Patent Publication Number: US-2007115212-A1

Title: Method of driving high definition opposed discharge plasma display panel

Description:
FIELD OF THE INVENTION  
      The present invention relates to opposed discharge plasma display panels (PDPs), and more particularly to a method of driving a high definition opposed discharge PDP in order to effectively eliminate noise caused by vibration of the opposed discharge PDP in discharge and greatly increase both light emitting efficiency and brightness of the opposed discharge PDP.  
     BACKGROUND OF THE INVENTION  
      A method of manufacturing a conventional opposed alternating current discharge (i.e., AC type) PDP  10  is illustrated in  FIG. 1 , wherein two different layers are formed on two opposed glass substrates  11  and  12 , the peripheries of the glass substrates  11  and  12  are sealed together to form a space between the two glass substrates, specific gas (e.g., helium (He), neon (Ne), xenon (Xe), or argon (Ar)) is mixed in a predetermined ratio and is filled in discharge cells  13  formed within the space between the two glass substrates  11  and  12 . The substrate facing a viewer is defined as a front substrate  11  in the PDP as shown in  FIG. 1 . On the inner side of the front substrate  11 , there are sequentially provided with a plurality of parallel transparent electrodes  111 , a plurality of bus electrodes  112 , a dielectric layer  113 , and a protection layer (e.g., MgO)  114 . On the inner side of the opposed rear substrate  12 , there are sequentially provided with a plurality of parallel data electrodes  121 , a dielectric layer  124 , a plurality of barrier ribs  122 , and phosphor  123  uniformly coated on each of the barrier ribs  122  in which the phosphor  123  can be a red, green, or blue phosphor. In response to applying voltage to the positions of electrodes  111 ,  112 , and  121 , the corresponding dielectric layers  113  and  124  discharge in the discharge cell  13  formed between the adjacent barrier ribs  122 , enabling the phosphor  123  in the discharge cell  13  to emit light with a corresponding color.  
      Referring to  FIG. 2 , in the conventional AC type PDP  10 , the electrodes  111  and  112  are typically made by utilizing sputtering and photolithography or printing techniques to form a plurality of spaced, parallel transparent electrodes  111  on the inner side of the front substrate  11 , and then utilizing sputtering (or vaporing) and photolithography techniques to form a plurality of bus electrodes  112  on the transparent electrodes  111  in order to decrease line impedance of the transparent electrodes  111  by utilizing the bus electrodes  112 . The transparent electrodes  111  (comprising the bus electrodes  112 ) and the corresponding data electrodes  121  on the rear substrate  12  together form two opposed electrodes. In response to applying voltage to the electrodes  111  and  121 , the dielectric layers  113  and  124  perform opposed discharges in the corresponding discharge cell  13 . As a result, the mixed gas filled in the discharge cell  13  discharges to emit ultraviolet (UV). And in turn, red, green, and blue light is emitted by the phosphor  123  coated on the discharge cell  13 . As a result, an image is shown. The conventional AC type PDP  10  is also called as opposed discharge PDP.  
      Referring to  FIGS. 1, 2 , and  3 , in the above opposed discharge PDP  10  the parallel data electrodes  121  of the rear substrate  12  are provided on bottom of the dielectric layer  124  and are disposed perpendicularly to the corresponding transparent electrodes (also called as scan electrodes or sustain electrodes)  111  of the front substrate  11  at the positions corresponding to the discharge cells  13 . A shadow mask  20  is formed on top of the dielectric layer  124 . A plurality of shadow holes  21  of the shadow mask  20  are employed as space for the discharge cell  13 . Also, metal conductor around each shadow hole  21  is served as barrier rib  122  around the discharge cell  13 .  
