Patent Publication Number: US-2007109226-A1

Title: Driving method of plasma display panel

Description:
CROSS-REFERENCE TO RELATED PATENT APPLICATIONS  
      This application claims priority to and the benefit of Korean Patent Application No. 10-2005-0108934, filed on Nov. 15, 2005, which is hereby incorporated by reference in its entirety.  
     BACKGROUND OF THE INVENTION  
      1. Field of the Invention  
      The present invention relates to a driving method of a plasma display panel, and more particularly, to a driving method of a plasma display panel, which is capable of uniformly performing in upper and lower portions of the plasma display panel.  
      2. Description of the Related Technology  
      Recently, plasma display panels (PDPs) have come to the attention of the public, as substitutes of conventional cathode ray tubes (CRTs). In a plasma display panel, a discharge gas is filled between two substrates on which a plurality of electrodes are formed, a discharge voltage is applied to the electrodes, and phosphor, formed with a predetermined pattern is excited due to ultraviolet rays generated by the discharge voltage, thereby displaying a desired image.  
       FIG. 1  is a diagram illustrating a conventional address display separation (ADS) driving method which is applied to scan electrodes.  
      Referring to  FIG. 1 , a unit frame is divided into a predetermined number of sub-fields, for example, 8 sub-fields SF 1  through SF 8  for time-division gray-scale display. Also, the sub-fields SF 1  through SF 8  are divided into reset periods (not shown), address periods A 1  through A 8 , and discharge sustain periods S 1  through S 8 , respectively.  
      In the reset period, all discharge cells are initialized. In the respective addressing periods A 1  through A 8 , addressing is sequentially performed from the upper portion of a plasma display panel toward the lower portion thereof. In the respective sustain periods S 1  through S 8 , sustain discharges are performed in discharge cells to be turned on, selected in the address periods A 1  through A 8 .  
      Accordingly, brightness of the plasma display panel is proportional to the total number of sustain discharge operations within the discharge sustain periods S 1  through S 8  included in a unit frame. If a frame forming an image consists of 8 sub-fields with 256 gray-scales, different gray scale weights of 1, 2, 4, 8, 16, 32, 64 and 128 can be allocated to the respective sub-fields in this order. In this case, in order to obtain brightness with 133 gray-scales, it is needed to address and sustain-discharge cells during a first sub-field period SF 1 , a third sub-field period SF 3 , and an eighth sub-field period SF 8 .  
      The number of the gray-scale weights allocated to each of the sub-fields can be set according to weight values of sub-fields on the basis of APC (Automatic Power Control). Also, the number of the gray-scale weights allocated to each of the sub-fields can be changed variously in consideration of panel characteristics.  
       FIG. 2  is a timing diagram of an example of conventional driving signals for driving a 3-electrode plasma display panel. Referring to  FIG. 2 , a sub-field SF includes a reset period PR, an address period PA and a sustain discharge period PS.  
      First, in the reset period PR, a rising ramp pulse and a falling ramp pulse are applied to scan electrodes and a bias voltage Vb 1  is applied to sustain electrodes from when the falling ramp pulse is applied, so that a reset discharge is performed in discharge cells. Due to the reset discharge, the state of wall charges in the entire discharge cells is initialized.  
      Then, in the address period PA, a scan pulse Vsc 11  is sequentially applied to the scan electrodes from the upper portion of the plasma display panel toward the lower portion thereof, and a display data signal Va 1  is applied to address electrodes in synchronization with the scan pulse so that an address discharge is performed in discharge cells to be turned on. After the address discharge is performed, the state of wall charges in the discharge cells is set to be suitable to be subjected to a sustain discharge in the following sustain discharge period PS.  
      Successively, in the sustain period PS, a sustain pulse Vs 1  is alternately applied to the scan electrodes and the sustain electrodes so that sustain discharge operations are performed according to a gray-scale weight corresponding to input data.  
      According to the conventional plasma display panel driving method as described above, the delay between the end of the address discharge and the beginning of the sustain discharge is shorter in the lower portion of the display than in the upper portion of the display. As a result, the sustain discharge characteristic or intensity of sustain discharge light varies between the upper and lower portions of the plasma display panel. Accordingly, a sustain discharge cannot be uniformly performed. Particularly, this problem is more significant when a high-definition plasma display panel is driven.  
     SUMMARY OF CERTAIN INVENTIVE ASPECTS  
      The present invention provides a driving method of a plasma display panel, which is capable of uniformly performing a sustain discharge in upper and lower portions of the plasma display panel.  
      One embodiment is a method of driving a plasma display panel, the plasma display panel including sustain electrodes, scan electrodes and address electrodes, the sustain electrodes and the scan electrodes being separated and extending substantially parallel to each other, the address electrodes intersecting the sustain electrodes and the scan electrodes, where discharge cells are defined near where the sustain electrodes intersect the scan electrodes, the discharge cells being divided into a plurality of groups. The method includes driving the discharge cells of each group during a unit frame, divided into a plurality of sub-fields, where each of the sub-fields is divided into a reset period, a mixing driving period, and a correction sustain period, driving the discharge cells for each group during the reset period so as to initialize the discharge cells, driving the discharge cells for each group during the mixing driving period so as to select certain discharge cells of each group and to perform at least one discharge operation for one or more of the plurality of groups, and driving the discharge cells for each group during the correction sustain period so as to correct the number of sustain discharge operations for each group so that a total number of sustain discharge operations corresponding to a gray scale weight determined for each sub-field is performed during each sub-field. The correction sustain period is divided into a selection sustain period and a common sustain period and a sustain discharge in each group is performed during the selection sustain period and the same number of sustain discharge operations for each of plurality of groups is performed during the common sustain period.  
      Another embodiment is a method of driving a plasma display panel, the plasma display panel including an array of discharge cells, the discharge cells being divided into a plurality of groups. The method includes driving the plurality of groups during a sub-field, the sub-field including a mixing driving period, and driving the plurality of groups during the mixing driving period so as to sequentially select certain discharge cells of a first group, perform at least one discharge operation for the selected cells of the first group, and select certain discharge cells of a second group. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
      The above and other features and advantages of the present invention will become more apparent through the description of embodiments thereof with reference to the attached drawings in which:  
       FIG. 1  is a view for explaining a conventional address display separation (ADS) driving method which is applied to scan electrodes;  
       FIG. 2  is a timing diagram of an example of conventional driving signals for driving a 3-electrode plasma display panel;  
       FIG. 3  illustrates an electrode arrangement of a plasma display panel to which a plasma display panel driving method can be applied;  
       FIG. 4  is a diagram illustrating an address display mixing (ADM) driving method according to an embodiment;  
       FIG. 5  is a diagram illustrating a driving operation of a first sub-field SF 1  illustrated in  FIG. 4 ;  
       FIG. 6  is a diagram illustrating a driving operation of a fourth sub-field SF 4  illustrated in  FIG. 4 ;  
       FIG. 7  is a timing diagram of driving signals in the fourth sub-field SF 4  illustrated in  FIG. 6 , according to an embodiment;  
       FIG. 8  is a timing diagram illustrating driving signals in a correction sustain period C 4  illustrated in  FIG. 7 ;  
       FIG. 9  is a timing diagram of driving signals in the fourth sub-field SF 4  illustrated in  FIG. 6 , according to another embodiment; and  
       FIG. 10  is a timing diagram illustrating driving signals in a correction sustain period C 4  illustrated in  FIG. 9 . 
    
