# US 12,007,432 B2 · Enhanced direct current (DC) built-in-self-test (BIST) coverage for optical engines and advanced packaging > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 12,007,432 B2 - Document ID: US12007432B2 - Status: Granted - Kind: B2 - Application number: 17/813,203 - Filed: 2022-07-18 - Published: 2024-01-18 - Granted: 2024-06-11 - Earliest claimed: 2022-07-18 - Assignees: Cisco Technology, Inc. - Applicants: Cisco Technology, Inc. - Inventors: Sanjay Sunder; Alexander C. Kurylak - Web page: https://patentgrep.com/patent/US12007432B2 ## CPC - G01R 31/2853: {Electrical testing of internal connections or -isolation, e.g. latch-up or chip-to-lead connections (G01R31/31717 takes precedence; test of chip-to-PCB or lead-to-PCB connections G01R31/66)} - G01R 31/311: of integrated circuits {(G01R31/31728 takes precedence)} - G01R 31/2856: {Internal circuit aspects, e.g. built-in test features; Test chips; Measuring material aspects, e.g. electro migration [EM]} - G01R 31/31717: {Interconnect testing (by scan techniques see G01R31/31855)} - G01R 31/31728: {Optical aspects, e.g. opto-electronics used for testing, optical signal transmission for testing electronic circuits, electro-optic components to be tested in combination with electronic circuits, measuring light emission of digital circuits (probes having electro-optic elements G01R1/071; electro-optic sampling for oscilloscopes G01R13/347; contactless testing of individual semiconductor devices by optical means G01R31/2656)} - G01R: MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES (indicating correct tuning of resonant circuits H03J3/12) ## Abstract Techniques for testing connectivity between a first integrated circuit (IC) and a second IC of an electronics package are described. An example technique involves controlling a switch(es) in the first IC to configure a bias direction of a photodiode of the second IC to forward biased. A connectivity test between the first and second ICs is performed, when the photodiode is forward biased. Another technique involves controlling a switch(es) in the first IC to configure a bias direction of a photodiode in the second IC to reverse biased. A first voltage is measured at an input of a transimpedance amplifier (TIA) in the first IC when the photodiode is reverse biased. The switch(es) are controlled to change the bias direction of the photodiode to forward biased. A second voltage is measured at the input of the TIA when the photodiode is forward biased. ## Claims ### Claim 1 A method for testing connectivity between a first integrated circuit (IC) and a second IC of an electronics package, the method comprising: determining a measure of connectivity between the first IC and a photodiode in the second IC when a bias direction of the photodiode is forward biased, wherein determining the measure of connectivity comprises measuring a current flow through the photodiode when the bias direction of the photodiode is forward biased; and determining whether there is a fault with at least one of the first IC or the second IC based on the measured current flow. ### Claim 2 (depends on 1) The method of claim 1, wherein the bias direction of the photodiode is forward biased when a switch in the first IC and coupled to a cathode of the photodiode is coupled to a reference potential node. ### Claim 3 (depends on 1) The method of claim 1, wherein: the bias direction of the photodiode is reverse biased when the first IC is in a first operation mode for measuring optical power incident on the photodiode in reverse bias; and the bias direction of the photodiode is forward biased when the first IC is in a second operation mode for measuring connectivity between the first IC and the second IC. ### Claim 4 (depends on 1) The method of claim 1, further comprising determining there is a fault when the measured current flow is below a threshold. ### Claim 5 (depends on 1) The method of claim 1, further comprising determining there is not a fault when the measured current flow is above a threshold. ### Claim 6 (depends on 1) The method of claim 1, wherein the measure of connectivity is determined via a built-in-self test and without use of an optical assembly. ### Claim 7 (depends on 1) The method of claim 1, wherein the measure of connectivity is determined during at least one manufacturing stage of the electronics package. ### Claim 8 An apparatus comprising: a first integrated circuit (IC) comprising measurement circuitry; and a second IC electrically coupled to the first IC and comprising a photodiode, wherein the measurement circuitry is adapted to: determine a measure of connectivity between the first IC and the photodiode in the second IC when a bias direction of the photodiode is forward biased, wherein, to determine the measure of connectivity, the measurement circuitry is adapted to measure a current flow through the photodiode when the bias direction of the photodiode is forward biased; and determine whether there is a fault with at least one of the first IC or the second IC based on the measured current flow. ### Claim 9 (depends on 8) The apparatus of claim 8, wherein the bias direction of the photodiode is forward biased when a switch in the first IC and coupled to a cathode of the photodiode is coupled to a reference potential node. ### Claim 10 (depends on 8) The apparatus of claim 8, wherein: the bias direction of the photodiode is reverse biased when the first IC is in a first operation mode for measuring optical power incident on the photodiode in reverse bias; and the bias direction of the photodiode is forward biased when the first IC is in a second operation mode for measuring connectivity between the first IC and the second IC. ### Claim 11 (depends on 8) The apparatus of claim 8, wherein the measurement circuitry is further adapted to determine there is a fault when the measured current flow is below a threshold. ### Claim 12 (depends on 8) The apparatus of claim 8, wherein the measurement circuitry is further adapted to determine there is not a fault when the measured current flow is above a threshold. ### Claim 13 (depends on 8) The apparatus of claim 8, wherein the measure of connectivity is determined via a built-in-self test and without use of an optical assembly. ### Claim 14 An electronics package comprising: a photonics integrated circuit (IC) comprising a photodiode; and an electrical IC disposed on the photonics IC and comprising measurement circuitry adapted to: determine a measure of connectivity between the electrical IC and the photodiode in the photonics IC when a bias direction of the photodiode is forward biased, wherein, to determine the measure of connectivity, the measurement circuitry is adapted to measure a current flow through the photodiode when the bias direction of the photodiode is forward biased; and determine whether there is a fault with at least one of the electrical IC or the photonics IC based on the measured current flow. ### Claim 15 (depends on 14) The electronics package of claim 14, wherein the bias direction of the photodiode is forward biased when a switch in the electrical IC and coupled to a cathode of the photodiode is coupled to a reference potential node. ### Claim 16 (depends on 14) The electronics package of claim 14, wherein: the bias direction of the photodiode is reverse biased when the electrical IC is in a first operation mode for measuring optical power incident on the photodiode in reverse bias; and the bias direction of the photodiode is forward biased when the electrical IC is in a second operation mode for measuring connectivity between the electrical IC and the photonics IC. ### Claim 17 (depends on 14) The electronics package of claim 14, wherein the measurement circuitry is further adapted to determine there is a fault when the measured current flow is below a threshold. ### Claim 18 (depends on 14) The electronics package of claim 14, wherein the measurement circuitry is further adapted to determine there is not a fault when the measured current flow is above a threshold. ### Claim 19 (depends on 14) The electronics package of claim 14, wherein the measurement circuitry is adapted to determine the measure of connectivity without use of an optical assembly. ### Claim 20 (depends on 14) The electronics package of claim 14, wherein the measurement circuitry is adapted to determine the measure of connectivity during at least one manufacturing stage of the electronics package.