Patent Publication Number: US-6714175-B1

Title: Plasma display panel and method for driving the panel

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a plasma display panel (PDP) of surface discharge type and the method for driving the PDP. 
     A plasma display panel is used widely for a television set or a computer monitor after the color display thereof has been successfully commercialized. In order to attain further wide use of the PDP, the structure thereof that is suitable for high definition is developing. 
     2. Description of the Prior Art 
     As a color display device, an AC type PDP having three-electrode surface discharging structure is commercialized. The surface discharge type has a first and second main electrode as anodes and cathodes arranged in parallel on the front and the back substrates in the display discharge securing intensity. As an electrode matrix structure of the surface discharge type plasma display panel, a “three-electrode structure” is known well in which third electrodes (address electrodes) are arranged so as to cross the main electrodes. One of the main electrode pair is used as a scanning electrode for row selection, so that address discharge is generated between the scanning electrode and the address electrode. Thus, addressing is performed for controlling wall discharge in accordance with contents of display. After the addressing, a sustaining voltage having alternating polarity is applied to the main electrode pair, so that the surface discharge is generated along the surface of the substrate only in the cell having a certain quantity of the wall charge. 
     A basic three-electrode structure has a pair of main electrodes arranged in each row of the screen. The distance between the main electrode pairs in each row (a surface discharge gap length) is set to a few tens of microns so that the discharge can occur by the application of 150-200 volts. 
     On the contrary, the distance between the electrodes of the neighboring rows (referred to as an inverse slit) is set to the value that is sufficiently larger than (as large as a few times) the surface discharge gap length so as to prevent undesired surface discharge between rows and to decrease the capacitance. Namely, the distance between the main electrodes of a row is different from that between rows. Another three-electrode structure has N+1 main electrodes (N is the number of rows in the screen) spaced uniformly. The neighboring electrodes constitute an electrode pair for generating the surface discharge. Main electrodes, except those at opposite ends of the arrangement, are related to the neighboring two rows. In the plasma display panel having this structure, interlaced scanning is performed for display. 
     The surface discharge type plasma display panel having the three-electrode structure includes partitions (i.e., barrier ribs) for defining the discharge space of each row. A stripe pattern of the partition in which partitions having a ribbon shape as a plan view are arranged has an advantage compared with a mesh pattern in which each cell is isolated. In the stripe pattern, the discharge space is continuous over the full length of the screen in each column. Therefore, the discharge probability can be increased by priming, fluorescent layer can be made uniform, and the exhausting process can be, performed easily. As the structure having the discharge space that is continuous in the row direction, a two-layer structure is also known, in which the mesh pattern and the stripe pattern are combined in the height direction. 
     In the conventional panel structure in which the discharge space is continuous in the column direction, there is a problem as follows. The address discharge in the row selected for addressing spreads excessively in the column direction, and undesired charge is accumulated in the area adjacent to the address electrode in the row neighboring the selected row. When the neighboring row becomes the selected row later, the charge that has been accumulated can lower the address voltage applied to the cell. The lowered address voltage cannot cause an address discharge, and incorrect addressing causes fluctuations of display. Especially in the structure having main electrodes spaced uniformly this can cause addressing errors easily. 
     SUMMARY OF THE INVENTION 
     An object of the present invention is to suppress the growing of the address discharge in the column direction so that the addressing accuracy can be improved. 
     In the present invention, the shape or the position of the address electrode is arranged so that the opposed area of the main electrode that is not used for row selection opposed to the address electrode via the decreased discharge space can be decreased. Thus, the address discharge is localized in the opposed portion of the address electrode, i.e., the portion opposed to the main electrode and to be used for row selection. 
     If the main electrode is made of a transparent conductive film and a metal film, the portion of the metal film opposed to the address electrode causes the address discharge. Therefore, the area of the metal film of the main electrode to be used for row selections opposed to the address electrode, is set sufficiently large so that the reliability of the address discharge can be secured. 
     According to a first aspect of the present invention, the plasma display panel includes a plurality of first main electrodes for row selection, a plurality of second main electrodes constituting electrode pairs with plural first main electrodes for generating surface discharge on each row, a plurality of address electrodes for column selection, and partitions for defining a discharge space for each column, which is continuous over the full length of the screen. The first main electrodes and the second main electrodes are arranged alternately. Each of the first main electrodes and the second main electrodes includes a transparent conductive film for securing electrode area and a metal film for reducing electric resistance. Each of the address electrodes crosses at least the metal film of the first main electrodes and is patterned in such a way that the area, opposed to the metal film, of the second main electrode is smaller than the area opposed to the metal film, of the first main electrode in the area between the partitions of each column of the screen. 
