JP2012027203A - Electronic apparatus and display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a display device capable of suppressing EMI caused by resonance between a chassis and a bezel.SOLUTION: A display device comprises: a display panel 2 comprising a front surface 21 including a display area for displaying images and a rear surface 22 on the opposite side of the front surface 21; a conductive chassis which is provided to the side of the rear surface 22 of the display panel 2 so that a principal surface 311 faces the rear surface 22 of the display panel 2; a conductive bezel which is provided to the side of the front surface 21 of the display panel 2 so that a principal surface 411 faces the front surface 21 of the display panel 2, and which comprises an opening 42 corresponding to the display area of the display panel 2; a conductive machine screw 71 which is fastened to both of the chassis and the bezel and fixes the display panel 2 to the chassis and the bezel; and a washer 8 which is interposed between the bezel and the machine screw 71 and has lower electrical conductivity than the chassis and the bezel.

Description

  The present invention relates to an electronic device typified by a display device, and more particularly to an electronic device and a display device that reduce electromagnetic waves radiated to the outside.

  In the display device, when the display panel displays an image, a digital signal for controlling the gradation expression of each color of RGB in each pixel of the display panel is transmitted within the printed circuit board. In recent years, there has been a need to transmit digital signals at higher speeds in order to increase the number of pixels and to realize high functions such as double speed or quadruple speed drive display functions.

  When a digital signal is transmitted through the printed circuit board at a high speed, a harmonic component of the digital signal is generated and leaks out of the printed circuit board as a noise current. Many display devices include a chassis that supports the display panel from the back surface, a bezel that has an opening corresponding to the display area and that supports the display panel from the front side of the panel, and a fastening member that fixes the chassis and the bezel. Have. When noise current flows to the chassis or the bezel, these members serve as antennas and radiate electromagnetic noise to the outside of the display device. When resonance occurs between the bezel and the chassis via a fastening member, the radiation amount of electromagnetic noise increases.

  This radiation of electromagnetic noise (hereinafter referred to as EMI (Electro Magnetic Interference)) may affect other electronic devices around the display device, such as malfunction. For this reason, regulatory values for EMI are set in each country. Since electronic device manufacturers cannot ship products unless the EMI generated from the products is kept below the regulation value, the importance of EMI countermeasures is increasing in product development.

  Regarding measures against EMI generated from a display device, conventionally, an internal casing (chassis) in which a reference potential is set, and a metal decorative plate (equivalent to a bezel, exhibiting behavior as an antenna generating EMI) Has been proposed that suppresses EMI by setting the interval between two adjacent connectors to a distance that does not resonate with an electromagnetic wave of a specified frequency when conducting a plurality of connectors (fastening members) (for example, , See Patent Document 1).

JP 2004-361913 A

  When the method described in Patent Document 1 is used to move the fastening member so that the spacing between the fastening members is equal to or less than the resonance length and the resonance with the chassis and bezel as the antenna is suppressed, the number of fastening points increases, and the components of the fastening member Costs and assembly man-hours during production increase. For example, when the resonance between the chassis and the decorative plate is to be suppressed by the method of Patent Document 1 in a frequency band of 1 GHz or less, the interval between the fastening members is 100 mm or less. When this is applied to a 52-inch display device having a long side dimension of 1200 mm, 13 fastening members are required in one long side direction.

  On the other hand, in a commercially available 52-inch liquid crystal television, for example, four metal screws are used in one long side direction for fastening the chassis and the bezel, and products related to problems other than EMI such as strength and vibration. There is an example that satisfies the quality. In this example, the distance between the fastening screws on the long side is 402 mm at the maximum, and using the mathematical formula described in Patent Document 1, there is a possibility that EMI due to resonance between the chassis and the bezel occurs in a frequency band of about 250 MHz or more. Arise.

  EMI becomes prominent when the frequency of a noise source such as a fundamental clock of a digital device and its harmonics overlaps with the resonance frequency of the chassis and the bezel as described above, and often causes a problem. In this case, a method of shifting the resonance frequency on the housing side is effective, but normally, when considering EMI countermeasures performed in the latter half of product development, problems other than EMI such as strength and vibration must be re-evaluated. Therefore, it is difficult to implement a measure for shifting the resonance frequency on the housing side due to the movement of the fastening screw.

