PATENT DOCUMENT

Publication Number: US-10739638-B2
Application Number: US-201916409688-A
Country: US
Kind Code: B2

Title: Backlight units with support posts and cavity height monitoring

Abstract:
An electronic device may have a display with a backlight. The backlight provides backlight illumination for an array of pixels that is displaying images. The backlight may include an array of cells. Each cell may contain a light source with one or more light-emitting diodes and a cavity reflector that reflects light from the light source outwardly through a diffuser for use in forming the backlight illumination. The light sources may be mounted to a printed circuit. Support posts on the printed circuit may be used to maintain the diffuser at a fixed distance from the printed circuit. Sensors on the printed circuit may be used to measure separation distances between the printed circuit and diffuser. Adjustments to pixel gain profiles can be made based on the measured separation distances.

Claims:
What is claimed is: 
     
       1. A display, comprising:
 an array of pixels configured to display images; 
 a backlight configured to produce backlight illumination for the array of pixels, wherein the backlight has a two-dimensional array of cells that each include a light source and a reflector, a printed circuit on which the light sources are mounted, a diffuser, and support posts interspersed that are configured to support the diffuser, wherein the support posts include clear polymer portions; and 
 an array of optical sensors on the printed circuit that measure respective separation distances between the diffuser and the printed circuit. 
 
     
     
       2. The display defined in  claim 1  wherein the support posts include white polymer portions. 
     
     
       3. The display defined in  claim 2  wherein each of the clear polymer portions covers at least part of a respective one of the white polymer portions. 
     
     
       4. The display defined in  claim 2  wherein the white polymer portions have rounded tips each of which is covered by a respective one of the clear polymer portions. 
     
     
       5. The display defined in  claim 2  wherein the white polymer portions are cylindrical. 
     
     
       6. The display defined in  claim 1  wherein the clear polymer portions are tapered. 
     
     
       7. The display defined in  claim 1  further comprising screws that each attach a respective one of the support posts to the printed circuit. 
     
     
       8. The display defined in  claim 7  further comprising elastomeric gaskets, wherein a respective one of the elastomeric gaskets is interposed between at least part of each screw and the printed circuit. 
     
     
       9. The display defined in  claim 1  wherein the support posts are formed from protrusions in the diffuser. 
     
     
       10. The display defined in  claim 1  wherein at least some of the support posts are conical. 
     
     
       11. The display defined in  claim 10  wherein the conical support posts have diameters that are smaller at the diffuser than at the printed circuit. 
     
     
       12. The display defined in  claim 1  wherein the support posts are interspersed with the optical sensors on the printed circuit. 
     
     
       13. The display defined in  claim 1  further comprising display driver circuitry with a look-up table configured to maintain a pixel gain profile that compensates the images for backlight intensity variations across the array of pixels. 
     
     
       14. The display defined in  claim 13  further comprising control circuitry that is configured to update the pixel gain profile in the look-up table in response to measurements of the separation distances from the array of optical sensors. 
     
     
       15. The display defined in  claim 1  wherein the optical sensors each include a light-emitting diode and a light detector configured to detect light from the light-emitting diode that has reflected from the diffuser. 
     
     
       16. A display, comprising:
 an array of pixels configured to display images; and 
 a backlight configured to produce backlight illumination for the array of pixels, wherein the backlight has a two-dimensional array of cells that each include a light source and a reflector, a printed circuit on which the light sources are mounted, a diffuser, and an array of support posts that are attached to the diffuser with adhesive and that are configured to separate the diffuser from the printed circuit, wherein the support posts have a lower cylindrical portion with a first diameter and an upper flared portion with an increasing diameter between the lower cylindrical portion and the diffuser, wherein the upper flared portion has a second diameter at the diffuser that is greater than the first diameter, wherein at least part of the upper flared portion comprises clear polymer, and wherein the clear polymer of the upper flared portion is configured to refract the backlight illumination. 
 
     
     
       17. The display defined in  claim 16  further comprising optical sensors on the printed circuit that are configured to measure respective separation distances between the diffuser and the printed circuit. 
     
     
       18. A display, comprising:
 an array of pixels configured to display images; and 
 a backlight configured to produce backlight illumination for the array of pixels, wherein the backlight has a two-dimensional array of cells that each include a light source and a reflector, a printed circuit on which the light sources are mounted, and a diffuser and wherein the backlight further comprises support posts that are configured to separate the diffuser from the printed circuit by a distance and optical sensors that measure respective distances between the printed circuit and the diffuser.

Description:
This application is a continuation of International Application PCT/US2018/022935, with an international filing date of Mar. 16, 2018, which claims priority to U.S. patent application Ser. No. 15/687,374, filed on Aug. 25, 2017, which claims the benefit of provisional patent application No. 62/501,002, filed on May 3, 2017, which are hereby incorporated by reference herein in their entireties. 
    
