Abstract:
Electronic displays encounter visibility issues due to varying ambient light conditions. An ambient light sensor can be provided to sense ambient light and dynamically adjust display brightness to compensate for changes in ambient light. A wave guide for improving angular response in a light sensor is provided.

Description:
FIELD 
       [0001]    The present specification relates generally to light sensors and more particularly relates to a wave guide for improving angular response in a light sensor. 
       BACKGROUND 
       [0002]    Flat panel displays such as liquid crystal displays (LCD) are now commonplace in portable electronic devices, computers, televisions, cellular telephones, and in other display applications. Ambient light conditions, however, can dramatically impact the display characteristics, resulting in poor display visibility. To compensate for varying ambient light conditions, and to take opportunities to reduce power consumption, ambient light sensors may be included in the displays. Such ambient light sensors attempt to detect the amount of ambient light and provide input to control circuitry which can automatically adjust the brightness of the display, according to the amount of sensed ambient light. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0003]      FIG. 1  is an isometric representation of a display assembly. 
           [0004]      FIG. 2  is a schematic cross-sectional representation of the light sensor of the assembly of  FIG. 1 , the cross-section being taken along the dashed-lines indicated as  2 - 2  in  FIG. 1 . 
           [0005]      FIG. 3  shows the window, wave guide and photodetector of  FIG. 2  in greater detail. 
           [0006]      FIG. 4  shows an idealized response curve of the intensity of light that reaches the sensor of  FIG. 3  as a result of the configuration of the wave guide of  FIG. 3 . 
           [0007]      FIG. 5  shows a first exemplary configuration of the wave guide of  FIG. 3 . 
           [0008]      FIG. 6  shows a second exemplary configuration of the wave guide of  FIG. 3 . 
           [0009]      FIG. 7  shows a third exemplary configuration of the wave guide of  FIG. 3 . 
           [0010]      FIG. 8  shows a fourth exemplary configuration of the wave guide of  FIG. 3 . 
           [0011]      FIG. 9  shows a plurality of further response curves. 
           [0012]      FIG. 10  shows a light sensor assembly as a variation on the assembly of  FIG. 2 . 
       