  For actual EMI countermeasures for display devices, use a resin washer at the fastening part with screws to make the conductive part non-conductive, or use conductive tape, etc. Measures are taken by cutting and trying to shift the resonance frequency with the bezel. The above cut-and-try countermeasures are taken until the EMI problem is settled, and this may cause risks in the product development process, such as delays in product development due to delays in EMI countermeasures and an increase in usage fees at EMI measurement sites. Become.

  The present invention has been made in view of the above-mentioned problems, and its main purpose is not to rely on the above-described cut-and-try method, and is concluded for measures against EMI like the method described in Patent Document 1. The present invention provides an electronic device represented by a display device that realizes an EMI countermeasure by resonance between a chassis and a bezel without increasing the number of locations.

  An electronic device according to the present invention is interposed between a conductive casing, a conductive fastening member fixed to the casing, and the casing and the fastening member, and has an electric conductivity higher than that of the casing and the fastening member. A low-resistance high-resistance member.

  A display device according to the present invention includes a display panel, a conductive chassis, a conductive bezel, a conductive fastening member, and a high resistance member having a lower electrical conductivity than the chassis and the bezel. The display panel has a front surface and a back surface opposite to the front surface, and has a display area for displaying an image on the front surface. The chassis is disposed on the back side of the display panel. The bezel is disposed on the surface side of the display panel, and an opening corresponding to the display area of the display panel is formed. The fastening member is fastened to both the chassis and the bezel, and fixes the display panel to the chassis and the bezel. The high resistance member is interposed between the chassis or bezel and the fastening member.

  In the above display device, the display device further includes one or more substrates electrically connected to the display panel, and the high resistance member is a fastening member disposed in a region where the chassis or the bezel and the substrate are disposed. You may interpose between.

  In the display device, a plurality of fastening members are provided, and the high resistance member may be interposed between the chassis or the bezel and at least one of the plurality of fastening members.

  In the above display device, even if the resistance value of the high resistance member is in the range of (3-2√2) / 2 times or more (3 + 2√2) / 2 times or less of the characteristic impedance value between the chassis and the bezel. Good.

  According to the electronic device of the present invention, EMI due to resonance between the chassis and the bezel can be suppressed.

It is a disassembled perspective view which shows typically the principal part of the display apparatus which concerns on one embodiment of this invention. It is a front view in the state where the display shown in Drawing 1 was assembled. It is sectional drawing of the display apparatus which follows the III-III line | wire in FIG. It is a disassembled perspective view which shows typically the principal part of the conventional display apparatus used as a comparative example. It is a graph which shows the result of having calculated | required the radiation amount of the electromagnetic wave noise in the point 3 m away from each display apparatus which concerns on the comparative examples 1 and 2 by the electromagnetic field analysis. It is a graph which shows the result of having calculated | required the radiation amount of the electromagnetic wave noise in the point 3 m away from each display apparatus which concerns on Comparative Examples 1 and 2 and Example 3 by the electromagnetic field analysis. It is a graph which shows the result of having calculated | required the radiation amount of the electromagnetic wave noise in the point 3 m away from each display apparatus which concerns on Comparative Examples 1 and 2 and Example 4 by the electromagnetic field analysis. It is a graph which shows the result of having calculated | required the radiation amount of the electromagnetic wave noise in the point 3 m away from each display apparatus which concerns on Comparative Examples 1 and 2 and Example 5 by the electromagnetic field analysis. It is a figure which shows the position of the display apparatus in the electric field strength distribution map of FIG. 10, and the position of screw. In the comparative example 2, it is a 200MHz electric field strength distribution map in the cross section 50mm above a display apparatus front surface. FIG. 6 is an equivalent circuit diagram around a conductive fastening member in consideration of a characteristic impedance between a chassis and a bezel. In the equivalent circuit diagram of FIG. 11, the power consumed by the resistor 93 when the node on the opposite side of the resistor 93 is made non-reflective among the transmission line models 91 and 92 is a diagram showing the power consumed by the resistor 93.

  Embodiments of the present invention will be described below with reference to the drawings. In the following drawings, the same or corresponding parts are denoted by the same reference numerals, and description thereof will not be repeated.

