PATENT DOCUMENT

Publication Number: US-9541794-B2
Application Number: US-201414502199-A
Country: US
Kind Code: B2

Title: High dynamic range liquid crystal display

Abstract:
A display may have a first stage such as a color liquid crystal display stage and a second stage such as a monochromatic liquid crystal display stage that are coupled in tandem so that light from a backlight passes through both stages. The dynamic range of the display may be enhanced by using the second stage to perform local dimming operations. The pixel pitch of the second stage may be greater than the pixel pitch of the first stage to ease alignment tolerances and reduce image processing complexity. The color stage and monochromatic stages may share a polarizer. A color filter in the color stage may have an array of red, green, and blue elements or an array of white, red, green, and blue elements. The color stage may be a fringe field display and the monochrome stage may be an in-plane switching display or a twisted nematic stage.

Claims:
What is claimed is: 
     
       1. A display, comprising:
 a color stage having pixels with a first pitch; 
 a monochromatic stage having pixels with a second pitch that is greater than the first pitch; 
 backlight structures that include a light source, that include a quantum dot structure that receives light from the light source, and that include a light guide plate that receives light from the quantum dot structure and provides backlight, wherein the color stage and monochromatic stage are coupled in tandem so that the backlight passes through both the color stage and the monochromatic stage; and 
 display circuitry that receives red-green-blue image data, converts the red-green-blue image data into white-red-green-blue image data, computes a brightness setting to be supplied to a backlight controller based on the red-green-blue image data, and splits the white-red-green-blue image data into a first channel supplied to the color stage and a second channel supplied to the monochromatic stage. 
 
     
     
       2. The display defined in  claim 1  wherein the color stage comprises:
 a thin-film transistor layer; 
 a color filter layer that includes white, red, green, and blue color filter elements; and 
 a liquid crystal layer interposed between the thin-film transistor layer and the color filter layer. 
 
     
     
       3. The display defined in  claim 1  further comprising a common polarizer that is shared between the color stage and the monochromatic stage. 
     
     
       4. The display defined in  claim 3  wherein:
 the color stage comprises:
 a first thin-film transistor layer; 
 a color filter layer; and 
 a first liquid crystal layer between the first thin-film transistor layer and the color filter layer; and 
 
 the monochromatic lower stage comprises:
 a second thin-film transistor layer; 
 a transparent substrate; and 
 a second liquid crystal layer between the second thin-film transistor layer and the transparent substrate. 
 
 
     
     
       5. The display defined in  claim 4  wherein the common polarizer is interposed between the first thin-film transistor layer and the transparent substrate. 
     
     
       6. A display, comprising:
 a color stage having a first layer of liquid crystal material and having pixels with a first pixel pitch; 
 a monochromatic stage having a second layer of liquid crystal material and having pixels with a second pixel pitch that is greater than the first pixel pitch; 
 a backlight that produces light using a light source, wherein the color stage and monochromatic stage are coupled in tandem so that the light from the backlight passes through both the color stage and the monochromatic stage, wherein the color stage has a first polarizer, and wherein the monochromatic stage has a second polarizer; 
 a common polarizer that is shared by the color stage and the monochromatic stage; 
 a white-red-green-blue converter that is configured to receive red-green-blue image data and convert the red-green-blue image data into white-red-green-blue image data, wherein the white-red-green-blue converter is configured to compute a brightness setting for the backlight based on the red-green-blue image data; 
 a backlight controller configured to receive the brightness setting from the white-red-green-blue converter and adjust the output of the light source in the backlight based on the brightness setting; 
 a color space converter configured to convert the white-red-green-blue image data into a color space; and 
 an image splitter configured to split the white-red-green-blue image data into a first channel supplied to the color stage and a second channel supplied to the monochromatic stage. 
 
     
     
       7. The display defined in  claim 6  wherein the backlight includes quantum dot structures, wherein the color stage has a color filter layer with white, red, green, and blue color filter elements, and wherein the pixels of the monochromatic stage comprise pixels selected from the group consisting of: twisted nematic pixels and in-plane switching pixels. 
     
     
       8. The display defined in  claim 6 , wherein the color space converter is configured to convert the white-red-green-blue image data into the CIE XYZ color space. 
     
     
       9. A display, comprising:
 a color stage having a first layer of liquid crystal material and having pixels with a first pixel pitch; 
 a monochromatic stage having a second layer of liquid crystal material and having pixels with a second pixel pitch that is greater than the first pixel pitch; and 
 a backlight that produces light, wherein the color stage and monochromatic stage are coupled in tandem so that the light from the backlight passes through both the color stage and the monochromatic stage, wherein:
 the pixels of the color stage are fringe field switching pixels; and 
 the pixels of the monochromatic stage comprise pixels selected from the group consisting of: twisted nematic pixels and in-plane switching pixels. 
 