    
     BACKGROUND 
     This relates generally to displays, and, more particularly, to backlit displays. 
     Electronic devices often include displays. For example, computers and cellular telephones are sometimes provided with backlit liquid crystal displays. Edge-lit backlight units have light-emitting diodes that emit light into an edge surface of a light guide plate. The light guide plate then distributes the emitted light laterally across the display to serve as backlight illumination. Direct-lit backlight units have arrays of light-emitting diodes that emit light vertically through the display. 
     Direct-lit backlights may have locally dimmable light-emitting diodes that allow dynamic range to be enhanced. If care is not taken, however, the light produced by a direct-lit backlight may not be sufficiently uniform. For example, variations in the distance between the light-emitting diodes and an overlapping diffuser layer may lead to undesired uniformity variations in a backlight. 
     SUMMARY 
     An electronic device may have a display with a backlight. The backlight provides backlight illumination for an array of pixels that is displaying images. The backlight may include an array of backlight cells. Each cell may contain a light source with one or more light-emitting diodes and a cavity reflector that reflects light from the light source outwardly through a diffuser for use in forming the backlight illumination. 
     The light sources may be mounted to a printed circuit. Support posts may be used to maintain the diffuser at a fixed distance from the printed circuit. The support posts may be formed as integral protrusions of the diffuser, may be separate polymer structures formed from polymers such as clear and white polymers, and may be coupled to the printed circuit and diffuser using adhesive, screws, or other attachment mechanisms. 
     Optical sensors may be provided on the printed circuit. The optical sensors may each include a light-emitting device such as a light-emitting diode and a light detector. The optical sensors can measure light from the light-emitting diode that has reflected from the diffuser through respective openings in the cavity reflectors. Separation between the diffuser and the printed circuit can be measured with the optical sensors and used by control circuitry to update pixel gain profiles that correct images for variations in backlight intensity across the display. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a diagram of an illustrative electronic device having a display in accordance with an embodiment. 
         FIG. 2  is a cross-sectional side view of an illustrative display in accordance with an embodiment. 
         FIG. 3  is a top view of an illustrative backlight cell array having rows and columns of light source cells for a direct-lit backlight unit in accordance with an embodiment. 
         FIG. 4  is a cross-sectional side view of an illustrative light source such as a light-emitting diode in a cavity reflector of a backlight cell in accordance with an embodiment. 
         FIG. 5  is a cross-sectional side view of an illustrative transparent support post for a backlight in accordance with an embodiment. 
         FIG. 6  is a cross-sectional side view of an illustrative support post having a white shot of plastic that is at least partly covered by a clear shot of plastic in accordance with an embodiment. 
         FIG. 7  is a cross-sectional side view of a portion of an illustrative support post having a white shot of plastic with a rounded tip that is at least partly covered by a clear shot of plastic in accordance with an embodiment. 
         FIG. 8  is a cross-sectional side view of a portion of an illustrative diffuser layer with a support post of the type that may be formed form an integral portion of the diffuser layer in accordance with an embodiment. 
         FIG. 9  is a cross-sectional side view of an illustrative support post for a backlight having an inverted cone shape in accordance with an embodiment. 
         FIG. 10  is a cross-sectional side view of an illustrative cavity reflector formed over a solid supporting structure that can serve as supporting structures for a diffuser layer in accordance with an embodiment. 
         FIG. 11  is a cross-sectional side view of an illustrative diffuser layer height sensor in a backlight in accordance with an embodiment. 
         FIG. 12  is a top view of an illustrative array of support posts and diffuser layer height sensors for a backlight in accordance with an embodiment. 
         FIG. 13  is a graph showing how backlight intensity may vary as a function of lateral position and how backlight intensity may vary when a portion of a backlight is compressed in accordance with an embodiment. 
         FIG. 14  is a graph of illustrative pixel gain profiles that may be applied to image data for a pixel array in a display to compensate for backlight intensity variations across the display in accordance with an embodiment. 
         FIG. 15  is a circuit diagram showing illustrative circuitry for an electronic device having a display with optical diffuser position sensors in accordance with an embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     Electronic devices may be provided with backlit displays. The backlit displays may include liquid crystal pixel arrays or other display structures that are backlit by light from a direct-lit backlight unit. A perspective view of an illustrative electronic device of the type that may be provided with a display having a direct-lit backlight unit is shown in  FIG. 1 . Electronic device  10  of  FIG. 1  may 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&#39;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. 
     As shown in  FIG. 1 , device  10  may have a display such as display  14 . Display  14  may be mounted in housing  12 . Housing  12 , 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. Housing  12  may be formed using a unibody configuration in which some or all of housing  12  is 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.). 
     Housing  12  may have a stand such as optional stand  18 , may have multiple parts (e.g., housing portions that move relative to each other to form a laptop computer or other device with movable parts), may have the shape of a cellular telephone or tablet computer (e.g., in arrangements in which stand  18  is omitted), and/or may have other suitable configurations. The arrangement for housing  12  that is shown in  FIG. 1  is illustrative. 
     Display  14  may be a touch screen display that incorporates a layer of conductive capacitive touch sensor electrodes or other touch sensor components (e.g., resistive touch sensor components, acoustic touch sensor components, force-based touch sensor components, light-based touch sensor components, etc.) or may be a display that is not touch-sensitive. Capacitive touch screen electrodes may be formed from an array of indium tin oxide pads or other transparent conductive structures. 
