1. Field of the Invention
The present invention relates to cost reduction and noise reduction of plasma display devices.
2. Related Background Art
With the decline in prices and the development of high-quality picture technologies, plasma display devices having advantages such as thin bodies and large screen sizes have spread rapidly and have been used widely as large screen television receivers and the like.
A plasma display device includes, as main components, a plasma display panel and a shield case that encloses the plasma display panel.
This plasma display panel is a display in which ultraviolet rays generated by gas discharge excite phosphors to emit visible light as display light. In the plasma display panel, a plurality of electrodes (display electrodes and address electrodes) are arranged in a grid pattern, and discharge cells formed at respective intersections of these electrodes are made to emit light selectively. Thereby, images are formed. Based on this principle, when a drive current flows through the electrodes, this drive current generates an electromagnetic field in the plasma display panel.
The shield case encloses the plasma display panel by connecting, with conductive glass pressing pieces, a front glass attached with a conductive filter and arranged in front of the plasma display panel and a conductive back cover arranged behind the plasma display panel. Thereby, the generated electromagnetic field is shielded electromagnetically.
A contact impedance exists at each contact portion between the respective components of the shield structure. When this contact impedance increases due to poor contact between them, the shielding performance of the shield case is degraded.
As a specific example of a conventional shield structure in such a plasma display device, JP 11(1999)-272183 A discloses a structure in which glass pressing pieces and another member are integrated into one unit so as to reduce the contact impedance.
However, the above-mentioned conventional structure, in which the glass pressing pieces press the four sides of the front glass from the back surface side thereof to hold it, as disclosed in JP 11(1999)-272183 A, has the following problems.
As shown in
The present invention has achieved a solution to the above problems, and it is an object of the present invention to provide a plasma display device having a shield structure strong enough to shield the electromagnetic field without increasing the cost and man hours for assembling more than necessary.
The plasma display device according to the present invention includes: a plasma display panel having a rectangular display screen on its front surface; a plate-like front glass arranged in front of the display screen of the plasma display panel; a conductive filter attached to a front surface or a back surface of the front glass; a conductive back cover arranged behind the plasma display panel; and a plurality of glass pressing pieces each of which presses a corresponding one of four sides of the front glass and makes the conductive filter and the back cover be connected electrically. Among the plurality of glass pressing pieces, glass pressing pieces disposed on one pair of opposite sides of the front glass press the front glass from the front surface side thereof and are electrically connected with the conductive filter, and glass pressing pieces disposed on the other pair of opposite sides of the front glass press the front glass from the back surface side thereof and are electrically connected with the conductive filter.
According to the present invention, it is possible to provide a plasma display device having a shield structure strong enough to shield the electromagnetic field without increasing the cost and man hours for assembling more than necessary.
Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. In the following embodiments, the same components are designated by the same numerals.
As shown in
In the plasma display panel 1, sustain discharge electrodes (hereinafter referred to as “X electrodes”) 20a and sustain/scan discharge electrodes (hereinafter referred to as “Y electrodes”) 20b, each extending in the width direction (in the horizontal direction in
As shown in
In the plasma display device 100, the ground of the X electrode driving circuit and one of the end portions of the aluminum chassis 2 (the left end portion in
A commonly-used method for driving the plasma display device 100 is a sub-field driving method in which the gray scale display is controlled by changing the number of discharges. Each sub-field includes a reset period, an address period and a sustain discharge period.
The operation of the plasma display device in these periods will be described respectively. During the reset period, a reset pulse voltage is applied between each pair of the X electrode 20a and the Y electrode 20b so as to generate a discharge in all the cells, thereby erasing the wall charges remaining in the previous sub-field. During the address period, a scan pulse voltage is applied sequentially to respective Y electrodes 20b, and simultaneously an address pulse voltage is applied selectively to the address electrodes 21 of the pixels corresponding to images to be displayed. This selective input of the address pulse voltage generates an address discharge between each pair of the Y electrode 20b and the address electrode 21. Thereby, the wall charges are accumulated in the corresponding cells. During the sustain discharge period, a sustain discharge pulse voltage is applied between each pair of the X electrode 20a and the Y electrode 20b so as to generate a sustain discharge in the cells in which the wall charges have been accumulated.
Vacuum ultraviolet rays are generated in the cells by the sustain discharge. The vacuum ultraviolet rays are radiated to phosphors arranged in the cells to emit visible light. Thereby, the corresponding pixels are lit up. During the sustain discharge period, a driving voltage of several hundreds volts and several hundreds kHz is applied alternately to the X electrodes 20a and the Y electrodes 20b so as to generate a discharge in the cells between these electrodes 20a and 20b. Thereby, during the sustain discharge period, a great amount of current flows in the plasma display panel instantaneously.