 
     
     
       10. The display defined in  claim 9  wherein the backlight includes quantum dot structures, wherein the display comprises a shared polarizer that forms part of the color stage and part of the monochromatic stage, and wherein the shared polarizer includes at least two negative birefringence layers.

Description:
This application claims the benefit of provisional patent application No. 61/926,012, filed Jan. 10, 2014, which is hereby incorporated by reference herein in its entirety. 
    
    
     BACKGROUND 
     This relates generally to electronic devices and, more particularly, to electronic devices with displays. 
     Electronic devices often include displays. For example, cellular telephones, computers, and televisions have displays. 
     Liquid crystal displays create images by modulating the intensity of light that is being emitted from a backlight. The perceived quality of a liquid crystal display is affected by its dynamic range. The dynamic range of a display is the ratio of the output of the display at its brightest setting to the output of the display at its dimmest setting. Because it is not possible to completely extinguish the light produced by the backlight in a liquid crystal display, the dynamic range of a liquid crystal display is limited. A typical liquid crystal display has a dynamic range of about 1000:1. When viewing content such as movies where dark areas are often present, the limited dynamic range of a conventional display can have an adverse impact on picture quality. For example, black areas of an image may appear to be dark gray rather than black. 
     It would therefore be desirable to be able to provide improved displays such as improved liquid crystal displays. 
     SUMMARY 
     Electronic devices may be provided with displays. A display may have a first stage such as a color liquid crystal display stage and a second stage such as a monochromatic liquid crystal display stage. The first and second stages may be coupled in series so that light from a backlight passes through both the first and second stages. The first stage may be used to display color images. The second stage may be used to perform local dimming operations, thereby enhancing the dynamic range of the display. The pixel pitch of the second stage may be greater than the pixel pitch of the first stage to ease alignment tolerances and reduce image processing complexity. 
     The color stage and monochromatic stage may share a polarizer or separate sets of polarizers may be used for the color stage and for the monochromatic stage. A polarizer may include compensation layers. A shared polarizer may have a polarizer layer that is sandwiched between upper and lower sets of compensation films. 
     A color filter in the color stage may have an array of red, green, and blue elements or an array of white, red, green, and blue elements. Display control circuitry may be used to perform color space conversion operations and to split image data into a color channel for the color stage and a monochromatic channel for the monochromatic stage. 
     The color stage of the display may be a fringe field display and the monochrome stage may be an in-plane switching display or a twisted nematic stage. The backlight in the display may have a quantum dot structure that is illuminated with a blue light source. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of an illustrative electronic device such as a laptop computer with display structures in accordance with an embodiment. 
         FIG. 2  is a perspective view of an illustrative electronic device such as a handheld electronic device with display structures in accordance with an embodiment. 
         FIG. 3  is a perspective view of an illustrative electronic device such as a tablet computer with display structures in accordance with an embodiment. 
         FIG. 4  is a perspective view of an illustrative electronic device such as a display for a computer or television with display structures in accordance with an embodiment. 
         FIG. 5  is a cross-sectional side view of illustrative display structures in accordance with an embodiment. 
         FIG. 6  is a cross-sectional side view of an illustrative two stage liquid crystal display in accordance with an embodiment. 
         FIG. 7  is a top view of an illustrative two stage liquid crystal display showing how lower resolution monochromatic localized dimming pixels in one stage may overlap multiple higher resolution color display pixels in another stage in accordance with an embodiment. 
         FIG. 8  is a top view of a portion of a display in accordance with an embodiment. 
         FIG. 9  is a cross-sectional side view of a pixel in an illustrative fringe field switching display stage in accordance with an embodiment. 
         FIG. 10  is a cross-sectional side view of a pixel in an illustrative twisted nematic display stage in accordance with an embodiment. 
         FIG. 11  is a cross-sectional side view of a pixel in an illustrative in-plane switching display in accordance with an embodiment. 
         FIG. 12  is a cross-sectional side view of an illustrative display having a pair of tandem stages in accordance with an embodiment. 
         FIG. 13  is a cross-sectional side view of an illustrative polarizer that may be used in a display of the type shown in  FIG. 12  in accordance with an embodiment. 
         FIG. 14  is a cross-sectional side view of an illustrative display with two stages that share a common polarizer in accordance with an embodiment. 
         FIG. 15  is a cross-sectional side view of an illustrative polarizer that may be used for the shared polarizer of  FIG. 14  in accordance with an embodiment. 
         FIG. 16  is a side view of an illustrative backlight having a quantum dot structure in accordance with an embodiment. 
         FIG. 17  is a graph of an output spectrum of an illustrative backlight of the type shown in  FIG. 16  in accordance with an embodiment. 
         FIG. 18  is a diagram of an illustrative red-green-blue color filter element pattern that may be used for the color filter layer in a display stage in accordance with an embodiment. 
