Patent Publication Number: US-2009231238-A1

Title: Plasma display device

Description:
BACKGROUND OF THE INVENTION 
     1. Technical Field 
     The technical field relates to a plasma display device that is known as a thin large-screen display device. 
     2. Background 
     Spontaneous light-emitting type display devices such as a plasma display device and a CRT display (Cathode-Ray Tube display) device are widely used since they do not have a viewing angle dependency and can display natural images. In particular, a plasma display device is thin and suitable for forming a large screen, and therefore it is becoming increasingly popular. 
     A plasma display device mainly includes a plasma display module section having a plasma display panel and a shield case surrounding the module section. 
     This plasma display panel excites a phosphor provided in each discharge cell by an ultraviolet ray generated by gas discharge so as to emit visible light as display light. The plasma display panel includes a plurality of pairs of scan electrodes and sustain electrodes and a plurality of address electrodes, which are arranged in a lattice. The plasma display panel forms an image by emitting light selectively in a discharge cell that is an intersection portion of the electrodes. With this principle, since large driving current flows in electrodes, an electromagnetic field is generated from a plasma display module due to this current. 
     Therefore, the plasma display device has a configuration in which a shield case for shielding a generated electromagnetic field is formed, for example, by coupling a front glass to which a conductive filter is attached and a conductive back cover of the rear surface side to each other by using a conductive member to surround a plasma display module. With such a configuration, a generated electromagnetic field is electromagnetically shielded. 
     However, with the increase in a driving electric power according to the recent improvement of the image quality, it has been difficult to reliably reduce an electromagnetic field by a conventional configuration of a shield case. In particular, in low frequency regions of several tens MHz or less, such an electromagnetic field cannot be sufficiently reduced by a conventional shield case and may be radiated to the outside as a noise. 
     In order to solve such a problem, Japanese Patent Unexamined Publication No. 2001-83909 discloses a configuration in which an adjacent conductive cylinder is provided on a ground-return conductor plate for connecting between a driving substrate provided at one end of the plasma display device and a driving substrate provided at the other end of the plasma display device. Thus, a plasma display device has been proposed to cancel the inductance of the ground-return conductive plate by an eddy current generated in this adjacent conductive cylinder. 
     Furthermore, Japanese Patent Unexamined Publication No. 2002-372917 proposes a plasma display device whose shielding performance is enhanced by doubling an electromagnetic shield in a front cabinet by holding and sandwiching a peripheral portion of a front glass of the plasma display device together with a pressing metal. 
     Furthermore, Japanese Patent Unexamined Publication No. 2005-221797 proposes a plasma display device in which a closed electric current path between a driving source and a load circuit forms at least two loop-structured circuits, so that the magnetic field generated in each loop-structured circuit is cancelled by each other. 
     Furthermore, Japanese Patent Unexamined Publication No. H10-282896 proposes a plasma display device having a configuration in which a chassis conductor holding a plasma display panel is coupled to a back cover and surrounds a drive circuit board to form a shield. 
     However, in the plasma display device described in Japanese Patent Unexamined Publication No. 2001-83909, when the adjacent conductive cylinder having a size that can be expected to have a reducing effect is inserted inside the plasma display panel and the ground-return conductor plate, an entire area of the loop of an electric current that is a generating source of an electromagnetic field is enlarged. As a result, electromagnetic fields to be reduced are increased, thus deteriorating the effect of reducing electromagnetic fields. 
     Furthermore, in the plasma display device described in Japanese Patent Unexamined Publication No. 2002-372917, the front cabinet having double electromagnetic shield is positioned only in a side surface portion of the entire device. Therefore, the effect by the double shield is limited only to this portion. Consequently although the shielding effect is improved, the effect is not sufficient from the viewpoint of reducing an electromagnetic field caused by a driving current. 
     Furthermore, in the plasma display device described in Japanese Patent Unexamined Publication No. 2005-221797, since a driving current path itself is extended, it is necessary to adjust a drive signal waveform and the like. Furthermore, since it is difficult to completely cancel electromagnetic fields generated in the two loop structures, it is difficult to achieve a sufficient reducing effect. 
     Furthermore, in the plasma display device described in Japanese Patent Unexamined Publication No. H10-282896, the shielding effect of the drive circuit board itself is increased. However, an electromagnetic field generated by an electric current flowing between the plasma display panel and the chassis conductor cannot be reduced sufficiently. 
     SUMMARY 
     A plasma display device of the present invention includes a plasma display module and a cylindrical conductor portion. 
     The plasma display module includes a front glass plate and a rear glass plate provided with a plurality of electrodes that are in parallel to each other, a plasma display panel having a plurality of discharge cells divided by barrier ribs, a circuit board for applying a voltage to an electrode, and a chassis conductor configured to hold a plasma display panel and to which ground of a circuit board is coupled. 
     The cylindrical conductor configured to surround a plasma display module by a first conductor portion located at the front surface side of the plasma display module, and a second conductor portion located at the pair of the side surface and at a rear surface which a plasma display module faces. 
     A loop formed by the cylindrical conductor is substantially in parallel to a loop formed by a current flowing in a circuit board, an electrode and a chassis conductor in a plasma display module. 
     With such a configuration, by a cancelling effect by the cylindrical conductor, it is possible to provide a plasma display device capable of efficiently reducing an interfering electromagnetic wave caused by a driving current flowing a plasma display panel. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic cross-sectional view showing a configuration of a plasma display device in accordance with a first embodiment of the present invention. 
         FIG. 2  is a schematic longitudinal sectional view showing a plasma display device in accordance with the first embodiment of the present invention. 
         FIG. 3  is a perspective view to illustrate a configuration of the plasma display module. 