      Referring to FIGS.  1  to  3  again, in the above opposed discharge PDP  10  portion of a shadow mask  20  of a 34″ opposed discharge PDP  10  having Video Graphics Adapter (VGA) resolution is shown. Each pixel containing three discharge cells for emitting red, green, and blue light respectively has a size of 1080 μm×1080 μm. That is, each discharge cell has a size of 360 μm×1080 μm. Referring to  FIG. 4 , a driving scheme is created by a driving circuit of the PDP  10  for showing each sub-field. The driving scheme comprises three driving sequences, i.e., a first addressing sequence, a second sustaining sequence, and a third erasing sequence wherein, in the addressing sequence, the driving circuit applies a negative voltage pulse to each bus electrode  112 . At the same time, the driving circuit applies a positive data pulse to the address electrode  121  based on an image to be displayed. At this time, due to the shadow mask  20  is made by the conductive metal material, electric field in the discharge cell  13  becomes non-uniform, i.e. the electric field adjacent to the wall of the shadow hole  21  (i.e., barrier rib  122 ) is relatively strong and the electric field at a center of the shadow hole  21  is relatively weak. Discharge first occurs at wall of the shadow hole  21  when an addressing pulse is applied to the discharge cell  13 , which enables the charged particles in the discharge cell  13  quickly spread and propagate toward the center of the shadow hole  21  so as to induce an opposed discharge between the bus electrodes  112  and the data electrodes  121 . The opposed discharge scheme not only greatly increases light emitting efficiency of the PDP  10  but also obtains advantages such as high contrast, high writing speed, and low cost.  
      Referring to  FIGS. 1 and 2  again, in the above opposed discharge PDP  10  however, the barrier rib  122  of the rear substrate  12  is formed of metal conductor around each shadow hole  21  of the shadow mask  20 . Noise generated by the metal barrier rib  122  is far more serious than that generated by a barrier rib formed of the well known glass substrate when discharge occurs in the discharge cell  13 . Referring to  FIG. 4  again, for the above opposed discharge PDP  10  in the sustaining period a phase of the sustaining pulse of the nth sustain electrode is the same as that of the sustaining pulse of the n+1 th  sustain electrode. That is, phase of the odd number pixels and that of the even number pixels are the same with respect to voltage shape in the sustaining sequence. Thus, vibration direction of noise generated by the discharge cells  13  in the discharge is the same. As a result, noise is significantly serious. Therefore, if an intimate contact between an inner surface of the front substrate  11  and the shadow mask  20  is not made in the process of manufacturing, gap formed therebetween will further deteriorate the noise problem caused in the opposed discharge PDP  10 . Thus, it is desirable to strictly control flatness of the front and rear substrates  11  and  12  and the shadow mask  20  in order to decrease the gap created due to an irrregularity between the front substrate  11  and the shadow mask  20  in the manufacturing process. The decreased gap can effectively decrease the noise problem. However, such strict control results in a great increase of process difficulty and a decreased yield.  
      Referring to  FIGS. 1, 2  and  5 , moreover in the above opposed discharge PDP  10  portion of a shadow mask  20  of a 34″ opposed discharge PDP  10  having VGA resolution is shown. Since each pixel contains three discharge cells for emitting red, green, and blue light respectively, each discharge cell corresponding to each shadow hole  21  of the shadow mask  20  has a size of 360 μm×1080 μm and is elongate. Such elongate discharge cells  13  may cause discharge to concentrate on a center thereof. This can greatly decrease light emitting efficiency of phosphor coated on distal ends relative to the center of the discharge cell  13 . As a result, the total light emitting efficiency is very low. Thus, a need for improvement exists.  
     SUMMARY OF THE INVENTION  
      After considerable research and experimentation, a method of driving a high definition opposed discharge plasma display panel (PDP) according to the present invention has been devised so as to overcome the above drawbacks (e.g., noise and low light emitting efficiency) of the prior art.  
