Patent Publication Number: US-2021191477-A1

Title: Display device

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     The present application claims priority from Japanese Application JP2019-229643, the content of which is hereby incorporated by reference into this application. 
     BACKGROUND ART 
     Technical Field 
     The disclosure relates to a display device that includes an antenna for reading a communication medium, such as an integrated circuit (IC) card. 
     Description of the Background Art 
     A recent study addresses installing an antenna for short-range wireless communication (e.g., NFC or near-field communication) on a display device. Unfortunately, upon voltage signal application to pixel circuits included in a display unit, such a display device generates noise that affects the communication performance of its antenna, thus degrading the antenna communication performance. 
     Japanese Patent Application Laid-Open No. 2016-143971, for instance, proposes a display device that includes an adjuster for reducing the influence of noise generated from its display unit on antenna communication. 
     SUMMARY 
     Other than display devices, such as television sets, a display device with an antenna is applicable to small and thin display devices, such as watches and mobile terminals. However, the display unit and antenna get closer to each other along with decrease in the size and thickness of the display device, and the noise from the display unit greatly affects antenna communication. This considerably degrades the communication performance of the antenna. In the display device in Japanese Patent Application Laid-Open No. 2016-143971 for instance, size and thickness reduction causes such an unstable reading of a communication medium (e.g., an IC card) as to hinder user use. 
     To solve this problem, it is an object of the disclosure to provide a small and thin display device capable of preventing reduction in the communication performance of its antenna. 
     To solve the problem, a first aspect of the disclosure provides a display device that includes that following: a display unit including a pixel circuit; an antenna including at least one antenna element that is flat; a noise barrier plate made of metal or magnetic substance; and a casing having a bottom made of metal or resin. The at least one antenna element is disposed under the display unit, the noise barrier plate is disposed under the at least one antenna element, and the bottom is disposed under the noise barrier plate, where a direction for the display unit to display an image is defined as an upper side, where another direction opposite to the direction is defined as a lower side. 
     The above configuration offers a small and thin display device capable of preventing reduction in the communication performance of its antenna to such an extent as not to hinder user use. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic cross-sectional view of the configuration of a display device  1  according to a first preferred embodiment; 
         FIG. 2  is a plan view of the arrangement of an antenna  20  and a noise barrier plate  30  included in the display device  1  according to the first preferred embodiment; 
         FIG. 3  is a schematic cross-sectional view of the configuration of main components of a display device  1 A according to a second preferred embodiment; 
         FIG. 4  is a plan view of the arrangement of an antenna  20 A and the noise barrier plate  30  included in the display device  1 A according to the second preferred embodiment; 
         FIG. 5  is a plan view of another example configuration of the antenna included in the display device according to the second preferred embodiment; 
         FIG. 6  is a block diagram illustrating an example configuration of main components of a display device according to a third preferred embodiment; and 
         FIG. 7  is a graph illustrating an example operation of the display device according to the third preferred embodiment. 
     
    
    
     DETAILED DESCRIPTION OF THE DISCLOSURE 
     With reference to the accompanying drawings, preferred embodiments of the disclosure will be detailed. Identical or equivalent components in the drawings will be denoted by the same signs and will not be elaborated upon. For easy description, the accompanying drawings show simplified or schematic configurations, and omit some of the components. The dimensional ratio between the components in each of the accompanying drawings is not necessarily equal to the actual dimensional ratio. 
     Each preferred embodiment of the disclosure describes a liquid-crystal display by way of example. Nevertheless, the disclosure is not limited to a liquid-crystal display and is also applicable to other kinds of display device, including an organic electro-luminescence (EL) display. 
     First Preferred Embodiment 
       FIG. 1  is a schematic cross-sectional view of the configuration of a display device  1  according to a first preferred embodiment. The display device  1  includes a display unit  10 , an antenna  20 , a noise barrier plate  30 , a casing  40 , and a rim sheet  50 , as illustrated in  FIG. 1 . 