         FIG. 4A  is a perspective view to illustrate an electrode structure of the plasma display panel in a plasma display device in accordance with the first embodiment. 
         FIG. 4B  is a sectional view to illustrate an electrode structure of the plasma display panel in a plasma display device in accordance with the first embodiment. 
         FIG. 5  is a perspective view to illustrate a structure of a conductive front filter of a plasma display panel in the plasma display device in accordance with the first embodiment. 
         FIG. 6  is a conceptual view to illustrate a principle in which undesirable radiation of an interfering electromagnetic wave occurs due to a panel driving current by a plasma display panel in the plasma display device in accordance with the first embodiment. 
         FIG. 7A  is a perspective view to illustrate a position relation between an electrode structure of the plasma display panel and a first conductive filter in accordance with the second embodiment. 
         FIG. 7B  is a sectional view to illustrate a position relation between an electrode structure of the plasma display panel and a first conductive filter in accordance with the second embodiment. 
         FIG. 8  is a schematic cross-sectional view to illustrate a configuration of a plasma display device in accordance with a third embodiment of the present invention. 
         FIG. 9  is a schematic cross-sectional view to illustrate a configuration of a plasma display device in accordance with a fourth embodiment of the present invention. 
         FIG. 10  is a schematic cross-sectional view to illustrate a configuration of another example of a plasma display device in accordance with a fourth embodiment of the present invention. 
         FIG. 11A  is a schematic cross-sectional view to illustrate a configuration of a plasma display device in accordance with a fifth embodiment of the present invention. 
         FIG. 11B  is a partial enlarged view showing a back cover of the plasma display device in accordance with a fifth embodiment of the present invention. 
         FIG. 12  is a schematic cross-sectional view to illustrate a configuration of a plasma display device in accordance with a sixth embodiment of the present invention. 
         FIG. 13A  is a perspective view to illustrate a structure of electrodes of a plasma display panel of a plasma display device in accordance with the sixth embodiment of the present invention. 
         FIG. 13B  is a sectional view to illustrate a structure of electrodes of a plasma display panel of a plasma display device in accordance with the sixth embodiment of the present invention. 
         FIG. 14  is a sectional view showing a plasma display panel in a plasma display device in accordance with a seventh embodiment. 
         FIG. 15  is a sectional view showing a plasma display panel in a plasma display panel of a plasma display device in accordance with an eighth embodiment. 
         FIG. 16  is a schematic cross-sectional view to illustrate a configuration of a plasma display device in accordance with a ninth embodiment of the present invention. 
         FIG. 17A  is a schematic cross-sectional view to illustrate a configuration of a plasma display device in accordance with a tenth embodiment of the present invention. 
         FIG. 17B  is a partial enlarged view showing a back cover of a plasma display device in accordance with the tenth embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     Hereinafter, embodiments of the present invention are described with reference to drawings. Note here that the same reference numerals are given to the same elements carrying out the same operations in the embodiments. 
     First Embodiment 
       FIGS. 1 to 4A  and  4 B show plasma display device  1  in accordance with a first embodiment.  FIG. 1  is a schematic cross-sectional view taken along the x-y plane to illustrate a configuration of plasma display device  1  in accordance with the first embodiment of the present invention.  FIG. 2  is a schematic longitudinal sectional view taken along the x-z plane. Note here that  FIGS. 1 and 2  show only a structure that deeply relates to radiation of undesirable electromagnetic wave in the first embodiment.  FIG. 3  is a perspective view to illustrate a configuration of plasma display module  2 .  FIG. 4A  is a perspective view to illustrate a structure of electrodes of plasma display panel  10  in plasma display device  1  in accordance with the first embodiment.  FIG. 4B  is a sectional view thereof.  FIG. 5  is a perspective view to illustrate a structure of conductive front filter  20 . 
     Hereinafter, for the sake of convenience, a normal direction of a display surface of plasma display device  1  is referred to as an x-axis, a longitudinal direction of a display surface of plasma display device  1  is referred to as a y-axis, and a direction orthogonal to the x-axis and y-axis is referred to as a z-axis. 
     In  FIGS. 1-3 , plasma display module  2  of plasma display device  1  in accordance with the first embodiment of the present invention includes plasma display panel  10  having a plurality of scan-sustain electrodes  14  that are electrodes parallel to each other in the longitudinal direction and address electrodes  15  that are parallel to each other in the short direction. In plasma display module  2 , chassis conductor  11  that is a holder plate of plasma display panel  10  is disposed at the opposite side to the display surface of plasma display panel  10  via a thermal conductive sheet (not shown). 
     Firstly a configuration for driving scan-sustain electrodes  14  and address electrode  15  is described. Scan-sustain electrodes drive circuit board  12   a,  address electrode drive circuit board  12   b,  junction circuit board  12   c,  and discharge control circuit board  12   d,  which function as circuit boards for applying a voltage to electrodes, are disposed at the rear side of chassis conductor  11 . A drive signal generated from scan-sustain electrodes drive circuit board  12   a  for driving scan-sustain electrodes  14  is transmitted to scan-sustain electrodes  14  of plasma display panel  10  by flexible cable  13   a.  In order to drive address electrode  15 , firstly, a high frequency signal generated at discharge control circuit board  12   d  is transmitted to junction circuit board  12   c  by flexible cable  13   d.  Next, the high frequency signal is transmitted to address electrode drive circuit board  12   b  by flexible cable  13   c.  Then, a drive signal is generated in address electrode drive circuit board  12   b  and transmitted to address electrode  15  of plasma display panel  10  by flexible cable  13   b.    
     At the outside of plasma display module  2 , cylindrical conductor portion  3   a  is provided in a way in which it surrounds and encloses plasma display module  2 . Cylindrical conductor portion  3   a  includes conductive filter  301  as a first conductor portion and second conductor portion  302 . At the outside of cylindrical conductor portion  3   a,  back cover  16 , glass pressing metal  17 , front protective glass  18 , front cabinet  19 , conductive front filter  20  and conductive gasket  21  form a shield case. 
