EP3447756A1 - Procédé de détection de lumière incidente sur un dispositif électronique - Google Patents

Procédé de détection de lumière incidente sur un dispositif électronique Download PDF

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Publication number
EP3447756A1
EP3447756A1 EP17187115.5A EP17187115A EP3447756A1 EP 3447756 A1 EP3447756 A1 EP 3447756A1 EP 17187115 A EP17187115 A EP 17187115A EP 3447756 A1 EP3447756 A1 EP 3447756A1
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EP
European Patent Office
Prior art keywords
frame
display
light
level
sensor arrangement
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Withdrawn
Application number
EP17187115.5A
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German (de)
English (en)
Inventor
Steven Li
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Ams Osram AG
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Ams AG
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Publication date
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Priority to EP17187115.5A priority Critical patent/EP3447756A1/fr
Publication of EP3447756A1 publication Critical patent/EP3447756A1/fr
Withdrawn legal-status Critical Current

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    • G—PHYSICS
    • G09—EDUCATION; CRYPTOGRAPHY; DISPLAY; ADVERTISING; SEALS
    • G09G—ARRANGEMENTS OR CIRCUITS FOR CONTROL OF INDICATING DEVICES USING STATIC MEANS TO PRESENT VARIABLE INFORMATION
    • G09G3/00—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes
    • G09G3/20—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes for presentation of an assembly of a number of characters, e.g. a page, by composing the assembly by combination of individual elements arranged in a matrix no fixed position being assigned to or needed to be assigned to the individual characters or partial characters
    • G—PHYSICS
    • G09—EDUCATION; CRYPTOGRAPHY; DISPLAY; ADVERTISING; SEALS
    • G09G—ARRANGEMENTS OR CIRCUITS FOR CONTROL OF INDICATING DEVICES USING STATIC MEANS TO PRESENT VARIABLE INFORMATION
    • G09G2360/00—Aspects of the architecture of display systems
    • G09G2360/14—Detecting light within display terminals, e.g. using a single or a plurality of photosensors
    • G09G2360/144—Detecting light within display terminals, e.g. using a single or a plurality of photosensors the light being ambient light
    • G—PHYSICS
    • G09—EDUCATION; CRYPTOGRAPHY; DISPLAY; ADVERTISING; SEALS
    • G09G—ARRANGEMENTS OR CIRCUITS FOR CONTROL OF INDICATING DEVICES USING STATIC MEANS TO PRESENT VARIABLE INFORMATION
    • G09G3/00—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes
    • G09G3/20—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes for presentation of an assembly of a number of characters, e.g. a page, by composing the assembly by combination of individual elements arranged in a matrix no fixed position being assigned to or needed to be assigned to the individual characters or partial characters
    • G09G3/22—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes for presentation of an assembly of a number of characters, e.g. a page, by composing the assembly by combination of individual elements arranged in a matrix no fixed position being assigned to or needed to be assigned to the individual characters or partial characters using controlled light sources
    • G09G3/30—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes for presentation of an assembly of a number of characters, e.g. a page, by composing the assembly by combination of individual elements arranged in a matrix no fixed position being assigned to or needed to be assigned to the individual characters or partial characters using controlled light sources using electroluminescent panels
    • G09G3/32—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes for presentation of an assembly of a number of characters, e.g. a page, by composing the assembly by combination of individual elements arranged in a matrix no fixed position being assigned to or needed to be assigned to the individual characters or partial characters using controlled light sources using electroluminescent panels semiconductive, e.g. using light-emitting diodes [LED]

