PATENT DOCUMENT

Publication Number: US-9612152-B2
Application Number: US-201314074547-A
Country: US
Kind Code: B2

Title: Ambient light sensor with internal light cancellation

Abstract:
An electronic device includes a transparent surface, a light emitting device that emits light through the transparent surface, and a light sensor for receiving ambient light and providing an ambient light value. A retarder and a linear polarizer are placed between the transparent surface and the light emitting device. The retarder and linear polarizer may attenuate internal reflections from the transparent surface. The light sensor may have two channels and a second linear polarizer may attenuate the ambient light directed toward a second channel. A second retarder may be used with the second linear polarizer to attenuate the ambient light directed toward the second channel. A light detection circuit may use the difference between the two channels of the light sensor to provide the ambient light value.

Claims:
What is claimed is: 
     
       1. An electronic device comprising:
 a transparent surface; 
 a light sensor; 
 a light emitting device between the transparent surface and the light sensor, the light emitting device to emit light through the transparent surface; 
 a first retarder between the transparent surface and the light emitting device; 
 a first linear polarizer between the first retarder and the light emitting device; 
 wherein the light sensor is for receiving ambient light that passes through the transparent surface, then the first retarder, and then the first linear polarizer, the light sensor including
 a first channel for receiving both light from the light emitting device and ambient light, and to provide a first light level value, and 
 a second channel with a second linear polarizer oriented to attenuate ambient light that has been polarized by the first linear polarizer, the second channel for receiving light from the light emitting device, and to provide a second light level value. 
 
 
     
     
       2. The electronic device of  claim 1  further comprising an ambient light detection circuit coupled to the light sensor, the ambient light detection circuit configured to provide an ambient light level value responsive to a difference between the first light level value and the second light level value. 
     
     
       3. A method for detecting an ambient light level falling on a transparent surface of an electronic device with a light sensor, the electronic device including a light emitting device between the light sensor and the transparent surface, the light emitting device to emit light through the transparent surface, the method comprising:
 placing a first retarder between the transparent surface and the light emitting device; 
 placing a first linear polarizer between the first retarder and the light emitting device; 
 receiving ambient light that falls on the transparent surface and then passes through the transparent surface, then the first retarder, and then the first linear polarizer with a first channel of the light sensor, the first channel also receiving the light emitted by the light emitting device; 
 receiving the light emitted by the light emitting device with a second channel of the light sensor; 
 attenuating ambient light directed to the second channel with a second linear polarizer; and 
 providing an ambient light level value responsive to a difference between the first channel and the second channel. 
 
     
     
       4. An electronic device comprising:
 a transparent surface; 
 means for sensing light 
 means for emitting light through the transparent surface, the means for emitting light placed between the means for sensing light and the transparent surface; 
 first means for circularly polarizing light placed between the transparent surface and the means for emitting light; 
 first means for linearly polarizing light placed between the transparent surface and the means for emitting light; and 
 means for receiving ambient light and also receiving light emitted by the means for emitting light, the ambient light falling on the transparent surface and then passing through the first transparent surface, the means for circularly polarizing light, and the means for linearly polarizing light; 
 means for receiving only the light emitted by the means for emitting light means for attenuating ambient light directed to the means for receiving only the light emitted by the means for emitting light and 
 means for providing an ambient light level value responsive to a difference between the means for receiving ambient light and also receiving light emitted by the means for emitting light and the means for receiving only the light emitted by the means for emitting light. 
 
     
     
       5. An electronic device comprising:
 a transparent surface; 
 a light sensor; 
 a light emitting device between the transparent surface and the light sensor, the light emitting device to emit light through the transparent surface; 
 a first linear polarizer between the transparent surface and the light emitting device; 
 a first retarder between the first linear polarizer and the light emitting device; 
 wherein the light sensor is positioned to receive ambient light that passes through the transparent surface, then the first linear polarizer, and then the first retarder, the light sensor including
 a first channel positioned to receive light from both the light emitting device and ambient light, and configured to provide a first light level value, and 
 a second channel with a second retarder and a second linear polarizer oriented to attenuate ambient light that has been linearly polarized by the second retarder, the second channel positioned to receive light from the light emitting device, and configured to provide a second light level value. 
 