     Plasma display panel  10  has a structure in which front glass plate  101  and rear glass plate  102  are attached to each other as shown in  FIGS. 4A and 4B . On front glass plate  101 , dielectric layer  103  is formed. A large number of scan-sustain electrodes  14  each consisting of a scan electrode  14   a  and sustain electrode  14   b  are formed in a way in which they are protected by dielectric layer  103 . Dielectric layer  103  is formed also on rear glass plate  102 . A large number of address electrodes  15  are formed in a way in which they are protected by dielectric layer  103 . 
     A portion that is a crossing position of scan-sustain electrodes  14  and address electrode  15  and that is surrounded by scan-sustain electrodes  14  and address electrode  15  is discharge cell  104 . Discharge cell  104  is filled with a discharge gas including a noble gas such as helium (He), neon (Ne) and xenon (Xe). Discharge cells  104  are divided by barrier ribs  105  and the inside of each discharge cell  104  is differently colored by red, blue and green phosphors  106   a  to  106   c.    
     Chassis conductor  11  is made of a plate of metal such as aluminum and copper having high thermal conductivity and electrical conductivity. Plasma display panel  10  is attached to one surface (front surface) of chassis conductor  11  via a thermal conductive sheet. Furthermore, drive circuit boards and the like is attached to the other surface (rear surface) of chassis conductor  11  in parallel to chassis conductor  11  and coupled to ground of each circuit board. Therefore, chassis conductor  11  holds plasma display panel  10  and drive circuit boards and the like, and functions as a reinforcing material for maintaining the strength thereof. Furthermore, chassis conductor  11  also functions as an electric ground of each drive circuit board. As shown in  FIG. 3 , for example, a signal ground of scan-sustain electrodes drive circuit board  12   a  is point A, a signal ground of address electrode drive circuit board  12   b  is point B, a signal ground of junction circuit board  12   c  is point C, and a signal ground of discharge control circuit board  12   d  is point D. Then, each signal ground is grounded on chassis conductor  11  that is a frame ground, respectively. 
     Conductive front filter  20  includes base layer  201 , conductive layer  202 , metal end portion  203  and protective film  204  as shown in  FIG. 5 . Base layer  201  is made of, for example, polyester film. Conductive layer  202  is formed on base layer  201  by metal mesh formation or sputter formation. Metal end portion  203  is formed on the peripheral portion of conductive layer  202 . Protective film  204  is formed of a transparent insulating resin on conductive layer  202 . Since metal end portion  203  is not covered with protective film  204 , it functions as an electric connection portion. 
     Note here that conductive layer  202  uses metal mesh such as copper mesh and sputter formation such as silver sputtering. When the metal mesh is used, a higher shielding effect can be obtained because the resistance rate is low. When the sputter formation is used, construction can be carried out at a lower cost. 
     As shown in  FIGS. 1 and 2 , front protective glass  18  is disposed at the front surface side of plasma display panel  10 . Conductive front filter  20  is attached to the rear surface of front protective glass  18 , that is, at the side opposite to the display surface. 
     Glass pressing metal  17  fixes front protective glass  18  by holding it between glass pressing metal  17  and front cabinet  19 . Furthermore, glass pressing metal  17  is disposed in a way in which it is brought into electrical contact with metal end portion  203  of conductive front filter  20  attached to front protective glass  18  via conductive gasket  21  that is a conductive contacting member. Furthermore, glass pressing metal  17  is also brought into contact with back cover  16  via conductive gasket  21 . 
     Note here that the conductive gasket is made by, for example, attaching metal fiber to an elastic material like a sponge. Herein, as a conductive contacting member, a conductive gasket is used but the member is not necessarily limited to this. That is to say, any members having an electrical conductivity and securing stability in electrical contact between two members may be used. For example, glass pressing metal  17  may be provided with a conductive spring portion. Thus, the cost can be lowered. 
     Back cover  16  is formed by press molding a conductive metal plate. Back cover  16  is fixed to glass pressing metal  17  so as to cover the rear surface of plasma display panel  10  and drive circuit boards, and the like. It plays a role of shielding an electromagnetic wave radiated from plasma display panel  10 , each drive circuit board, and the like. 
     Cylindrical conductor portion  3   a  includes a conductor portion consisting of conductive filter  301  that is a first conductor portion located at the front surface side of plasma display panel  10  and second conductor portion  302  located at a pair of side-surfaces facing each other (right and left side-surfaces in this embodiment) and the rear surface side of plasma display module  2 . Conductive filter  301  and second conductor portion  302  are electrically coupled to each other so as to form a loop. The role of the formed loop is detailed below in detail. 
     Conductive filter  301  is a flat-shaped filter having a light transmission property and an example of the first conductor portion. That is to say, the first conductor portion is configured to face the image display surface of plasma display panel  10 , and includes conductive filter  301  as a first conductive filter having a light transmission property and a substantially rectangular surface. Furthermore, second conductor portion  302  has a substantially rectangular U-letter cross section coupled to two facing sides of conductive filter  301 . That is to say, cylindrical conductor portion  3   a  has a substantially cylindrical shape having an opening on the upper and lower side surfaces of plasma display module  2  and configures to surround plasma display module  2 . 
     Conductive filter  301  has the same configuration as that of conductive front filter  20 . Furthermore, second conductor portion  302  is formed of metal having high electrical conductivity, for example, aluminum, copper, and the like. 
     When conductive front filter  20  is formed of a metal mesh, it is preferable that conductive filter  301  has a conductive layer formed by sputtering. This is preferable because if two metal mesh films are laminated onto each other, an interference fringe may be observed when they are seen from the display surface, thus deteriorating an image quality. 