      It is an object of the present invention to provide a method of driving a high definition opposed discharge PDP comprising transversely disposing a barrier rib on a center of any one of a plurality of elongate discharge cells in any one of a plurality of pixels of the opposed discharge PDP wherein the discharge cell is divided into two sub-cells by the barrier rib; disposing a sustain electrode on a front substrate corresponding to either sub-cell; causing a driving circuit to apply a sustaining pulse to each of the plurality of sustain electrodes in a sustaining period of each sub-field; and causing a phase of the sustaining pulse on the sustain electrode corresponding to one sub-cell to have a phase difference of 180 degrees relative to that of the sustaining pulse on the sustain electrode corresponding to the other adjacent sub-cell. By utilizing this method, discharge direction of the sub-cell corresponding to odd number pixel is opposite to that of the sub-cell corresponding to even number pixel in order to effectively eliminate noise caused by vibration of the opposed discharge PDP in discharge. Moreover, a reduction of peak current and electromagnetic interference is made possible. In addition, area coated with phosphor is significantly increased because the discharge cell is divided into two sub-cells. As a result, both light emitting efficiency and brightness of the opposed discharge PDP are greatly increased, and thus image with high quality is shown.  
      One aspect of the present invention the method comprises causing a driving circuit to apply a sustaining pulse to each of the plurality of sustain electrodes; and causing a phase of the sustaining pulse on the sustain electrode corresponding to one sub-cell to have a phase difference of 180 degrees relative to that of the sustaining pulse on the sustain electrode corresponding to the other adjacent sub-cell. By utilizing this method, discharge directions of two adjacent sub-cells of the discharge cell are opposite in order to substantially eliminate noise caused by vibration of the opposed discharge PDP in discharge due to opposite vibration directions.  
      Another aspect of the present invention the method comprises lighting spaced sub-cells; and causing a waveform of a voltage pulse of one sub-cell is delayed half period (i.e., phase difference of 180 degrees) relative to that of the other spaced sub-cell in a sustaining period in order to let discharge directions of two spaced sub-cells to be opposite with each other. By utilizing this method, the brightness of the opposed discharge PDP decreases to about half of that when both sub-cells are lit. As a result, an overall brightness of the opposed discharge PDP is decreased in order to adjust the brightness of each gray-scale for decreasing a minimum brightness and obtaining a fine image in low gray-scales of the opposed discharge PDP.  
      The above and other objects, features and advantages of the present invention will become apparent from the following detailed description taken with the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       FIG. 1  is a sectional view of a conventional opposed discharge PDP;  
       FIG. 2  is an exploded perspective view of the PDP of  FIG. 1  showing its front and rear substrates;  
       FIG. 3  is a sectional view showing a configuration of the discharge cells, the bus electrodes, and the barrier rib in the PDP of  FIG. 1 ;  
       FIG. 4  is a graph of a driving scheme created by a driving circuit of the PDP of  FIG. 1  for showing each sub-field;  
       FIG. 5  is a photograph of an enlarged pixel of the PDP of  FIG. 1 ;  
       FIG. 6  is a sectional view showing a configuration of discharge cells according to opposed discharge PDP of a first preferred embodiment of the invention;  
       FIG. 7  is a sectional view showing a configuration the discharge cells, the barrier ribs, and the electrode lines in the PDP of  FIG. 6 ;  
       FIG. 8  is a graph of a driving scheme created by a driving circuit of the PDP of FIG.  6  for showing each sub-field;  
       FIG. 9  schematically depicts an opposed discharge between two adjacent sub-cells in discharge where the sub-cells correspond to odd number and even number pixels of the PDP of  FIG. 6  respectively;  
       FIG. 10  is a sectional view showing a configuration of the discharge cells, the barrier ribs, and the electrode lines according to opposed discharge PDP of a second preferred embodiment of the invention;  
       FIG. 11  is a graph of a driving scheme created by a driving circuit of the PDP of  FIG. 10  for showing each sub-field;  
       FIG. 12  schematically depicts an opposed discharge between two adjacent sub-cells in discharge where the sub-cells correspond to odd number and even number pixels of the PDP of  FIG. 10  respectively;  
       FIG. 13  is a graph of a driving scheme created by a driving circuit of opposed discharge PDP according to a third preferred embodiment of the invention for showing each even number sub-field;  
       FIG. 14  schematically depicts an opposed discharge between two adjacent sub-cells in discharge where the sub-cells correspond to odd number and even number pixels of the PDP of  FIG. 13  respectively;  