Definitions

  • the invention relates to a method for light sensing, in particular for light sensing of ambient light incident on a display.
  • Light sensors such as ambient light sensors (ALS) and color sensors
  • ALS and color sensors are widely used in mobile devices such as mobile phones, smartphones, computers and tablets.
  • ALS and color sensors provide information about the level and color of ambient light, respectively, which can be used to support display control such as a backlight LED power circuit.
  • display control such as a backlight LED power circuit.
  • the backlight of a LCD panel in a smartphone accounts for around 40% of the device's total power consumption.
  • the brightness of the display can be reduced to save power. This is also easier on the user's eyes, and so improves the user experience at the same time.
  • a light sensor to measure the illuminance and correlated color temperature (CCT) of the environment under the touch panel.
  • CCT correlated color temperature
  • One of the challenges of measuring the ambient light is to remove the stray light generated by the display.
  • the light sensor often has additional functionality such as proximity detection as thus should be placed close to the display in order to function correctly.
  • the following relates an improved concept for sensing light being incident on an electronic device.
  • the improved concept employs ways to cancel out stray light originating from a display by modulating the brightness the display then cancel out the stray light by a mathematical operation.
  • a method for sensing light employs an electronic device.
  • the electronic device comprises a display and a light sensor arrangement mounted behind the display. Light being incident on the display may traverse through the display and can be received by the light sensor arrangement.
  • the term "behind” denotes that the light sensor arrangement is placed on or into a body of the electronic device and is covered by the display. In this configuration, light which is incident on the electronic device traverses through the display and eventually reaches the light sensor arrangement.
  • Light detected by the light sensor arrangement basically comprises contributions from at least two sources. First, ambient light from the devices environment, e.g. sun light, room lighting, light emitted by other devices etc., may strike the display and be incident on the light sensor arrangement. Second, the display emits light, e.g. by means of active pixels or by backlighting etc., which may be guided or reflected back towards the light sensor arrangement.
  • the light sensor arrangement can be implemented by various types of light sensors including ambient light sensors and/or color sensors.
  • the term "arrangement" indicates an integrated circuit which may have various on-chip components for signal acquisition or (pre-) processing.
  • the light sensor arrangement may have a single or a number of light sensors which are packaged into a common integrated circuit or spread over different locations of the electronic device.
  • the method for sensing light being incident on the electronic device comprises the following steps.
  • the display is periodically switched on and off.
  • a period is defined by a succession of an on-state and an off-state of the display.
  • a frame is defined by an on-state of the display.
  • a frame may display a certain content of frame, i.e. a video frame, a single image, such as icons of applications of a computer or mobile device or photograph, etc.
  • a frame may have a characteristic brightness distribution.
  • the display shows a certain content for the duration of a single frame, i.e. for the duration of an on-state.
  • the display may irradiate with a constant distribution of light intensity, i.e. light emission and/or color may be known for each location on the display.
  • a display brightness is set to a first level.
  • a first frame count is determined by integrating the incident light by means of the light sensor arrangement during the first frame.
  • the display brightness is set to a second level.
  • the second level can be higher or lower than the first level leading to a higher or lower display brightness.
  • a second frame count is determined by integrating the incident light by means of the light sensor arrangement during the second frame.
  • an ambient light level is determined depending on the first and the second frame counts. In fact, the ambient light level is a function of the first and the second frame counts.
  • a content of the second frame can be different compared to the first frame or both contents can be the same. It could be easier for the implementation if the contents of the two frames are the same in some cases.
  • display brightness can be considered a parameter to alter characteristic properties of the display, in particular, display emission. For example, by setting the display brightness to a certain level, the luminance is adjusted. Luminance relates to an amount of light that passes through, is emitted or reflected from a particular area of the display, and falls within a given solid angle. Thus, the display brightness can be adjusted locally, e.g. by altering luminance of an area of the display and a given solid angle. Alternatively, display brightness can be adjusted globally, e.g. by altering luminance of the whole area of the display and a given solid angle. However, the term “display brightness” can also relate to a color or color information to be displayed.
  • the color or correlated color temperature, CCT or Tcp, of an active element or area of the display and/or a display backlight is adjusted.
  • the display brightness may be given by arithmetic mean color coordinates such as red, green, and blue, RGB, or any other color coordinates.
  • the ambient light level can be determined, and accounted for.
  • the ambient light level can even be determined when the light sensor arrangement resides behind the active display.
  • other solutions may suffer from interference and superposition with the light emitted by the display itself.
  • the proposed method allows for canceling out stray light caused by the display.
  • adjusting display brightness between the frames can be done in a way that the end user cannot notice there is any change.
