characterized by a first capacitance and a first resistor characterized by a first resistance, the first capacitor and the first resistor connected in series at a first connection node;
• and
• a second arm connecting a second input node to the first common node, the second arm comprising a second capacitor characterized by the first capacitance and a second resistor characterized by the first resistance, the second capacitor and the second resistor connected in series at a second connection node;
• a first differential amplifier coupled to the RC network and configured to receive a filtered input signal from the AC-coupling network and generate an output signal, the first differential amplifier including:
• a differential pair of transistors including:
• a first transistor comprising a first gate connecting to the first arm at the first connection node;
• and
• a second transistor comprising a second gate connecting to the second arm at the second connection node;
• a common-mode measurement network, coupled to source terminals of the first and the second transistors, and configured to measure a common-mode voltage of the source terminals of the first and the second transistors;
• and
• a first operational amplifier coupled to the AC-coupling network and to the common-mode measurement network, the first operational amplifier configured to provide a feedback to the AC-coupling network at the first common node such that the common-mode voltage of the source terminals of the first and second transistors of the differential pair of transistors tracks a reference voltage, the first operational amplifier comprising:
• a non-inverting input terminal configured to receive the reference voltage;
• an inverting input terminal connecting to a second common node of the common-mode measurement network;
• and
• an output terminal connecting to the first common node of the AC-coupling network.