     The display unit  10  is composed of an image display component, such as a liquid-crystal display module. The display unit  10  includes a backlight  100  and a liquid-crystal panel  110 . The liquid-crystal panel  110  has a stack of, in sequence, a lower polarizer plate  111 , a lower substrate  112 , a liquid-crystal layer  113 , an upper substrate  114 , an upper polarizer plate  115 . In the following description, a direction where the liquid-crystal panel  110  is located when viewed from the backlight  100  (i.e., a direction where the display unit  10  displays an image) is defined as the upper side of the display device  1 , and the opposite direction is defined as the lower side of the same. 
     The backlight  100  emits planar light upward. The backlight  100  includes a light source (e.g., LEDs or light-emitting diodes) and a light-guiding plate that diffuses, in a planar manner, light emitted from the light source, and radiates the light upward. For instance, the backlight  100  includes LEDs on the side of the light-guiding plate, and includes a reflective plate under the light-guiding plate. The lower polarizer plate  111  selectively transmits a component contained in light from the backlight  100  and oscillating in a first direction. 
     The liquid-crystal layer  113  is disposed between the lower substrate  112  and the upper substrate  114 . The lower substrate  112  includes pixel circuits (e.g., TFTs or thin film transistors) for voltage application to liquid crystals within the liquid-crystal layer  113 . These liquid crystals change their orientation according to applied voltage, and this orientation controls the direction of oscillation of light passing through the liquid-crystal layer  113 . 
     The upper substrate  114  has a color filter that selectively transmits components contained in light passing through the liquid-crystal layer  113 , and having particular wavelength bands (colors). For instance, the color filter has a predetermined pattern of arrangement (e.g., a stripe arrangement and a mosaic arrangement) composed of a filter that transmits red light, a filter that transmits green light, and a filter that transmits blue light. The color filter is disposed in a display region DA, the outside of which is a black matrix region BM provided with a light blockage filter. The upper polarizer plate  115  selectively transmits a component contained in each color of light passing through the color filter of the upper substrate  114 , and oscillating in a second direction. 
     When the first and second directions are perpendicular for instance, upon change in the direction of oscillation caused by the liquid crystals, light passing through the lower polarizer plate  111  and oscillating in the first direction has increased components that oscillate in the second direction. Such a change in the oscillation direction caused by the liquid crystals allows the light passing through the lower polarizer plate  111  to pass through the upper polarizer plate  115 . On the other hand, the light passing through the lower polarizer plate  111  and oscillating in the first direction is blocked by the upper polarizer plate  115  unless the oscillation direction is changed by the liquid crystals. 
     When the first and second directions are parallel for instance, upon change in the direction of oscillation caused by the liquid crystals, light passing through the lower polarizer plate  111  and oscillating in the first direction has decreased components that oscillate in the second direction. Such a change in the oscillation direction caused by the liquid crystals causes the light passing through the lower polarizer plate  111  to be blocked by the upper polarizer plate  115 . On the other hand, the light passing through the lower polarizer plate  111  and oscillating in the first direction passes through the upper polarizer plate  115  unless the oscillation direction is changed by the liquid crystals. 
     As described above, the display unit  10  controls the alignment direction of the liquid crystals by regulating voltage applied to the liquid crystals, and controls light passing through the upper polarizer plate  115 . This enables the display unit  10  to display an image. 
     The antenna  20  is used for short-range wireless communication, and communicates with a communication medium (e.g., an IC card) brought close to the upper surface of the display unit  10  (i.e., an image display surface). The antenna  20  is disposed under the display unit  10 . 
     The noise barrier plate  30  is made of metal or magnetic substance, and is disposed under the antenna  20 . The noise barrier plate  30  reduces the influence of noise generated from the display unit  10 , when the antenna  20  communicates with a communication medium. For instance, the noise barrier plate  30  is made of ferrite magnetic substance containing an iron oxide. 