  FIG. 1 is an exploded perspective view schematically showing a main part of a display device 1 according to an embodiment of the present invention. FIG. 2 is a front view of the display device 1 shown in FIG. 1 assembled. FIG. 3 is a cross-sectional view of the display device 1 taken along line III-III in FIG.

  As shown in FIGS. 1-3, the display apparatus 1 as an example of an electronic device has the display panel 2, the chassis 3, the bezel 4, the printed circuit board 5, the spacer 6, the fastening screws 71 to 75, and the electrical loss. Mainly equipped with washer 8, etc. The chassis 3 and the bezel 4 form a conductive casing of the display device 1. The display panel 2 and the printed board 5 are accommodated in a housing formed by the chassis 3 and the bezel 4. The printed circuit board 5 forms a conductive electromagnetic wave generator that generates an electromagnetic wave. In this specification, the washer 8 “has an electrical loss” means that when a current flows through the washer 8, the washer 8 becomes a resistor and electric energy is consumed and lost.

  Hereinafter, each component of the display device 1 will be described. The display panel 2 has a surface 21 and a back surface 22 opposite to the surface 21. The display panel 2 has a display area for displaying an image on the surface 21. When the display panel 2 is incorporated in the display device 1, the display panel 2 is supported by the support portion 322 of the chassis 3, and the outer edge of the surface 21 having the display area is covered by the front portion 41 of the bezel 4.

  The chassis 3 has a main surface 311 as a chassis main surface, and is disposed on the back surface 22 side of the display panel 2 so that the main surface 311 faces the back surface 22 of the display panel 2. The chassis 3 is formed by bending a conductive metal plate. The chassis 3 includes a rectangular bottom surface portion 31 and rising portions 32 that stand on each side of the bottom surface portion 31.

  The rising portion 32 includes a connection portion 321 rising from the bottom surface portion 31 and a support portion 322 that is connected to the connection portion 321 and supports the front portion 61 of the display panel 2 and the spacer 6. The pair of support portions 322 in the long side direction includes an outer frame portion 323 that is bent so as to face the connection portion 321.

  The bezel 4 is a conductive metal structure that supports the display panel 2 from the front side. The bezel 4 has a front portion 41 formed by assembling rectangular plate-like four members into a rectangular shape. In the bezel 4 facing the display panel 2, an opening 42 for exposing a video display area is formed on the surface side of the display device 1. The opening 42 is formed corresponding to the video display area of the display panel 2.

  The front portion 41 of the bezel 4 has a main surface 411 as a bezel main surface, and is disposed on the surface 21 side of the display panel 2 so that the main surface 411 faces the surface 21 of the display panel 2. The bezel 4 has a side surface portion 43 standing on each side of the front surface portion 41, and the side surface portion 43 is disposed so as to face the outer frame portion 323 of the chassis 3 when the display device 1 is assembled. Yes. The side surface portion 43 is formed by assembling a rectangular plate with an elongated plate-like member attached to the outer edge of each member of the front surface portion 41. The bezel 4 has an L-shaped cross-sectional shape in which a front part 41 and a side part 43 are combined.

  A printed circuit board 5 as a substrate is electrically connected to the display panel 2. The printed circuit board 5 is formed between the outer frame portion 323 of the chassis 3 having one surface 3231 as one surface of the chassis and the side surface portion 43 of the bezel 4 having one surface 431 as one surface of the bezel facing the one surface 3231 of the outer frame portion 323. Placed in. The printed circuit board 5 is connected to the display panel 2 with a connecting portion 53 protruding outward from the side portion of the display panel 2. The printed circuit board 5 is not limited to the structure connected to the display panel 2, and may be arranged inside the display device 1 by any other structure.

  One surface 3231 of the chassis 3 forms an outer side surface of the chassis 3. One surface 431 of the bezel 4 forms an inner side surface of the side surface portion 43 of the bezel 4. The printed circuit board 5 is disposed so as to be interposed between one surface 3231 of the chassis 3 and one surface 431 of the bezel 4 facing each other.