For example, when a driving voltage is applied to the X electrodes 20a, a great amount of current flows in a loop path from the driving portion of the X electrode driving circuit, through the X electrodes 20a, the atmosphere in the cells, the Y electrodes 20b, the ground of the Y electrode driving circuit, and the aluminum chassis 2, and back to the ground of the X electrode driving circuit. The great amount of current that flows in the loop generates a large magnetic field.
Next, a structure in the vicinity of the front glass of the plasma display device 100 according to the present embodiment will be described. As shown in
As shown in
Specifically, the glass-pressing metal pieces 30 each are a conductive member formed by pressing a strip-shaped metal plate. The glass-pressing metal piece 30 has a pressing portion 30a that extends along and parallel to the shorter side of the front glass 5 on the back surface 5b side thereof, a fixed portion 30c that is fastened to the frame 9 together with the back cover 7 with screws or the like, and a connecting portion 30b for connecting the pressing portion 30a and the fixed portion 30c. The pressing portion 30a has a pressing surface 30d for pressing the front glass 5. This pressing surface 30d faces the back surface 5b of the front glass 5. When the fixed portion 30c of the glass-pressing metal piece 30 is fastened to the frame 9, the pressing surface 30d presses the front glass 5 from the back surface 5b side thereof via the gasket 10 and the conductive tape 12. Thereby, the glass-pressing metal piece 30 is electrically connected with the conductive filter 6 through the gasket 10 and the conductive tape 12.
Specifically, the glass-pressing metal pieces 31 each are a conductive member formed by pressing a strip-shaped metal plate. The glass-pressing metal piece 31 has a pressing portion 31a that extends along and parallel to the longer side of the front glass 5 on the front surface 5a thereof, a fixed portion 31c that is fastened to the frame 9 together with the back cover 7 with screws, and a connecting portion 31b for connecting the pressing portion 31a and the fixed portion 31c. The connecting portion 31b of the glass-pressing metal piece 31 is longer than the connecting portion 30b of the glass-pressing metal piece 30. The pressing portion 31a has a pressing surface 31d for pressing the front glass 5. This pressing surface 31d faces the front surface 5a of the front glass 5. When the front glass 5 is pressed forward by the auxiliary pressing piece 11, the pressing surface 31d of the glass-pressing metal piece 31 presses the front glass 5 from the front surface 5a side via the gasket 10, the conductive tape 12 and the conductive filter 6. Thereby, the glass-pressing metal piece 31 is electrically connected with the conductive filter 6 through the gasket 10 and the conductive tape 12.
Assume that the back surface side connecting structure as shown in
In contrast, the present embodiment has the following advantage. According to the connecting structure of the present embodiment, the glass pressing pieces 31 disposed on one pair of opposite sides of the front glass 5 are electrically connected with the conductive filter 6 on the front surface 5a side of the front glass 5, and the glass pressing pieces 30 disposed on the other pair of opposite sides of the front glass 5 are electrically connected with the conductive filter 6 on the back surface 5b side of the front glass 5. Accordingly, even if the front glass 5 is pressed by the glass-pressing metal pieces 30 from the back surface 5b side thereof, the glass-pressing metal pieces 31 disposed on the front surface 5a side of the front glass 5 prevent the pressure from being applied to the frame 9 directly, thus preventing the frame 9 from being deformed. As a result, it is possible to prevent the reduction of electrical contact between the glass-pressing metal pieces 30 and 31 and the conductive filter 6 and thus maintain a high shielding effect. Furthermore, in the present embodiment, the contact area between the conductive tape 12 and the conductive filter 6 is pressed directly by the glass-pressing metal piece 31. Therefore, the increase of contact resistance caused by the peeling or the like in this contact area also can be suppressed.
Furthermore, even if the thickness of the gasket 10 provided between the front glass 5 and the glass-pressing metal pieces 30 and 31 is decreased, since the frame 9 is hardly deformed, the electrical contact between the glass-pressing metal pieces 30 and 31 and the conductive filter 6 can be maintained sufficiently. In addition, the present embodiment employs a structure in which two pairs of opposite sides press against each other to hold the front glass 5, which allows the front glass 5 to be held in a stable manner.
In the present embodiment, the conductive tapes 12 are applied also on the upper and lower sides, but the present invention is not limited to this structure. It is also possible to bring the glass-pressing metal pieces 31 into direct contact with the conductive filter 6 without the conductive tapes 12. In this case, the contact resistance and the cost further can be reduced.
In the present embodiment, the upper and lower sides of the front glass 5 are pressed by using the auxiliary pressing pieces 11 secondarily, but the present invention is not limited to this structure. Since the front glass 5 is pressed by the right and left glass-pressing metal pieces 30 from the back surface side thereof, the front glass 5 can be held in a stable manner even without the auxiliary pressing pieces 11. In this case, the cost can be reduced further.