  • Measurement of the various signal counts is performed an activated display (on-state). This way the frame counts represents ambient light samples from the display and ambient light.
  • the first and second frame counts differ from each other in a known way and, thus, can be combined to extract the ambient light level.
  • the method can be used with various devices effectively reducing the impact of device to device variation and aging.
  • first frame and the second frame define successive on states of the display.
  • first frame and the second frame are successive in time.
  • the succession of frames can be determined by a refresh rate or a frame rate. These rates are a measure of how many frames may be displayed by the display per time, e.g. the refresh rate or frame rate lies between 40 HZ to 100 Hz.
  • the refresh rate may be 60 Hz.
  • the periodical switching of the display depends on a control signal.
  • the control signal may be provided by a power circuit of the electronic device, such as a backlight LED power circuit.
  • the control signal may be pulsed in the sense that it comprises consecutive high and low levels.
  • the display is turned on or off depending on whether the control signal is at a high and low level.
  • the control signal may be independent, i.e. not controlled by the display or a display driver.
  • a first sensor signal is generated by integrating the incident light by means of the light sensor arrangement. Integration lasts for a first integration time.
  • the light sensor arrangement comprises means to collect incident light by integrating the signal generated by the light sensor, such as integrators of various types, light-to-frequency or light-to-voltage converters.
  • the first frame count is determined from the first sensor signal and, thus, is indicative of an amount of integrated incident light during an on-state.
  • the sensor signal collected or integrated within the first integration time can be translated into the first frame count and can be interpreted as a measure of intensity.
  • the second frame count is determined from a second sensor signal and, thus, is indicative of an amount of integrated incident light during an on-state.
  • generating the first and/or second sensor signal is synchronized to the control signal. This way it may be assured that the first and the second frame counts are determined during an on-state only.
  • the first frame and the second frame are arranged to follow each other in time such that a change in ambient light level can be assumed constant in value.
  • ambient light can be assumed constant on the timescale of 1 to 100 milliseconds.
  • a frame rate or succession of the first and second frames can be in the frequency range of 100 Hz to 120 Hz.
  • a normal frequency of an AC power supply e.g. of the electronic device or ambient light sources such as room lighting, typically is operated and 50 Hz to 60 Hz.
  • the frame rate can be adjusted to cancel out variations caused by the AC power supply and still assume constant ambient lighting between successive frames.
  • the first frame and the second frame immediately follow each other in time and are only separated by an off-state of the display.
  • the first frame and the second frame follow each other in time with the number of off states of the display in between. Whether one or the other alternative is possible or implemented may depend on the variations or expected variations in ambient light level.
  • the electronic device provides means, such as a control unit or microprocessor, to adjust a delay on number of intermediate off states between successive first and second frames.
  • the ambient light level is determined from the difference of the first frame count can be expressed in terms of the second frame count or vice versa.
  • the knowledge about the first and second brightness levels can be employed, respectively.
  • the first frame count is determined by a sum of a first ambient light level, denoted AL1, and the display brightness at the first level, denoted DL1.
  • the second frame count, denoted FC2 is determined by a sum of a second ambient light level, denoted AL2, and the display brightness at the second level, denoted DL2.
  • the first frame count and the second frame count differ by of brightness factor, denoted p%.
  • the second level of display brightness can be higher or lower than the first level of display brightness leading to a higher or lower display brightness.
  • the frames of the display have a duration which is determined by a frame rate of the display.
  • the frame rate is 50 to 100 Hz and/or the duration of a frame, including the first and second frames, recites between 1 to 20 milliseconds.
  • the integration time for integrating the incident light by means of the light sensor arrangement depends on the frame rate. In particular, the integration time is set to 1 to 20 milliseconds.
  • the refresh rate of an OLED display is about 60 Hz, so each frame takes about 16.7 milliseconds.
  • the normal frequency of an AC power supply resides in the range of 50Hz to 60Hz.
  • Light intensity of the ambient light e.g. indoor light, can vary at a frequency of 100 Hz or 120 Hz. If the light sensor arranged is set to integrate the incident light for 10 milliseconds, then variations caused by the AC power supply can be cancelled out to a higher degree. Further, it can be assumed that the ambient light will not change in level within 20 milliseconds.
  • the light sensor arrangement comprises a light sensor.
  • the ambient light level can be used to adjust the display brightness.
  • the light sensor arrangement comprises a color light sensor.
  • the ambient light level can be used to adjust a display color, in particular, a color temperature value of the display.
  • the color light sensor can be used to adjust both display brightness and display color.
  • consecutive frames are used as first and second frames to determine the ambient light level, respectively.
  • a number of first frames and a number of second frames are combined to determine the ambient light level.
  • the number of first frames can be accumulated within a certain time period or several frames may be combined together into a single first frame, e.g. as mean or median frame. The same may be done for the number of second frames. Whether such an approach is practical may be determined on the temporal changes in ambient light level.