     Display  14  may include an array of pixels  16  formed from liquid crystal display (LCD) components or may have an array of pixels based on other display technologies. A cross-sectional side view of display  14  is shown in  FIG. 2 . 
     As shown in  FIG. 2 , display  14  may include a pixel array such as pixel array  24 . Pixel array  24  may include an array of pixels such as pixels  16  of  FIG. 1  (e.g., an array of pixels having rows and columns of pixels  26 ). Pixel array  24  may be formed from a liquid crystal display module (sometimes referred to as a liquid crystal display or liquid crystal layers) or other suitable pixel array structures. A liquid crystal display for forming pixel array  24  may, as an example, include upper and lower polarizers, a color filter layer and a thin-film transistor layer interposed between the upper and lower polarizers, and a layer of liquid crystal material interposed between the color filter layer and the thin-film transistor layer. Liquid crystal display structures of other types may be used in forming pixel array  24 , if desired. 
     During operation of  14 , images may be displayed on pixel array  24 . Backlight unit  42  (which may sometimes be referred to as a backlight, backlight layers, backlight structures, a backlight module, a backlight system, etc.) may be used in producing backlight illumination  44  that passes through pixel array  24 . This illuminates any images on pixel array  24  for viewing by a viewer such as viewer  20  who is viewing display  14  in direction  22 . 
     Backlight unit  42  may have optical films  26 , a light diffuser such as light diffuser (light diffuser layer)  34 , and light source array  36 . Light source array  36  may contain a two-dimensional array of light sources  38 . Each light source  38  may contain one or more light-emitting diodes and may be associated with a respective one of backlight cells  38 C. Cells  38 C may contain reflectors for reflecting light through pixel array  24 . Cells  38 C may be arranged in an array with rows and columns in the X-Y plane of  FIG. 2 . 
     Light sources  38  in cells  38 C may be controlled in unison by control circuitry in device  10  or may be individually controlled (e.g., to implement a local dimming scheme that helps improve the dynamic range of images displayed on pixel array  24 ). The light produced by each cell  38 C may travel upwardly along dimension Z through light diffuser  34  and optical films  26  before passing through pixel array  24 . Light diffuser  34  may contain light-scattering structures that diffuse the light from light-emitting diode array  36  and thereby help provide uniform backlight illumination  44 . Optical films  26  may, as an example, include films such as dichroic filter  32 , phosphor layer  30 , and films  28 . Films  28  may include brightness enhancement films that help to collimate light  44  and thereby enhance the brightness of display  14  for user  20  and/or other optical films (e.g., compensation films, etc.). 
     The light-emitting diodes of light sources  38  may emit light of any suitable color. With one illustrative configuration, the light-emitting diodes emit blue light. Dichroic filter layer  32  may be configured to pass blue light from light-emitting diodes  38  while reflecting light at other colors. Blue light from light-emitting diodes  38  may be converted into white light by a photoluminescent material such as phosphor layer  30  (e.g., a layer of white phosphor material or other photoluminescent material that converts blue light into white light). If desired, other photoluminescent materials may be used to convert blue light to light of different colors (e.g., red light, green light, white light, etc.). For example, layer  30  (which may sometimes be referred to as a photoluminescent layer or color conversion layer) may include quantum dots that convert blue light into red and green light (e.g., to produce white backlight illumination that includes, red, green, and blue components, etc.). Configurations in which light-emitting diodes  38  emit white light (e.g., so that layer  30  may be omitted, if desired) and/or in which light-emitting diodes  38  emit blue or ultraviolet pump light for pixels containing quantum dots may also be used. 
     In configurations in which layer  30  emits white light such as white light produced by phosphorescent material in layer  30 , white light that is emitted from layer  30  in the downwards (−Z) direction may be reflected back up through pixel array  24  as backlight illumination by dichroic filter layer  32  (i.e., layer  32  may help reflect backlight outwardly away from array  36 ). In configurations in which layer  30  includes, for example, red and green quantum dots, dichroic filter  32  may be configured to reflect red and green light from the red and green quantum dots, respectively to help reflect backlight outwardly away from array  36 . By placing the photoluminescent material of backlight  42  (e.g., the material of layer  30 ) above diffuser layer  34 , light-emitting diodes  38  may be configured to emit more light towards the edges of the light-emitting diode cells (tiles) of array  36  than at the centers of these cells, thereby helping enhance backlight illumination uniformity. 
       FIG. 3  is a top view of an illustrative light source array for backlight  42 . As shown in  FIG. 3 , array  36  may contain row and columns of light-sources  38 . Each light source  38  may be associated with a respective cell  38 C. The length D of the edges of cells  38 C may be 2 mm, 18 mm, 1-10 mm, 1-4 mm, 10-30 mm, more than 5 mm, more than 10 mm, more than 15 mm, more than 20 mm, less than 25 mm, less than 20 mm, less than 15 mm, less than 10 mm, or other suitable size. If desired, hexagonally tiled arrays and arrays with light sources  38  that are organized in other suitable array patterns may be used. In arrays with rectangular cells, each cell may have sides of equal length (e.g., each cell may have a square outline in which four equal-length cell edges surround a respective light-emitting diode) or each cell may have sides of different lengths (e.g., a non-square rectangular shape). The configuration of  FIG. 3  in which array  36  has rows and columns of square light-emitting regions such as cells  38 C is merely illustrative. 
     If desired, each cell  38 C may have a light source that is formed from an array of light-emitting diode dies (e.g., multiple individual light-emitting diodes  38 D arranged in an array such as a 2×2 cluster of light-emitting diodes forming a four-die light source  38  at the center of each cell  38 C). This type of configuration is illustrated by light source  38  in the leftmost and lowermost cell  38 C of  FIG. 3 , which has been formed from a 2×2 array of light-emitting diodes  38 D (e.g., four separate light-emitting diode dies). The diodes  38 D in light source  38  in the lower left corner of array  36  of  FIG. 3  may be mounted on a common package substrate, may be mounted on a printed circuit board substrate that extends across array  36 , or may be mounted in array  36  using other suitable arrangements. In general, each cell  38 C may include a light source  38  with a single light-emitting diode  38 D, a pair of light-emitting diodes  38 D, 2-10 light-emitting diodes  38 D, at least two light-emitting diodes  38 D, at least 4 light-emitting diodes  38 D, at least eight light-emitting diodes  38 D, fewer than five light-emitting diodes  38 D, or other suitable number of light-emitting diodes. 