       FIG. 15  is a graph of a driving scheme created by a driving circuit according to the PDP of  FIG. 13  for showing each odd number sub-field; and  
       FIG. 16  schematically depicts an opposed discharge between two adjacent sub-cells in discharge where the sub-cells correspond to odd number and even number pixels of the PDP of  FIG. 15  respectively. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
      The invention is directed to a method of driving a high definition opposed discharge plasma display panel (PDP) comprising transversely disposing a barrier rib on a center of any elongate discharge cell in any pixel of the opposed discharge PDP wherein the discharge cell is divided into two sub-cells by the barrier rib; disposing a sustain electrode on a front substrate corresponding to either sub-cell; causing a driving circuit to apply a sustaining pulse to each of the plurality of sustain electrodes in a sustaining period of each sub-field; and causing a phase of the sustaining pulse on the sustain electrode corresponding to one sub-cell to have a phase difference of 180 degrees relative to that of the sustaining pulse on the sustain electrode corresponding to the other adjacent sub-cell such that two adjacent sub-cells may discharge in opposite directions. Alternatively, the method comprises causing a phase of the sustaining pulse on the sustain electrode corresponding to one sub-cell to have a phase difference of 180 degrees relative to that of the sustaining pulse on the sustain electrode corresponding to the other spaced sub-cell such that two spaced sub-cells may discharge in opposite directions.  
      Referring to  FIG. 6 , a first preferred embodiment of the invention is illustrated with respect to a 34″ opposed discharge PDP. Each pixel on the opposed discharge PDP has a size of 1080 μm×1080 μm. A transverse barrier rib  323  is provided on a center of any elongate discharge cell  33  in any pixel so as to divide the discharge cell  33  into two sub-cells  331  and  332 . That is, n th  row discharge cell is divided into n th -a row sub-cell  331  and n th -b row sub-cell  332 . Either sub-cell  331  or  332  has a size of 1080 μm×360 μm. Referring to  FIG. 7 , a sustain electrode Sa and a sustain electrode Sb are provided on a front substrate of the opposed discharge PDP and corresponds to the sub-cells  331  and  332  respectively. The adjacent sub-cells  331  and  332  are parallel and one ends thereof are coupled together to receive a voltage pulse sent from an electrode line  322 . Thus, a driving circuit (not shown) in the opposed discharge PDP is adapted to apply a sustaining pulse to each of a plurality of electrode lines in a sustaining period of each sub-field. As such, a phase of the sustaining pulse on the sustain electrode Sa (or Sb) corresponding to either sub-cell  331  (or  332 ) is adapted to have a phase difference of 180 degrees relative to that of the sustaining pulse on the sustain electrode Sa (or Sb) corresponding to the other adjacent sub-cell  331  (or  332 ) such that the sub-cells  331  and  332  of adjacent pixels may discharge in opposite directions.  
      Referring to  FIG. 8 , a driving scheme is created by the driving circuit of the opposed discharge PDP for showing each sub-field in the first preferred embodiment. The driving scheme comprises three driving periods (i.e., a first addressing period, a second sustaining period, and a third erasing period). Referring to  FIG. 9 , the driving circuit applies a negative voltage pulse to each of the sustain electrodes Sa and Sb in the addressing period. At the same time, the driving circuit applies a positive data pulse to the address electrode “A” based on an image to be displayed. Next, the driving circuit applies a sustaining pulse to each of a plurality of electrode lines  322  of the opposed discharge PDP (see  FIG. 7 ). As such, a phase of the sustaining pulse on the n th -a sustain electrode Sa (or n th -b sustain electrode Sb) has a phase difference of  ½ period (i.e., T/ 2) relative to that of the sustaining pulse on the n+1 th -a sustain electrode Sa (or n+1 th -b sustain electrode Sb). That is, waveform of voltage pulse of the sub-cell  331  corresponding to odd number pixel is delayed T/2 relative to that of the sub-cell  332  corresponding to even number pixel in a sustaining period. As a result, discharge direction of the sub-cell  331  corresponding to odd number pixel is opposite to that of the sub-cell  332  corresponding to even number pixel in order to effectively eliminate noise caused by vibration of the PDP in discharge as shown in  FIG. 9 . Finally, the driving circuit applies an erasing pulse to each of the plurality of sustain electrodes Sa and Sb of the PDP in the erasing period. As such, wall charge of each discharge cell is eliminated. In the embodiment waveform of a sub-cell  331  corresponding to the odd number pixel is delayed T/2 relative to that of a sub-cell  332  corresponding to the even number pixel in the sustaining period. Such driving method has advantages of without modifying driving scheme in reset period and addressing period.  
