# US 7,608,815 B2 · Photo detector with compensated output and method involving same > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 7,608,815 B2 - Document ID: US7608815B2 - Status: Granted - Kind: B2 - Application number: 11/476,498 - Filed: 2006-06-28 - Published: 2007-01-04 - Granted: 2009-10-27 - Earliest claimed: 2005-06-30 - Assignees: Streetlight Intelligence, Inc. - Inventors: Pratibha Sharma; Gerald E. Kurz; Yong Jeong Cho; James A. Anderson; J. David T. Anderson; Gregory A. Jacklin - Web page: https://patentgrep.com/patent/US7608815B2 ## CPC - H10F 77/953: {for devices having potential barriers} - H10F: INORGANIC SEMICONDUCTOR DEVICES SENSITIVE TO INFRARED RADIATION, LIGHT, ELECTROMAGNETIC RADIATION OF SHORTER WAVELENGTH OR CORPUSCULAR RADIATION ## Abstract A method of compensating a photo sensor (and a corresponding photo sensor with compensation) insures the accuracy of the photo sensor, e.g., over environmental variations or photo cell variations. The method comprises: providing a first signal indicative of a light level; providing a second signal indicative of an environmental parameter, e.g., temperature; and calculating, responsive to the first signal and the second signal, a compensated signal that is indicative of an absolute light level. The calculating can be performed by a processor and utilize calibration and compensation information or parameters, which can be obtained experimentally. ## Claims ### Claim 1 A photo sensor with compensation comprising: a photo cell for providing a first signal indicative of a light level; an environmental sensor configured to provide a second signal indicative of an environmental parameter; and a processor responsive to the first signal and the second signal and configured to provide a compensated signal that is indicative of an absolute light level; wherein the processor is further configured to determine the compensated signal based at least on one or more of the first signal and the second signal and wherein the processor adjusts the first signal to account for a sensitivity of the photo cell relative to the light level to provide the compensated signal; and wherein the processor adjusts the first signal in accordance with a light calibration coefficient and a calibration constant associated respectively with the slope and intercept of a line relating the first signal and the light level when the second signal is constant. ### Claim 2 (depends on 1) The photo sensor of claim 1 wherein the environmental sensor comprises a temperature sensor configured to provide the second signal indicative of an ambient temperature. ### Claim 3 (depends on 2) The photo sensor of claim 2 wherein the processor is further configured to provide the compensated signal dependent on ambient temperature as indicated by the temperature sensor and the light level as indicated by the photo cell. ### Claim 4 (depends on 1) The photo sensor of claim 1 where the processor is further configured to access a look up table to facilitate providing the compensated signal. ### Claim 5 (depends on 4) The photo sensor of claim 4 where the processor accesses the look up table in accordance with an index that depends on one or more of the first signal and the second signal. ### Claim 6 (depends on 1) The photo sensor of claim 1 further comprising an analog to digital converter configured to convert the first signal and the second signal to, respectively, a first digital value and a second digital value. ### Claim 7 (depends on 6) The photo sensor of claim 6 where a range of the first digital value is controlled using a resistive circuit that is selectively configured and coupled to the photo cell to set a range for the first signal. ### Claim 8 (depends on 6) The photo sensor of claim 6 further comprising a variable gain circuit coupled with the analog to digital converter and operative to adjust a voltage range of the first signal. ### Claim 9 (depends on 1) The photo sensor of claim 1 wherein the environmental sensor comprises one or more of a day night sensor, a humidity sensor, and a dust sensor. ### Claim 10 (depends on 1) The photo sensor of claim 1 further comprising a network interface coupled to the processor and configured to exchange information corresponding to the compensated signal with a remote location. ### Claim 11 A photo sensor with compensation comprising: a photo cell for providing a first signal indicative of a light level; an environmental sensor configured to provide a second signal indicative of an environmental parameter; and a processor responsive to the first signal and the second signal and configured to provide a compensated signal that is indicative of an absolute light level; wherein the processor is further configured to calculate the compensated signal based the first signal and the second signal and wherein the processor adjusts the first signal to account for a sensitivity of the photo cell relative to temperature to provide the compensated signal, the temperature indicated by the second signal, wherein the processor adjust the first signal in accordance with one or more temperature coefficients associated with a function relating the first signal to the temperature when the light level is constant to provide a temperature compensated signal, and wherein the processor adjusts the temperature compensated signal in accordance with a light calibration coefficient to provide the compensated signal that is indicative of the absolute light level. ### Claim 12 A method of determining parameters for compensation of a photo sensor, the method comprising: varying an input light level to the photo sensor while controlling a temperature of the photo sensor to provide first indications of the light level with each of the first indications corresponding to a respective one of a plurality of light levels; determining one or more light calibration coefficients based on the first indications of the light level; varying the temperature of the photo sensor while controlling the input light level to provide second indications of the light level with each of the second indications corresponding to a respective one of a plurality of temperatures; and determining one or more temperature coefficients based on the second indications of the light level, wherein the light calibration coefficients and the temperature coefficients are suitable for use in converting a light