 
     
     
       6. The electronic device of  claim 5  further comprising an ambient light detection circuit coupled to the light sensor, the ambient light detection circuit configured to provide an ambient light level value responsive to a difference between the first light level value and the second light level value. 
     
     
       7. A method for detecting an ambient light level falling on a transparent surface of an electronic device with a light sensor, the electronic device including a light emitting device between the light sensor and the transparent surface, the light emitting device emitting light through the transparent surface, the method comprising:
 placing a first linear polarizer between the transparent surface and the light emitting device; 
 placing a first retarder between the first linear polarizer and the light emitting device; 
 receiving ambient light that falls on the transparent surface and then passes through the transparent surface, then the first linear polarizer, and then the first retarder with a first channel of the light sensor, the first channel also receiving light emitted by the light emitting device; 
 receiving the light emitted by the light emitting device with a second channel of the light sensor; 
 attenuating ambient light directed to the second channel with a second retarder and a second linear polarizer; and 
 providing an ambient light level value responsive to a difference between the first channel and the second channel.

Description:
BACKGROUND 
     Field 
     Embodiments of the invention relate to the field of ambient light sensors; and more specifically, to ambient light sensors with cancellation of internal light sources. 
     Background 
     Electronic devices may include devices that emit light and devices that sense light. For example, a device may provide a display screen, such as a light emitting diode (LED) panel, and an ambient light sensor that detects an ambient light level that in turn is used to control the brightness of the display screen. It is necessary to avoid having light from the devices that emit light fall on the devices that sense light to provide accurate sensing. This may be done by physically separating the devices that emit light from the devices that sense light. For example, the devices that emit light may be viewed through apertures in a device housing that are separate from other apertures in the device housing that admit light to the devices that sense light. 
     Generally it is desirable to minimize the number of apertures in the device housing both to better seal the housing for the protection of the contained components and to improve the aesthetics of the housing. A display screen and other devices that emit light are sometimes mounted below a transparent surface that forms a surface of the device housing. It would be desirable to provide a structure that allows devices that emit light and devices that sense light to be mounted below the same transparent surface of the device housing while minimizing the effect of light from the devices that emit light on the devices that sense light to provide accurate sensing. 
     SUMMARY 
     An electronic device includes a transparent surface, a light emitting device that emits light through the transparent surface, and a light sensor for receiving ambient light and providing an ambient light value. A retarder and a linear polarizer are placed between the transparent surface and the light emitting device. The retarder and linear polarizer may attenuate internal reflections from the transparent surface. The light sensor may have two channels and a second linear polarizer may attenuate the ambient light directed toward a second channel. A second retarder may be used with the second linear polarizer to attenuate the ambient light directed toward the second channel. A light detection circuit may use the difference between the two channels of the light sensor to provide the ambient light value. 
     Other features and advantages of the present invention will be apparent from the accompanying drawings and from the detailed description that follows below. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention may best be understood by referring to the following description and accompanying drawings that are used to illustrate embodiments of the invention by way of example and not limitation. In the drawings, in which like reference numerals indicate similar elements: 
         FIG. 1  is a pictorial view of an electronic device  100  that embodies the invention. 
         FIG. 2  is a schematic representation of a cross-section of an electronic device that embodies the invention. 
         FIG. 3  is a schematic representation of a cross-section of another electronic device that embodies the invention. 
         FIG. 4  is a schematic representation of a cross-section of yet another electronic device that embodies the invention. 
     