     The casing  40  is a box having an open upper side, and houses the display unit  10 , the antenna  20 , the noise barrier plate  30 , and the rim sheet  50 . The casing  40  has a bottom  41  disposed under the noise barrier plate  30  and made of metal or resin. It is noted that parts of the casing  40  other than the bottom  41  may be also made of the same metal or resin as the bottom  41 . It is also noted that for metal, the casing bottom  41  is preferably formed using a low-conductivity metal, such as stainless steel, in order to reduce noise influence. It is also noted a small and thin display device (e.g., a watch and a mobile terminal) requires a thin and sufficiently strong casing  40 ; hence, the bottom  41  and by extension the casing  40  are preferably made of stainless steel. 
     The rim sheet  50  is disposed between the backlight  100  and the liquid-crystal panel  110  and outside the display region DA. The rim sheet  50  is made of, for instance, elastic resin, and functions as a buffer and a waterproof material. 
       FIG. 2  is a plan view of the arrangement of the antenna  20  and noise barrier plate  30  included in the display device  1  according to the first preferred embodiment.  FIG. 2  is a plan view of the display unit  10  viewed from above, and shows only the antenna  20  and the noise barrier plate  30 . 
     The antenna  20  includes a flexible printed circuit (FPC) board  21 , an antenna element  22 , and two feeder lines  23 , as illustrated in  FIG. 2 . The antenna element  22  and the feeder lines  23  are disposed on the FPC board  21 . The antenna element  22  is flat and composed of, for instance, a loop antenna, a helical antenna, or a spiral antenna. Each feeder line  23  is connected to the antenna element  22  and transmits a signal that is sent and received via the antenna element  22 . 
     When the antenna element  22  is composed of a multi-turn loop antenna, as illustrated in  FIG. 2  for instance, one of the feeder lines  23  is connected to one end of the antenna element  22  and the other feeder line  23  is connected to the other end of the antenna element  22 . In this case, the end of the antenna element  22  wound inside and the feeder line  23  may be connected together on the FPC board  21  to which an element, a wire, and other things are attached externally. 
     Alternatively, the FPC board  21  may be formed to have a multi-layer structure (e.g., a structure with conductors on both surfaces), in which the end of the antenna element  22  and the feeder line  23  may be connected together via a wire provided in a layer where the antenna element  22  and the feeder line  23  are not located. 
     As illustrated in  FIG. 2 , the entire antenna element  22  is disposed on the noise barrier plate  30  in a plan view when the display unit  10  is viewed from above. That is, the antenna element  22  is encompassed by the noise barrier plate  30  in this plan view. 
     As described above, the display device  1  includes the antenna element  22  under which the noise barrier plate  30  and the bottom  41  are disposed. The noise barrier plate  30  is made of metal or magnetic substance, and the bottom  41  is made of metal or resin. This configuration enables the display device  1  that is small and thin to prevent reduction in the communication performance of the antenna  20  to such an extent as not to hinder user use. 
     In particular, the noise barrier plate  30 , which is made of ferrite magnetic substance, and the bottom  41  of the casing  40 , which is made of stainless steel, can achieve a synergistic effect of noise prevention, thus effectively preventing reduction in the communication performance of the antenna  20 . 
     It is noted that the entire antenna element  22  does not necessarily have to be disposed on the noise barrier plate  30  in a plan view when the display unit  10  is viewed from above. However, to sufficiently prevent reduction in the antenna communication performance, more than a half of the antenna element  22  is preferably disposed on the noise barrier plate  30  in this plan view. Placing the entire antenna element  22  on the noise barrier plate  30  in a plan view when the display unit  10  is viewed from above can minimize reduction in the antenna communication performance. 
     Second Preferred Embodiment 
     A second preferred embodiment will be described.  FIG. 3  is a schematic cross-sectional view of the configuration of main components of a display device  1 A according to the second preferred embodiment.  FIG. 3  shows only the lower substrate  112 , an antenna  20 A, the noise barrier plate  30 , the casing  40 , and a source driver  60 . The source driver  60  is electrically connected to pixel circuits at an end  1121  of the lower substrate  112 , and inputs, to the pixel circuits, a voltage signal having a level corresponding to image data. 