         FIG. 19  is a diagram of an illustrative red-green-blue-white color filter element pattern that may be used for the color filter in a display stage in accordance with an embodiment. 
         FIG. 20  is a system diagram of a two-stage display and circuitry used for controlling the display in accordance with an embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     Electronic devices may be provided with displays. The displays may be liquid crystal displays. To enhance dynamic range, a display may be provided with multiple stages. For example, a display may be provided with tandem upper and lower display stages. One of the stages (e.g., the upper stage) may have an array of pixels and a corresponding color filter layer that provide the upper stage with the ability to display color images. Another of the stages (e.g., the lower stage) may have an array of pixels that serve as monochromatic light shutters to selectively increase the dimming of sections of the higher resolution color display pixels. If, for example, an area of dark content is being displayed by the display, the lower stage may be adjusted to add additional dimming to the dark content area. The use of the lower stage therefore helps enhance the dynamic range of the display. 
     Because localized dimming from the lower stage need not be performed at the same resolution as the array of pixels in the upper stage, the lower stage may have pixels that are larger than the display pixels of the upper stage. If desired, a high dynamic range multi-stage display may have three or more tandem stages. The use of displays with a pair of tandem stages is described herein as an example. 
     Illustrative electronic devices of the types that may be provided with high dynamic range displays are shown in  FIGS. 1, 2, 3, and 4 . 
     Electronic device  10  of  FIG. 1  has the shape of a laptop computer and has upper housing  12 A and lower housing  12 B with components such as keyboard  16  and touchpad  18 . Device  10  has hinge structures  20  (sometimes referred to as a clutch barrel) to allow upper housing  12 A to rotate in directions  22  about rotational axis  24  relative to lower housing  12 B. Display  14  is mounted in housing  12 A. Upper housing  12 A, which may sometimes be referred to as a display housing or lid, is placed in a closed position by rotating upper housing  12 A towards lower housing  12 B about rotational axis  24 . 
       FIG. 2  shows an illustrative configuration for electronic device  10  based on a handheld device such as a cellular telephone, music player, gaming device, navigation unit, or other compact device. In this type of configuration for device  10 , housing  12  has opposing front and rear surfaces. Display  14  is mounted on a front face of housing  12 . Display  14  may have an exterior layer that includes openings for components such as button  26  and speaker port  28 . 
     In the example of  FIG. 3 , electronic device  10  is a tablet computer. In electronic device  10  of  FIG. 3 , housing  12  has opposing planar front and rear surfaces. Display  14  is mounted on the front surface of housing  12 . As shown in  FIG. 3 , display  14  has an opening to accommodate button  26 . 
       FIG. 4  shows an illustrative configuration for electronic device  10  in which device  10  is a computer display, a computer that has an integrated computer display, or a television. Display  14  is mounted on a front face of housing  12 . With this type of arrangement, housing  12  for device  10  may be mounted on a wall or may have an optional structure such as support stand  30  to support device  10  on a flat surface such as a tabletop or desk. 
     Display  14  may be a liquid crystal display having multiple layers of liquid crystal material in multiple respective stages. For example, display  14  may have an upper liquid crystal layer in an upper stage and a lower liquid crystal layer in a lower stage. Using a two-stage configuration of display  14  may enhance the dynamic range of display  14 . 
     A cross-sectional side view of an illustrative one-stage liquid crystal display is shown in  FIG. 5 . As shown in  FIG. 5 , display  14  may include a backlight such as backlight unit  42  for producing backlight  44 . During operation, backlight  44  travels outwards (vertically upwards in dimension Z in the orientation of  FIG. 5 ) and passes through display pixel structures in display layers  46 . This illuminates any images that are being produced by the display pixels for viewing by a user. For example, backlight  44  may illuminate images on display layers  46  that are being viewed by viewer  48  in direction  50 . 
     Display layers  46  may be mounted in chassis structures such as a plastic chassis structure and/or a metal chassis structure to form a display module for mounting in housing  12  or display layers  46  may be mounted directly in housing  12  (e.g., by stacking display layers  46  into a recessed portion in housing  12 ). 
     Display layers  46  may include a liquid crystal layer such a liquid crystal layer  52 . Liquid crystal layer  52  may be sandwiched between display layers such as display layers  58  and  56 . Layers  56  and  58  may be interposed between lower (innermost) polarizer layer  60  and upper (outermost) polarizer layer  54 . 
     Layers  58  and  56  may be formed from transparent substrate layers such as clear layers of glass or plastic. Layers  56  and  58  may be layers such as a thin-film transistor layer and/or a color filter layer. Conductive traces, color filter elements, transistors, and other circuits and structures may be formed on the substrates of layers  58  and  56  (e.g., to form a thin-film transistor layer and/or a color filter layer). Touch sensor electrodes may also be incorporated into layers such as layers  58  and  56  and/or touch sensor electrodes may be formed on other substrates. 