  The printed circuit board 5 is disposed such that the main surface 51 faces the one surface 3231 of the outer frame portion 323 of the chassis 3 and the main surface 52 faces the one surface 431 of the side surface portion 43 of the bezel 4. When the display device 1 is assembled, the printed circuit board 5 extends in the long side direction from the center of the outer frame portion 323 located on the lower side of the chassis 3 and is disposed between both outer frame end portions 324. ing. In the present embodiment, the main surfaces 51 and 52 of the printed circuit board 5 are arranged so as to be orthogonal to the surface 21 including the display area of the display panel 2.

  The spacer 6 is a resin structure formed in a rectangular frame shape. The spacer 6 has a function of forming a gap between the chassis 3 and the bezel 4 so that the chassis 3 and the bezel 4 do not directly contact each other. The spacer 6 also has a function of forming a gap between the printed circuit board 5 and the chassis 3 so that the terminals on the printed circuit board 5 are not in contact with the chassis 3 and are electrically short-circuited.

  The spacer 6 has a front surface portion 61 and side surface portions 62 erected on each side of the front surface portion 61. The front part 61 of the spacer 6 is fixed between the front part 41 of the bezel 4 and the support part 322 of the chassis 3. Further, the front portion 61 of the spacer 6 sandwiches the display panel 2 using an impact resistant member. The impact resistant member is not shown for simplicity.

  The long side of the side surface portion 62 of the rectangular frame spacer 6 is disposed between the outer frame portion 323 of the chassis 3 and the side surface portion 43 of the bezel 4, and the printed circuit board 5 and the outer frame portion of the chassis. H.323. The short side of the side surface portion 62 of the spacer 6 is disposed between the support portion 322 of the chassis 3 and the side surface portion 43 of the bezel 4.

  In order to fasten the bezel 4, the display panel 2, the front portion 61 of the spacer 6, and the support portion 322 of the chassis 3, a screw hole 44 is provided in the front portion 41 of the bezel 4 as shown in FIG. 1. The screw holes 44 are formed at locations corresponding to screws 71 to 75 as fixing means for fixing the display panel 2 to the chassis 3 and the bezel 4. The screw holes 44 are formed in the front part 41 of the bezel 4, the front part 61 of the spacer 6, and the support part 322 of the chassis 3. The screws 71 to 75 are made of a conductive metal material. A plurality of screws 71 to 75 are provided.

  As shown in FIG. 2, the screws 71 to 75 as fastening members are arranged symmetrically with respect to the surface 21 of the display device 1. Focusing on the long side where the printed circuit board 5 is arranged, for example, at a position where the distance between the screws 71 and 73 and between the screws 72 and 74 are both 402 mm and the distance between the screws 71 and 72 is 158 mm. 71-75 are arranged.

  As shown in FIG. 2, the screws 71 and 72 are disposed in a region where the printed circuit board 5 is disposed when viewed from the front of the display device 1, and are fastened to both the chassis 3 and the bezel 4. The present embodiment is characterized in that there is an electrical loss in conduction through at least one or all of the screws 71 and 72 in the region.

  FIG. 3 shows a cross section of the display device 1 at a portion where the chassis 3 and the bezel 4 are fixed by screws 71 as a representative example. As shown in FIG. 3, the screw 71 fixes the front part 41 of the bezel 4, the display panel 2, the front part 61 of the spacer 6, and the support part 322 of the chassis 3. The screw 71 is fixed to the bezel 4 with a polywasher 8 having electrical loss between the head and the front portion 41 of the bezel 4. A poly washer 8 as a high resistance member is interposed between the bezel 4 and the screw 71. The polywasher 8 has a lower electrical conductivity than the chassis 3, the bezel 4 and the screw 71.

  At this time, the diameter of the screw hole 44 is made larger than the outer diameter of the shaft portion of the screw 71 and smaller than the diameter of the head portion of the screw 71. Accordingly, since the poly washer 8 is disposed, the fastening portion of the screw hole 44 has an electrical loss property, and the bezel 4 and the chassis 3 can be fastened via the spacer 6.

The washer 8 having electrical loss can be realized with a material having a low volume resistivity in which carbon fiber is added to a resin such as nylon. As an example, polyamide MXD6 resin Reny (registered trademark) C36 manufactured by Mitsubishi Engineering Plastics Co. has a volume resistivity of 6.0e ⁻³ [Ω · m], which is used for an outer diameter of 10 mm and a hole diameter of 5 mm. A washer 8 having a thickness of 1 mm may be formed. In this case, the resistance value of the washer 8 can be lowered to 0.10Ω.