       FIG. 4  is a plan view of the arrangement of the antenna  20 A and noise barrier plate  30  included in the display device  1 A according to the second preferred embodiment.  FIG. 4  is a plan view of the display unit  10  viewed from above, and shows only the antenna  20 A and the noise barrier plate  30 . 
     The antenna  20 A is spaced away from the end  1121  of the lower substrate  112 , as illustrated in  FIGS. 3 and 4 . To be specific, the antenna  20 A includes an antenna element  22 A spaced away from the end  1121  of the lower substrate  112  by equal to or more than 10 mm in a plan view when the display unit  10  is viewed from above. 
     A diligent study conducted by the inventors has demonstrated that preventing reduction in the communication performance of the antenna  20 A requires the antenna element  22 A to be spaced away not from the source driver  60  per se, but from the end  1121  of the lower substrate  112 , which is electrically connected to the source driver  60 . In addition, placing the antenna element  22 A away from the end  1121  of the lower substrate  112  by equal to or more than 10 mm in a plan view when the display unit  10  is viewed from above, can effectively prevent reduction in the communication performance of the antenna  20 A. 
     For instance, the source driver  60  can be mounted on an FPC board, and the FPC board can be connected to the end  1121  of the lower substrate  112 ; in this case, the antenna element  22 A still needs to be spaced away from the end  1121 , which is connected to the FPC board. 
     In some cases, the feeder lines  23  need to be placed so as to extend from the antenna element  22 A toward the end  1121 , unlike the example in  FIG. 4 ; accordingly, the feeder lines  23  are affected by noise, thus possibly degrading the communication performance. In extending the feeder lines  23  toward the end  1121 , it is accordingly preferable that the feeder lines  23  be designed to be less susceptible to noise. 
       FIG. 5  is a plan view of another example configuration of the antenna included in the display device according to the second preferred embodiment.  FIG. 5  is similar to  FIG. 4 .  FIG. 5  shows an antenna  20 B that includes the FPC board  21  having a multi-layer structure (e.g., a structure with conductors on both surfaces).  FIG. 5  also shows two feeder lines  23 B overlapping each other in a plan view when the display unit  10  is viewed from above. Such two feeder lines  23 B, which are supplied with reverse current to cancel out a magnetic field, can be less susceptible to noise. 
     Third Preferred Embodiment 
     A third preferred embodiment will be described.  FIG. 6  is a block diagram illustrating an example configuration of main components of a display device according to a third preferred embodiment.  FIG. 6  shows a display device  1 C that includes a controller  70  that controls the operation of the display unit  10 . 
     The controller  70  is composed of, for instance, a computing unit (e.g., a CPU or central processing unit) and a recording unit (e.g., a semiconductor memory). The controller  70  controls the operation of the display unit  10  on the basis of an antenna operation signal indicating whether an antenna communicates with a communication medium. 
       FIG. 7  is a graph illustrating an example operation of the display device according to the third preferred embodiment. The lateral axis of the graph represents time, and the longitudinal axis of the graph represents whether pixel circuits are driven. The drive of the pixel circuits refers to applying, to the pixel circuits, a voltage signal corresponding to image data. In  FIG. 7 , ON represents that the pixel circuits are driven, and OFF represents that the pixel circuits are not driven. Thus in  FIG. 7 , the number of times of switch to ON per unit time corresponds to the refresh rate of the display unit  10 .  FIG. 7  also shows a comparison between an antenna non-operation period, during which the antenna does not communicate with the communication medium, and an antenna operation period, during which the antenna communicates with the communication medium. 
     The controller  70  sets the refresh rate of the display unit  10  in the antenna operation period to be smaller than the refresh rate in the antenna non-operation period, as illustrated in  FIG. 7 . For instance, the controller  70  sets the refresh rate of the display unit  10  in the antenna non-operation period to be 60 Hz, and sets the refresh rate of the same in the antenna operation period to be equal to or less than 10 Hz. 