       FIG. 4  is a cross-sectional side view of an illustrative backlight cell  38 C in backlight  42 . As shown in  FIG. 4 , each cell  38 C in array  36  may have a reflector such as cavity reflector  68 . Reflector  68  may have a square outline (i.e., a square footprint when viewed from above) or may have other suitable shapes and may be formed from sheet metal (e.g., stamped sheet metal), metallized polymer film, a thin-film metal on a plastic carrier, a dielectric thin-film stack that forms a dielectric mirror (a thin-film interference mirror) on a polymer film or molded plastic carrier, a white reflective film (e.g., a glossy white polymer sheet formed from a white ink layer or other white layer on a polymer carrier covered with a glossy coating such as a glossy polymer coating), or other suitable reflector structure. 
     An opening may be formed in reflector  68  in each cell  38 C to accommodate a respective light source  38 . The light source  38  in each cell may have an upper portion that protrudes through the opening in reflector  68  and a lower portion with contacts that are soldered or otherwise mounted to metal traces in printed circuit  60 . 
     The reflectors in cells  38 C may have cross-sectional profiles with curved portions to help reflect light from light sources  38  upwards as backlight illumination  44 . With one illustrative configuration, a polymer film (e.g., a film coated with a dielectric thin-film interference mirror surface or a glossy white reflective surface) may be embossed using a roller (e.g., the film may be thermoformed using patterned structures on a heated roller). Following thermoforming operations to form the curved walls of reflector  68  in each cell  38 C, a die cutting tool or other cutting apparatus may cut openings for each of light sources  38 . 
     As shown in  FIG. 4 , a transparent structure such as transparent dome structure  70  may be formed over each light source  38  to help laterally distribute light  80  that has been emitted by that light source. Dome structure  70  may be formed from a bead of clear silicone or other transparent polymer (as an example). During operation, light source  38  emits light  80  that is refracted away from the Z axis by dome structure  70 . 
     Some rays of light  80  are oriented at relatively large angles with respect to the Z axis of  FIG. 4 . These off-axis rays of light  80  are reflected upwardly in direction Z from reflector  68 . Other rays of light  80  are oriented at smaller angles with respect to the Z axis (surface normal of display  14 ). If desired, backlight  42  may include an optional filter layer with an angularly dependent light transmission characteristic such as filter layer  97 . Diffuser layer  34  may include light-diffusing layer  34 ′. Layer  34 ′ may include light-scattering particles such as particles  72  in a polymer binder and/or may have other light-scattering structures for diffusing light  80  from light sources  38 . Filter layer  97  may be a thin-film interference filter formed from multiple dielectric layers  97 ′ or other suitable filter with an angularly dependent light transmission characteristic. Filter layer  97  may be formed on a substrate that is separate from layer  34 ′ or may be formed on layer  34 ′ in diffuser  34  as shown in the illustrative configuration of  FIG. 4 . 
     The layers of display  14  may not be perfectly flat due to external pressure, due to expansion and/or contraction caused by thermal fluctuations, and/or due to manufacturing variations. This may create undesired fluctuations in the separation distance H (sometimes referred to as optical distance H) between printed circuit  60  and diffuser  34 . With one illustrative configuration, display  14  may include an array of supporting posts in backlight  42  that help maintain a desired fixed value for height H across display  14 . 
       FIG. 5  is a cross-sectional side view of an illustrative portion of backlight  42  showing how backlight  42  may include a support post. As shown in  FIG. 5 , support post  90  may extend between the upper surface  60 U of printed circuit  60  and the opposing lower surface (surface  34 L) of diffuser  34  (as an example). Posts  90  may be cylindrical (radially symmetric) or may have other shapes (e.g., shapes in which one or more sides of posts  90  have flat portions). Radially symmetric arrangements for posts  90  may help to reduce shadows. 
     The presence of support posts such as support post  90  of  FIG. 5  may help maintain a fixed separation height H between diffuser  34  and printed circuit  60  and may therefore help to stabilize the vertical separation between light sources  38  in array  36  and diffuser  34 . This stabilization will help reduce fluctuations in light intensity that might otherwise result in hotpots and dark zones in areas of display  14 . 
     As shown in  FIG. 5 , support post  90  may have a lower portion such as lower portion  90 B and an upper portion such as upper portion  90 F. Portion  90 B may have straight sides (e.g., portion  90 B may be a cylinder) and portion  90 F may be tapered outwardly (e.g., portion  90 F may have an inverted cone shape). Reflector  68  may have an array of openings with each opening receiving a respective support post  90 . There may be a support post at each corner of each cell  38 C or support posts  90  may be more sparsely arrayed in backlight  42  (e.g., to accommodate separation height measurement sensors, etc.). 
     Support post  90  of  FIG. 5  may be attached to layer  60  using adhesive  94  and/or using a screw such as screw  96 . Screw  96  may have a shaft that passes through an opening in printed circuit substrate  60  and engages threads in a threaded opening in portion  90 B of post  90 . Upper portion  90 F of post  90  may be attached to diffuser  34  using adhesive  92 . To prevent dark spots from forming on backlight  42  due to the presence of posts  90 , post  90  may be formed from a transparent material such a clear polymer. Adhesive  92  may also be formed from a clear material (e.g., a clear polymer). During operation, light  80  from light source  38  may strike portion  90 F of post  90  and may be redirected within post  90  as illustrated by light ray  80 - 1  (e.g., by refraction). Refraction at the interface between post  90  and diffuser  34  may cause light ray  80 - 2  to be angled at a non-zero angle with respect to light ray  80 - 1  and refraction at the interface between diffuser  34  and air (or other materials) above diffuser  34  may cause light ray  44  (e.g. the backlight illumination exiting diffuser  34 ) to be angled at a non-zero angle with respect to light ray  80 - 2 . Light  80 - 2  may also be scattered by scattering features in diffuser  34 . The flared shape of portion  90 F and the transparency of portion  90 F may help guide off-axis light rays such as illustrative ray  80  over post  90 , so that illumination  44  is present over post  90 . As a result, local dark spots in backlight illumination  44  due to the presence of posts  90  may be reduced or eliminated. 