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
       [0013]    An aspect of this specification provides a display assembly comprising: a display; a light sensor module mounted proximally to said display; a controller connected to said light sensor module and configured to receive an electronic signal representing a measurement of ambient light incident on said display; said controller connected to said display and configured to adjust brightness of said display based on said electronic signal; said light sensor module comprising a window for transmitting ambient light; a light sensor for receiving said ambient light and configured to generate said electronic signal; a wave guide comprising a textured surface disposed between said window and said light sensor; said textured surface having a geometric structure; said geometric structure configured according to a material and a thicknesses of said window; said geometric structure further configured to guide ambient light travelling through said window onto said light sensor such that an intensity of ambient light that strikes said sensor varies substantially proportionally according to a function comprising a cosine of an angle of incidence of ambient light striking said window. 
         [0014]    The geometric structure can be further configured such that said ambient light strikes said sensor at an angle that is substantially normal to said sensor regardless of said angle of incidence. 
         [0015]    The display assembly can further comprise a substrate; said textured surface applied to said substrate; said substrate for mechanically affixing said wave guide to said window. The substrate can be affixed via an adhesive. The geometric structure can be further configured according to a material and thickness of said substrate. 
         [0016]    The textured surface can be integrally formed into said window. 
         [0017]    The textured surface can comprise a plurality of bosses. 
         [0018]    The bosses can be trapeziums, partial-spheroids, or four-sided pyramids. 
         [0019]    The bosses can be regularly spaced, or irregularly spaced. 
         [0020]    The textured surface can be made from one of polymethyl methacrylate, polyethylene terephthalate, acrylic, or epoxy. 
         [0021]    The wave guide can be made from a material having a refractive index of between about 1.4 and about 1.7. 
         [0022]    The light sensor module can further comprise a light emitter configured to emit light at a first angle; said wave guide configured to scatter light emitted from said light emitter out of said window at angle wider than said first angle. 
         [0023]    The display assembly can be configured for incorporation into a portable electronic device and said light emitter is configured to indicate a status of said portable electronic device. 
         [0024]    Another aspect of the specification provides a light sensor module according to any of the foregoing. 
         [0025]    Another aspect of the specification provides a wave guide according to any of the foregoing. 
         [0026]    Referring now to  FIG. 1 , a display assembly is indicated generally at  50 . Display assembly  50  comprises a display  54 , a light sensor module  58 , and a controller  62 . Display assembly  50  can be incorporated into any electronic apparatus having a display, including but not limited to portable electronic devices, computers, televisions, cellular telephones, desktop telephones, and major appliances. 
         [0027]    Display  54  comprises one or more light emitters such as an array of light emitting diodes (LED), liquid crystals, plasma cells, or organic light emitting diodes (OLED). Other types of light emitters are contemplated. Such light emitters, when activated by controller  62 , produce emitted light, as indicated by the arrows labeled “EL” in the Figures. Emitted light EL is shown as being emitted substantially normally from the surface of display  54 , although the actual viewing range can be much wider. 
         [0028]    Display  54  is also subject to incident ambient light AL. In  FIG. 1 , ambient light AL is shown as incident in a direction that is substantially normal to the surface of display  54 . Those skilled in the art will appreciate that ambient light AL can reduce the visibility of emitted light EL. Controller  62  is therefore configured to receive an electrical signal from sensor module  58  representing an intensity of ambient light AL and to adjust the brightness of emitted light EL to compensate for reduced visibility of emitted light EL due to ambient light AL. As will be discussed further below, display assembly  50  is configured to respond to ambient light AL that is incident from a range of different angles. 
         [0029]    As best seen in  FIG. 2 , light sensor module  58  comprises a light sensor or other type of photodetector  66  that is configured to convert ambient light AL that is incident on photodetector  66  into an electrical signal ES. Electrical signal ES has a voltage or other electrical characteristic that is generally proportional to the intensity (expressed as, for example, in units of lux) of ambient light AL that lands on photodetector  66 . Electrical signal ES is received at controller  62  which is configured to brighten or dim display  54  accordingly. 
         [0030]    Light sensor module  58  also comprises a housing  70  and a cover  74 . Housing  70  comprises a chassis  72  that is shaped so as to define a light transmissive chamber  78 , and photodetector  66  is disposed within the end of chamber  78  that is opposite to cover  74 . Chamber  78 , in a present embodiment, contains air and is therefore transmissive of ambient light EL. 
         [0031]    Cover  74  comprises a frame  76  that overlays chassis  72 . Frame  72  is also shaped to define a window  82 . A wave guide  86  is disposed within chamber  78  between window  82  and photodetector  66 . In a present embodiment, wave guide  86  abuts window  82 . As will be discussed in greater detail below, wave guide  86  can be a separate item from window  82 , or wave guide  86  can be integrally formed into window  82 . 
         [0032]    Chassis  72  and frame  76  are substantially mechanical in function and therefore can be of any suitable material to achieve the desired mechanical characteristics of the corresponding display assembly  50  application. For example, where display assembly  58  is part of a display in a portable electronic device, chassis  72  and frame  76  will be made from materials and dimensioned to be rugged enough to mechanically support window  82 , wave guide  86  and photodetector  66 , within light sensor module  58 , and also be rugged enough to withstand dropping or other types of physical blows to which a portable electronic device can be commonly subjected. 
         [0033]    By the same token, window  82 , wave guide  86 , chamber  78  and photodetector  66  are substantially optical in function, (or in the case of photodetector  66 , electro-optical), and as will be discussed further below, are therefore selected from materials that provide the desired optical, (or electro-optical) characteristics. Again, within the context of display assembly  58  being used within a portable electronic device, window  82 , wave guide  86  and photodetector  66  are also configured to provide a certain degree of mechanical ruggedness, again so that the entire display assembly  50  can withstanding the physical blows to which a portable electronic device can be commonly subjected. 
         [0034]    As will be discussed further below, wave guide  86  can be physically integrated into window  82 , or each can be separate items which are mechanically affixed to each other (e.g. via an adhesive) at the time of assembly. 
         [0035]      FIG. 3  shows an embodiment of window  82 , wave guide  86  and photodetector  86  in greater detail. In  FIG. 3 , wave guide  86  includes a substrate  88  and a textured surface  90 .  FIG. 3  also shows two separate representative beams of ambient light AL- 1 , and AL- 2 . 
         [0036]    Ambient light AL- 1  is shown as incident at an angle AI 1  that is normal to the surface of window  82 . Angle AI 1  is assigned the variable Θ 1  in  FIG. 3 , where Θ 1  equals ninety degrees. Ambient light AL- 1  is also shown as having intensity I 1  when ambient light l 1  strikes the surface of window  82 . Intensity I 1  is assigned the variable X in  FIG. 3 . I 1  can be expressed in units of lux. For purposes of explaining this embodiment, X can be any value associated with ambient light conditions. 
         [0037]    Ambient light AL- 2  is shown as incident at an angle AI 2  that is less than ninety degrees to the surface of window  82 . Angle AI 2  is assigned the variable Θ 2  in  FIG. 3 . Ambient light AL- 2  is also shown as having intensity I 2  when ambient light l 2  strikes the surface of window  82 . For purposes of explaining this embodiment, I 2  is deemed to equal I 1 , and therefore I 1 =X. 
         [0038]    Window  82  can be characterized in terms of its material with an associated index of refraction n 1 , and having a particular thickness T 1 . The index of refraction n 1  of window  82  is represented in  FIG. 3  by the change in angle of ambient light AL- 2  as ambient light AL- 2  travels through window  82 . 
         [0039]    Substrate  88  can be also characterized in terms of its material with an associated index of refraction n 2 , and having a particular thickness T 2 . The index of refraction n 2  of substrate  88  is represented in  FIG. 3  by the change in angle of ambient light AL- 2  as ambient light AL- 2  travels through substrate  88 . 
         [0040]    What is not represented in  FIG. 3 , but will occur to those of skill in the art, are the reflections at the junctions between different adjacent materials. Thus, a certain amount of ambient light AL- 1  will be internally reflected as ambient light AL- 1  enters and exits window  82 , and enters and exits substrate  88 , and enters and exits textured surface  90 . Accordingly, in an actual implementation, the actual intensity of ambient light AL- 1  and ambient light AL- 2  entering chamber  78  will be less than intensity I 1  and intensity I 2  due to attenuation and losses resulting from passing through window  82  and wave guide  86 . Such attenuation is not represented in  FIG. 3  for purposes of simplifying explanation. 
         [0041]    Textured surface  90  is defined by a three-dimensional geometric structure that is configured based on the materials and thicknesses of window  82  and substrate  88 , such that the intensity of ambient light that strikes photodetector  66  varies substantially proportionally to the cosine of the angle of incidence of the ambient light striking window  82 . Additionally, the three-dimensional geometric structure of textured surface  90  is configured such that ambient light strikes photodetector  66  at an angle that is substantially normal to photodetector  66 , regardless of the angle that the ambient light actually strikes window  82 . 
         [0042]    (It should now be apparent that in certain configurations, textured surface  90  can be integrally formed with window  82 , thereby obviating the need for substrate  88 . In this configuration, the same principles as the previous paragraph apply, except that only the material and thickness of window  82  need be considered.) 
         [0043]    In  FIG. 3 , the intensity of ambient light AL that strikes the surface of sensor  66  is represented by the variable Y. Thus, in mathematical terms, the geometric structure of textured surface is configured according the following function: 
         [0000]        Y=I (cos( AI ))  Function 1:
 
