Electronic device with polarized ambient light sensor

An electronic device may be provided with an ambient light sensor. The ambient light sensor may be a color ambient light sensor or a monochrome ambient light sensor. The electronic device may have a light-emitting component such as a display. During operation of the display, the display emits light. To reduce noise due to the emitted light while measuring ambient light, the ambient light sensor may have optical structures such as wave plates and polarizers. Theses optical structures may overlap light detectors. The optical structures may be configured to prevent ambient light from reaching a first of the light detectors while allowing ambient light to reach a second of the light detectors. The ambient light sensor may be configured to receive ambient light that has passed thorough an inactive area of a display or that has passed through a pixel array in an active area of a display.

BACKGROUND

This relates generally to electronic devices, and, more particularly, to light sensors for electronic devices.

Electronic devices such as laptop computers, cellular telephones, and other equipment are sometimes provided with light sensors. For example, ambient light sensors may be incorporated into a device to provide the device with information on current lighting conditions. Ambient light readings may be used in controlling the device. If, for example bright daylight conditions are detected, an electronic device may increase display brightness to compensate. Color ambient light sensors can detect changes in the color of ambient light so that compensating color cast adjustments can be made to displayed content.

It can be challenging to incorporate ambient light sensors into electronic devices. If care is not taken, an ambient light sensor may consume more space in an electronic device than desired. In some arrangements, there may be challenges associated with operating an ambient light sensor accurately due to potential interference from other components.

SUMMARY

An electronic device may be provided with a light-detecting component such as an ambient light sensor. The ambient light sensor may be a color ambient light sensor or a monochrome ambient light sensor. Control circuitry in the electronic device may use information from the ambient light sensor in adjusting the operation of the electronic device. For example, the electronic device may be provided with a display. The brightness and/or color of the display may be adjusted dynamically based on intensity and/or color measurements from the ambient light sensor.

During operation of the electronic device, the display in the electronic device may emit light. To reduce noise from the emitted light and thereby enhance the accuracy of the ambient light sensor, the ambient light sensor may have optical structures such as wave plates and polarizers. These optical structures may overlap light detectors in the ambient light sensor. In an illustrative configuration, the optical structures of the ambient light sensor are configured to prevent ambient light from reaching a first of the light detectors while allowing ambient light to reach a second of the light detectors. The control circuitry can process the output of the first and second light detectors to remove display noise contributions from ambient light measurements.

The display of the electronic device may be an organic light-emitting diode display or other display with an array of light-emitting diode display pixels or may be a liquid crystal display or other display. The ambient light sensor may be configured to receive ambient light that has passed thorough an inactive area of a display or may be configured to receive ambient light that has passed through a pixel array in an active area of a display.

DETAILED DESCRIPTION

An illustrative electronic device of the type that may be provided with one or more light sensors is shown inFIG. 1. Electronic device10may be a computing device such as a laptop computer, a computer monitor containing an embedded computer, a tablet computer, a cellular telephone, a media player, or other handheld or portable electronic device, a smaller device such as a wrist-watch device, a pendant device, a headphone or earpiece device, a device embedded in eyeglasses or other equipment worn on a user's head, or other wearable or miniature device, a television, a computer display that does not contain an embedded computer, a gaming device, a navigation device, an embedded system such as a system in which electronic equipment with a display is mounted in a kiosk or automobile, equipment that implements the functionality of two or more of these devices, or other electronic equipment.

Input-output circuitry in device10such as input-output devices12may be used to allow data to be supplied to device10and to allow data to be provided from device10to external devices. Input-output devices12may include buttons, joysticks, scrolling wheels, touch pads, key pads, keyboards, microphones, speakers, tone generators, vibrators, cameras, light-emitting diodes and other status indicators, data ports, etc. A user can control the operation of device10by supplying commands through input-output devices12and may receive status information and other output from device10using the output resources of input-output devices12.

Input-output devices12may include one or more displays such as display14. Display14may be a touch screen display that includes a touch sensor for gathering touch input from a user or display14may be insensitive to touch. A touch sensor for display14may be based on an array of capacitive touch sensor electrodes, acoustic touch sensor structures, resistive touch components, force-based touch sensor structures, a light-based touch sensor, or other suitable touch sensor arrangements.