    
    
     DETAILED DESCRIPTION 
     In the following description, numerous specific details are set forth. However, it is understood that embodiments of the invention may be practiced without these specific details. In other instances, well-known circuits, structures and techniques have not been shown in detail in order not to obscure the understanding of this description. 
     In the following description, reference is made to the accompanying drawings, which illustrate several embodiments of the present invention. It is understood that other embodiments may be utilized, and mechanical compositional, structural, electrical, and operational changes may be made without departing from the spirit and scope of the present disclosure. The following detailed description is not to be taken in a limiting sense, and the scope of the embodiments of the present invention is defined only by the claims of the issued patent. 
     The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. Spatially relative terms, such as “beneath”, “below”, “lower”, “above”, “upper”, and the like may be used herein for ease of description to describe one element&#39;s or feature&#39;s relationship to another element(s) or feature(s) as illustrated in the figures. It will be understood that the spatially relative terms are intended to encompass different orientations of the device in use or operation in addition to the orientation depicted in the figures. For example, if the device in the figures is turned over, elements described as “below” or “beneath” other elements or features would then be oriented “above” the other elements or features. Thus, the exemplary term “below” can encompass both an orientation of above and below. The device may be otherwise oriented (e.g., rotated 90 degrees or at other orientations) and the spatially relative descriptors used herein interpreted accordingly. 
     As used herein, the singular forms “a”, “an”, and “the” are intended to include the plural forms as well, unless the context indicates otherwise. It will be further understood that the terms “comprises” and/or “comprising” specify the presence of stated features, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, steps, operations, elements, components, and/or groups thereof. 
       FIG. 1  shows a pictorial view of an electronic device  100  that embodies the invention. The electronic device  100  includes a transparent surface  102  that forms a wall of the housing  104  that encloses the device. A light emitting device  106  is located in the housing  104  such that light is emitted through the transparent surface  102 . For example, the light emitting device  106  may be a display screen that is viewable through the transparent surface  102  as shown in the figure. A light sensor  108  is also located in the housing  104  such that ambient light falling on at least a portion of the transparent surface  102  is received by the light sensor to provide an ambient light value responsive to the level of ambient light. 
       FIG. 2  shows a schematic representation of a cross-section of an electronic device that embodies the invention. A retarder  200  and a linear polarizer  202  are placed between the transparent surface  102  and the light emitting device  106 . Ambient light  220  passes through the retarder  200  and the linear polarizer  202  after passing through the transparent surface  102  to reach the light sensor  108 . The retarder may provide a nominal quarter wave retardation to transform linearly polarized light to circularly polarized light. The retarder may be a birefringent material such as a stretched polymer (PET, COP etc.) or a birefringent inorganic (Quartz, Sapphire, etc.). 
     In the embodiment shown in  FIG. 2 , the linear polarizer  202  is between the retarder  200  and the light emitting device  106  such that the ambient light  220  passes through the transparent surface  102 , then the retarder  200 , and then the linear polarizer  202  before being received by the light sensor  108 . 
     In the embodiment shown in  FIG. 2 , the light sensor  108  is adjacent the light emitting device  106 . A photosensitive surface of the light sensor  108  is at substantially the same distance from the transparent surface  102  as a light emitting surface of the light emitting device  106 , such that light emitted by the light emitting device is not directly incident on the photosensitive surface of the light sensor. It will be appreciated that the light sensor may be located in other ways so that light emitted by the light emitting device is not directly incident on the photosensitive surface of the light sensor. 
     Light  210  that is emitted by the light emitting device  106  and reflected internally by the transparent surface  102  is attenuated by the retarder  200  and linear polarizer  202  so that the effect of the internally reflected light  212  on the light sensor  108  is minimized. The emitted light  210  first passes through the linear polarizer  202  and only linearly polarized light emerges. The emerging light is polarized in a first direction as determined by the linear polarizer  202 . The linearly polarized light then passes through the retarder  200  and emerges as circularly polarized light with a given handedness, for example right hand circularly polarized. The circularly polarized light then passes through the transparent surface  102 . 