  The amount of addition of the conductive material typified by carbon fiber to the insulating base material typified by resin in the material forming the washer 8 is not limited to the above material, and can be arbitrarily adjusted. In addition, the shape of the washer 8 is not limited to the above shape, and the thickness of the washer 8, for example, can be arbitrarily adjusted. By these adjustments, it is possible to realize the washer 8 having an arbitrary resistance value. At this time, an electrically conductive coating may be applied to the contact surface of the washer 8 with the screw 71 and the contact surface of the washer 8 with the bezel 4. This is preferable because the contact resistance value between the washer 8 and the screw 71 can be stabilized and the contact resistance value between the washer 8 and the bezel 4 can be stabilized.

  As described above, in the display device 1 according to the present embodiment, the electrical conductivity of the washer 8 disposed between the screw 71 and the bezel 4 is set lower than that of the chassis 3, the bezel 4 and the screw 71. A washer 8 having an electrical conductivity lower than that of the chassis 3, the bezel 4, and the screw 71 and having an electrical resistance is disposed between the screw 71 and the bezel 4. Thereby, even if electromagnetic wave noise is conducted from the printed circuit board 5 to the chassis 3 or the bezel 4 and electromagnetic resonance occurs, the resonance energy is converted into heat energy by the washer 8 and consumed. As a result, since the peak value of the electric field strength is lowered, EMI due to resonance between the chassis 3 and the bezel 4 can be suppressed, and EMI can be reduced.

  In the description so far, the display device 1 has been described as an example including one printed circuit board 5, but a plurality of printed circuit boards 5 may be provided. That is, the display device 1 may include one or more substrates between the one surface 3231 of the chassis 3 and the one surface 431 of the bezel 4.

  The poly washer 8 is disposed so as to be interposed between the screws 71 and 72 and the bezel 4, but may be disposed so as to be interposed between the chassis 3 and the screw. The polywasher 8 may be interposed between the chassis 3 or the bezel 4 of the display device 1 that can function as an antenna for electromagnetic noise and the screw. The polywasher 8 may be disposed only between one screw 71 and the chassis 3 or the bezel 4 or may be disposed between a larger number of screws and the chassis 3 or the bezel 4. The polywasher 8 may be interposed between the chassis 3 or the bezel 4 and at least one of the plurality of screws 71 to 75.

  The printed circuit board 5 is disposed between the one surface 3231 that forms the outer surface of the chassis 3 and the one surface 431 that forms the inner surface of the bezel 4, but the arrangement of the printed circuit board 5 is not limited to this. The printed circuit board 5 may be disposed at an arbitrary position inside the display device 1. For example, the printed circuit board 5 may be disposed so as to be interposed between any surface of the chassis 3 and any surface of the bezel 4. In this case, the polywasher 8 is attached to the screw that fastens the chassis 3 and the bezel 4 in the region where the printed circuit board 5 is disposed, so that the above-described effect of reducing the EMI can be obtained similarly.

  According to another aspect of the present embodiment, the screw 71 is formed using a material having a low volume resistivity without using the washer 8 having electrical loss, so that the fastening portion between the bezel 4 and the chassis 3 is formed. Electrical loss may be realized.

  FIG. 4 is an exploded perspective view schematically showing a main part of a conventional display device used as a comparative example. The difference between the display device 1 according to the embodiment of the present invention and the conventional display device is that the conduction between the bezel 4 and the chassis 3 in the fastening portion using the screw 71 has an electrical loss. . As for the other components, the conventional display device and the display device 1 of the embodiment of the present invention have the same configuration.

  The EMI reduction effect of the present invention was confirmed by electromagnetic field analysis by the FDTD method (Finite Difference Time Domain method). As comparative examples, two cases were analyzed: 1) when all of screws 71 to 75 in FIG. 2 were made conductive; and 2) when screw 71 was made non-conductive using an insulating polywasher. The comparative example 1 is intended for a display device before the EMI countermeasures are studied, and the comparative example 2 is intended for a display device in which countermeasures are taken by cut-and-try.