     With one illustrative configuration, layer  58  may be a thin-film transistor layer that includes an array of thin-film transistors and associated electrodes (display pixel electrodes) for applying electric fields to liquid crystal layer  52  and thereby displaying images on display  14 . Layer  56  may be a color filter layer that includes an array of color filter elements for providing display  14  with the ability to display color images. If desired, layer  58  may be a color filter layer and layer  56  may be a thin-film transistor layer. 
     During operation of display  14  in device  10 , control (e.g., one or more integrated circuits on a printed circuit such as integrated circuits  68  on printed circuit  66 ) may be used to generate information to be displayed on display  14  (e.g., display data). The information to be displayed may be conveyed to a display driver integrated circuit such as circuit  62  in region  82  using a signal path such as a signal path formed from conductive metal traces in a rigid or flexible printed circuit such as printed circuit  64  (as an example). 
     Backlight structures  42  may include a light guide plate such as light guide plate  78 . Light guide plate  78  may be formed from a transparent material such as clear glass or plastic. During operation of backlight structures  42 , a light source such as light source  72  may generate light  74 . Light source  72  may be, for example, an array of light-emitting diodes. 
     Light  74  from light source  72  may be coupled into edge surface  76  of light guide plate  78  and may be distributed in dimensions X and Y throughout light guide plate  78  due to the principal of total internal reflection. Light guide plate  78  may include light-scattering features such as pits or bumps. The light-scattering features may be located on an upper surface and/or on an opposing lower surface of light guide plate  78 . 
     Light  74  that scatters upwards in direction Z from light guide plate  78  may serve as backlight  44  for display  14 . Light  74  that scatters downwards may be reflected back in the upwards direction by reflector  80 . Reflector  80  may be formed from a reflective material such as a layer of white plastic, a layer of metal, or other shiny materials. 
     To enhance backlight performance for backlight structures  42 , backlight structures  42  may include optical films  70 . Optical films  70  may include diffuser layers for helping to homogenize backlight  44  and thereby reduce hotspots, optical compensation films for optically compensating layers in display  14  and thereby enhancing off-axis viewing, and brightness enhancement films (also sometimes referred to as turning films) for collimating backlight  44 . Optical films  70  may overlap the other structures in backlight unit  42  such as light guide plate  78  and reflector  80 . For example, if light guide plate  78  has a rectangular footprint in the X-Y plane of  FIG. 5 , optical films  70  and reflector  80  may have a matching rectangular footprint. If desired, compensation films may be incorporated into other portions of display  14 . For example, compensation films may be incorporated into polarizers. 
     The dynamic range of a single-stage display of the type shown in  FIG. 5  can be enhanced by incorporating one or more additional liquid crystal display stages into display  14 . As shown in  FIG. 6 , display  14  may, for example, be provided with a pair of tandem display stages such as upper stage  14 A and lower stage  14 B. 
     To provide display  14  with the ability to display images, display  14  may be provided with an array of color filter elements. The color filter element array may be formed by patterning colored photoimageable polymer areas on the underside of a transparent glass or plastic substrate (see, e.g., color filter layer  56  of  FIG. 5 ). Only one of the display stages in display  14  need be provided with a color filter array. In the example of  FIG. 6 , upper stage  14 A has an array of color filter elements and lower stage  14 B does not have any color filter elements. Lower stage  14 B is a monochromatic (gray-level) display that can modulate the intensity of backlight  44 , but does not impart color information to backlight  44 . Upper stage  14 A contains a color filter array and has corresponding pixels to create color images for viewer  48 . Because upper stage  14 A has the ability to display color images, upper stage  14 A may sometimes be referred to as a color stage. Because lower stage  14 B displays only pixels of varying shades of gray (ranging from black to white), lower stage  14 B may sometimes be referred to as a monochromatic stage, shutter stage, or localized dimming stage. In the illustrative configuration of  FIG. 6 , the upper stage of display  14  is a color stage and the lower stage of display  14  is a monochromatic stage, but the upper stage may be monochromatic and the lower stage may be a color stage, if desired. 
     It is not necessary for both display stages in display  14  to be high resolution stages (i.e., both stages need not have small pixel pitches). Rather, one of the stages such as upper stage  14 A may have a relatively high resolution (e.g., the overall display resolution desired for display  14 ), whereas the other stage such as lower stage  14 B may have a reduced resolution. Local stage  14 B may be used to apply local dimming to dark areas of the image being displayed on display  14 , rather using stage  14 B to display full-resolution images. The use of localized dimming helps enhance dynamic range. For example, in an image that has dark areas, the darkness of the dark areas can be enhanced by locally dimming the dark areas with stage  14 B (i.e., by creating additional dimming in addition to darkening the pixels of the dark areas with stage  14 A). 