Input-output devices12may also include sensors18. Sensors18may include a capacitive sensor, a light-based proximity sensor, a magnetic sensor, an accelerometer, a force sensor, a touch sensor, a temperature sensor, a pressure sensor, a compass, a microphone, a radio-frequency sensor, a three-dimensional image sensor, a camera, a light-based position sensor (e.g., a lidar sensor), and other sensors. Sensors18may also include one or more light detectors that are configured to detect ambient light. Sensors18may, for example, include one or more monochrome ambient light sensors and one or more color ambient light sensors that are configured to measure ambient light from the environment in which device10is operated. A monochrome ambient light sensor may be used to measure ambient light intensity. A color ambient light sensor may be used to measure the color (color spectrum, color temperature, color coordinates, etc.) of ambient light and may be used to measure ambient light intensity.

To make color measurements, a color ambient light sensor in device10may have a light detector such as a photodiode that is overlapped by a tunable wavelength filter and/or may have multiple channels each of which has a light detector such as a photodiode that is overlapped by a filter that passes a different color of light (e.g., a different wavelength band) to that light detector. By processing the readings from each of the multiple channels, the relative intensity of each of the different colors of light can be determined. Using data from the different channels in a color ambient light sensor, control circuitry16can therefore produce ambient light color temperature measurements and other color measurements (e.g., colors represented in color coordinates, etc.). The ambient light spectrum information may be used in controlling display14and/or in taking other actions in device10. As an example, the color cast of images displayed on display14can be adjusted based on ambient light color measurement (e.g., to make the images on display14yellower in warm ambient lighting conditions and to make the images on display14bluer in cold ambient lighting conditions). If desired, display brightness may be automatically increased by control circuitry16in response to detection of bright ambient light conditions and may be automatically decreased by control circuitry16in response to detection of dim ambient light conditions.

Electronic device10may include one or more ambient light sensors. Illustrative arrangements in which device10includes a single ambient light sensor are sometimes described herein as an example. The ambient light sensor may be located behind a window in a housing member, under an inactive portion of a display (e.g., a border portion of a display that does not contain pixels) and/or may be located elsewhere within device10. If desired, electronic device10may have an ambient light sensor that is overlapped by pixel array in an active area of a display (e.g., a portion of the display that is configured to display images). The display may have transparent portions (e.g., transparent gaps between metal traces and other opaque structures) so that ambient light may pass through the pixel array to the overlapped ambient light sensor. By locating the ambient light sensor behind the active area of the display in this way, the appearance of device10may be enhanced and the amount of space consumed by the ambient light sensor may be reduced. Configurations in which the ambient light sensor is located under an inactive display area or is located elsewhere within device10may also be used.

A perspective view of an illustrative electronic device of the type that may include an ambient light sensor is shown inFIG. 2. In the example ofFIG. 2, device10includes a display such as display14mounted in housing22. Display14may be a liquid crystal display, an electrophoretic display, an organic light-emitting diode display or other display with an array of light-emitting diodes (e.g., a display that includes pixels having diodes formed from crystalline semiconductor dies), may be a plasma display, may be an electrowetting display, may be a display based on microelectromechanical systems (MEMS) pixels, or may be any other suitable display. Display14may have an array of pixels26that extend across some or all of front face F of device10and/or other external device surfaces. The pixel array may be rectangular or may have other suitable shapes. Display14may be protected using a display cover layer such as a layer of transparent glass, clear plastic, sapphire, or other clear layer. The display cover layer overlaps an array of pixels26.

Housing22, which may sometimes be referred to as an enclosure or case, may be formed of plastic, glass, ceramics, fiber composites, metal (e.g., stainless steel, aluminum, etc.), other suitable materials, or a combination of any two or more of these materials. Housing22may be formed using a unibody configuration in which some or all of housing22is machined or molded as a single structure or may be formed using multiple structures (e.g., an internal frame structure, one or more structures that form exterior housing surfaces, etc.).

Pixels26may cover substantially all of the front face of device10or display14may have inactive areas (e.g., notches or other regions) that are free of pixels26. The inactive areas may be used to accommodate an opening for a speaker and windows for optical components such as image sensors, an ambient light sensor, an optical proximity sensor, a three-dimensional image sensor such as a structured light three-dimensional image sensor, a camera flash, etc. Pixels26may, for example, extend over front surface F of device10and may overlap ambient light sensor30. In this type of arrangement, ambient light may pass to ambient light sensor30through the array of pixels26in display14.