  • the frames used to determine the ambient light level are inserted into a stream of content frames.
  • the first and second frames are intermediate frames which comprise constant and predetermined brightness distributions and, thus, establish a sensor signal or frame counts that can be correlated to the predetermined conditions.
  • the first and second frames, as intermediate may not be distinguishable for an end user. The proposed method may not interfere with the end user experience.
  • the display brightness at the first and/or second level is set for a region of interest.
  • the light sensor arrangement integrates the incident light locally from the region of interest.
  • any frame of the display may be used as first or second frame to determine the ambient light level.
  • the region of interest can be arranged to have a predetermined or known brightness and the light sensor arrangement determines the corresponding frames counts. This way only a small part of the display may be used to determine the ambient light level. The small part may not be apparent for an end user such that the proposed method may not interfere with the end user experience.
  • the display brightness at the first and/or second level is set for the whole display.
  • the light sensor arrangement integrates the incident light globally for the whole display, e.g. for first/second frames as intermediate frames.
  • the first/second frames can be recorded at brightness levels that appear the same to the end user or at differences in level that do not interfere with the end user experience.
  • Figure 1 shows an example method for sensing light.
  • the drawing shows a first frame FR1 and a second frame FR2 which closely follow each other in time, e.g. are two consecutive frames of the display 11.
  • a frame is defined by an on-state ON of the display 11.
  • the frames are displayed by means of an electronic device.
  • the electronic device comprises a display 11 and a light sensor arrangement 12 mounted behind the display 11 such as to receive incident light through the display 11 (see Figure 2 ).
  • the display 11 can be periodically switched on and off depending on a control signal CS, e.g. a PWM signal provided by control electronics of display driver circuitry (not shown).
  • a period PD is determined by a picture refresh signal PR or by a refresh rate of the display 11 which is a number of times in a second that a display hardware updates an image.
  • the refresh rate is known from the specifications of the display or can be set by the user.
  • a frame is defined by an on-state ON of the display 11. Furthermore, a duration of an off-state OFF and an on-state ON is determined by a duty cycle DC of the display 11.
  • the duty cycle DC is a fraction of one period PD in which a signal or system is active. The period PD thus corresponds to the time it takes for display 11, or control signal CS, to complete an on-and-off cycle, i.e. a succession of one on-and one off-state ON, OFF.
  • the duty cycle DC typically is either known or can be set by the user.
  • the display 11 can be adjusted in brightness.
  • the first frame FR1 and the second frame FR2 comprise the same content, i.e. have the same or similar brightness distribution. However, considered as a whole, or globally, the two frames FR1 and FR2 have a different brightness level.
  • the first frame FR1 has a first level of brightness L1 and the second frame FR2 has a second level of brightness L2.
  • the second level L2 is 10% smaller than the first level L1.
  • the light sensor arrangement is set to generate a sensor signal which is indicative of light incident on the display and of light emitted by the display or its backlighting.
  • the sensor signal is generated by integrating the light which reaches the light sensor arrangement through the display.
  • a first sensor signal is generated for the duration of the first frame FR1.
  • a second sensor signal is generated for the duration of the second frame FR2.
  • the light sensor arrangement integrates the incident light for a first and second integration time T1, T2, respectively.
  • the integration time is set to 10 ms and a frame has a duration of about 16.7 ms.
  • a refresh rate an OLED display is 60 Hz, so each frame takes 16.7 ms.
  • the normal frequency of AC power is 50Hz or 60Hz, so the light intensity of indoor light can vary at a frequency of 100 Hz or 120 Hz.
  • the first frame FR1 results in a first frame count of FC1.
  • the consecutive second frame FR2, having same content, is the same as the first frame FR1 except for a different brightness level.
  • the second frame FR2 results in a second frame count of FC2.
  • the brightness level L2 of the second frame is 10% lower than the brightness level of the second frame L2.
  • the first frame count, denoted FC1 is determined by a sum of a first ambient light level, denoted AL1, and the display brightness at the first level, denoted DL1.
  • the second frame count, denoted FC2 is determined by a sum of a second ambient light level, denoted AL2, and the display brightness at the second level, denoted DL2.
  • the determined ambient light level can be used for further purposes, including adjusting brightness and/or color of the display.
  • Figure 2 shows an exemplary embodiment of an electronic device with a display and light sensor arrangement.
  • the electronic device has a surface 13 and the display 11 is arranged on the surface.
  • the display 11 comprises a panel of pixels 14, a backlight panel 15 and a reflector 16.
  • the light sensor arrangement 12 is arranged behind the display 11 (with respect to the main direction of emission).
  • the display may contribute to the sensor signal generated by the light sensor arrangement.
  • a fraction of the emitted light EL emitted by the display may be reflected back towards the light sensor arrangement as indicated by arrows in the drawing.
  • the emitted light may partly stem from the pixels arranged in panel 14 and/or from LEDs used for backlighting the display.
  • ambient light from different sources may strike the display 11 and traverse towards the light sensor arrangement 12 with gives rise to a contribution to the sensor signal.
  • the electronic device depicted in Figure 2 illustrates one possible embodiment. Other types of displays and arrangements are possible without restricting the scope of the proposed concept.

