# US 11,994,425 B2 · Optical sensor and apparatus comprising an optical sensor > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 11,994,425 B2 - Document ID: US11994425B2 - Status: Granted - Kind: B2 - Application number: 18/370,637 - Filed: 2023-09-20 - Published: 2024-01-11 - Granted: 2024-05-28 - Earliest claimed: 2019-01-16 - Assignees: STMicroelectronics (Research & Development) Limited; STMicroelectronics (Grenoble 2) SAS - Applicants: STMicroelectronics (Research & Development) Limited; STMicroelectronics (Grenoble 2) SAS - Inventors: Jeffrey M. Raynor; Sophie Taupin; Jean-Jacques Rouger; Pascal Mellot - Web page: https://patentgrep.com/patent/US11994425B2 ## CPC - G01J 1/0214: {Constructional arrangements for removing stray light} - G01J 1/4204: {with determination of ambient light (solar light G01J2001/4266)} - G01J 1/44: Electric circuits {(for command of an exposure part G03B7/02)} - G01J 3/0262: {Constructional arrangements for removing stray light} - H04N 25/57: Control of the dynamic range - H04N 25/77: Pixel circuitry, e.g. memories, A/D converters, pixel amplifiers, shared circuits or shared components - H04N 25/772: comprising A/D, V/T, V/F, I/T or I/F converters - H04N 25/773: comprising photon counting circuits, e.g. single photon detection [SPD] or single photon avalanche diodes [SPAD] - H10F 39/103: {the at least one element covered by H10F30/00 having potential barriers, e.g. integrated devices comprising photodiodes or phototransistors} - H10F 39/107: {having multiple elements covered by H10F30/00 in a repetitive configuration, e.g. radiation detectors comprising photodiode arrays} - H10F 77/953: {for devices having potential barriers} - H10W 42/00: Arrangements for protection of devices (arrangements for thermal protection H10W40/00) - G01J 2001/446: {Photodiode} - G01J 2001/448: {Array [CCD]} - G01J: MEASUREMENT OF INTENSITY, VELOCITY, SPECTRAL CONTENT, POLARISATION, PHASE OR PULSE CHARACTERISTICS OF INFRARED, VISIBLE OR ULTRAVIOLET LIGHT; COLORIMETRY; RADIATION PYROMETRY (light sources F21, H01J, H01K, H05B; investigating properties of materials by optical means G01N) - H04N: PICTORIAL COMMUNICATION, e.g. TELEVISION - H10F: INORGANIC SEMICONDUCTOR DEVICES SENSITIVE TO INFRARED RADIATION, LIGHT, ELECTROMAGNETIC RADIATION OF SHORTER WAVELENGTH OR CORPUSCULAR RADIATION - H10W: GENERIC PACKAGES, INTERCONNECTIONS, CONNECTORS OR OTHER CONSTRUCTIONAL DETAILS OF DEVICES COVERED BY CLASS H10 ## Abstract An optical sensor includes pixels. Each pixel has a photodetector. A readout circuit performs a process over an exposure time where the photodetector is connected to a reverse bias voltage supply to reset a voltage across the photodetector, and the photodetector is disconnected from the reverse bias voltage supply until that the voltage across the photodetector decreases in response to received ambient light. An ambient light level is then determine an based on a number of times the voltage across the photodetector is reset over the exposure time. ## Claims ### Claim 1 An ambient light sensor, comprising: a plurality of pixels; wherein each pixel comprises a photodetector; and a readout circuit configured to determine an ambient light level, said readout circuit comprising: a reset transistor coupled between a reset voltage node and the photodetector; a source-follower transistor having a control terminal coupled to the photodetector and an output terminal configured to provide a photodetector voltage; a comparator having a first input configured to receive the photodetector voltage and a second input configured to receive a threshold voltage, wherein the comparator is configured to assert a reset signal applied to a control terminal of the reset transistor; and a first counter circuit having an input configured to receive the reset signal, said counter circuit configured to count a number of times the reset signal is asserted over an exposure time, wherein the number of times counted is indicative of the ambient light level. ### Claim 2 (depends on 1) The ambient light sensor of claim 1, further comprising a second counter reset in response to beginning of the exposure time and configured to count a number of pulses of a clock signal, where a combination of the number of times counted by the first counter and the number of pulses counted by the second counter is indicative of the ambient light level. ### Claim 3 (depends on 2) The ambient light sensor of claim 2, wherein the second counter is configured to inhibit counting of the pulses of a clock signal for a duration of time in response to each assertion of the reset signal. ### Claim 4 (depends on 2) The ambient light sensor of claim 2, further comprising a combiner circuit configured to combine the number of times (Coarse value) counted by the first counter and the number of pulses (Fine value) counted by the second counter to generate a combined value (COM) in accordance with the following formula: C ⁢ O ⁢ M = Coarse ⁢ value × Fine ⁢ value Fine ⁢ value ⁢ when ⁢ Coarse ⁢ value ⁢ was last ⁢ incremented . ### Claim 5 (depends on 4) The ambient light sensor of claim 4, further comprising a conversion of the combined value (COM) to a Lux value indicating the ambient light level. ### Claim 6 (depends on 1) The ambient light sensor of claim 1, wherein each pixel further comprises a guard ring around the photodetector. ### Claim 7 (depends on 6) The ambient light sensor of claim 6, wherein the photodetector and the guard ring are dimensioned so that a fill factor of the pixel is less than or equal to 50%. ### Claim 8 (depends on 7) The ambient light sensor of claim 7, wherein the photodetector and the guard ring are dimensioned so that the fill factor of the pixel is greater than or equal to 33%. ### Claim 9 (depends on 6) The ambient light sensor of claim 6, wherein the plurality of pixels are part of a one dimensional array of pixels aligned along a first direction and wherein a width of the guard ring along the first direction is greater than a width of the guard ring along a second direction perpendicular to the first direction. ### Claim 10 (depends on 6) The ambient light sensor of claim 6, wherein the plurality of pixels are part of a two dimensional array of pixels aligned along a first direction and a second direction perpendicular to the first direction, and wherein a width of the guard ring along the first direction is equal to a width of the guard ring along the second direction. ### Claim 11 (depends on 6) The ambient light sensor of claim 6, wherein each pixel comprises a band pass filter arranged over the photodetector. ### Claim 12 (depends on 11) The ambient light sensor of claim 11, wherein the band pass filter is arranged over the guard ring. ### Claim 13 (depends on 6) The ambient light sensor of claim 6, wherein each pixel comprises an optically reflective coating arranged over the guard ring.