FIG. 3is a cross-sectional side view of device10ofFIG. 2in an illustrative configuration in which pixels26overlap ambient light sensor30. As shown inFIG. 3, housing22of device10may enclose interior region23. Electrical components38(see, e.g., control circuitry16and input-output devices12) may be mounted within interior region23(e.g., on one or more printed circuits such as printed circuit36).

Pixel array40includes an array of pixels26. Pixels26extend over front face F of device10and form in an active area for display14in which images are displayed. Display cover layer32may overlap pixel array40. Each pixel26may be formed from thin-film transistors and other components (e.g., liquid crystal display pixel components such as pixel electrodes, light-emitting diode pixel components such as light-emitting diodes, etc.). Metal traces and other opaque structures in pixels26may block light, however, pixel array40may also include transparent regions between the opaque structures. The presence of transparent areas in pixel array40allows ambient light34to pass through pixel array40among pixels26to reach ambient light sensor30.

As the example ofFIG. 3demonstrates, ambient light sensor30may, in some configurations, be mounted under pixel array40. In this location within interior23of housing22, the active area of display14that is formed by pixel array40overlaps ambient light sensor30when viewed from the exterior of device10. By mounting ambient light sensor30behind pixel array40in this way, the overall size of device10can be reduced, the appearance of device10may be enhanced, and inactive display area may be reduced.

During operation of display14to display content for a user, display14emits light. Some of the emitted light may leak into interior region23and may reach ambient light sensor30. This emitted light therefore represents a potential source of noise that has the potential to interfere with accurate measurements of ambient light34. To ensure that accurate ambient light sensor measurements are made even in the presence of light from display14, ambient light sensor30may be provided with optical structures that help discriminate between ambient light and emitted display light. The optical structures may include, for example, wave plates and polarizers. By configuring ambient light sensor30to discriminate between ambient light and emitted display light, control circuitry16can remove emitted noise contributions such as display light contributions from ambient light sensor readings before control circuitry uses these readings in making display adjustments or taking other action.

FIG. 4is a cross-sectional side view of an illustrative pixel array and ambient light sensor. In the example ofFIG. 4, pixel array40is a light-emitting diode pixel array. Each pixel26in pixel array40includes a light-emitting diode26′ (e.g., an organic light-emitting diode or a light-emitting diode formed from a crystalline semiconductor die). To suppress reflections of ambient light34from pixel array40as display14is viewed by user33in direction35, display14may be provided with circular polarizer46. Circular polarizer46may include linear polarizer42and quarter wave plate44.

Light that is emitted outwardly by diodes26′ may be viewed as images on display14. Some of this emitted light may scatter from the structures of display14and other structures in device10and may leak into interior region23, where this leaked light is detected by ambient light sensor30(see, e.g., emitted display light48). To help determine which portion of the light received at ambient light sensor30corresponds to ambient light34that has passed through pixel array40and which portion of the light received at ambient light sensor30corresponds to emitted display light48, ambient light sensor30may be provided with optical structures57and multiple light detectors (see, e.g., light detectors58-1and58-2, which may be formed from individually controlled photodetectors or other light detecting devices).

There may, in general, be any suitable number of photodetectors or other light detectors in ambient light sensor30(e.g., two, at least four, at least six, at least 10, fewer than 50, fewer than 30, etc.). In color ambient light sensors, there may be, for example, multiple different color channels (e.g., red, blue, green, etc.) each of which detects light in a different band of wavelengths and each of these color channels may include a pair of photodetectors such as illustrative light detectors58-1and58-2. In a monochrome ambient light sensor configuration, light detectors58-1and58-2may both be monochrome light detectors. An illustrative monochrome configuration for ambient light sensor30is described herein as an example. If desired, ambient light sensor30may be configured to make color ambient light sensor measurements by including pairs of detectors such as detectors58-1and58-2, each pair corresponding to a different color channel.

In the illustrative monochrome ambient light sensor configuration, ambient light sensor30includes first detector58-1and second detector58-2and each of these light detectors is overlapped by respective optical structures. As shown inFIG. 4, for example, first detector58-1may be overlapped by waveplate (retarder)52and polarizer50and second detector58-2may be overlapped by waveplate56and polarizer54. Waveplate52and polarizer50are configured to block ambient light34. As ambient light34passes from exterior region37to interior23of device10through display14, this ambient light passes through linear polarizer42. Linear polarizer42converts the ambient light to linearly polarized ambient light. The linearly polarized ambient light then passes through quarter-wave plate44of circular polarizer46and becomes circularly polarized. There may be one or more layers (e.g., a polyimide substrate layer, etc.) in pixel array40that are birefringent. As the circularly polarized ambient light passes through pixel array40, the birefringence that may be present in pixel array40may cause the circularly polarized ambient light to become elliptically polarized.