     Other configurations for supporting diffuser  34  in backlight  42  may be used, if desired. In the illustrative configuration of  FIG. 6 , post  90  includes multiple shots of plastic. A first shot of plastic such as a white polymer is used in forming lower post portion  90 W. A second shot of plastic, which is formed at least partly on top of portion  90 W is used in forming upper post portion  90 C. Portion  90 C may be transparent (e.g., portion  90 C may be formed from clear polymer). With this type of configuration, a light ray such as illustrative off-axis light ray  80  may enter clear portion  90 C and refract to form light ray  80 A. Light ray  80 A may reflect off of reflective white surface  92  of portion  90 W to form reflected ray  80 B. Ray  80 B may reflect from the inner surface of portion  90 C (e.g., the interface between portion  90 C and surrounding air in the space between diffuser  34  and printed circuit  60 ) in accordance with the principal of total internal reflection, thereby forming reflected ray  80 C. Ray  80 C may enter diffuser  34  and, following passage through diffuser  34  and possible scattering by diffuser  34 , can exit diffuser  34  as backlight illumination  44 . Different rays may take different paths through post  90  and layer  34 . Nevertheless, as the illustrative path of ray  80  of  FIG. 6  demonstrates, the presence of white portion  90 W of post  90  may help to reflect light so that light is not absorbed and lost at post  90  and the presence of clear portion  90 C may help redirect light above post  90  to serve as illumination  44 . As a result, post structures of the type shown in  FIG. 6  may help reduce dark spots that might otherwise arise from incorporating supports into backlight  42 . 
     In the illustrative configuration of  FIG. 7 , post  90  includes portion  90 WR (e.g., a white polymer portion) and portion  90 C (e.g., a clear polymer portion). Surface  92  of post portion  90 WR is rounded. This shape may help redirect light upwards through diffuser  34  (e.g., less light may be reflected laterally and more light may be reflected upwards). Portion  90 C can be flared (tapered) outwardly (e.g., so that the top of portion  90 C adjacent to diffuser  34  is wider than the bottom of portion  90 C adjacent to post portion  90 WR) so as to facilitate the redirection of light that passes through portion  90 C upwards through diffuser  34 . Other shapes may be used for post portions  90 WR and  90 C if desired. The configuration of  FIG. 7  is merely illustrative. 
     As shown in  FIG. 8 , support posts for backlight  42  may be formed from integral portions of diffuser  34 . In the example of  FIG. 8 , portion  34 P of diffuser  34  is serving as a support post and extends between the lower surface of diffuser  34  and the opposing upper surface of printed circuit  60 . Portion  34 P may be formed from the same material(s) as diffuser  34  and may, for example, be formed by molding a diffuser  34  with integral support posts  34 P so that these integral support posts are protrusions from the planar portion of diffuser  34 . Configurations in which posts such as post  34 P of  FIG. 8  are formed separately from diffuser  34  and attached to diffuser  34  (e.g., using adhesive or other attachment mechanisms) may also be used. Support post  34 P may be formed from clear or translucent plastic (e.g., transparent polymer, transparent polymer with light-scattering particles or other light-scattering features, etc.). The lower portion of support post  34 P may be cylindrical and the upper portion of support post  34 P may have a curved outwardly flared profile. Other shapes may be used for integral support posts such as support post  34 P, if desired. 
     Support post  34 P may be attached to printed circuit  60  using adhesive, a screw, or other attachment mechanisms. Printed circuit  60  may overlap a metal backlight chassis layer such as metal chassis  61  or other suitable support structure. This type of arrangement may be used in backlight  42  whenever it is desired to provide additional support for the layers of backlight  42 . 
     In the example of  FIG. 8 , support post  34 P is configured to receive a screw such as screw  96  (e.g., support post  34 P may have a threaded opening that receives a threaded shaft portion of screw  96 ). Elastomeric gasket  100  (e.g., a ring-shaped washer) may be received in opening  101  of metal chassis  61 . The shaft of screw  96  may pass through an opening in gasket  100  and an opening in layer  60  (e.g., an opening that is wider than the shaft of screw  96 ). The presence of gasket  100  between a head portion of screw  96  and metal chassis  61  may help accommodate lateral mismatch between the locations of posts  34 P and the locations of openings  101  in printed circuit  60  (e.g., to satisfy alignment tolerances, to accommodate lateral shifts due to thermal expansion and contraction, etc.). 
     As shown in  FIG. 9 , support post  90  (e.g., a clear polymer support post, a white polymer support post, etc.) may have an inverted cone shape or other configuration that minimizes the size (diameter W) of the upper portion of post  90  where post  90  contacts diffuser  34 . In configurations in which the ratio of diffuser thickness T to post top diameter W is sufficient (e.g., at least 1, at least 2, at least 3, less than 100, etc.), shadowing of light from light sources  38  will be minimized and the presence of posts  90  will not significantly disrupt the uniformity of emitted backlight illumination  44 . 
     If desired, a molded support structure such as support structure  102  of  FIG. 10  may be used in supporting cavity reflector  68 . Support structure  102  may, for example, have a curved profile in each cell  38 C that allows reflector  68  to reflect light upwards to form backlight illumination  44 . Support structure  102  may have openings to accommodate light sources  38 . Reflector  68  may be laminated to the surface of support structure  102 , may be deposited on the surface of support structure  102 , or may be integrated into support structure  102  (e.g., by forming support structures  102  from a reflective material such as white plastic). Molded support structures  102  of  FIG. 10  may be sufficiently robust to support diffuser  34  and can therefore be used to reduce or eliminate the use of support posts  90  in backlight  42 . 