     In the above-mentioned configuration, as shown in  FIG. 1 , a loop shown by a dotted-line arrow is a loop formed by a conductor portion of cylindrical conductor portion  3   a.  On the other hand, a loop shown by a solid-line arrow is a loop formed by a driving current in plasma display module  2 . That is to say, the loop formed by a conductor portion of cylindrical conductor portion  3   a  is substantially in parallel to the loop formed by a current flowing in scan-sustain electrodes drive circuit board  12   a,  scan-sustain electrodes  14  as an electrode and chassis conductor  11  in plasma display module  2  (substantially parallel to the x-y plane). 
     Herein, in plasma display device  1  in accordance with this embodiment, the principle and operation in which undesirable radiation of interfering electromagnetic wave due to the driving current is reduced are described based on the operation principle of a plasma display panel. 
     Firstly the image display principle of plasma display panel  10  is described. Firstly, a voltage is applied to all lines of scan electrode  14   a  so as to carry out initializing discharge causing discharge in all discharge cells  104 . Next, a voltage is sequentially applied to scan electrode  14   a  and a voltage is also applied to address electrode  15  that intersects with discharge cell  104  to emit light on scan electrode  14   a  to which a voltage is applied. This is called address discharge, and discharge cell  104  in a position where scan electrode  14   a  to which a voltage is applied and address electrode  15  intersect with each other emits light and discharge cell  104  is selected as a light emission cell. Thereafter, sustain discharge in which an AC voltage is applied between scan electrode  14   a  and sustain electrode  14   b  is carried out. By sustain discharge, only a previously selected light emitting cell emits light, and a plasma display panel displays an image. That is to say an electrode is scan electrode  14   a  and sustain electrode  14   b,  and scan-sustain electrodes  14  that are elements constituting discharge cell  104 . 
     Next, the principle and operation in which undesirable radiation of interfering electromagnetic waves due to a driving current is reduced is described with reference to  FIG. 6 .  FIG. 6  is a conceptual view to illustrate a principle in which undesirable radiation of interfering electromagnetic waves due to a panel driving current is reduced. 
     In general, when loop current  30  flows, strong generated magnetic field  31  is generated in the direction perpendicular to a plane forming a loop by Ampere&#39;s right handed screw rule. When ring-shaped conductor  32  is placed in a position encompassing loop current  30 , a counter electromotive force is generated on this conductor due to the electromagnetic induction effect. At this time, induced current  33  is induced in ring-shaped conductor  32  in the direction opposite to the original loop current  30 . This ring-shaped conductor  32  is referred to as a short ring. This induced generated magnetic field  34  by induced current  33  is generated in the reverse direction with respect to generated magnetic field  31  by loop current  30 . Therefore, generated magnetic field  34  has an effect of cancelling original generated magnetic field  31 . 
     In the configuration of  FIG. 1 , a driving current driven by scan-sustain electrodes drive circuit board  12   a  flows in flexible cable  13   a,  scan-sustain electrodes  14  of plasma display panel  10  and chassis conductor  11  so as to form a loop-shaped driving current. 
     Furthermore, the loop-shaped driving current generates a magnetic field in the vertical direction by the right screw rule. Note here that the vertical direction means a direction parallel to the z-direction in  FIG. 1 . 
     Herein, the loop formed by cylindrical conductor portion  3   a  is substantially in parallel to the loop of the driving current in plasma display module  2 . Therefore, according to the above-mentioned principle, a loop current in the reverse direction with respect to the driving current is excited in cylindrical conductor portion  3   a  so as to cancel the magnetic field generated from plasma display module  2 . 
     Thus, with respect to an alternative magnetic field formed by a loop of a driving current generated at the time of sustain discharge when a particularly large current flows, cylindrical conductor portion  3   a  plays a role of a short ring. Thus, an effect of cancelling a magnetic field can be achieved, and as a result, a large effect of reducing a noise can be achieved. 
     In this embodiment, second conductor portion  302  of cylindrical conductor portion  3   a  has substantially rectangular U-shaped cross section. However, the shape is not limited to this alone. In short, it may have a configuration in which a current flows in the reverse direction with respect to the driving current loop. For example, both ends of conductive filter  301  may be bent in the direction toward back cover  16  so as to be brought into contact with a flat plane shaped second conductor portion  302 . This can simplify the structure of second conductor portion  302 . 
     Second Embodiment 
     Next, a second embodiment of the present invention is described with reference to  FIGS. 7A and 7B . The same reference numerals are given to the same configuration as in the first embodiment and detailed description thereof is omitted. In the first embodiment, as conductive filter  301  that is the first conductor portion, a flat-shaped filter having a light transmission property is used. However, the second embodiment is different from the first embodiment in that the first conductor portion is conductive filter  301   a  having metal thin wires  108  located above barrier ribs between discharge cells  104  seen from a viewer. 
       FIG. 7A  is a perspective view to illustrate the position relation between an electrode structure of plasma display panel  10  and conductive filter  301   a  in accordance with the second embodiment.  FIG. 7B  is a sectional view thereof. 
     Conductive filter  301   a  as the first conductive filter includes base material  107  made of resin and a plurality of metal thin wires  108  arranged in parallel to scan-sustain electrodes  14  as electrodes on base material  107 . Metal thin wires  108  are disposed in a way in which they are located above the front surface of barrier ribs  105  seen from the side of a viewer, that is, the side opposite to back cover  16  so as not to block the side of the display surface of discharge cell  104 . That is to say, metal thin wires  108  are disposed in a way in which they are located above the barrier ribs  105  between discharge cells  104  of plasma display panel  10 . Therefore, it is possible to use metal thin wire  108  that is thicker as compared with the case where a general metal mesh filter is used. 