Waveplate52may be configured to convert the circularly or elliptically polarized state of the ambient light that has passed through pixel array40into linearly polarized light. If, for example, the ambient light passing through pixel array40is circularly polarized, waveplate52may be a quarter-wave plate. If the ambient light passing through pixel array40is elliptically polarized, waveplate52may have a different configuration (e.g., waveplate52may be a ⅛-wave plate, a ⅜-wave plate, etc.). A satisfactory configuration for waveplate52may be selected based on experimental measurements of the polarization state of light after passing through pixel array40.

Due to the presence of waveplate52, the ambient light that has passed through pixel array40and waveplate52will be linearly polarized. To block this light and thereby prevent ambient light34from being detected by detector58-1, polarizer50may be a linear polarizer having a pass axis that is oriented to be perpendicular to the linear polarization orientation of the light that has passed through waveplate52. Display light48will be unpolarized or will have another polarization state that is different than the linear polarization of the light that has passed through waveplate52. As a result, detector58-1will detect emitted display light48that has leaked into interior23but will not detect ambient light34.

The optical structures above detector58-2may be configured so that detector58-2detects ambient light34. These optical structures may also be configured to help reduce the amount of emitted display light48that is detected by detector58. As an example, the optical structures above detector58-2may include waveplate56and polarizer54. Waveplate56may be configured to convert ambient light34to linearly polarized light (e.g., waveplate56may have the same configuration as waveplate52). Polarizer54may be a linear polarizer having a pass axis that is oriented to be parallel to the linear polarization orientation of the light that has passed through waveplate56. As a result, waveplate56and polarizer54will tend to allow all of ambient light34that has passed through display14pass to detector58-2. At the same time, waveplate56and polarizer54may help to reduce the amount of emitted display light48that is sensed by detector58-2. For example, if emitted display light48is unpolarized, the presence of polarizer54will cut the intensity of emitted display light48in half.

During ambient light sensor characterization operations (e.g., during design and testing), the output of detectors58-1and58-2under different conditions can be characterized. For example, display14may be turned off while a known amount of ambient light illuminates device10. Detector58-1will not pick up any ambient light due to the waveplate and polarizer above detector58-1. The sensitivity of detector58-2to ambient light can be determined by measuring the output of detector58-2at different ambient light levels. In a further set of characterization measurements, device10may be operated in a dark environment in which ambient light34is not present. During these measurements, display14may be operated to produce emitted display light48and the outputs of detectors58-1and58-2may be collected. In an illustrative configuration in which light48is not polarized, the output of detectors58-1and58-2may be equal when being exposed to light48and not being exposed to light34.

In mixed lighting conditions in which both ambient light34and display light48illuminate ambient light sensor30, the outputs of detectors58-1and58-2will have intermediate values that can be processed to determine the relative contributions of ambient light34and emitted display light48. If desired, weighting factors can be applied to the outputs of each detector in ambient light sensor30to produce individual readings of the intensity of ambient light34and emitted display light48. The equations used for mapping raw readings from detectors58-1and58-2to readings of ambient light and emitted display light may be stored in control circuitry16during calibration operations (e.g., ambient light sensor30can be calibrated based on the results of sensor characterization measurements made during initial design and testing of sensor30and device10).

As this example demonstrates, control circuitry16can be calibrated so that the relative amounts of ambient light34and emitted display light48that are present can be deter mined using the outputs of detectors58-1and58-2. In a color ambient light sensor, the relative contributions of ambient light and emitted display light in each color channel can be determined. After determining intensity and/or color of ambient light that is present by removing the noise associated with emitted display light48from the measurements made by sensor30, control circuitry16can adjust display14or take other action.

In general, pixel array40may include pixels of any suitable type (e.g., light-emitting diode pixels, liquid crystal display pixels, etc.). Ambient light sensor30may be overlapped by pixel array40as shown inFIG. 4or may, if desired, be located in an inactive area of display14.FIG. 5is a cross-sectional side view of device10in an illustrative configuration in which display14has an active area AA with an array of pixels to display images and an inactive area IA that is free of pixels. In theFIG. 5example, display14is a liquid crystal display having a layer of liquid crystal material (liquid crystal layer64) sandwiched between upper layer62and lower layer66. Upper layer62may be, for example, a color filter layer having an array of color filter elements and lower layer66may be a thin-film transistor layer having an array of thin-film pixel circuits for the pixels of display14. If desired, upper layer62may be a thin-film transistor layer and lower layer66may be a color filter layer or these layers may be formed on a single substrate. Layers62and66may have glass substrates or other transparent substrates and may be sandwiched between upper linear polarizer60and lower linear polarizer68.