     The number of times of voltage signal input to the pixel circuits decreases along with decrease in the refresh rate of the display unit  10 . This reduces the number of times of noise generation from the display unit  10  per unit time. Accordingly, setting the refresh rate of the display unit  10  in the antenna operation period to be smaller than the refresh rate of the display unit  10  in the antenna non-operation period can prevent reduction in the communication performance of the antenna communicating with the communication medium. 
     In particular, the display unit  10  having a drawing rate of 10 Hz or less per unit time in the antenna operation period can sufficiently prevent reduction in the antenna communication performance. 
     A reduction in the refresh rate causes the pixel circuits to hold accumulated charges for a long time, during which current leakage changes liquid-crystal alignment, possibly degrading image quality. 
     The controller  70  may accordingly control the display unit  10  to display a simple image including only characters, such as “Hold the card over here”, in the antenna operation period. The controller  70  controls the display unit  10  in such a manner. This enables image quality degradation resulting from a lowered refresh rate to be less recognized by a user. 
     The pixel circuits may be formed using an oxide semiconductor. An example of the oxide semiconductor is an In—Ga—Zn—O semiconductor (e.g., indium gallium zinc oxide). The In—Ga—Zn—O semiconductor is a ternary oxide of indium (In), gallium (Ga), and zinc (Zn); the ratio (compositional ratio) between In, Ga, and Zn may be expressed as, for instance, In:Ga:Zn=2:2:1, In:Ga:Zn=1:1:1, or In:Ga:Zn=1:1:2. 
     A pixel circuit of oxide semiconductor can offer an extremely smaller leakage current than a pixel circuit of amorphous silicon or other materials. For instance, a pixel circuit of In-Ga—Zn—O semiconductor can offer a smaller leakage current than a pixel circuit of amorphous silicon by less than one hundredth. A pixel circuit of oxide semiconductor, by extension, of In-Ga—Zn—O semiconductor enables image quality degradation resulting from a lowered refresh rate in the antenna operation period to be less recognized by the user. 
     The pixel circuits may be formed using an oxide semiconductor other than an In-Ga—Zn—O semiconductor. The circuits may include, for instance, an In—Sn—Zn—O semiconductor (e.g., In 2 O 3 —SnO 2 —ZnO, InSnZnO) The In—Sn—Zn—O semiconductor is a ternary oxide of indium (In), tin (Sn), and zinc (Zn). Alternatively, the pixel circuits may be formed using an oxide semiconductor, including an In—Al—Zn—O semiconductor, an In-AI-Sn—Zn—O semiconductor, a Zn—O semiconductor, an In—Zn—O semiconductor, a Zn—Ti—O semiconductor, a Cd—Ge—O semiconductor, a Cd—Pb—O semiconductor, CdO or cadmium oxide, a Mg—Zn—O semiconductor, an In—Ga—Sn—O semiconductor, an In—Ga—O semiconductor, a Zr—In—Zn—O semiconductor, and a Hf—In—Zn—O semiconductor. 
     Modifications and Others 
     The foregoing preferred embodiments are mere examples for implementing the disclosure. The disclosure is thus not limited to the foregoing preferred embodiments; various modifications can be devised, as appropriate, without departing from the scope of the disclosure. 
     In the first and second preferred embodiments for instance, the FPC board  21  may have a multi-layer structure (e.g., a structure with conductors on both surfaces); in addition, a plurality of antenna elements  22 ,  22 A, and  22 B may be provided so as to overlap each other in a plan view when the display unit  10  is viewed from above, to thus establish electrical connection. In this case, near a location of connection with the feeder lines  23  for instance, the antenna elements  22 ,  22 A, and  22 B may be in contact with each other within the FPC board  21  to establish electrical connection. 