       Where: 
       [0044]    Y is the intensity of ambient light that strikes the surface of photodetector  66   
         [0045]    I is the intensity of light that strikes the surface of window  82   
         [0046]    AI is the angle of incidence of light as it strikes the surface of window  82 . 
         [0047]    A graph of plotting Function 1, where I=1, is shown in  FIG. 4 . 
         [0048]    Various materials for wave guide  86  are contemplated, including polycarbonate, polymethyl methacrylate, polyethylene terephthalate, acrylic, and epoxy. As desired for a particular configuration, such materials can also be used for window  82 . 
         [0049]    Presently, any material can be chosen that has suitable mechanical properties and has a refractive index of between about 1.4 and about 1.7. 
         [0050]    Presently, textured surface  90  is configured for range of the visible electro-magnetic spectrum, and certain wavelengths at the periphery of that spectrum, specifically wavelengths of between about 350 nanometers and about 900 nanometers. 
         [0051]      FIG. 5  shows a non-limiting exemplary embodiment of a specific geometric structure for textured surface  90 , although in  FIG. 5  the textured surface of this specific embodiment is indicated at reference  90 A, within a specific wave guide  86 A. Textured surface  90 A is thus comprised of a plurality of bosses in the form of trapeziums  94 A. While  FIG. 5  shows each trapezium  94 A as aligned, in variations the trapeziums can be irregularly aligned. 
         [0052]    The thickness of textured surface  90 A is, in the present embodiment, between about 0.001 millimeters and about five millimeters, and the material for textured surface  90 A can be polycarbonate, polymethyl methacrylate, polyethylene terephthalate, acrylic, or epoxy. In a present embodiment substrate  88 A is integral with window  82 A. In the present embodiment, substrate  88 A is etched directly onto window  82 A. Substrate  88 A has a thickness of about 0.05 millimeters to about two millimeters. Window  82 A has a thickness of about 0.1 millimeters to about five millimeters. Table I shows the various dimensions for each trapezium  94 A. 
         [0000]    
       