During operation, light-emitting diodes74may emit light72into an adjacent edge of light guide layer70. This light may be guided within light guide layer70in accordance with the principal of total internal reflection. Some of this light may be scattered outwardly through the pixels of active area AA and therefore serves as backlight for display14(e.g., light guide layer70and diodes74and optional additional structures such as reflector layers, diffuser layers, and/or other layers may serve as a backlight unit for display14). While the backlight is being produced for display14, some of the light in light guide layer70may be scattered out of light guide layer70and display14to locations in interior region23and can then be detected by ambient light sensor30as emitted display light48(e.g., light48may leak out of display14and may reach ambient light sensor30).

In inactive area IA, lower display layer66may be transparent and liquid crystal layer64may be absent. Upper polarizer60may overlap inactive area IA. Lower polarizer68may be absent from inactive area IA. Opaque masking layer76(e.g., a black ink layer) may be formed between layers62and66to help hide internal components from view from the exterior of device10. A window such as ambient light sensor window78(e.g., a transparent window formed from an opening in layer76and/or a transparent material in an opening in layer76) may be formed in inactive area IA in alignment with ambient light sensor30, so that ambient light sensor30receives ambient light34. As described in connection with display14ofFIG. 4, ambient light that passes through display14(e.g., through upper polarizer60in inactive area IA in the example ofFIG. 5) may become linearly polarized. Ambient light sensor30ofFIG. 5may therefore have a first detector such as detector58-1ofFIG. 4that is covered with an orthogonal linear polarizer and may have a second detector such as detector58-2ofFIG. 5that is covered with a parallel polarizer. In this example, wave plates52and56may be omitted, because the ambient light that passes through upper polarizer60becomes linearly polarized.

In general, any configuration for optical structures57that allows detectors58-1and58-2to produce readings that differentiate between ambient light and emitted display light (or light from other noise sources) may be used in ambient light sensor30. For example, waveplate56and/or polarizer54ofFIG. 4may be omitted from ambient light sensor30ofFIG. 4, etc. In the illustrative arrangement ofFIG. 6, ambient light sensor30has a single light detector such as detector58(e.g., a single photodetector or, in a color ambient light sensor arrangement a single set of photodetectors overlapped by a single corresponding set of respective color filters). Polarizer80may be an electrically adjustable polarizer. Optional waveplate82may be configured to convert incoming circularly polarized ambient light34ofFIG. 4to linearly polarized light as described in connection with wave plates52and56ofFIG. 4or may be omitted (e.g., in an arrangement of the type show inFIG. 5). When it is desired to make ambient light measurements, control circuitry16may use control input84to adjust the polarization state of adjustable polarizer80(e.g., to switch from linearly polarized to block ambient light to unpolarized or to switch between any other suitable set of distinct polarization states). The output from detector58in each of the different polarization states may then be processed (e.g., using weighting factors or other suitable processing techniques that remove the noise contribution from the measured data) to determine an accurate ambient light sensor reading.

FIG. 7is a flow chart of illustrative operations involved in using ambient light sensor30in device10.

During the operations of block90, control circuitry16may make a first measurement with sensor30(e.g., a measurement with detector58-1or a measurement with detector58ofFIG. 6while an adjustable optical component in sensor30such as adjustable polarizer80is in a first state). During the operations of block92, control circuitry16may make a second measurement with sensor30(e.g., a measurement with detector58-2or a measurement with detector58ofFIG. 6while the adjustable optical component in sensor30such as adjustable polarizer80is in a second state). These measurements (and additional measurements from additional detectors in configurations in which ambient light sensor30is a color ambient light sensor with multiple color channels of different colors) may be processed during the operations of block94to separate out the ambient light contribution to the measurements from the non-ambient-light contribution. The ambient light contribution, which represents an accurate measurement of ambient light34, can then be used to take action during the operations of block96. For example, control circuitry16can adjust the brightness (luminance) of display14based on measured ambient light sensor intensity and/or may adjust the color cast of display14based on measured ambient light color.