     According to a second aspect of the present invention, the first main electrodes and the second main electrodes are spaced uniformly. 
     According to a third aspect of the present invention, the first main electrodes and the second main electrodes are spaced uniformly and the transparent conductive films of the first main electrodes and the second main electrodes are patterned so as to protrude, at each end of the metal film overlaying thereon, in the column direction and so as to form a T-shape. 
     According to a fourth aspect of the present invention, each of the address electrodes crosses the metal film of the first main electrodes at the center of the area in the row direction. 
     According to a fifth aspect of the present invention, each of the address electrodes is patterned in a linear ribbon shape, whose width changes periodically, so that the width at the portion crossing the metal films of the first main electrodes is larger than that at the portion crossing the metal films of the second main electrode. 
     According to a sixth aspect of the present invention, the first main electrodes and the second main electrodes are spaced uniformly, the transparent conductive films of the first main electrodes and the second main electrodes are patterned so as to protrude, at each end of the metal film overlaying thereon, in the column direction and so as to form a T-shape, each of the address electrodes is patterned in a linear ribbon shape and whose width changes periodically so that the width at the portion crossing the metal films of the first main electrodes is larger than that at the portion crossing the metal films of the second main electrode, and each of the address electrodes is arranged at the center of the area in the row direction. 
     According to a seventh aspect and a twelfth aspect of the present invention, a method of driving a plasma display panel is provided. The method comprises the steps of displaying odd fields and even fields of an object image; controlling a potential of each of the first main electrodes and the address electrodes independently so as to perform addressing of odd rows, and then applying a voltage for generating surface discharge to the electrode pair of the odd row periodically, while displaying odd fields, and controlling a potential of each of the first main electrodes and the address electrodes one by one so as to perform addressing of even rows, and then applying a voltage for generating surface discharge to the electrode pair of the even rows periodically, while displaying even fields. 
     According to an eighth aspect of the present invention, a plasma display panel is provided that includes a plurality of first main electrodes for row selection, a plurality of second main electrodes constituting electrode pairs with the plural first main electrodes for generating surface discharge on each row, a plurality of address electrodes for column selection, and partitions for defining a discharge space for each column, which is continuous over the full length of the screen. The first main electrodes and the second main electrodes are arranged alternately. Each of the plural address electrodes is patterned so as to cross the first main electrodes and not to cross the second main electrodes in the area between the partitions of each row in the screen. 
     According to a ninth aspect of the present invention, the portions of the address electrodes crossing the second main electrodes are insulated by the partition from the discharge space. 
     According to a tenth aspect of the present invention, the first main electrodes and the second main electrodes are spaced uniformly. 
     According to an eleventh aspect of the present invention, the first main electrodes and the second main electrodes are spaced uniformly and the transparent conductive films of the first main electrodes and the second main electrodes are patterned so as to protrude at each end of the metal film overlaying thereon in the column direction and so as to form a T-shape. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a diagram showing the internal construction of a plasma display panel according to the present invention. 
     FIGS. 2A-2C show the positional relationship between the main electrode and the address electrode. 
     FIG. 3 shows a second example of the shape of the address electrode. 
     FIG. 4 shows a third example of the shape of the address electrode. 
     FIG. 5 shows a fourth example of the shape of the address electrode. 
     FIG. 6 shows voltage waveforms in an example of a drive sequence. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 1 is a diagram showing the internal construction of a plasma display panel according to the present invention. 
     The illustrated plasma display panel  1  is an AC type color plasma display panel having a surface discharge structure having a pair of substrata structures, or substrates,  10 ,  20 . In each cell (display element) making up a screen, a pair of main electrodes X, Y cross an address electrode A that is patterned in a special shape unique to the present invention. The main electrodes X, Y are arranged alternately and spaced uniformly on the inner surface of the glass plate  11  of the front side substrata structure  10 . Each of the main electrodes X, Y includes a transparent conductive film  41  that defines a surface discharge gap for each cell and a metal film (a bus electrode)  42  in a linear ribbon shape extending over the full length of the row. The metal film  42  has a three-layer structure such as chrome-copper-chrome, and is disposed at the center of the transparent conductive film  41  in the column direction. These main electrodes X, Y are covered with a dielectric layer  17  having thickness of approximately 30-50 μm, and the dielectric layer  17  is covered with a protection layer  18  of magnesia (MgO). 