         
               
             
               
               
               
               
               
             
               
               
               
               
               
             
           
               
                 TABLE I 
               
             
             
               
                   
               
               
                 Dimensions for Trapezium 94A 
               
             
          
           
               
                 Dimension 
                   
                   
                   
                   
               
               
                 reference 
                 Type 
                 Dimension 
                 Unit 
                 Tolerance 
               
               
                   
               
             
          
           
               
                  98A 
                 Angle 
                 48 
                 Degree 
                 +/−12  
               
               
                 100A 
                 Length 
                 0.01 
                 mm 
                 +5/−0.01 
               
               
                 104A 
                 Radius 
                 0.01 
                 mm 
                 +0.5/−0.01     
               
               
                 108A 
                 Length 
                 0.05 
                 mm 
                 +5/−0.04 
               
               
                   
               
             
          
         
       
     
         [0053]      FIG. 6  shows another non-limiting exemplary embodiment of another specific geometric structure for textured surface  90 , although in  FIG. 6  the textured surface of this specific embodiment is indicated at reference  90 B, within a specific wave guide  86 B. Textured surface  90 B is thus comprised of a plurality of bosses in the form of partial-spheroids  94 B. While  FIG. 6  shows each semi-spheroid  94 B as aligned, in variations the partial-spheroids  94 B can be irregularly aligned. 
         [0054]    The thickness of textured surface  90 B is, in the present embodiment, between about 0.001 millimeters and about five millimeters, and the material for textured surface  90 B can be polycarbonate, polymethyl methacrylate, polyethylene terephthalate, acrylic, or epoxy. In a present embodiment substrate  88 B is integral with window  82 B. In the present embodiment, substrate  88 B is etched directly onto window  82 B. Substrate  88 B has a thickness of about 0.05 millimeters to about two millimeters. Window  82 B has a thickness of about 0.1 millimeters to about five millimeters. Table II shows the various dimensions for each partial-spheroid  94 B. 
         [0000]    
       
         
               
             
               
               
               
               
               
             
               
               
               
               
               
             
           
               
                 TABLE II 
               
             
             
               
                   
               
               
                 Dimensions for Partial-Spheroid 94B 
               
             
          
           
               
                 Dimension 
                   
                   
                   
                   
               