       FIG. 7  is a top view of an illustrative layout that may be used for the pixels in display  14 . High resolution pixels  100  may be part of upper stage  14 A and may be arranged in an array having numerous rows and columns. The color filter array in upper stage  14 A may have a corresponding array of color filter elements. Each color filter element in upper stage  14 A may be associated with a corresponding one of pixels  100  in upper stage  14 A. Low resolution (local dimming) pixels such as pixels  102  may overlap sets of high-resolution display pixels  100 . Local dimming pixels  102  in lower (local dimming) stage  14 B may be formed in an array having fewer rows and columns than the array formed form pixels  100  in upper stage  14 A. In particular, the pixel-to-pixel spacing (“pixel pitch”) of pixels  100  may be less than the pixel pitch of pixels  102 . In the example of  FIG. 7 , each local dimming pixel  102  overlaps a 10×10 subarray of display pixels  100  so that each local dimming pixel  102  is used in performing local dimming operations for a set of 100 pixels  100  in upper stage  14 A (i.e., the pixel pitch of pixels  100  is one tenth of the pixel pitch of pixels  102 ). If desired, larger or smaller numbers of pixels  100  may be covered by each local dimming display pixel  102  (i.e., the pixel pitch of pixels  100  may be another suitable fraction of the pixel pitch of pixels  102 ). 
     Pixels in display  14  may have associated borders formed from an opaque layer of material that is sometimes referred to as black mask. To minimize potential visible artifacts such as Moiré patterns due to optical interference between the array of pixels  100  in stage  14 A and the array of pixels  102  in stage  14 B, the black mask patterns used around the borders of pixels  102  may be provided with a wavy shape, as shown by black mask  106  in the portion of display stage  14 B that is shown in  FIG. 8 . Wavy lines of black mask  106  may, for example, be provided in an undulating sinusoidal pattern. Other shapes for the lines of black mask in display  14  may be used, if desired. The illustrative wavy black mask pattern of  FIG. 8  is merely illustrative. 
     Stages  14 A and  14 B may be formed using any suitable type or types of liquid crystal display technology.  FIGS. 9, 10, and 11  are cross-sectional side views of illustrative pixels (without upper and lower polarizer layers) that may be used in stage  14 A and/or stage  14 B. 
     An illustrative configuration for a pixel in stage  14 A and/or stage  14 B of the type that is sometimes referred to as a fringe field switching (FFS) pixel is shown in  FIG. 9 . In this type of arrangement, a display pixel  108  (e.g., display pixel  100  in stage  14 A or display pixel  102  in stage  14 B) may have liquid crystal layer  114 . Electric field lines  118  are established between electrode fingers  116  on dielectric layer  112  and electrode  110 . The strength of electric field  118  controls the orientation of the liquid crystals in layer  114  and is used for controlling the operation of display pixel  108 . Layer  122  may be a substrate for thin-film transistor layer  124 . Layer  120  may be a color filter layer for a color display stage or a transparent substrate for a monochrome display stage. 
     An illustrative configuration for pixel  108  of the type that is sometimes referred to as twisted nematic pixel is shown in  FIG. 10 . In this arrangement, liquid crystal layer  114  of display pixel  108  (e.g., display pixel  100  in stage  14 A or display pixel  102  in stage  14 B) is sandwiched between a upper electrode  128  on substrate  126  and lower electrode  130  on substrate  132 . Electric field  134  can be adjusted by adjusting the voltage between electrodes  128  and  130 . In a monochrome display stage, substrate  126  may be a transparent substrate layer and layer  132  may be a thin-film transistor layer (as an example). 
     An illustrative configuration for pixel  108  of the type that is sometimes referred to as an in-plane switching pixel is shown in  FIG. 11 . In this arrangement, liquid crystal layer  114  is sandwiched between substrate layers  140  and  136 . A voltage is applied across electrodes  138  and  142 , giving rise to controllable electric field strength for electric field  144 . The strength of electric field  144  controls the light transmission through display pixel  108 . Layer  136  (and electrodes  138  and  142 ) may form a thin-film transistor layer. Layer  140  may be a color filter layer for a color display stage or a transparent substrate for a monochrome display stage. 
     In general, any of the display pixel designs of  FIGS. 9, 10, and 11  or other suitable display pixel designs may be used in stage  14 A and/or in stage  14 B. With one suitable arrangement upper stage  14 A is a fringe field switching stage using pixels of the type shown in  FIG. 9  to provide display  14  with the ability to produce satisfactory images (e.g., images with satisfactory color gamut, etc.) and lower stage  14 B is an in-plane switching display stage using in-plane pixels of the type shown in  FIG. 11  or is a twisted nematic display stage using twisted nematic display pixels of the type shown in  FIG. 10 . In-plane switching stages and twisted nematic stages can offer desirable off-axis viewing performance characteristics (i.e., these stages can have off-axis performance patterns that are spatially distributed in a different way than fringe field switching stages), so the use of an in-plane switching design or twisted nematic design for lower stage  14 B may help avoid poor off-axis performance for display  14 . Designs for lower stage  14 B such as twisted nematic designs may also exhibit high aperture ratios and may exhibit flat (wavelength-independent) transmission spectra in the visible light range. In-plane switching designs for lower stage  14 B may offer benefits such as simplified polarizer selection. Other types of displays may be used in forming stages  14 A and  14 B and other combinations of stages in a two-stage display may be used, if desired. The use of a fringe field upper stage and an in-plane switching or twisted nematic lower stage (or vice versa) is merely illustrative. 