  First, the EMI reduction effect by the conventional cut-and-try will be described using Comparative Examples 1 and 2. FIG. 5 is a graph showing the results of electromagnetic field noise emission obtained at a point 3 m away from each display device according to Comparative Examples 1 and 2 by electromagnetic field analysis. FIG. 5 shows the radiation amount of electromagnetic noise at a point 3 m away from the display device, obtained by electromagnetic field analysis of Comparative Examples 1 and 2. The horizontal axis of the graph in FIG. 5 indicates the frequency (unit: MHz). The vertical axis of the graph in FIG. 5 represents an electric field strength value (unit: dBV / m) representing the magnitude of electromagnetic wave noise. In the graph of FIG. 5, the analysis result of Comparative Example 1 is indicated by a thin solid line, and the analysis result of Comparative Example 2 is indicated by a dotted line.

  In the display device of Comparative Example 1, the distance between the screws 71 to 73 and the distance between the screws 72 to 74 are 402 mm. Between these screws, since the chassis 3 and the bezel 4 are resonating at 1 / 2λ, an EMI peak appears at a frequency of 270 MHz.

  The display device of Comparative Example 2 differs from the display device of Comparative Example 1 in that the screw 71 is non-conductive. In Comparative Example 2, the EMI peak at a frequency of 270 MHz generated in Comparative Example 1 is reduced by about 6 dB. In Comparative Example 1, 270 MHz EMI was generated from both the screw 71 to the screw 73 and between the screw 72 to the screw 74. However, in the comparative example 2, the screw 71 was made non-conductive. It is thought that the EMI component due to resonance was reduced. On the other hand, in Comparative Example 2, a new resonance system is generated between the screws 72 and 73, and EMI peaks are observed at frequencies of 200 MHz and 420 MHz. Resonance at 200 MHz and 420 MHz is considered to resonate between the screw 72 and the screw 73 at half wavelength and one wavelength, respectively.

  The validity of the above EMI radiation mechanism was verified. FIG. 10 is an electric field intensity distribution diagram at 200 MHz in a cross section 50 mm above the front surface of the display device in Comparative Example 2. 9 is a diagram showing the position of the display device and the position of the screw in the electric field intensity distribution diagram of FIG. As shown in FIG. 10, a strong electric field is seen at the center between the screws 72 to 73. This is because the bezel 4 and the chassis 3 are short-circuited at the positions of the screw 72 and the screw 73, so that a 1 / 2λ resonance system having an electric field as an antinode is generated between the screw 72 and the screw 73. This means that it is radiating.

  Similarly, when a distribution diagram in a section 50 mm above the front surface of the display device was confirmed for 270 MHz of Comparative Example 1 and 270 MHz and 420 MHz of Comparative Example 2, the electric field intensity distribution was consistent with the above mechanism. The reason why 200 MHz and 420 MHz are not in a multiple relationship is considered to be due to the influence of parasitic components due to the detailed structure of the display device.

  As described above, in the conventional EMI countermeasure method by cut-and-try, the resonance frequency can be moved and the peak due to resonance can be reduced. However, an EMI peak due to a new resonance is generated, and as an EMI countermeasure, trial and error are repeated. There is a possibility of falling.

  Next, as an embodiment of the present invention, 3) a case where a resistance of 10Ω is provided at both conduction points of the screws 71 and 72, 4) a case where a resistance of 10Ω is provided at a conduction point of the screw 71, and 5) conduction of the screw 71. In the case of having a resistance of 100Ω at the location, an electromagnetic field analysis was performed on three cases. FIGS. 6-8 is a graph which shows the result of having calculated | required the radiation amount of the electromagnetic wave noise in the point 3 m away from each display apparatus which concerns on each of the comparative examples 1 and 2 and Examples 3-5 by the electromagnetic field analysis. . 6 to 8 indicate the frequency (unit: MHz). The vertical axis of the graphs of FIGS. 6 to 8 represents an electric field intensity value (unit: dBV / m) representing the magnitude of electromagnetic wave noise.

  With reference to FIG. 6, the EMI reduction effect of Example 3 which is one aspect of the Example of this invention is demonstrated. In FIG. 6, in addition to the radiation amount of electromagnetic noise at a point 3 m away from the above-described Comparative Examples 1 and 2, the result of Example 3 is indicated by a thick solid line.

