# US 2021/0173085 A1 · Time of flight sensing system and image sensor used therein > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 2021/0173085 A1 - Document ID: US20210173085A1 - Status: Published application - Kind: A1 - Application number: 16/890,132 - Filed: 2020-06-02 - Published: 2021-06-10 - Earliest claimed: 2019-12-09 - Assignees: SK hynix Inc. - Applicants: SK hynix Inc. - Inventors: Yujin PARK; Sungwook SEO; Jeongeun SONG; Jinuk JEON; Ohjun KWON; Hansang KIM; Kangbong SEO; Minseok SHIN - Web page: https://patentgrep.com/patent/US20210173085A1 ## CPC - G01S 17/894: Three-dimensional [3D] imaging with simultaneous measurement of time-of-flight at a two-dimensional [2D] array of receiver pixels, e.g. time-of-flight cameras or flash lidar - G01S 7/48: of systems according to group G01S17/00 - G01S 7/4863: Detector arrays, e.g. charge-transfer gates - G01S 17/34: using transmission of continuous, frequency-modulated waves while heterodyning the received signal, or a signal derived therefrom, with a locally-generated signal related to the contemporaneously transmitted signal - G01S: RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES ## Abstract An image sensor employed in a time-of-flight (TOF) sensing system includes a pixel array including plural pixels, each pixel including at least one photo diode and each pixel generating an amount of charge corresponding to an incident light, comparing circuitry configured to compare voltage levels, each voltage level individually changed based on the amount of charge outputted from each pixel, with a reference voltage to output a comparison result, and calibration circuitry configured to adjust the voltage levels equally based on the comparison result. ## Claims ### Claim 1 An image sensor employed in a time-of-flight (TOF) sensing system, comprising: a pixel array including plural pixels, each pixel including at least one photo diode and each pixel generating an amount of charge corresponding to an incident light; comparing circuitry configured to compare voltage levels, each voltage level individually changed based on the amount of charge outputted from each pixel, with a reference voltage to output a comparison result; and calibration circuitry configured to adjust the voltage levels equally based on the comparison result. ### Claim 2 (depends on 1) The image sensor according to claim 1, wherein the calibration circuitry is configured to maintain a difference between the voltage levels when adjusting the voltage levels by a predetermined amount. ### Claim 3 (depends on 1) The image sensor according to claim 1, wherein the calibration circuitry is further configured to supply a preset amount of current into the pixel array. ### Claim 4 (depends on 1) The image sensor according to claim 1, wherein the pixel comprises: a reset gate coupled to the at least one photo diode and configured to reset the amount of charge in response to a reset signal; a transfer gate configured to output a pixel voltage based on the amount of charge in response to a modulation signal; an access gate configured to be turned on in response to the pixel voltage transferred from the transfer gate; and a select gate configured to selectively output a voltage outputted from the access gate in response to a selection signal. ### Claim 5 (depends on 4) The image sensor according to claim 4, wherein the calibration circuitry is further configured to: check a potential, varied based on the amount of charge, between the transfer gate and the at least one photo diode; and adjust the pixel voltage between the transfer gate and the access gate. ### Claim 6 (depends on 1) The image sensor according to claim 1, wherein the calibration circuitry includes a current source configured to supply a current to the pixel array for adjusting the voltage levels. ### Claim 7 (depends on 6) The image sensor according to claim 6, wherein the current resource comprises: a switching transistor coupled to each pixel and turned on in response to the comparison result; and a variable resistor coupled to a power supply and configured to determine an amount of the current. ### Claim 8 (depends on 1) The image sensor according to claim 1, wherein the plural pixels are arranged along a plurality of rows and a plurality of columns, and wherein the calibration circuitry controls pixels row by row. ### Claim 9 (depends on 1) The image sensor according to claim 1, further comprising current supply circuitry configured to determine an amount of current supplied by the calibration circuitry in response to a current control signal, wherein the current supply circuitry and the calibration circuitry works as a current mirror. ### Claim 10 (depends on 9) The image sensor according to claim 9, wherein the calibration circuitry is configured to increase the voltage levels by a predetermined amount, and wherein the predetermined amount is proportional to the amount of current and inversely proportional to a driving frequency of each pixel. ### Claim 11 A time-of-flight (TOF) sensing system, comprising: an emitter configured to output a modulated signal having a preset phase; a receiver including an image sensor configured to receive a reflected signal which is reflected from a target; and signal processing circuitry configured to determine a distance from the target based on a phase relationship between the modulated light and the reflected light, wherein the image sensor comprises: a pixel array including plural pixels, each pixel including at least one photo diode and each pixel generating an amount of charge corresponding to the reflected light; comparing circuitry configured to compare voltage levels, each voltage level individually changed based on the amount of charge outputted from each pixel, with a reference voltage to output a comparison result; and calibration circuitry configured to adjust the voltage levels equally based on the comparison result. ### Claim 12 (depends on 11) The TOF sensing system according to claim 11, wherein the calibration circuitry is configured to maintain a difference between the voltage levels when adjusting the voltage levels by a predetermined amount. ### Claim 13 (depends on 11) The TOF sensing system according to claim 11, wherein the calibration circuitry is further configured to supply a preset amount of current into the pixel array. ### Claim 14 (depends on 11) The TOF sensing system according to claim 11, wherein the pixel comprises: a reset gate coupled to the at least one photo diode and configured to reset the amount of charge in response to a reset signal; a transfer gate configured to output a pixel voltage based on the amount of charge in response to a modulation signal; an access gate configured to be turned on in response to the pixel voltage transferred from the transfer gate; and a select gate configured to selectively output a voltage outputted from the access gate in response to a selection signal. ### Claim 15 (depends on 14) The TOF sensing system according to claim 14, wherein the calibration circuitry is further configured to: check a potential, varied based on the amount of charge, between the transfer gate and the at least one photo diode; and adjust the pixel voltage between the transfer gate and the access gate. ### Claim 16 (depends on 11) The TOF sensing system according to claim 11, wherein the calibration circuitry includes a current source configured to supply a current to the pixel array for adjusting the voltage levels. ### Claim 17 (depends on 16) The TOF sensing system according to claim 16, wherein the current resource comprises: a switching transistor coupled to each pixel and turned on in response to the comparison result; and a variable resistor coupled to a power supply and configured to determine an amount of the current. ### Claim 18 (depends on 11) The TOF sensing system according to claim 11, wherein the plural pixels are arranged along a plurality of rows and a plurality of columns, and wherein the calibration circuitry controls pixels row by row. ### Claim 19 (depends on 11) The TOF sensing system according to claim 11, further comprising a current supply circuitry configured to determine an amount of current supplied by the calibration circuitry in response to a current control signal, wherein the current supply circuitry and the calibration circuitry works as a current mirror. ### Claim 20 (depends on 19) The TOF sensing system according to claim 19, wherein the calibration circuitry is configured to increase the voltage levels by a predetermined amount, and wherein the predetermined amount is proportional to the amount of current and inversely proportional to a driving frequency of each pixel.