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  • Engineering & Computer Science (AREA)
  • Physics & Mathematics (AREA)
  • Computer Hardware Design (AREA)
  • General Physics & Mathematics (AREA)
  • Theoretical Computer Science (AREA)
  • Liquid Crystal Display Device Control (AREA)
  • Control Of El Displays (AREA)
EP17187115.5A 2017-08-21 2017-08-21 Procédé de détection de lumière incidente sur un dispositif électronique Withdrawn EP3447756A1 (fr)

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EP17187115.5A EP3447756A1 (fr) 2017-08-21 2017-08-21 Procédé de détection de lumière incidente sur un dispositif électronique

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Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP3816977A1 (fr) * 2019-10-29 2021-05-05 Beijing Xiaomi Mobile Software Co., Ltd. Procédé, dispositif et terminal de détection de lumière ambiante
WO2021185979A1 (fr) * 2020-03-19 2021-09-23 ams Sensors Germany GmbH Capteur de couleur multicanal

Citations (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US20080284716A1 (en) * 2005-12-13 2008-11-20 Koninklijke Philips Electronics, N.V. Display Devices With Ambient Light Sensing

Patent Citations (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US20080284716A1 (en) * 2005-12-13 2008-11-20 Koninklijke Philips Electronics, N.V. Display Devices With Ambient Light Sensing

Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP3816977A1 (fr) * 2019-10-29 2021-05-05 Beijing Xiaomi Mobile Software Co., Ltd. Procédé, dispositif et terminal de détection de lumière ambiante
US11094291B2 (en) 2019-10-29 2021-08-17 Beijing Xiaomi Mobile Software Co., Ltd. Method and device for detecting ambient light and terminal
WO2021185979A1 (fr) * 2020-03-19 2021-09-23 ams Sensors Germany GmbH Capteur de couleur multicanal

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