Common-mode current adjustment in a receiver

A receiver, comprising:

• a photodetector to receive a PAM4 optical signal and generate an input photocurrent;
• a common-mode adjustment circuit coupled to the photodetector to receive the input photocurrent and to generate an adjusted input current by reducing a common-mode current from the input photocurrent;
• an analog front-end (AFE) coupled to the common-mode adjustment circuit, wherein the AFE generates a differential voltage based on the adjusted input current, wherein the AFE comprises:
• a current-to-voltage converter coupled to the common-mode adjustment circuit to receive the adjusted input current and generate a single-ended voltage;
• and
• a differential voltage generator coupled to the current-to-voltage converter to receive the single-ended voltage and generate the differential voltage by removing an average voltage of the single-ended voltage from the single-ended voltage;
• an eye scan circuit coupled to the AFE to generate eye scan information based on the differential voltage, wherein the eye scan information defines a first outer eye and a second outer eye in an eye diagram;
• and
• a control unit coupled to the eye scan circuit and the common-mode adjustment circuit, wherein the control unit tunes the common-mode adjustment circuit based on a height difference between a first height of the first outer eye and a second height of the second outer eye to remove a portion of the common-mode current from the input photocurrent.

An electronic system, comprising:

• a circuit board;
• a processing resource mounted on the circuit board;
• a storage medium mounted on the circuit board and communicatively coupled to the processing resource;
• and
• a receiver communicatively coupled to the processing resource and comprising:
• a photodetector to receive a PAM4 optical signal and generate an input photocurrent;
• a common-mode adjustment circuit coupled to the photodetector to receive the input photocurrent and to generate an adjusted input current by reducing a common-mode current from the input photocurrent;
• an AFE coupled to the common-mode adjustment circuit, wherein the AFE generates a differential voltage based on the adjusted input current, wherein the AFE comprises:
• a current-to-voltage converter coupled to the common-mode adjustment circuit to receive the adjusted input current and generate a single-ended voltage;
• and
• a differential voltage generator coupled to the current-to-voltage converter to receive the single-ended voltage and generate the differential voltage by removing an average voltage of the single-ended voltage from the single-ended voltage;
• an eye scan circuit coupled to the AFE to generate eye scan information based on the differential voltage, wherein the eye scan information defines a first outer eye and a second outer eye in an eye diagram;
• and
• a control unit coupled to the eye scan circuit and the common-mode adjustment circuit, wherein the control unit tunes the common-mode adjustment circuit based on a height ratio of a first height of the first outer eye and a second height of the second outer eye to remove a portion of the common-mode current from the input photocurrent based.