      Referring to the above first preferred embodiment again, discharge direction (i.e., vibration direction) of the sub-cell  331  corresponding to the odd number pixel is opposite to that of the sub-cell  332  corresponding to the even number pixel. Thus, noise generated by the sub-cell  331  is opposite to that generated by the sub-cell  331  and they are cancelled each other due to opposite vibration directions. As an end, noise generated by vibration of the PDP in discharge is substantially eliminated. Moreover, a reduction of peak current and electromagnetic interference is made possible. In addition, area coated with phosphor is significantly increased because the discharge cell  33  is divided into two sub-cells  331  and  332 . Further, distance between discharge center and phosphor on either upper end (or lower end) of the original discharge cell  33  is greatly decreased. As a result, UV is sufficiently employed, light emitting efficiency of phosphor is greatly improved, both light emitting efficiency and brightness of the opposed discharge PDP are greatly increased, and thus image with high quality is shown.  
      Referring to  FIG. 10 , a second preferred embodiment of the invention is illustrated with respect to an opposed discharge PDP. A transverse barrier rib  423  is provided on a center of any elongate discharge cell  43  in any pixel so as to divide the discharge cell  43  into two sub-cells  431  and  432 . That is, n th  row discharge cell is divided into n th -a row sub-cell  431  and n th -b row sub-cell  432 . A sustain electrode Sa and a sustain electrode Sb are provided on a front substrate of the opposed discharge PDP and corresponds to the sub-cells  431  and  432  respectively. Thus, a driving circuit (not shown) in the opposed discharge PDP is adapted to apply a sustaining pulse to each of a plurality of sustain electrodes Sa and Sb in a sustaining period of each sub-field. As such, a phase of the sustaining pulse on the sustain electrode Sa corresponding to the sub-cell  431  is adapted to have a phase difference of 180 degrees relative to that of the sustaining pulse on the sustain electrode Sb corresponding to the adjacent sub-cell  432  such that the sub-cells  431  and  432  of the discharge cell  43  in the same pixel may discharge in opposite directions.  
      Referring to  FIGS. 11 and 12 , in the second preferred embodiment, the driving circuit applies a negative voltage pulse to each of the sustain electrodes Sa and Sb of the PDP for showing each sub-field in the addressing period. At the same time, the driving circuit applies a positive data pulse to the address electrode “A” based on an image to be displayed. Next, the driving circuit applies a sustaining pulse to each of a plurality of sustain electrodes Sa and Sb of the opposed discharge PDP. As such, a waveform of the sustaining pulse on the nth-a sustain electrode Sa is delayed T/2 relative to that of the sustaining pulse on the adjacent n th -b sustain electrode Sb. Also, a waveform of the sustaining pulse on the n+1 th -a sustain electrode Sa is delayed T/2 relative to that of the sustaining pulse on the adjacent n+1 th -b sustain electrode Sb and so on. As a result, discharge direction of the sub-cell  431  of the discharge cell  43  is opposite to that of the sub-cell  432  thereof in the same pixel in order to effectively eliminate noise caused by vibration of the PDP in discharge as shown in  FIG. 12 .  