     In some configurations, diffuser height (separation) sensors can be incorporated into backlight  42 . This type of arrangement is shown in the cross-sectional side view of backlight  42  of  FIG. 11 . As shown in  FIG. 11 , reflector  68  may have openings such as opening  106  between respective cells  38 C. Each opening  106  may allow light to be reflected off of lower surface  34 L of diffuser  34 . During operation of device  10 , when the value of the height H between lower diffuser surface  34 L and the corresponding upper surface of printed circuit  60  varies (e.g., due to external pressure, thermal effects, layer warping, etc.) the value of height H can be dynamically measured and used in supplying corrective calibration information (e.g., pixel gain adjustments) to display driver circuitry in device  10 . The calibration information allows any brightness variations that result from variations in H to be dynamically removed, thereby ensuring that images on the array of pixels  16  of display  14  do not exhibit undesired hotspots and dark regions. 
     The value of height (distance) H can be measured using any suitable sensors (e.g., capacitive sensors, electromechanical displacement sensors, acoustic sensor, force sensors, etc.). With one suitable configuration, which is illustrated in  FIG. 11 , an array of optical sensors is used to monitor the shape of diffuser  34 . As shown in  FIG. 11 , for example, optical sensor  104  may be aligned with opening  106  in reflector  68 . Optical sensor  104  may include a light source such as light source  104 L and may include a detector such as detector  104 D. Light source  104 L may be, for example, a light-emitting diode or a laser. Light source  104 L may emit light such as infrared light that is not visible to a user and therefore does not affect images being displayed on the pixels of display  14  and/or light source  104 L may emit low power visible light (e.g., pulsed visible light at intensities that are not disruptive to a user&#39;s viewing of display images). Light detector  104 D may be configured to measure light that has been emitted by light source  104 L after that light has passed upwards through opening  106  and has reflected off of lower diffuser surface  34 L and returned back through opening  106  to detector  104 D. 
     The distance of opening  106  from diffuser  34  varies as height H varies (e.g., as diffuser  34  moves relative to substrate  60 , where sensor  104  is mounted using solder or other conductive materials). As the separation between opening  106  and surface  34 L varies, the amount of light from light source  104 L that is able to reflect from surface  34 L and return to detector  104 D varies by a corresponding amount. If, for example, surface  34 L is close to opening  106 , a relatively large amount of light from source  104 L will reflect from surface  34 L and return to detector  104 D. If surface  34 L is far from opening  106 , the amount of reflected light from surface  34 L that is detected by detector  104 D will decrease. As a result, sensors such as sensor  104  of  FIG. 11  serve as proximity (distance) sensors that can dynamically measure the height H of diffuser  34  at various sensor locations across backlight  42 . 
     Sensors  104  may, if desired, be interspersed with support posts  90  (e.g., sensors  104  and posts  90  may be interspersed with each other in an array in which sensors and posts are located at the corners of cells  38 C). An illustrative pattern of the type that may be used in distributing support posts  90  and sensors  104  across backlight  42  is shown in  FIG. 12 . In this arrangement, there are more support posts  90  than sensors  104 . There may, in general, be any suitable number of support posts  90  and any suitable number of sensors  104  (e.g., one sensor for every 1-5 support posts, etc.). The arrangement of  FIG. 12  is illustrative. 
     The graphs of  FIGS. 13 and 14  illustrate how sensor measurements may be used to dynamically compensate display  14  to reduce or eliminate image intensity variations due to variations in H across display  14 . In the graph of  FIG. 13 , backlight output intensity I (e.g., the intensity of illumination  44 ) has been plotted as a function of lateral distance X across backlight  42 . The region of backlight  42  that is covered in the graph of  FIG. 13  covers two cells  38 C and two corresponding light sources  38 . Due to the presence of light sources  38  at the center of cells  38 C, there may be localized peaks in light output at the center of each cell, as indicated by solid lines  108  and  110  (the output of each cell  38 C) and solid line  112  (the resulting combined output of both cells  38 C). To eliminate the intensity variations associated with line  112  in the final images displayed for a user of device  10 , display driver circuitry in device  10  may be provided with a compensating pixel gain profile such as pixel gain profile  114  of  FIG. 14 . By locally reducing pixel gain at locations where backlight intensity has a local peak and vice versa, the final images displayed on display  14  for the user will not exhibit significant intensity fluctuations due to backlight intensity variations. 
     In the event that distance H decreases (as an example) in the vicinity of the cells of  FIGS. 13 and 14 , the light output profiles from each of the cells will become narrower and more pronounced, as indicated by curves  108 ′ and  110 ′. This is because a decrease in H will place diffuser  34  closer to light sources  38 . The resulting intensity profile for backlight  42  will therefore change from curve  112  to curve  112 ′. By measuring the decrease in H with one or more sensors  104 , the pixel gain curve can be updated accordingly. For example, display driver circuitry for display  14  may be provided with pixel gain curve look-up table entries that correspond to curve  114 ′ of  FIG. 14  rather than curve  114 . By updating the pixel gain profile dynamically based on sensor data from sensors  104 , changes in the transmission of pixels  16  can compensate for changes in backlight illumination intensity, thereby ensuring the images on display  14  are free from hotspots and dark areas. 
       FIG. 15  is a circuit diagram of device  10 . As shown in  FIG. 15 , device  10  may have control circuitry  120 . Control circuitry  120  may include storage and processing circuitry for supporting the operation of device  10 . The storage and processing circuitry may include storage such as hard disk drive storage, nonvolatile memory (e.g., flash memory or other electrically-programmable-read-only memory configured to form a solid state drive), volatile memory (e.g., static or dynamic random-access-memory), etc. Processing circuitry in control circuitry  120  may be used to control the operation of device  10 . The processing circuitry may be based on one or more microprocessors, microcontrollers, digital signal processors, baseband processors, power management units, audio chips, application specific integrated circuits, etc. 