  In Example 3, since the resonance systems of both the screws 71 to 73 and between the screws 72 to 74 have electrical losses, the EMI peak due to the 270 MHz resonance is reduced by about 13 dB compared to the comparative example 1. It was. Further, it was confirmed that no EMI peak due to a new resonance system as in Comparative Example 2 occurred.

  With reference to FIG. 7, the effect of Example 4 which is the other situation of the Example of this invention is demonstrated. In FIG. 7, in addition to the results of Comparative Examples 1 and 2, the radiation amount of electromagnetic wave noise at a point 3 m away from Example 4 is indicated by a thick solid line.

  In Example 4, it was confirmed that the peak at 270 MHz that occurred in Comparative Example 1 was reduced to the same extent as in Comparative Example 2. This is because a resistance of 10Ω is provided as an electrical loss at a conduction point by the screw 71, so that the peak of EMI due to resonance at 270 MHz between the screws 71 to 73 is lowered, and the screw having no electrical loss is the same as the comparative example 2. It is thought that the influence of EMI by the resonance system between 72 and screw 74 appears. On the other hand, since it has a resistance of 10Ω as an electrical loss at the conduction point by the screw 72, the conventional peak of 270 MHz is reduced without generating new peaks such as 200 MHz and 420 MHz that were generated in Comparative Example 2. The effect is confirmed.

  With reference to FIG. 8, the EMI reduction effect of Example 5 which is another aspect of the Example of this invention is demonstrated. In FIG. 8, in addition to the results of Comparative Examples 1 and 2, the radiation amount of electromagnetic noise at a point 3 m away from Example 5 is indicated by a thick solid line. In the fifth embodiment, the resistance of the screw 71 same as that of the fourth embodiment is changed to 100Ω.

  In Example 5, it can be seen that the peak at 270 MHz generated in Comparative Example 1 is reduced as in Example 4. Compared with Example 4, the effect of reducing the EMI peak is reduced, but it was confirmed that the EMI peak due to resonance between 200 MHz and 420 MHz newly generated in Comparative Example 2 also has a reduction effect.

  Further, in common with the third, fourth, and fifth embodiments, the EMI is reduced in the band having a frequency of 100 MHz or less as compared with the first and second comparative examples. From this result, it was confirmed that the present invention can provide an EMI reduction effect even in a frequency region lower than the EMI peak due to resonance.

  As described above, according to the present invention, it has been confirmed that an effect of reducing EMI can be obtained by disposing a high resistance member having electrical loss at a conduction point by the fastening member. Furthermore, from Examples 4 and 5, although the EMI reduction effect of the present invention increases or decreases depending on the resistance value of the high resistance member, the EMI peak due to resonance is higher than that according to the conventional cut and try method. It was also confirmed that there was an effect to reduce.

  Here, the resistance value of the high resistance member which gives the electrical loss property to the conduction | electrical_connection location by a fastening member is demonstrated using FIG. 11 and FIG. FIG. 11 is an equivalent circuit diagram around the conductive fastening member in consideration of the characteristic impedance between the chassis and the bezel. FIG. 12 is a diagram showing the power consumed by the resistor 93 when the node on the side opposite to the resistor 93 is made non-reflective in the transmission line models 91 and 92 in the equivalent circuit diagram of FIG.

  In the present invention, when the chassis 3 and the bezel 4 are fixed with a conductive fastening member to establish conduction, an electromagnetic loss that can cause EMI is consumed as thermal energy by providing an electrical loss. The display device used in this example has the cross-sectional shape shown in FIG. Based on this cross-sectional shape, the characteristic impedance value between the chassis 3 and the bezel 4 was calculated by electromagnetic field analysis and found to be 46.2Ω.

  FIG. 11 shows an equivalent circuit diagram around the conductive fastening member. The chassis 3 and the bezel 4 are represented as transmission line models 91 and 92 having a characteristic impedance of 46.2 Ω, and a conduction point by a fastening member having electrical loss is represented as a resistor 93.