      Referring to  FIGS. 13 and 14 , a third preferred embodiment of the invention is illustrated with respect to the same configuration of the sustain electrodes shown in  FIG. 10 . The driving circuit applies a negative voltage pulse to each of the sustain electrodes Sa and Sb of the PDP for showing each sub-field in the addressing period. At the same time, the driving circuit applies a positive data pulse to the address electrode “A” based on an image to be displayed. Next, the driving circuit applies a sustaining pulse to each of a plurality of spaced sustain electrodes Sa and Sb of the opposed discharge PDP. As such, a waveform of the sustaining pulse on the n th -a sustain electrode Sa is delayed T/2 relative to that of the sustaining pulse on the adjacent n+1 th -b sustain electrode Sa. No voltage is applied to the n th -b sustain electrode Sb and the n+1 th -b sustain electrode Sb in order to delay a waveform of the voltage pulse on the sustain electrode Sa T/2 relative to that of the voltage pulse on the spaced sustain electrode Sb in sustaining period. As a result, discharge direction of the sub-cell  531  is opposite to that of the spaced sub-cell  532  (see  FIG. 14 ).  
      Referring to  FIG. 14  in conjunction with the waveform of  FIG. 13  an interlace based discharge method of the third preferred embodiment is illustrated. For showing even number fields, both the n th -b and the n+1 th -b sustain electrodes Sb are maintained at zero potential and a phase of the waveform of the n th -a sustain electrode Sa has a phase difference of 180 degrees relative to that of the n+1 th -a sustain electrode Sa. Likewise, referring to  FIG. 16  in conjunction with the waveform of  FIG. 15  for showing odd number fields, both the n th -a and the n+1 th -a sustain electrodes Sa are maintained at zero potential and a phase of the waveform of the nth-b sustain electrode Sb has a phase difference of 180 degrees relative to that of the n+1 th -b sustain electrode Sb. Thus, the n th -a sustain electrode Sa is a sustain electrode adapted to drive independently relative to the n th -b sustain electrode Sb and vice versa in order to control waveforms of the n th -a sustain electrode Sa and the n th -b sustain electrode Sb respectively. As an end, brightness of the corresponding sub-cell  531  can be controlled. Also, the n+1 th -a sustain electrode Sa is a sustain electrode adapted to drive independently relative to the n+1 th -b sustain electrode Sb and vice versa in order to control waveforms of the n+1 th -a sustain electrode Sa and the n+1 th -b sustain electrode Sb respectively. As an end, brightness of the corresponding sub-cell  532  can be controlled. For example, in a period of showing a specific sub-field waveform of voltage pulse the n th -a sustain electrode Sa is maintained as the waveform of voltage pulse in sustaining period and voltage of the n th -b sustain electrode Sb is maintained as constant. As such, only sub-cell  531  corresponding to the n th -a sustain electrode Sa may discharge to emit light while sub-cell  532  corresponding to the n th -b sustain electrode Sb may not discharge (i.e., no light is emitted). Such independent brightness control with respect to the sub-cell  531  (or the sub-cell  532 ) corresponding to the n th -a sustain electrode Sa and the n th -b sustain electrode Sb has the following advantages:  
      (i) A minimum brightness can be obtained. The sub-cell  531  corresponding to the n th -a sustain electrode Sa may discharge to emit light while the sub-cell  532  corresponding to the n th -b sustain electrode Sb is dark due to no light emission. Thus, brightness of the opposed discharge PDP is about half of that when both the sub-cell  531  corresponding to the n th -a sustain electrode Sa and the sub-cell  532  corresponding to the n th -b sustain electrode Sb are lit. As a result, a minimum brightness is obtained for rendering fine image in low gray-scales of the opposed discharge PDP.  
      (ii) Brightness in discharge can be finely adjusted. Either the sub-cell  531  corresponding to the nth-a sustain electrode Sa or the sub-cell  532  corresponding to the n th -b sustain electrode Sb can be prohibited from discharging when brightness in discharge is higher than an ideal value. As a result, brightness of the opposed discharge PDP is decreased and thus the purpose of adjusting brightness of each gray-scale is obtained.  
      While the invention herein disclosed has been described by means of specific embodiments, numerous modifications and variations could be made thereto by those skilled in the art without departing from the scope and spirit of the invention set forth in the claims.