     The address electrode A is arranged on the inner surface of the glass plate  21  of the back side substratal structure  20  and is covered with a dielectric layer  24 . On the dielectric layer  24 , a partition  29 , like a linear ribbon in a plan view and having a height of 150 μm, is disposed between the address electrodes A. The partitions  29  define a discharge space  30  in the row direction (the horizontal direction of the screen ES), and determine the gap size of the discharge space  30 . The inner surface of the back side including the upper portion of the address electrode A and the side face of the partition  29  is covered with three colors R, G and B of fluorescent layers  28 R,  28 G and  28 B for color display. The discharge space  30  is filled with a discharge gas including neon as a main component mixed with xenon. The fluorescent layers  28 R,  28 G and  28 B are pumped to emit light locally by the ultraviolet rays emitted by the xenon upon discharge. One pixel of display includes three subpixels arranged in the row direction. The structure in each subpixel is the cell C. The arrangement pattern of the partition  29  is a stripe pattern, so that the discharge space  30  corresponding to each column portion is continuous over all rows in the column direction. 
     FIGS. 2A-2C show the positional relationship between the main electrode and the address electrode. FIGS. 2B and 2C are a b-b cross section and a c-c cross section of FIG. 2A, respectively. 
     In the screen, the shape of the main electrode X and the main electrode Y as plan views are the same. In the uniformly spaced main electrodes X, Y, the main electrode X and the main electrode Y being adjacent to each other constitute an electrode pair  12  for generating the surface discharge, and define a row. Namely, main electrodes X, Y—except for the ends of the arrangement—work for displaying two rows (an odd row and an even row). The main electrode X on each end works for displaying rows. The row is a set of cells C having the same arrangement order in the column direction. In the illustrated example, the transparent conductive film  41  of the main electrodes X, Y includes a belt portion  411  in the column direction and belt portions  412  in the row direction that are connected to respective, opposite ends of the belt portion  411 . Thus, transparent conductive film  41  of the main electrodes X, Y is patterned so as to protrude, at each end of the metal film  42 , in the column direction in a T-shape. The transparent conductive film  41  is not limited to the illustrated shape that is independent for each cell, but can be continuous over the full length of the screen in the row direction. Since each of the main electrodes X, Y is shaped to protrude from the metal film  42  in the column direction, symmetrically in the T-shape, the surface discharge can be localized in the area around the surface discharge gap so that the definition can be improved in the column direction. In addition, since the belt portions  412  are spaced in the row direction and the main electrode gap is enlarged periodically along the row direction to be larger than the surface discharge gap, the capacitance becomes smaller than the case where the main electrode gap is constant over the full length of the row direction, so that the drive characteristics are improved. In addition, since the electrode area becomes smaller and the discharge current is decreased, the required current capacity of the drive circuit can be relieved. 
     The address electrode A is patterned in a meandering ribbon shape that crosses the metal film  42  of the main electrode Y used for row selection at the center of the row direction and does not cross the metal film  42  of the main electrode X in the area between the partitions  29 . Namely, the address electrode A is curved so as to avoid the transparent conductive film  41  of the main electrode X, and crosses the metal film  42  of the main electrode X under the partition  29 . This patterning enables the address electrode A substantially to cross only the main electrode Y, so that the address discharge is localized in the vicinity of each main electrode Y, and the interference of address discharge between neighboring rows is prevented. If the main electrode has the illustrated shape, a predetermined gap d between the belt portion  412  of the main electrode Y and the address electrode A improves the effect of protecting the spread of discharge. 
     Since the width of the address electrode A is uniform, the distance between the neighboring address electrodes A is constant along the column direction, and the capacitance between rows becomes the minimum value. In order to increase the area of the address electrode A opposed to the main electrode Y, the width of the address electrode A can be enlarged partially. 
     FIG. 3 shows a second example of the shape of the address electrode. FIG. 4 shows a third example of the shape of the address electrode. 
     In FIG. 3, the address electrode Ab is patterned so as to avoid the transparent conductive film  41  of the main electrode X and to cross each in the row direction. In FIG. 4, the address electrode Ac is patterned in a linear ribbon shape having a slit  51  and is arranged in the center of the row in the row direction. The slit  51  makes the area of the main electrode X opposed to the address electrode A smaller than the area of the main electrode Y opposed to the address electrode A, so that the spread of the address discharge is prevented. 
     FIG. 5 shows a fourth example of the shape of the address electrode. 