     Input-output circuitry in device  10  such as input-output devices  122  may be used to allow data to be supplied to device  10  and to allow data to be provided from device  10  to external devices. Input-output devices  122  may include buttons, joysticks, scrolling wheels, touch pads, key pads, keyboards, microphones, speakers, tone generators, vibrators, cameras, sensors (e.g., ambient light sensors, proximity sensors, orientation sensors, magnetic sensors, force sensors, touch sensors, pressure sensors, fingerprint sensors, etc.), light-emitting diodes and other status indicators, data ports, etc. A user can control the operation of device  10  by supplying commands through input-output devices  122  and may receive status information and other output from device  10  using the output resources of input-output devices  122 . 
     Device  10  may include one or more displays such as display  14 . Display  14  may include an array of pixels  16  such pixel array  24  that displays images in response to control and data signals from display driver circuitry  124 . Control circuitry  16  may be used to run software on device  10  such as operating system code and applications. During operation of device  10 , the software running on control circuitry  16  may display images on pixel array  24  by using display driver circuitry  124  to supply pixel array  24  with image data and control signals over path  138 . Display driver circuitry  124  may also issue backlight control commands to light sources  38  in array  36 , which is overlapped by pixel array  16 , thereby allowing display driver circuitry  124  to adjust both pixel transmission (e.g., by adjusting liquid crystal pixel transmission values) and backlight output (by adjusting the brightness of sources  38 ). The pixel data that is supplied to pixels  16  may be corrected by circuitry  124  for backlight intensity variations by applying a pixel gain profile stored in look-up table  128 . 
     Sensor data from an array of sensors  104  that is interspersed among cells  38 C of array  36  may be received by control circuitry such as sensor data processing circuitry  130 . Circuitry  130  may determine heights H in real time based on measurements from sensors  104  that are received via path  136 . In response, circuitry  130  may supply pixel gain profile updates to pixel gain profile look-up table  128  in display driver circuitry  124 , as described in connection with the illustrative pixel gain profiles of  FIG. 14 . If, for example, sensor data from sensors  104  indicates that the value of H is decreasing in a particular cell  38 C, the pixel gain curve for that cell may be updated from an old pixel gain curve such as curve  114  of  FIG. 14  to a new pixel gain curve of the type appropriate for a decreased H value such as pixel gain profile  114 ′ of  FIG. 14 . The gain profile that is updated in look-up table  128  may be a two-dimensional profile that covers pixel gain values in both the X and Y lateral dimension of pixel array  24 . 
     In accordance with an embodiment, a display is provided that includes an array of pixels configured to display images and a backlight configured to produce backlight illumination for the array of pixels, the backlight has a two-dimensional array of cells that each include a light source and a reflector, a printed circuit on which the light sources are mounted, a diffuser, and support posts interspersed that are configured to support the diffuser, the support posts include white polymer portions. 
     In accordance with another embodiment, the support posts include clear polymer portions. 
     In accordance with another embodiment, each of the clear polymer portions covers at least part of a respective one of the white polymer portions. 
     In accordance with another embodiment, the clear polymer portions are tapered. 
     In accordance with another embodiment, the white polymer portions have rounded tips each of which is covered by a respective one of the clear polymer portions. 
     In accordance with another embodiment, the white polymer portions are cylindrical. 
     In accordance with another embodiment, the display includes screws that each attach a respective one of the support posts to the printed circuit. 
     In accordance with another embodiment, the display includes elastomeric gaskets, a respective one of the elastomeric gaskets is interposed between at least part of each screw and the printed circuit. 
     In accordance with another embodiment, the support posts are formed from protrusions in the diffuser. 
     In accordance with another embodiment, at least some of the support posts are conical. 
     In accordance with another embodiment, the conical support posts have diameters that are smaller at the diffuser than at the printed circuit. 
     In accordance with another embodiment, the display includes an array of optical sensors on the printed circuit that measure respective separation distances between the diffuser and the printed circuit. 
     In accordance with another embodiment, the support posts are interspersed with the optical sensors on the printed circuit. 
     In accordance with another embodiment, the display includes display driver circuitry with a look-up table configured to maintain a pixel gain profile that compensates the images for backlight intensity variations across the array of pixels. 
     In accordance with another embodiment, the display includes control circuitry that is configured to update the pixel gain profile in the look-up table in response to measurements of the separation distances from the array of optical sensors. 
     In accordance with another embodiment, the optical sensors each include a light-emitting diode and a light detector configured to detect light from the light-emitting diode that has reflected from the diffuser. 
     In accordance with an embodiment, a display is provided that includes an array of pixels configured to display images and a backlight configured to produce backlight illumination for the array of pixels, the backlight has a two-dimensional array of cells that each include a light source and a reflector, a printed circuit on which the light sources are mounted, a diffuser, and an array of support posts that are attached to the diffuser with adhesive and that are configured to separate the diffuser from the printed circuit. 
     In accordance with another embodiment, the support posts include clear polymer portions adjacent to the diffuser. 
     In accordance with another embodiment, the display includes optical sensors on the printed circuit that are configured to measure respective separation distances between the diffuser and the printed circuit. 
     In accordance with an embodiment, a display is provided that includes an array of pixels configured to display images, and a backlight configured to produce backlight illumination for the array of pixels, the backlight has a two-dimensional array of cells that each include a light source and a reflector, a printed circuit on which the light sources are mounted, and a diffuser and the backlight includes support posts that are configured to separate the diffuser from the printed circuit by a distance and optical sensors that measure respective distances between the printed circuit and the diffuser. 
     The foregoing is merely illustrative and various modifications can be made to the described embodiments. The foregoing embodiments may be implemented individually or in any combination.