level indication from the photo sensor to a compensated signal indicative of an absolute light level. ### Claim 13 (depends on 12) The method of claim 12 further comprising setting up a calibrated light source before the varying the input light level and controlling the temperature at a known value. ### Claim 14 (depends on 12) The method of claim 12 where the determining one or more light calibrations coefficients further comprises determining a light calibration coefficient corresponding to a slope of a line between two or more of the first indications and a light calibration constant corresponding to an intercept of the line. ### Claim 15 (depends on 12) The method of claim 12 further comprising normalizing the second indications in accordance with the second indication obtained at a known temperature corresponding to the controlling the temperature and where the determining the one or more temperature coefficients is based on the second indications as normalized. ### Claim 16 (depends on 15) The method of claim 15 where the one or more temperature coefficients define a temperature calibration equation to facilitate temperature compensation of any indication of a light level. ### Claim 17 (depends on 16) The method of claim 16 where the any indication of a light level as temperature compensated is calibrated to provide an calibrated light level in accordance with the one or more light calibrations coefficients determined as a slope of a line between two or more of the first indications and a light calibration constant corresponding to an intercept of the line. ### Claim 18 A method of compensating an output of a photo sensor to provide a calibrated light reading comprising: obtaining one or more light calibration coefficients and one or more temperature coefficients corresponding to the photo sensor; getting a light output indication for the photo sensor and a temperature indication from a temperature sensor; and calculating the calibrated light reading based on the one or more temperature coefficients, the one or more light calibration coefficients, the temperature indication, and the light output indication, the calibrated light reading indicative of an absolute light level. ### Claim 19 (depends on 18) The method of claim 18 wherein obtaining one or more light calibration coefficients and one or more temperature coefficients further comprises obtaining one or more light calibration coefficients and one or more temperature coefficients from experimental results. ### Claim 20 (depends on 18) The method of claim 18 wherein calculating the calibrated light reading further comprises calculating a first compensated light output indication based on an equation corresponding to the one or more temperature coefficients. ### Claim 21 (depends on 20) The method of claim 20 wherein calculating the calibrated light reading further comprises converting the temperature indication to a temperature. ### Claim 22 (depends on 21) The method of claim 21 wherein calculating the calibrated light reading further comprises calculating the calibrated light reading based on the first compensated light output indication and the one or more light calibration coefficients. ### Claim 23 A method of compensating a photo sensor comprising; providing a first signal indicative of a light level; providing a second signal indicative of an environmental parameter; and calculating, responsive to the first signal and the second signal, a compensated signal that is indicative of an absolute light level; where calculating the compensated signal is based the first signal and the second signal and comprises adjusting the first signal to account for a sensitivity of a photo cell relative to the light level to provide the compensated signal, and wherein adjusting the first signal comprises adjusting the first signal in accordance with a light calibration coefficient and a calibration constant associated respectively with the slope and intercept of a line relating the first signal and the light level when the second signal is constant. ### Claim 24 (depends on 23) The method of claim 23 wherein calculating further comprises accessing a look up table to facilitate providing the compensated signal. ### Claim 25 (depends on 24) The method of claim 24 wherein accessing the look up table comprises accessing the look up table in accordance with an index that depends on one or more of the first signal and the second signal. ### Claim 26 (depends on 23) The method of claim 23 wherein providing the first signal and providing the second signal further comprises converting the first signal and the second signal to a, respective, first digital value and second digital value. ### Claim 27 (depends on 26) The method of claim 26 where a range of the first digital value is controlled using a resistive circuit that is selectively configured and coupled to a photo sensor to set a range for the first signal. ### Claim 28 (depends on 26) The method of claim 26 where a range of the first digital value is controlled using a variable gain circuit that is selectively configured and coupled to a photo sensor. ### Claim 29 (depends on 23) The method of claim 23 wherein calculating further comprises accessing a look up table at a remote location using a network interface to facilitate providing the compensated signal. ### Claim 30 A method of compensating a photo sensor comprising: providing a first signal indicative of a light level; providing a second signal indicative of an environmental parameter; and calculating, responsive to the first signal and the second signal, a compensated signal that is indicative of an absolute light level; wherein calculating the compensated signal is based the first signal and the second signal and comprises adjusting the first signal to account for a sensitivity of a photo cell relative to the light level to provide the compensated signal, wherein adjusting the first signal comprises adjusting the first signal in accordance with one or more temperature coefficients associated with a function relating the first signal to the temperature when the light level is constant to provide a temperature compensated signal,. wherein adjusting the first signal comprises adjusting the temperature compensated signal in accordance with a light calibration coefficient to provide the compensated signal that is indicative of the absolute light level.