     With such a configuration, an electric resistance of conductive filter  301   a  can be made smaller as compared with the case where a metal mesh is used. Thus, the electrical conductivity of cylindrical conductor portion  3   a  is increased and an induced current flows easily. As a result, it becomes possible to achieve a large effect of cancelling a magnetic field. Consequently, it is possible to achieve a large effect of reducing noise. 
     Furthermore, a plurality of metal thin wires  108  arranged in parallel to scan-sustain electrodes  14  can be formed without substantially blocking the transmittance of image light emitted from discharge cell  104 . Thus, hindrance to an image of the plasma display panel can be reduced. 
     Third Embodiment 
     Next, a third embodiment of the present invention is described with reference to  FIG. 8 . The same reference numerals are given to the same configuration as in the first embodiment and the detailed description thereof is omitted. In the first embodiment, as conductive filter  301  that is the first conductor portion, a flat-shaped filter having a light transmission property is used. However, the third embodiment is different in that the first conductor portion is first conductive filter  401 . Note here that second conductor portions  302  and  402  may have the same configuration. 
       FIG. 8  is a schematic cross-sectional view taken along the x-y plane to illustrate a configuration of plasma display device  4  in accordance with the third embodiment of the present invention. 
     As shown in  FIG. 8 , front protective glass  18  has conductive front filter  400  that is a second conductive filter provided at the side facing a display surface. Furthermore, first conductive filter  401  of cylindrical conductor portion  3   b  is attached to front protective glass  18  at the side opposite to the display surface. 
     Glass pressing metal  403  is brought into contact with conductive front filter  400  via conductive gasket  21  at the display surface side of the front protective glass  18 . Furthermore, first conductive filter  401  and second conductor portion  402  are brought into electrical contact with each other via conductive gasket  21 . 
     With such a configuration, since first conductive filter  401  is attached to the rear surface of front protective glass  18 , separate first conductive filter  301  as in the first embodiment shown in  FIG. 1  is not needed. Consequently, the thickness of plasma display device  4  can be further reduced. 
     Note here that first conductive filter  401  and conductive front filter  400  may have the same configuration as that of conductive front filter  20  described in the first embodiment. Therefore, as described above, it is not desirable that both first conductive filter  401  and conductive front filter  400  are formed of a metal mesh. This is because when two metal mesh films are laminated onto each other, an interference fringe may be observed seen from the display surface, thus deteriorating the image quality. It is preferable that both first conductive filter  401  and conductive front filter  400  have a conductive layer formed by sputtering. Furthermore, any one of first conductive filter  401  and conductive front filter  400  may be formed of a metal mesh and the other may be formed so as to have a conductive layer formed by sputtering. 
     Furthermore, since front protective glass  18  is prepared in a state in which first conductive filter  401  and conductive front filter  400  as the second conductive filter are attached from the beginning, assembly can be simplified as compared with the first embodiment. 
     As mentioned above, plasma display device  4  in accordance with this embodiment further includes front protective glass  18  provided at the side opposite to back cover  16  of plasma display module  2 . The second conductive filter is provided on the surface at the side opposite to back cover  16  of front protective glass  18 , and the first conductive filter is provided on the surface of front protective glass  18  at the side facing the plasma display panel  10 . 
     With such a configuration, also in the third embodiment, similar to the first embodiment, an effect of cancelling a magnetic field can be achieved. As a result, a large effect of reducing noise can be achieved. 
     Fourth Embodiment 
     Next, a fourth embodiment of the present invention is described with reference to  FIG. 9 . The same reference numerals are given to the same configuration as in the third embodiment and the detailed description thereof is omitted. In the third embodiment, second conductor portion  402  is used similar to second conductor portion  302  in the first embodiment. However, the fourth embodiment is different in that second conductor portion  502  is used in cylindrical conductor portion  3   c.  Note here that first conductive filters  401  and  501  may have the same configuration. 
       FIG. 9  is a schematic cross-sectional view to illustrate a configuration of plasma display device  5  in accordance with the fourth embodiment of the present invention. 
     As shown in  FIG. 9 , plasma display device  5  in accordance with this embodiment includes a conductor layer on chassis conductor  11  via an insulating layer. Grounds of various drive circuit boards are coupled to chassis conductor  11 . Furthermore, the conductor layer is disposed on chassis conductor  11  at the side opposite to the plasma display panel. The conductor layer is coupled to first conductive filter  501  as the first conductor portion so as to form second conductor portion  502 . That is to say, first conductive filter  501  and second conductor portion  502  as the conductor layer form cylindrical conductor portion  3   c.    
     Furthermore, second conductor portion  502  has a plurality of openings in a part thereof. Flexible cable  13   a  is coupled to second conductor portion  502  via the opening. Furthermore, grounds of various drive circuit boards are not brought into electrical contact with second conductor portion  502  but coupled to chassis conductor  11 . 
     With such a configuration, since second conductor portion  502  is laminated onto chassis conductor  11 , the thickness of plasma display device  5  can be further reduced as compared with the first to third embodiments. 
     Furthermore, since preparation of disposing a conductor layer on chassis conductor  11  via an insulating layer is carried out in advance, assembly can be further simplified as compared with the first embodiment. 
     With such a configuration, also in the third embodiment, similar to the first embodiment, an effect of cancelling a magnetic field can be achieved. As a result, a large effect of reducing noise can be achieved. 