     Such a configuration, which includes a parallel arrangement of the antenna elements  22 ,  22 A, and  22 B, can reduce resistance. Thus, elongating the antenna elements  22 ,  22 A, and  22 B can improve antenna communication performance. For instance, a multi-turn loop antenna with increased turns can improve the communication performance. Moreover, reducing the resistances of the antenna elements  22 ,  22 A, and  22 B enables the antenna elements  22 ,  22 A, and  22 B to have a narrow wire width. This enables the antenna elements  22 ,  22 A, and  22 B and the antennas  20 ,  20 A, and  20 B to be downsized. 
     The first to third preferred embodiments can be implemented independently or in combination with any preferred embodiment. 
     The display devices can be described as below. 
     A first aspect provides a display device that includes the following: a display unit including a pixel circuit; an antenna including at least one antenna element that is flat; a noise barrier plate made of metal or magnetic substance; and a casing having a bottom made of metal or resin. The at least one antenna element is disposed under the display unit, the noise barrier plate is disposed under the at least one antenna element, and the bottom is disposed under the noise barrier plate, where a direction for the display unit to display an image is defined as an upper side, where another direction opposite to the direction is defined as a lower side. This configuration offers a small and thin display device capable of preventing reduction in the communication performance of its antenna to such an extent as not to hinder user use. 
     A second aspect provides that in the first aspect, the noise barrier plate may be made of ferrite magnetic substance containing an iron oxide, and the bottom may be made of stainless steel. This configuration can achieve a synergistic effect of noise prevention, thus effectively preventing reduction in the antenna communication performance. 
     A third aspect provides that in the first or second aspect, more than a half of the at least one antenna element may be disposed on the noise barrier plate in a plan view when the display unit is viewed from above. This configuration can sufficiently prevent reduction in the antenna communication performance. 
     A fourth aspect provides that in the third aspect, the entire at least one antenna element may be disposed on the noise barrier plate in the plan view. This configuration can minimize reduction in the antenna communication performance. 
     A fifth aspect provides that in any one of the first to fourth aspects, the at least one antenna element may include a plurality of antenna elements electrically connected together, and the plurality of antenna elements may overlap each other in a plan view when the display unit is viewed from above. This configuration, which includes a parallel arrangement of the antenna elements, can reduce resistance. Thus, elongating the antenna elements can improve the antenna communication performance. In addition, reducing the wire widths of the antenna elements can downsize the antenna. 
     A sixth aspect provides that in any one of the first to fifth aspects, the display unit may include the following: a substrate on which the pixel circuit is disposed; and a driver element electrically connected to the pixel circuit at an end of the substrate. The driver element inputs, to the pixel circuit, a voltage signal having a level corresponding to image data. The at least one antenna element may be spaced away from the end by equal to or more than 10 mm in a plan view when the display unit is viewed from above. This configuration can effectively prevent reduction in the antenna communication performance. 
     A seventh aspect provides that in the sixth aspect, the antenna may include two feeder lines connected to the at least one antenna element, and in the plan view, the two feeder lines may extend from the at least one antenna element toward the end and overlap each other. In this configuration, the two feeder lines, which are supplied with reverse current to cancel out a magnetic field, can be less susceptible to noise. 
     An eighth aspect provides that the display device in any one of the first to seventh aspects may further include a controller that controls the refresh rate of the display unit. The controller may set the refresh rate in a period during which the antenna communicates with a communication medium to be smaller than the refresh rate in a period during which the antenna does not communicate with the communication medium. This configuration can prevent reduction in the communication performance of the antenna communicating with the communication medium. 
     A ninth aspect provides that in the eighth aspect, the controller may set the refresh rate in the period during which the antenna communicates with the communication medium to be equal to or less than 10 Hz. This configuration can sufficiently prevent reduction in the antenna communication performance. 
     A tenth aspect provides that in the eighth or ninth aspect, the pixel circuit may be made of oxide semiconductor. Furthermore, an eleventh aspect provides that in the tenth aspect, the pixel circuit may be made of In-Ga—Zn—O oxide semiconductor. This configuration enables image quality degradation resulting from a lowered refresh rate to be less recognized by a user when the antenna communicates with the communication medium.