       FIG. 12  is a cross-sectional side view of an illustrative two-stage display. As shown in  FIG. 12 , display  14  has upper stage  12 A and lower stage  12 B. Upper stage  14 A has upper polarizer  146  and lower polarizer  154 . Liquid crystal layer  150  is interposed between color filter layer  148  and thin-film transistor layer  152 . Upper stage  14 A may be a fringe field display stage or other suitable type of display stage. Color filter layer  148  may contain an array of color filter elements to provide upper stage  14 A with the ability to display color images. If desired, the positions of color filter layer  148  and thin-film transistor layer  152  may be swapped or other display configurations may be used for stage  12 A. The configuration of  FIG. 12  is merely illustrative. Adhesive  156  may be used to attach upper stage  14 A to lower stage  14 B. Adhesive layers may also be used elsewhere in display  14  to attach layers of material to each other. Adhesives such as adhesive layer  156  may be formed from liquid adhesive or pressure sensitive adhesive. 
     Lower stage  14 B of  FIG. 12  may have upper polarizer  158  and lower polarizer  166 . Liquid crystal layer  162  is interposed between substrate layer  160  and thin-film transistor layer  164 . Substrate layer  160  may be a clear layer of glass or plastic that does not contain any color filter elements (i.e., stage  14 B may be a monochromatic display stage). Rather, display  14  may be provided with the ability to display color images due to the presence of color filter layer  148  in upper stage  14 A. The omission of color filter elements from substrate  160  helps enhance light transmission and ease alignment tolerances. Alignment issues, optical interference issues, and control complexity can also be minimized by ensuring that stage  14 B has a greater pixel pitch than the pixels of stage  14 A (i.e., stage  14 B has a lower resolution than stage  14 A). 
       FIG. 13  is a cross-sectional side view of an illustrative polarizer that may be used in display  14 . As shown in  FIG. 8 , polarizer  168  may have a polymer polarizer film such as polarizer layer  172 . Layer  152  may be formed from a stretched polymer such as stretched polyvinyl alcohol (PVA) and may therefore sometimes be referred to as a PVA layer. A dichroic dye such as iodine or dichroic organic pigments may be added to the stretched PVA film to provide polarizer  168  with the ability to polarize light. Iodine may, for example, be coated onto the surface of layer  172  or may otherwise be used to dope layer  172 . Molecules of iodine align with the stretched film of layer  172  and form the active polarizing layer of polarizer  168 . Other polarizer films may be used if desired. 
     Polarizer film  172  may be sandwiched between other polymer layers. For example, the upper portion of layer  172  may be covered with one or more layers such as protective layer  170 . If desired, functional layers may also be added to polarizer  168  (e.g., antireflection films, antismudge and antiscratch coatings, etc.). Protective layer  170  may be formed from a clear polymer. For example, layer  170  may be formed from a material such as tri-acetyl cellulose (TAC) and may sometimes be referred to as a TAC film. The TAC layer or other layer may help support and protect the PVA film. Other films may be laminated to polarizer layer  172  if desired. For example, lower layer(s)  178  may be attached to the lower surface of polarizer layer  172 . As shown in  FIG. 13 , lower layers  178  may be formed from one or more compensation films (i.e., birefringent films such as cyclic olefin polymer films) such as negative birefringence compensation layer  174  and positive birefringence compensation layer  176 . The compensation layers enhance off-axis viewing performance for display  14 . Polarizer  168  of  FIG. 13  may be used to form polarizer  146  of  FIG. 12 , polarizer  154  of  FIG. 12 , polarizer  158  of  FIG. 12 , and/or polarizer  166  of  FIG. 12 . In some polarizers in display  14 , compensation films  178  may be omitted. As one example, compensation films  178  may be included in polarizer  146  and polarizer  158  but may be omitted from polarizer  154  and  166 . Compensation films may also be incorporated into layers  70  ( FIG. 5 ). If desired, the lowermost polarizer in display  14  may be a reflective polarizer to enhance backlight efficiency. 
     The display of  FIG. 13  uses four polarizers. If desired, display  14  may be implemented using three polarizers. As shown in  FIG. 14 , for example, polarizer  180  may be common to both upper stage  14 A and lower stage  14 B. Use of a shared polarizer such as polarizer  180  may reduce display cost and complexity and may help minimize light transmission losses. 
     If desired, the compensation films for display  14  may be incorporated into shared polarizer  180 . An illustrative configuration that may be used for shared polarizer  180  is shown in  FIG. 15 . As shown in  FIG. 15 , shared polarizer  180  may include a polymer polarizer film such as polarizer layer  186 . Layer  186  may be formed from a stretched polymer such as stretched polyvinyl alcohol. A dichroic dye such as iodine or dichroic organic pigments may be added to the stretched PVA film to provide polarizer layer  186  and polarizer  180  with the ability to polarize light. Polarizer layer  186  may be attached to other polymer layers. For example, polarizer layer  186  may be attached to TAC layer  188  and a polyvinyl alcohol polymer layer without iodine or other dichroic dye such as mechanical PVA layer  190 . Upper compensation films  196  may include negative birefringence compensation layer  182  and positive birefringence compensation layer  184  and may be used to provide compensation for stage  14 A. Lower compensation films  196  may be include negative birefringence compensation layer  192  and positive birefringence compensation layer  194  and may be used to provide compensation for stage  14 B. If desired, compensation films for display  14  of  FIG. 14  may be incorporated into layers  70  (see, e.g.,  FIG. 5 ) or other polarizers in display  14 . The configuration of  FIG. 15  is merely illustrative. 