Furthermore, in the present embodiment, the glass-pressing metal pieces 31 disposed on the upper and lower sides of the front glass 5 are electrically connected with the conductive filter 6 from the front surface 5a side of the front glass 5, and the glass-pressing metal pieces 30 disposed on the right and left sides of the front glass 5 are electrically connected with the conductive filter 6 from the back surface 5b side thereof. However, the present invention is not limited to this structure. For example, the glass-pressing metal pieces disposed on the right and left sides may be electrically connected with the conductive filter 6 from the front surface 5a side, and the glass-pressing metal pieces disposed on the upper and lower sides may be electrically connected with the conductive filter 6 from the back surface 5b side. In this case, if the auxiliary pressing pieces 11 are used secondarily, it is possible to shorten the length of the auxiliary pressing pieces 11 in the right-and-left arrangement relative to the upper-and-lower arrangement. Therefore, the cost can be reduced.
However, the structure in which the glass-pressing metal pieces disposed on the upper and lower sides of the front glass 5 are electrically connected with the conductive filter 6 from the front surface 5a side has the following advantageous effects over the structure in which the glass-pressing metal pieces disposed on the right and left sides are electrically connected with the conductive filter 6 from the front surface 5a side.
Assume that this principle is applied to the structure as shown in
Accordingly, the present embodiment, in which the front surface side connecting structure having a stronger contact is employed on the upper and lower sides while the right and left sides are pressed from the back surface side, makes it possible to achieve a higher shielding effect than the case where the front surface side connecting structure is employed on the right and left sides.
Next, the second embodiment of the present invention will be described with reference to
The right and left glass-pressing metal pieces 30 and the upper and lower glass-pressing metal pieces 31 respectively have connecting portions 32 to be connected with each other with connecting parts in such a manner that the connecting portions are laid one on the other. When the connecting portions 32 are fastened to each other with screws or the like (i.e., connecting parts), the right and left glass-pressing metal pieces 30 and the upper and lower glass-pressing metal pieces 31 apply pressure to the front glass 5 from both the front surface 5a side and the back surface 5b side, with the front glass 5 being sandwiched therebetween. Thus, the front glass 5 is held. As a result, the electrical contact between the glass-pressing metal pieces 30 and 31 and the conductive filter 6 also can be maintained sufficiently.
Moreover, since the plasma display device 100 of the second embodiment does not need the auxiliary pressing pieces 11, it can be realized at lower cost than that of the first embodiment.
In the present embodiment, screws are used as the connecting parts, but the present invention is not limited thereto as long as they connect the right and left glass-pressing metal pieces 30 and the upper and lower glass-pressing metal pieces 31 to each other. For example, the plasma display device 100 of the second embodiment may have a structure in which one end of a glass-pressing metal piece 30 and one end of a glass-pressing metal piece 31 are hooked to each other with a hook-like part, while the other end of the glass-pressing metal piece 30 and the other end of the glass-pressing metal piece 31 are screwed to each other with a screw. The cost of the connecting parts can be reduced by employing this connection structure.
Next, the third embodiment of the present invention will be described with reference to
The glass-pressing metal pieces 31 each have, on its pressing surface 31d, a convex shape portion 33 that bulges from both ends toward the center in a smooth curve in its longitudinal direction.
In the present embodiment, the convex shape portions 33 are provided only on the pressing surfaces 31d of the upper and lower glass-pressing metal pieces 31, but the present invention is not limited to this structure. The convex shape portions 33 may be provided only on the pressing surfaces 30d of the right and left glass-pressing metal pieces 30, or may be provided on the pressing surfaces 30d and 31d of all the upper and lower and right and left glass-pressing metal pieces 30 and 31. Furthermore, the convex shape portions 33 may be provided in the case where like the first embodiment, the glass-pressing metal pieces 30 and 31 have no connecting portions 32.
In the above-mentioned first through third embodiments, the conductive filter 6 is attached to the front surface 5a of the front glass 5. However, the present invention is also applicable to the case where the conductive filter 6 is attached to the back surface 5b of the front glass 5.
The invention may be embodied in other forms without departing from the spirit or essential characteristics thereof. The embodiments disclosed in this specification are to be considered in all respects as illustrative and not limiting. The scope of the invention is indicated by the appended claims rather than by the foregoing description, and all changes which come within the meaning and range of equivalency of the claims are intended to be embraced therein.
The present invention is applicable to reduction of unnecessary radiation of electromagnetic waves in a plasma display panel device.
Number | Date | Country | Kind |
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2008-018688 | Jan 2008 | JP | national |