     Furthermore, in this embodiment, second conductor portion  502  is disposed on chassis conductor  11  via an insulating layer. Therefore, chassis conductor  11  and second conductor portion  502  have a two-layered structure. Furthermore, grounds of various drive circuit boards are coupled to chassis conductor  11  at the side of plasma display panel  10 . However, plasma display device  5  in this embodiment is not necessarily limited to such a configuration.  FIG. 10  is a schematic cross-sectional view to illustrate a configuration of another example of plasma display device  5  in accordance with the fourth embodiment of the present invention. That is to say, as shown in  FIG. 10 , second conductor portion  502  as the conductor layer may be disposed on chassis conductor  11  at the side of plasma display panel  10 . Also with such a configuration, an effect of cancelling a magnetic field can be achieved. 
     As mentioned above, the plasma display device in this embodiment includes a conductor layer disposed on chassis conductor  11  via an insulating layer. Any one of chassis conductor  11  and the conductor layer of the plasma display device may be coupled to grounds of various drive circuit boards and the other may be coupled to the first conductor portion so as to form a second conductor portion. Also in this case, similar to the first embodiment, an effect of cancelling a magnetic field can be achieved, and as a result, a large effect of reducing noise can be achieved. 
     However, in a configuration in which grounds of various drive circuit boards are coupled to a conductor layer at the side of plasma display panel  10  as in this embodiment, since a loop of a driving current and a loop of cylindrical conductor portion  3   c  are interlinkaged more widely, the effect of reducing noise is increased. 
     Fifth Embodiment 
     Next, a fifth embodiment of the present invention is described with reference to  FIGS. 11A and 11B . The same reference numerals are given to the same configuration as in the third embodiment and the detailed description thereof is omitted. In the third embodiment, second conductor portion  402  of cylindrical conductor portion  3   b  is used to form cylindrical conductor portion  3   b.  The fifth embodiment is different in that second conductor portion  602  formed on back cover  600  is used so as to form cylindrical conductor portion  3   d.  Note here that first conductive filters  401  and  601  may have the same configuration. 
       FIG. 11A  is a schematic cross-sectional view to illustrate a configuration of plasma display device  6  in accordance with the fifth embodiment of the present invention.  FIG. 11B  is an expanded view showing a region X 10  in  FIG. 11A . 
     As shown in  FIG. 11B , in back cover  600  functioning as a conductive case, second conductor portion  602  of cylindrical conductor portion  3   d  is formed on the inner side of conductive back cover  600  via insulating layer  700  by conductive plating. Furthermore, as shown in  FIG. 11A , back cover  600  is electrically coupled to glass pressing metal  603  at the outer side surface via conductive gasket  21 . Furthermore, second conductor portion  602 , which is formed on the inner side by plating, of back cover  600  is brought into electrical contact with first conductive filter  601  via conductive gasket  21 . 
     At this time, the inside and outside of back cover  600  are electrically insulated from each other, and cylindrical conductor portion  3   d  is not electrically connected to back cover  600  or glass pressing metal  603 , which functions as a short ring function. 
     As mentioned above, plasma display device  6  in this embodiment has back cover  600  as a conductive case at the side opposite to a viewer of a plasma display module, that is, at the side opposite to the display surface. An insulating layer is formed on the inner side of the conductive case. Second conductor portion  602  is formed on an insulating layer of the conductive case by conductive plating. 
     With such a configuration, since second conductor portion  602  is formed on the inner side of back cover  600  by plating, separate second conductor portions  302  and  402  as in the first to third embodiments are not needed. Furthermore, since a two-layered structure of chassis conductor  11  and second conductor portion  502  as in the fourth embodiment is not also needed, the thickness of plasma display device  6  can be further reduced. 
     Furthermore, since preparation of subjecting back cover  600  to insulation treatment and plating treatment can be carried out in advance, assembly can be simplified as compared with the first to third embodiments. 
     Note here that the formation of second conductor portion  602  is not necessarily limited to plating. For example, the formation may be carried out by attaching with the use of, for example, a metal tape. 
     Also in this embodiment, similar to the first embodiment, an effect of cancelling a magnetic field can be achieved. As a result, a large effect of reducing noise can be achieved. 
     Sixth Embodiment 
     Next, a sixth embodiment of the present invention is described with reference to  FIG. 12  and  FIGS. 13A and 13B . The same reference numerals are given to the same configuration as in the first embodiment and the detailed description thereof is omitted. In the first embodiment, as conductive filter  301  that is a first conductor portion in cylindrical conductor portion  3   a,  a flat-shaped filter having a light transmission property is used. However, the sixth embodiment is different in that conductor wiring portion  701  is used as the first conductor portion. Note here that second conductor portions  302  and  702  may have the same configuration. 
       FIG. 12  is a schematic cross-sectional view to illustrate a configuration of plasma display device  7  in accordance with the sixth embodiment, which shows only a structure deeply relating to the radiation of undesirable electromagnetic wave as the embodiment.  FIG. 13A  is a perspective view to illustrate an electrode structure of plasma display panel  10  in plasma display device  7  in accordance with the sixth embodiment.  FIG. 13B  is a sectional view of  FIG. 13A . 
     In  FIG. 12 , cylindrical conductor portion  3   e  includes conductor wiring portion  701  as a first conductor portion formed on the display surface side of front glass plate  101  in plasma display panel  10 , that is, at the side opposite to back cover  16 , and second conductor portion  702  coupled to both ends of conductor wiring portion  701  and having substantially a rectangular U-shaped cross section. Cylindrical conductor portion  3   e  encloses plasma display module  2 . 
     As shown in  FIGS. 13A and 13B , conductor wiring portion  701  includes a plurality of metal wirings provided on the front surface side of front glass plate  101  of plasma display panel  10 . Conductor wiring portion  701  is formed by etching a metal material such as copper on front glass plate  101 . Furthermore, second conductor portion  702  is formed of a metal such as aluminum and copper having a high electrical conductivity. 