     Quantum dots may be used to provide backlight unit  42  with the ability to generate backlight having a spectrum that is peaked at wavelengths that are aligned with the colors in the color filter elements of color filter layer  148 . This allows display  14  to exhibit an enhanced color gamut. An illustrative backlight with a quantum dot structure is shown in  FIG. 16 . As shown in  FIG. 16 , backlight  42  may include light source  72 , quantum dot structure  200 , and light guide plate  78 . Light source  72  may include one or more blue light-emitting diodes that produce blue light  74 - 1 . Quantum dot structure  200  receives blue light  74 - 1  and outputs corresponding light  74 - 2  at wavelengths associated with red light R, green light G, and blue light B. An illustrative output spectrum for quantum dot structure  200  when illuminated with blue light from light source  72  is shown in  FIG. 17 . 
     Light  74 - 2  may be supplied to edge  76  of light guide plate. Light guide plate  78  may distribute this light laterally in dimensions X and Y, until the light is scattered upwards in direction Z as backlight  44 . Backlight  44  travels upwards through the layers of display  14  in direction Z. The spectral peaks of backlight  44  (i.e., the red peak R, green peak G, and blue peak B in the example of  FIG. 17 ) may be aligned with the transmission peaks of the color filter elements in color filter layer  148 . For example, if color filter layer  148  has red, green, and blue color filter elements, the transmission spectra of the red, green, and blue color filter elements and the output spectrum of quantum dot structure may be configured so that the red output of structure  200  is aligned with the red transmission wavelength of the red color filter element, so that the green output of structure  200  is aligned with the green transmission wavelength of the green color filter element, so that the blue output of structure  200  is aligned with the blue transmission wavelength. 
       FIG. 18  is a top view of an illustrative set of color filter elements that may be used in color filter layer  148  in a display having a color filter array with an array of red, green, and blue color filter elements. Red filter elements such as red element  202  may be used to provide red pixels in upper stage  14 A with the ability to supply red light components of an image, green filter elements such as green element  204  may be used to provide green pixels in upper stage  14 A with the ability to supply green light components of an image, and blue filter element such as blue element  206  may be used to provide blue pixel in upper stage  14 B with the ability to supply blue light components of an image. If desired, light output efficiency may be enhanced by minimizing color filter layer transmission losses. This may be accomplished by incorporating white color filter elements into the color filter array of color filter layer  148 . As shown in  FIG. 19 , each set of color filter elements in this type of configuration will include a white (clear) element such as element  208  in addition to the red, green, and blue elements. The clear color filter element efficiently passes backlight  44  to the viewer without significant transmission losses from light filtering. The backlight that passes through the clear (white) color filter element will appear white due to the presence of color components in the red, green, and blue portions of the spectrum. Configurations of the type shown in  FIG. 18  may sometimes be said to use RGB color filters or RGB sub-pixel structures. Configurations of the type shown in  FIG. 19  may sometimes be said to use RGBW color filters or RGBW sub-pixel structures. 
       FIG. 20  is a diagram of illustrative display control circuitry that may be used in displaying images on display  14 . The circuitry of  FIG. 20  may be implemented in a display driver circuit (e.g., a timing controller chip), may be implemented using a video card in device  10 , may be implemented using other circuitry in device  10  (e.g., microprocessors, application-specific integrated circuits, field-programmable gate arrays, system-on-chip integrated circuits, etc.), or may be implemented using a combination of these resources. The circuitry of  FIG. 20  may transform image data that is encoded in red-green-blue format to image data that is encoded in white-red-green-blue format and may perform image splitting operations in which control signals for different aspects of an image to be displayed are allocated between upper stage  14 A and lower stage  14 B. As shown in  FIG. 20 , image data to be displayed may be encoded in a red-green-blue (RGB) color space and may be provided to input  210  from control circuitry in device  10 . White-red-green-blue (WRGB) converter  212  receives the RGB data on input  210 . Converter  212  computes a brightness setting to be used for backlight unit  42  from the data supplied to input  210  and supplies a corresponding brightness control signal to backlight controller  216 . Backlight controller  216  adjusts the output produced by light source  72  (see, e.g.,  FIG. 16 ) accordingly. 
     Converter  212  maps RGB data to WRGB data. Color space converter  214  converts the WRGB data to an appropriate color space such as the CIE XYZ color space. Image data can then be split into two channels by image splitter  220 . Image splitter  220  may, for example, provide a high resolution color image data component of the image data to upper stage  14 A while simultaneously providing a low resolution monochromatic localized dimming component of the image data to lower stage  14 B. The local dimming channel of the image data may be derived from the square of luminance Y in the XYZ color space. The color image data channel of the image data may be formed by dividing the Y channel by the square of Y and using this new Y data with corresponding X and Z data to form the final color image data. When displaying the color component of the image on display stage  14 A and the lower-resolution local dimming component of the image on display stage  14 B, gamma look-up tables may be used to convert the data from image splitter  220  into WRGB data. 
     The foregoing is merely illustrative and various modifications can be made by those skilled in the art without departing from the scope and spirit of the described embodiments. The foregoing embodiments may be implemented individually or in any combination.