In the transmission line models 91 and 92 shown in FIG. 11, when the nodes 94 and 95 are made non-reflective, the power P consumed by the resistor 93 is expressed by Equation 1. (Z ₀ : characteristic impedance between chassis 3 and bezel 4, r: resistance value of resistor 93, V: voltage value of node 94)

  Here, in order to simplify the explanation, the transmission line models 91 and 92 are made non-reflective on the side opposite to the resistor 93. However, the power consumed by the resistor 93 of the reflected component is further applied with Equation 1. It is possible to obtain it.

FIG. 12 is a graph showing the power P consumed by the resistor 93 when the resistance value r is a variable. For further generalization, the horizontal axis represents the resistance value r normalized using V and Z _0, and the vertical axis represents the power P normalized using V and Z ₀ . The condition for maximizing the power P consumed by the resistor 93 is expressed by Equation 2, and the maximum value P _max of P at that time is expressed by Equation 3.

From Equation 2, it is desirable that the resistance value r of the conducting portion by the fastening member is ½ of the characteristic impedance value Z ₀ between the chassis 3 and the bezel 4, but the fourth embodiment which is an example of this embodiment. As shown in FIGS. 5 and 5, the electric power is consumed at the conduction point by the fastening member having electrical loss even with respect to other resistance values. Therefore, the effect of the present invention is expected.

As an example, when the power consumed by the resistor 93 is desired to be 1/2 or more of P _max in Expression 3, the range of r is determined from Expression 1 as Expression 4.

In the practical use of the present invention, a parasitic inductor component is generated in series with the resistor 93 due to the structure of the chassis 3 and the bezel 4 at the conduction point by the fastening member having electrical loss characteristics, and the frequency increases. The impedance is expected to increase. Including this impedance component, in order to approximate the conducting portion by the fastening member to the 1/2 of the characteristic impedance Z _0, it is desirable to lower the resistance value than 1/2 of the characteristic impedance Z _0.

  In this example, comparison was made in the characteristics up to 500 MHz. For the 52-inch long side direction (length: 1200 mm), according to the method of Patent Document 1, since the interval between the fastening members must be 200 mm or less, seven fastening members are required. And four fastening members were able to reduce EMI.

  Although the embodiment of the present invention has been described as above, the embodiment disclosed this time should be considered as illustrative in all points and not restrictive. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

  The present invention is applicable to a display device having a chassis and a bezel. In addition to a display device, in an electronic device having a conductive casing and a conductive structure, and the casing and the structure are fixed by a plurality of conductive fastening members Applicable.

  DESCRIPTION OF SYMBOLS 1 Display apparatus, 2 Display panel, 3 Chassis, 4 Bezel, 5 Printed circuit board, 6 Spacer, 8 Poly washer, 21 Surface, 22 Back surface, 31 Bottom surface part, 32 Rising part, 41 Front part, 42 Opening part, 43 Side part, 44 Screw hole, 51, 52 Main surface, 61 Front portion, 62 Side portion, 71-75 Screw, 311, 411 Main surface, 321 Connection portion, 322 Support portion, 323 Outer frame portion, 324 Outer frame both end portion, 431 3231 One side.

Claims (5)

A conductive housing;
A conductive fastening member fixed to the housing;
An electronic apparatus comprising: a high resistance member that is interposed between the housing and the fastening member and has a lower electrical conductivity than the housing and the fastening member. A display panel having a surface and a back surface opposite to the surface, and having a display area for displaying an image on the surface;
A conductive chassis disposed on the back side of the display panel;
A conductive bezel disposed on the surface side of the display panel and having an opening corresponding to a display area of the display panel;
A conductive fastening member fastened to both the chassis and the bezel and fixing the display panel to the chassis and the bezel;
A display device comprising: a high resistance member interposed between the chassis or the bezel and the fastening member and having a lower electrical conductivity than the chassis and the bezel. The display device further includes one or more substrates electrically connected to the display panel,
The display device according to claim 2, wherein the high resistance member is interposed between the chassis or the bezel and the fastening member disposed in a region where the substrate is disposed. A plurality of the fastening members are provided,
The display device according to claim 2, wherein the high resistance member is interposed between the chassis or the bezel and at least one of the plurality of fastening members.   The resistance value of the high resistance member is in a range of (3-2√2) / 2 times or more (3 + 2√2) / 2 times or less of a characteristic impedance value between the chassis and the bezel. The display device according to claim 4.