               
                 reference 
                 Type 
                 Dimension 
                 Unit 
                 Tolerance 
               
               
                   
               
             
          
           
               
                  98B 
                 Angle 
                 44.91 
                 Degrees 
                 +/−15  
               
               
                 100B 
                 Length 
                 0.03 
                 mm 
                 +5/−0.03 
               
               
                 104B 
                 Radius 
                 0.01 
                 mm 
                 +5/−0.01 
               
               
                   
               
             
          
         
       
     
         [0055]      FIG. 7  shows another non-limiting exemplary embodiment of another specific geometric structure for textured surface  90 , although in  FIG. 7  the textured surface of this specific embodiment is indicated at reference  90 C, within a specific wave guide  86 C. Textured surface  90 C is thus comprised of a plurality of bosses in the form of four-sided pyramids  94 C. While  FIG. 7  shows each four-sided pyramid  94 C as aligned, in variations the four-sided pyramids  94 C can be irregularly aligned. 
         [0056]    The thickness of textured surface  90 C is, in the present embodiment, between about 0.001 millimeters and about five millimeters, and the material for textured surface  90 B can be polycarbonate, polymethyl methacrylate, polyethylene terephthalate, acrylic, or epoxy. In a present embodiment substrate  88 C is integral with window  82 C. In the present embodiment, substrate  88 C is etched directly onto window  82 C. Substrate  88 C has a thickness of about 0.05 millimeters to about two millimeters. Window  82 C has a thickness of about 0.1 millimeters to about five millimeters. Table III shows the various dimensions for each four-sided pyramid  94 C. 
         [0000]    
       
         
               
             
               
               
               
               
               
             
               
               
               
               
               
             
           
               
                 TABLE III 
               
             
             
               
                   
               
               
                 Dimensions for Four-Sided pyramids 94C 
               
             
          
           
               
                 Dimension 
                   
                   
                   
                   
               
               
                 reference 
                 Type 
                 Dimension 
                 Unit 
                 Tolerance 
               
               
                   
               
             
          
           
               
                  98C 
                 Angle 
                 75 
                 Degrees 
                 +15/−15    
               
               
                 100C 
                 Length 
                 0.018 
                 millimeters 
                 +5/−0.015 
               
               
                 104C 
                 Length 
                 0.015 
                 millimeters 
                 +5/−0.015 
               
               
                   
                 (between each 
               
               
                   
                 pyramid) 
               
               
                 108C 
                 Radius 
                 Zero 
                 millimeters 
                 +/−2   
               
               
                   
               
             
          
         
       
     
         [0057]      FIG. 8  shows another non-limiting exemplary embodiment of another specific geometric structure for textured surface  90 , although in  FIG. 8  the textured surface of this specific embodiment is indicated at reference  90 D, within a specific wave guide  86 D. Textured surface  90 D is thus comprised of a plurality of bosses in the form of four-sided pyramids  94 D. While  FIG. 8  shows each four-sided pyramid  94 D as aligned, in variations the four-sided pyramids  94 C can be irregularly aligned. 
         [0058]    The thickness of textured surface  90 D is, in the present embodiment, between about 0.001 millimeters and about five millimeters, and the material for textured surface  90 D can be polycarbonate, polymethyl methacrylate, polyethylene terephthalate, acrylic, or epoxy. In a present embodiment substrate  88 D is integral with window  82 D. In the present embodiment, substrate  88 D is etched directly onto window  82 D. Substrate  88 D has a thickness of about 0.05 millimeters to about two millimeters. Window  82 D has a thickness of about 0.1 millimeters to about five millimeters. Table IV shows the various dimensions for each four-sided pyramid  94 D. 
         [0000]    
       
         
               
             
               
               
               
               
               
             
               
               
               
               
               
             
           
               
                 TABLE IV 
               
             
             
               
                   
               
               
                 Dimensions for Four-Sided pyramids 94D 
               
             
          
           
               
                 Dimension 
                   
                   
                   
                   
               
               
                 reference 
                 Type 
                 Dimension 
                 Unit 
                 Tolerance 
               
