# US 12,003,279 B2 · Common-mode current adjustment in a receiver > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 12,003,279 B2 - Document ID: US12003279B2 - Status: Granted - Kind: B2 - Application number: 17/694,866 - Filed: 2022-03-15 - Published: 2023-09-21 - Granted: 2024-06-04 - Earliest claimed: 2022-03-15 - Assignees: Hewlett Packard Enterprise Development LP - Applicants: Hewlett Packard Enterprise Development LP - Inventors: David Ritter Thomas; Laurel Abeyta; Jason Douglas Jung; Kit Maccarthy Morton; Daniel Alan Berkram - Web page: https://patentgrep.com/patent/US12003279B2 ## CPC - H04B 10/07953: {Monitoring or measuring OSNR, BER or Q} - H04B 10/697: {Arrangements for reducing noise and distortion} - H04B 10/524: Pulse modulation - H04B 10/691: {Arrangements for optimizing the photodetector in the receiver} - H04B: TRANSMISSION ## Abstract Examples described herein relate to a method and a system for removing the common-mode current. The receiver includes a photodetector, a common-mode adjustment circuit, an analog front-end, an eye scan circuit, and a control unit. The photodetector generates an input photocurrent responsive to a received optical signal. The common-mode adjustment circuit generates an adjusted input current based on the input photocurrent. The analog front-end generates a differential voltage based on the adjusted input current. Based on the differential voltage, the eye scan circuit generates an eye scan information defining a first outer eye and a second outer eye in an eye diagram. The control unit tunes the common-mode adjustment circuit based on a relative height metric 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. ## Claims ### Claim 1 A method, comprising: determining, by a control unit, a first height of a first outer eye and a second height of a second outer eye based on eye scan information defining at least three eyes in an eye diagram, wherein the eye scan information is based on an input photocurrent generated by a photodetector in an optoelectronic receiver based on a received multi-level pulse amplitude modulated (PAM) data signal, wherein the input photocurrent comprises a common-mode current that is controlled by a common-mode adjustment circuit disposed in the optoelectronic receiver and coupled to the photodetector and the control unit; generating a differential voltage based on an adjusted input current, by: receiving the adjusted input current and generating a single-ended voltage; and receiving the single-ended voltage and generating the differential voltage by removing an average voltage of the single-ended voltage from the single-ended voltage; determining, by the control unit, whether a relative height metric based on the first height and the second height is greater than a threshold value; in response to determining that the relative height metric is greater than the threshold value: updating, by the control unit, a common-mode calibration value based on the first height and the second height; and tuning, by the control unit, the common-mode adjustment circuit to remove a portion of the common-mode current from the input photocurrent based on the common-mode calibration value. ### Claim 2 (depends on 1) The method of claim 1, further comprising repeating the steps of determining the first height and the second height, determining whether the relative height metric is greater than the threshold value, updating the common-mode calibration value, and tuning the common-mode adjustment circuit until the relative height metric becomes smaller than or equal to the threshold value. ### Claim 3 (depends on 1) The method of claim 1, wherein the multi-level PAM optical signal is a PAM four-level (PAM4) optical signal. ### Claim 4 (depends on 1) The method of claim 1, wherein the first outer eye and the second outer eye are the outermost eyes in the eye diagram. ### Claim 5 (depends on 1) The method of claim 1, wherein the eye scan information is generated based on the differential voltage, wherein the differential voltage is generated based on an adjusted input current. ### Claim 6 (depends on 1) The method of claim 1, wherein updating the common-mode calibration value comprises increasing the common-mode calibration value by a predetermined amount in response to determining that the first height is smaller than the second height. ### Claim 7 (depends on 1) The method of claim 1, further comprising determining whether the first height is greater than the second height, wherein updating the common-mode calibration value comprises decreasing the common-mode calibration value by a predetermined amount in response to determining that the first height is greater than the second height. ### Claim 8 (depends on 1) The method of claim 1, wherein the relative height metric is a difference between the first height and the second height, and wherein the threshold value is a threshold height difference. ### Claim 9 (depends on 1) The method of claim 1, wherein the relative height metric is a ratio of the first height and the second height, and wherein the threshold value is a threshold ratio. ### Claim 10 (depends on 1) The method of claim 1, wherein removal of the portion of the common-mode current from the input photocurrent causes a reduction in a bit error rate of the optoelectronic receiver. ### Claim 11 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. ### Claim 12 (depends on 11) The receiver of claim 11, wherein the control unit: determines whether the height difference is greater than a threshold height difference; and updates a common-mode calibration value based on the first height and the second height in response to determining that height difference is greater than the threshold height difference, wherein the control unit tunes the common-mode adjustment circuit to remove the common-mode current from the input photocurrent based on the common-mode calibration value. ### Claim 13 (depends on 12) The receiver of claim 12, wherein the control unit: determines whether the first height is smaller than or equal to the second height; and increases the common-mode calibration value by a predetermined amount in response to determining that the first height is smaller than or equal to the second height. ### Claim 14 (depends on 12) The receiver of claim 12, wherein the control unit: determines whether the first height is greater than the second height; and decreases the common-mode calibration value by a predetermined amount in response to determining that the first height is greater than the second height. ### Claim 15 (depends on 11) The receiver of claim 11, wherein the control unit tunes the common-mode adjustment circuit to remove the common-mode current such that the adjusted input current is maintained within an input operating range of the current-to-voltage converter. ### Claim 16 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. ### Claim 17 (depends on 16) The electronic system of claim 16, wherein the control unit: determines whether the height ratio is greater than a threshold ratio; and updates a common-mode calibration value based on the first height and the second height in response to determining that the height ratio is greater than the threshold ratio, wherein the control unit tunes the common-mode adjustment circuit to remove the common-mode current from the input photocurrent based on the common-mode calibration value. ### Claim 18 (depends on 17) The electronic system of claim 17, wherein the control unit: determines whether the first height is smaller than or equal to the second height; and increases the common-mode calibration value by a predetermined amount in response to determining that the first height is smaller than or equal to the second height, or decreases the common-mode calibration value by a predetermined amount in response to determining that the first height is greater than the second height.