Metadata:
Filing Date: 20140930
Publication Date: 20170110
Grant Date: 20170110
Priority Date: 20140110
Inventors: WU JIAYING
CHEN WEI
CHEN CHENG
RIEDEL WILLIAM MATHEWS
QI JUN
ZHONG JOHN Z.
MARCU GABRIEL
Assignee: APPLE INC
CPC Classifications: [{"code": "G02F1/133514", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02F1/13471", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02F1/1336", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02F1/1368", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02F2413/14", "inventive": false, "first": false, "tree": "[]"}, {"code": "G02F1/13363", "inventive": true, "first": true, "tree": "[]"}, {"code": "G02F1/133528", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02F2001/133614", "inventive": false, "first": false, "tree": "[]"}, {"code": "G02F2413/13", "inventive": false, "first": false, "tree": "[]"}, {"code": "G02F1/13471", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02F1/1368", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02F1/13363", "inventive": true, "first": true, "tree": "[]"}, {"code": "G02F2413/14", "inventive": false, "first": false, "tree": "[]"}, {"code": "G02F1/133528", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02F1/133514", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02F2413/13", "inventive": false, "first": false, "tree": "[]"}, {"code": "G02F1/13471", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02F1/133614", "inventive": false, "first": false, "tree": "[]"}, {"code": "G02F1/13363", "inventive": true, "first": true, "tree": "[]"}, {"code": "G02F1/133614", "inventive": false, "first": false, "tree": "[]"}, {"code": "G02F1/1336", "inventive": true, "first": false, "tree": "[]"}]
Family ID: 53521254