               
                   
               
             
          
           
               
                  98D 
                 Angle 
                 86 
                 Degrees 
                 +/−10  
               
               
                 100D 
                 Length 
                 0.03 
                 millimeters 
                 +5/−0.03 
               
               
                 104D 
                 Length 
                 0.02 
                 millimeters 
                 +5/−0.02 
               
               
                   
                 (between each 
               
               
                   
                 pyramid) 
               
               
                 108D 
                 Radius 
                 0.015 
                 millimeters 
                  +2/−0.015 
               
               
                   
               
             
          
         
       
     
         [0059]    It is to be understood that Function 1 in  FIG. 4  is an idealized target profile for Y (where Y varies to Intensity I and Angle of Incidence AI) in the establishment of a configuration of textured surface  90 . The actual function that can result in relation to a particular geometric structure of textured surface  90  has a range of acceptable deviation from Function 1, such that in certain embodiments the geometric structure of textured surface  90  results in a profile that substantially conforms with Function 1, without exactly matching Function 1.  FIG. 9  shows a variety of different curves to illustrate. In  FIG. 9 , curve  150  is the curve that corresponds with Function 1 and as shown in  FIG. 4 . Curve  154  shows the response curve associated with textured surface for four-sided pyramid  94 C when ambient light AL is incident along the plane shown in  FIG. 3 . Curve  158  shows the response curve associated with textured surface for four-sided pyramid  94 C when ambient light is incident along the plane that is normal to the plane shown in  FIG. 3 . 
         [0060]    Again recall that curve  150  is the curve that corresponds with Function 1 and as shown in  FIG. 4 . Ranges of design tolerances for curve  150  are also proposed herein, including curve  162  shows an exemplary upper tolerance boundary for design specifications for the geometric structure of textured surface  90 , while curve  166  shows an exemplary lower tolerance boundary for design specifications the geometric structure of textured surface  90 . Presently, an upper tolerance from Function 1 can be about positive five percent (+5%) a lower tolerance from Function 1 can be about negative five percent (−5%). 
         [0061]    Curve  170  shows a measured response for a prior art device that does not include wave guide  86 . The prior art device is a BlackBerry Bold™ from Research in Motion Inc., of Waterloo, Ontario Canada. 
         [0062]    Variations the foregoing are contemplated. For example, chamber  78  can be a vacuum or filled with a light transmissive medium. However, adjustments to wave guide  86  will be made to accommodate the index of refraction and other optical characteristics whatever medium is used within chamber  78 . As another example the means by which light sensor module  58  incorporates wave guide  86  is not particularly limited. For example, wave guide  86  can be produced as a separate item that is affixed to window  82 . Alternatively, textured surface  90  can be formed directly on the surface of window  82  that is nearest to chamber  78 , thereby obviating the need for substrate  88  altogether. 
         [0063]    A still further variation is shown in  FIG. 10 , which shows a light sensor module  58 E. Light sensor module  58 E includes many of the same components of light sensor module  58 , and accordingly like elements bear like references, except followed by the suffix “E”. However, in light sensor module  58 E, photodetector  66 E is reduced in size to allow for alight emitter such as a light emitting diode (LED)  200 E. Light sensor module  58 E can be incorporated into a portable electronic device where LED  200 E can be used as an indicator light. The indicator light can be used, for example, to indicate a low battery condition of the device. Other functions for the indicator light are contemplated. For example, where the portable electronic device includes wireless telephony or email messaging capability, then LED  200 E can be used to indicate the presence of a wireless network. LED  200 E can also be of the type that is configured to generate multiple colours. In module  58 E, wave guide  86 E has two functions: first to direct ambient light onto photodetector  66 E as previously discussed, and second to help scatter light emitted from LED  200 E out of window  82 E across a wider range of angles. 
         [0064]    While certain specific embodiments have been discussed herein, combinations, subsets and variations of those embodiments are contemplated. It is the claims attached hereto that define the scope of time-limited exclusive privilege of this specification.