Metadata:
Filing Date: 20190510
Publication Date: 20200811
Grant Date: 20200811
Priority Date: 20170503
Inventors: LIU, RONG
SUN, YU P.
ZWEIGLE, ERIK A.
QI, JUN
YIN, VICTOR H.
HONG, ZIRUO
BAE, Sungwon
Assignee: APPLE INC
CPC Classifications: [{"code": "G09G3/3406", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02F1/133605", "inventive": true, "first": false, "tree": "[]"}, {"code": "G09G3/3648", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02F1/133605", "inventive": true, "first": true, "tree": "[]"}, {"code": "G02F1/133606", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02F1/133608", "inventive": true, "first": true, "tree": "[]"}, {"code": "G02F1/133603", "inventive": true, "first": false, "tree": "[]"}, {"code": "F21K9/68", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02F1/133603", "inventive": false, "first": false, "tree": "[]"}, {"code": "G02F1/133611", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02F1/133611", "inventive": true, "first": false, "tree": "[]"}, {"code": "F21K9/64", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02F1/133605", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02F1/133606", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02F1/133608", "inventive": true, "first": true, "tree": "[]"}, {"code": "G02F1/133608", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02F1/133606", "inventive": true, "first": false, "tree": "[]"}, {"code": "F21K9/68", "inventive": true, "first": false, "tree": "[]"}, {"code": "G09G3/3648", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02F1/133611", "inventive": true, "first": false, "tree": "[]"}, {"code": "F21K9/64", "inventive": true, "first": false, "tree": "[]"}, {"code": "G09G3/3406", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02F1/133608", "inventive": true, "first": true, "tree": "[]"}, {"code": "G02F1/133603", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02F1/133605", "inventive": true, "first": false, "tree": "[]"}]
Family ID: 68531590