     In FIG. 5, the address electrode Ad is patterned in a linear ribbon shape, whose width varies periodically in such a way that the width is larger at the portion where the main electrode Y overlays the transparent conductive film  41  than the other portion and is arranged in the center portion of the column in the row direction. The small width of the electrode makes the area of the main electrode X opposed to the address electrode A smaller than the area of the main electrode Y opposed to the address electrode A, so that the spread of the address discharge is prevented. The transparent conductive film  41  of the main electrode Y and the main electrode X is patterned in the shape having a linear portion  413  extending along the full length of the screen in the row direction and the T-shaped portion  414  that protrudes at each end of the linear portion  413  of each column. The metal film  42  overlays the linear portion  413  completely in the screen. The length of the portion of the address electrode Ad whose width is large is set within a range of the head to head distance between the pair of T-shaped portions  414  extending in the row direction, considering the effect of preventing the spread of address discharge. 
     FIG. 6 shows voltage waveforms in an example of a drive sequence. 
     The plasma display panel  1  is driven by dividing a frame, that is, image information of a scene, into an odd field and an even field. Then, an odd row is displayed in an odd field period Tf 1 , and an even row is displayed in the even field period Tf 2 . Namely, the information of one scene is displayed by an interlace format. 
     Each of the odd field and the even field is divided into eight subframes for example, so that gradation display (color reproduction) is performed by controlling on and off in binary value. In other words, each field is replaced with a set of eight subframes. The relative intensity ratios of these subfields are set to approximately 1:2:4:8:16:32:64:128, so that the number of sustaining discharge for each subfield is determined. Since 256 steps of intensity can be set for each color of red, green and blue by the combination of on and off for each subfield, 256 3  colors can be reproduced. However, it is not necessary to display the subfields in the order of the intensity. 
     The subfield period (Tsf j (j=&#39;1-8)) assigned to each subfield includes a preparation period TR for equalizing charge distribution in the entire screen, an addressing period TA for forming charge distribution corresponding to the contents of display, a sustaining period TS for sustaining the on state to secure the intensity corresponding to the gradation level. In each subfield period Tsf j , the length of the addressing preparation period TR and the addressing period TA is constant despite the weight of the intensity, but the length of the sustaining period TS is larger, for a larger weight of the intensity. Namely, the respective lengths of the eight subfield periods Tsf j  corresponding to one field f are different from each other. 
     As shown in FIG. 6, concerning each subfield of the odd field, a write pulse Prx having a peak level larger than the discharge starting voltage is first applied to each of the main electrodes X in the preparation period TR. On this occasion, a pulse Pra for canceling the write pulse Prx is applied to each of the address electrode A. The application of the write pulse Prx causes the surface discharge and so that excessive wall charge is generated in each cell, and the wall charge will disappear substantially by self erase discharge at the falling edge of the pulse. Next, in the addressing period TA, a scanning pulse Py is applied to each main electrode Y sequentially for the row selection. In synchronization with the scanning pulse Py, an addressing pulse Pa is applied to the address electrode A corresponding to the cell to be lightened in the selected row so that the address discharge is generated. In addition, the pulse is applied alternately to the odd number of the main electrode X and the even number of the main electrode X so that an appropriate surface discharge is generated in the odd row. In the sustaining period TS, a sustaining pulse Ps is applied to the main electrode X and the main electrode Y at the alternate timing for the odd row and at the simultaneous timing for the even row. 
     Concerning each subfield of the even field too, the write pulse Prx is applied to each of the main electrode X in the preparation period TR so as to erase the wall charge. In the addressing period TA too, the scanning pulse Py is applied to each main electrode Y sequentially in the same way as the odd field, and the addressing pulse Pa is applied to a predetermined address electrode A. However, in the even field, the pulse is applied alternately to the odd number of the main electrode X and the even number of the main electrode X in synchronization with the scanning pulse Py so that an appropriate surface discharge is generated in the even row. In addition, the sustaining pulse Ps is applied to the main electrode X and the main electrode Y in the sustaining period TS, at the alternate timing for the even row and at the simultaneous timing for the odd row. 
     In the above-explained example, the structure of the PDP (so-called a reflection type) in which the main electrodes are arranged on the front side substrate is illustrated. 
     However, the present invention can be applied to the other structure (a transparent type) in which the main electrodes are arranged on the backside substrate. In the case of the transparent type, the main electrode can be made of a non-transparent material such as a metal film. The shape of the main electrode can be changed within the range where the discharge characteristics of each row can remain uniform. In addition, the present invention can be applied to a three-electrode structure in which a pair of main electrodes is arranged for each row. 
     As explained above, the present invention can provide a PDP with high accuracy of addressing by suppressing the spread of address discharge in the column direction and a high definition display without errors.