     With such a configuration, since conductor wiring portion  701  is attached to the surface of front glass plate  101  of plasma display panel  10 , a separate first conductor portion as in the first embodiment of  FIG. 1  is not needed. Consequently, the thickness of plasma display device  7  can be further reduced as compared with the first embodiment. 
     Furthermore, since plasma display panel  10  can be prepared in a state in which conductor wiring portion  701  is attached from the beginning, assembly can be simplified as compared with the first embodiment. 
     Furthermore, a plurality of metal wirings arranged in parallel to scan-sustain electrodes  14  are disposed in a way in which they are located above the front surface of barrier ribs  105  between discharge cells  104  seen from the side of a viewer, that is, the side opposite to back cover  16  so as not to block the side of the display surface of discharge cell  104 . That is to say, a plurality of metal wirings of conductor wiring portion  701  are disposed in a way in which they are located above barrier ribs  105  between discharge cells  104  of plasma display panels  10 . Thus, they can be formed in the position that is closer to barrier ribs  105  as compared with the second embodiment. Thus, they can be formed without substantially blocking the transmittance of image light emitted from discharge cell  104 . Thus, hindrance to an image of the plasma display panel can be reduced. 
     Also in the seventh embodiment, an effect of reducing noise similar to that in the first embodiment can be achieved. 
     Seventh Embodiment 
     Next, a seventh embodiment is described with reference to  FIG. 14 .  FIG. 14  is a sectional view showing plasma display panel  10  in accordance with the seventh embodiment. The same reference numerals are given to the same configuration as in the sixth embodiment and the detailed description thereof is omitted. 
     Conductor wiring portion  801  of this embodiment is different from conductor wiring portion  701  shown in  FIG. 13B  in the sixth embodiment in that conductor wiring portion  801  is formed on the surface opposite to the display surface of front glass plate  101 . 
     That is to say, the first conductor portion includes conductor wiring portion  801  having a plurality of metal wirings provided at the display surface side of front glass plate  101  of plasma display panel  10 , that is, on the surface of the side of back cover  16 . 
     Furthermore, a plurality of conductor wirings arranged in parallel to scan-sustain electrodes  14  are disposed in a way in which they are located above the front surface of barrier ribs  105  seen from the side of a viewer, that is, the side opposite to back cover  16  so as not to block the side of the display surface of discharge cell  104 . That is to say, the conductor wirings are disposed in a way in which they are located above barrier ribs  105  between discharge cells  104  of plasma display panels  10 . As a result, the conductor wirings can be formed in the position that is more closer to barrier ribs  105  as compared with the sixth embodiment. Thus, they can be formed without substantially blocking the transmittance of image light emitted from discharge cell  104 . Thus, hindrance to an image of the plasma display panel can be reduced. 
     With such a configuration, at the same time when scan-sustain electrodes  14  are formed, conductor wiring portion  801  can be formed. Therefore, processes are not increased more than necessary, so that manufacturing can be simplified. 
     Eighth Embodiment 
     Next, an eighth embodiment is described with reference to  FIG. 15 .  FIG. 15  is a sectional view showing plasma display panel  10  in accordance with the eighth embodiment. The same reference numerals are given to the same configuration as in the seventh embodiment and the detailed description thereof is omitted. 
     Conductor wiring portion  901  of this embodiment is different from conductor wiring portion  701  of the sixth embodiment shown in  FIG. 13B  in that it is formed on rear glass plate  102  at the side facing the chassis conductor  11 . Furthermore, at this time, conductor wiring portion  901  is formed on the surface at the rear surface side of rear glass plate  102  with respect to discharge cell  104 . Therefore, since it is not necessary to consider the transmittance of image light emitted from discharge cell  104 , conductor wiring portion  901  is not necessarily formed in a wiring shape. Therefore, conductor wiring portion  901  may be attached to the entire surface of rear glass plate  102 . Note here that conductor wiring portion  901  is formed of a metal material such as copper. 
     As mentioned above, the first conductor portion of plasma display panel  10  in this embodiment includes conductor wiring portion  901  formed on the entire surface of glass plate  102  at the rear side of discharge cell  104 . 
     Thus, since conductor wiring portion  901  can be formed of a metal material such as copper on the entire surface of rear glass plate  102 , the resistivity of conductor wiring portion  901  can be reduced as compared with that of conductor wiring portion  701  in accordance with the seventh embodiment. Therefore, an induced current flows easily in conductor wiring portion  901 , thus enabling a large cancelling effect to be achieved. Furthermore, since it is not necessary to make conductor wiring portion  901  in a wiring shape, manufacturing is simplified. 
     Ninth Embodiment 
     Next, a ninth embodiment of the present invention is described with reference to  FIG. 16 . The same reference numerals are given to the same configuration as in the sixth embodiment and the detailed description thereof is omitted. In the sixth embodiment, second conductor portion  702  is used similarly to second conductor portion  302  in the first embodiment. However, the ninth embodiment is different in that second conductor portion  1002  is used in cylindrical conductor portion  3   f.  Note here that conductor wiring portions  701  and  1001  may have the same configuration. 
       FIG. 16  is a schematic cross-sectional view to illustrate a configuration of plasma display device  8  in accordance with the ninth embodiment of the present invention. 
     As shown in  FIG. 16 , plasma display device  8  in this embodiment includes a conductor layer on chassis conductor  11  via an insulating layer. Grounds of various drive circuit boards are coupled to chassis conductor  11 . Furthermore, the conductor layer is disposed on chassis conductor  11  at the side opposite to the plasma display panel. The conductor layer is coupled to first conductive filter  1001  as a first conductor portion so as to form second conductor portion  1002 . That is to say, first conductive filter  1001  and the conductor layer form cylindrical conductor portion  3   f.    