     However, depending on the angle of incidence with the transparent surface  102 , all or some portion of the incident emitted light  210  that is circularly polarized may be internally reflected by the transparent surface  102 . The internally reflected light  212  is circularly polarized with an opposite handedness from the circularly polarized incident emitted light  210 , for example left hand circularly polarized. The internally reflected light  212  that is now circularly polarized then passes through the retarder  200  and emerges as linearly polarized light. Because the internally reflected light  212  is circularly polarized with the opposite handedness from the circularly polarized incident emitted light  210 , the internally reflected light  212  emerges from the retarder  200  linearly polarized in a second direction that is orthogonal to the first direction of linear polarization of the emitted light  210  that emerges from the linear polarizer  202 . The emerging linearly polarized internally reflected light  212  is therefore substantially attenuated by the linear polarizer  202 . Thus little of the emitted light  210  that is emitted by the light emitting device  106  and reflected internally by the transparent surface  102  reaches the light sensor  108 . The attenuation of the emerging linearly polarized internally reflected light  212  depends on extinction ration of the polarizer, and birefringence of the path that light travels. An extinction ratio of 100:1 or higher is achievable. 
       FIG. 3  shows a schematic representation of a cross-section of another electronic device that embodies the invention. A first linear polarizer  202  is between the retarder  200  and the light emitting device  106  such that the ambient light  220  passes through the transparent surface  102 , then the retarder  200 , and then the first linear polarizer  202  before being received by the light sensor  308 . Light  210  that is emitted by the light emitting device  106  and reflected internally by the transparent surface  102  is attenuated before reaching the light sensor  308  as described above for the embodiment shown in  FIG. 2 . 
     In the embodiment shown in  FIG. 3 , the light sensor  308  is located such that some light  310 ,  312  emitted by the light emitting device  106  is directly incident on the photosensitive surface of the light sensor. The light sensor has two channels  308 ,  309 . Ambient light  220  and light  310  emitted by the light emitting device  106  reaches the first channel  308  of the light sensor to produce a first light level value. 
     The ambient light  220  is linearly polarized by the first linear polarizer  202 . A second linear polarizer  304  attenuates the ambient light  220  directed toward a second channel  309  of the light sensor because the second linear polarizer is oriented orthogonally to the first linear polarizer  202 . The amount of ambient light  220  that is not attenuated by the second linear polarizer  304  and which therefore reaches the second channel  309  of the light sensor is negligible. Thus, primarily light  312  emitted by the light emitting device  106  reaches the second channel  309  of the light sensor. The second channel  309  of the light sensor produces a second light level value that is responsive to the amount of light  312  emitted by the light emitting device  106 . 
     The first light level value produced by the ambient light that falls on the first channel  308  of the light sensor will be approximately double the second light level value produced by the ambient light that passes through the second linear polarizer  304  and then falls on the second channel  309  of the light sensor. The ratio of the first light level value to the second light level value can be calibrated. The difference between the first light level value and the second light level value can be used to remove the effect of the light  310 ,  312  emitted by the light emitting device  106  when determining the ambient light level. 
     An ambient light detection circuit  330  is coupled to first channel  308  and the second channel  309  of the light sensor. The ambient light detection circuit  330  provides an ambient light level value  332  responsive to the difference between the first light level value and the second light level value. The ambient light level value  332  is indirectly responsive to amount of ambient light  220  reaching the first channel  308  of the light sensor because the effect of the light  312  emitted by the light emitting device  106  is cancelled by taking the difference between the two channels of the light sensor. The ambient light level values may be analog voltages, digitally encoded values, or other representations of the ambient light level as may be used by ambient light detection circuit  330  and/or the other circuits within the electronic device  100 . 