     Furthermore, second conductor portion  1002  has the same configuration as that of second conductor portion  502  in the fourth embodiment. That is to say, it has a plurality of openings in a part thereof. Flexible cable  13   a  is coupled to second conductor portion  1002  via the opening. Furthermore, grounds of various drive circuit boards are not brought into electrical contact with second conductor portion  1002  and coupled to chassis conductor  11 . 
     With such a configuration, since second conductor portion  1002  is laminated on chassis conductor  11 , it is possible to further reduce the thickness of plasma display device  8  as compared with the sixth embodiment. 
     Furthermore, preparation of disposing a conductor layer on chassis conductor  11  via an insulating layer can be carried out in advance. Therefore, assembly can be further simplified as compared with the sixth embodiment. 
     Also in this embodiment, similar to the first embodiment, an effect of cancelling a magnetic field can be achieved. As a result, a large effect of reducing noise can be achieved. 
     Furthermore, in this embodiment, second conductor portion  1002  is disposed on chassis conductor  11  via an insulating layer. Chassis conductor  11  and second conductor portion  1002  have a two-layered structure. Furthermore, grounds of various drive circuit boards are coupled to a conductor layer at the side facing the plasma display panel  10 . However, plasma display device  8  in this embodiment is not necessarily limited to this configuration. That is to say, as shown in the other example of the fourth embodiment, second conductor portion  1002  may be disposed on chassis conductor  11  at the side facing the plasma display panel  10 . Also with such a configuration, an effect of cancelling a magnetic field can be achieved. 
     As mentioned above, a conductor layer may be disposed on chassis conductor  11  via an insulating layer, and any one of chassis conductor  11  and the conductor layer may be coupled to grounds of various drive circuit boards as a circuit board and the other may be coupled to the first conductor portion so as to form a second conductor portion. 
     However, as in this embodiment, a configuration in which grounds of various drive circuit boards are coupled to the conductor layer at the side of plasma display panel  10  can provide a large effect of reducing noise since a loop of the driving current and a loop of cylindrical conductor portion  3   f  are interlinkaged to each other more widely. 
     Tenth Embodiment 
     Next, plasma display device  9  in accordance with a tenth embodiment of the present invention is described with reference to  FIGS. 17A and 17B . The same reference numerals are given to the same configuration as in the sixth and ninth embodiments and the detailed description thereof is omitted. In the sixth and ninth embodiments, conductor wiring portions  601  and  701  are used as the first conductor portion, respectively. However, the tenth embodiment is different in that second conductor portion  1102  formed on back cover  1100  is used so as to form cylindrical conductor portion  3   g  as in the fifth embodiment. Note here that conductor wiring portions  701 ,  1001  and  1101  may have the same configuration. 
       FIG. 17A  is a schematic cross-sectional view to illustrate a configuration of plasma display device  9  in accordance with the tenth embodiment of the present invention.  FIG. 17B  is an expanded view showing region X 11  by expanding thereof. 
     As shown in  FIG. 17B , in back cover  1100  functioning as a conductive case, second conductor portion  1102  of cylindrical conductor portion  3   g  is formed on the inner side of conductive back cover  1100  via insulating layer  1200  by conductive plating. Furthermore, as shown in  FIG. 17A , back cover  1100  is electrically coupled to glass pressing metal  1103  at the outer side surface via conductive gasket  21 . Furthermore, second conductor portion  1102 , which is formed on the inner side by plating, of back cover  1100  is brought into electrical contact with conductor wiring portion  1101  via conductive gasket  21 . 
     At this time, the inside and outside of back cover  1100  are electrically insulated from each other, and cylindrical conductor portion  3   g  is not electrically connected to back cover  1100  or glass pressing metal  1103 , which functions as a short ring function. 
     As mentioned above, plasma display device  9  in this embodiment has back cover  1100  as a conductive case at the opposite side to a viewer of plasma display module  2 . An insulating layer is formed at the inside of the conductive case. Second conductor portion  1102  is formed on an insulating layer of the conductive case by conductive plating. 
     With such a configuration, since second conductor portion  1102  is formed on the inner side of back cover  1100  by plating, a separate second conductor portion as in the sixth to ninth embodiments is not needed. Furthermore, since a two-layered structure chassis conductor  11  as in the ninth embodiment is not also needed, the thickness of plasma display device  9  can be further reduced. 
     Furthermore, since preparation of subjecting back cover  1100  to insulation treatment and plating treatment can be carried out in advance, assembly can be simplified as compared with seventh to tenth embodiments. 
     Note here that the formation of second conductor portion  1102  is not necessarily limited to plating. For example, the formation may be carried out by attaching with the use of, for example, a metal tape. 
     Furthermore, plasma display device  9  in accordance with this embodiment is brought into electrical contact with conductor wiring portion  1101  via conductive gasket  21 . Conductor wiring portion  1101  has a metal wiring thin wires similar to conductor wiring portion  701  as described in the sixth embodiment. 
     With such a configuration, also in this embodiment, a large effect of reducing noise similar to the first embodiment can be achieved. 
     Furthermore, any embodiments employ a configuration of cylindrical conductor in which a driving current loop at the time of sustain discharge is cancelled. However, the configuration is not limited to this alone. For example, at the time of address discharge, a current loop flowing in the longitudinal direction (for example, the x-z plane in  FIG. 2 ) is formed. Therefore, by configuring a cylindrical conductor in accordance with this, it is possible to reduce an interfering electromagnetic wave generated at the time of address discharge. 
     Specific numeric values and the like used in the above-mentioned embodiments are just examples and can be set appropriately and suitably in accordance with the properties of display devices, specification of image display devices, and the like. 
     The above-mentioned embodiments are just a few of many possible examples. The present invention is not limited to the above-mentioned embodiments and various modifications are encompassed within the scope of the appended claims.