       FIG. 4  shows a schematic representation of a cross-section of yet another electronic device that embodies the invention. A first retarder  400  is between a first linear polarizer  402  and the light emitting device  106 . The first retarder  400  may also provide additional benefits such as reducing the reflectance of the light emitting device&#39;s internal layers such as wires, and traces. Ambient light  220  passes through the first linear polarizer  402  and then the first retarder  400  before being received by the light sensor  408 . 
     In the embodiment shown in  FIG. 4 , the light sensor  408  is located such that some light  410 ,  412  emitted by the light emitting device  106  is directly incident on the photosensitive surface of the light sensor. The light sensor has two channels  408 ,  409 . Ambient light  220  and light  410  emitted by the light emitting device  106  reaches the first channel  408  of the light sensor to produce a first light level value. 
     The ambient light  220  is linearly polarized by the first linear polarizer  402  and then circularly polarized by the first retarder  400 . A second retarder  440  is in the path of the ambient light  220  directed to the second channel  409  of the light sensor. The second retarder  440  has the opposite handedness from the first retarder  400 . The second retarder  440  linearly polarizes the circularly polarized ambient light  220  orthogonally to the direction of polarization by the first linear polarizer  402 . 
     A second linear polarizer  442  attenuates the ambient light  220  directed toward the second channel  409  of the light sensor because the second linear polarizer is oriented orthogonally to the direction of polarized light emanating from the second retarder  440 . Thus, primarily light  412  emitted by the light emitting device  106  reaches the second channel  409  of the light sensor. The amount of ambient light  220  that is not attenuated by the second linear polarizer  442  and which therefore reaches the second channel  409  of the light sensor is negligible. The second channel  409  of the light sensor produces a second light level value that is responsive to the amount of light  412  emitted by the light emitting device  106 . 
     An ambient light detection circuit  430  is coupled to first channel  408  and the second channel  409  of the light sensor. The ambient light detection circuit  430  provides an ambient light level value  432  responsive to the difference between the first light level value and the second light level value. The ambient light level value  432  is indirectly responsive to amount of ambient light  220  reaching the first channel  408  of the light sensor because the effect of the light  410  emitted by the light emitting device  106  is cancelled by taking the difference between the two channels of the light sensor adjusted for the attenuation of the light emitted by the light emitting device by the second retarder  440  and the second linear polarizer  442 . 
     The portion of the first light level value produced by the light  410  emitted by the light emitting device  106  that falls on the first channel  408  of the light sensor will be approximately double the second light level value produced by the light emitted by the light emitting device that passes through the second retarder  440  and the second linear polarizer  442  and then falls on the second channel  409  of the light sensor. The ratio of the first light level value to the second light level value can be calibrated. The ambient light level values may be analog voltages, digitally encoded values, or other representations of the ambient light level as may be used by ambient light detection circuit  430  and/or the other circuits within the electronic device  100 . 
     While certain exemplary embodiments have been described and shown in the accompanying drawings, it is to be understood that such embodiments are merely illustrative of and not restrictive on the broad invention, and that this invention is not limited to the specific constructions and arrangements shown and described, since various other modifications may occur to those of ordinary skill in the art. The description is thus to be regarded as illustrative instead of limiting.

Metadata:
Filing Date: 20131107
Publication Date: 20170404
Grant Date: 20170404
Priority Date: 20131107
Inventors: DEJONG ERIK G.
GUILLOU JEAN-PIERRE S.
AFLATOONI KOOROSH
Assignee: APPLE INC
CPC Classifications: [{"code": "G01J1/32", "inventive": true, "first": false, "tree": "[]"}, {"code": "G01J1/0429", "inventive": true, "first": false, "tree": "[]"}, {"code": "G01J1/4204", "inventive": true, "first": true, "tree": "[]"}, {"code": "G01J1/4204", "inventive": true, "first": true, "tree": "[]"}, {"code": "G01J1/0429", "inventive": true, "first": false, "tree": "[]"}, {"code": "G01J1/32", "inventive": true, "first": false, "tree": "[]"}]
Family ID: 52513694