    
     DETAILED DESCRIPTION OF CERTAIN INVENTIVE ASPECTS  
       FIG. 3  illustrates an electrode arrangement of a plasma display panel to which a plasma display panel driving method discussed herein can be applied.  
      Referring to  FIG. 3 , scan electrodes Y 1 , . . . , Y n  and sustain electrodes X 1 , . . . , X n  extend parallel to each other, and address electrodes A 1 , . . . , A m  intersect the scan electrodes Y 1 , . . . , Y n  and the sustain electrodes X 1 , . . . , X n . Discharge cells are defined where the scan electrodes Y 1 , . . . , Y n , the sustain electrodes X 1 , . . . , X n , and the address electrodes A 1 , . . . , A m  intersect to each other.  
      Hereinafter, Japanese Laid-open Application No. 1999-120924 disclosing an example of a plasma display panel will be described. Referring to the disclosure, the plasma display panel includes address electrodes, dielectric layers, scan electrodes, sustain electrodes, phosphor layers, barrier ribs, and a MgO protection layer, between a front substrate and a rear substrate.  
      The address electrodes are formed in a pattern on the upper surface of the rear substrate. A rear dielectric layer covers the upper surfaces of the address electrodes. The barrier ribs are formed parallel to the address electrodes on the surface of the rear dielectric layer. The barrier ribs partition discharge spaces of the respective discharge cells and prevent optical interferences between the respective discharge cells. The phosphor layers are formed between the barrier ribs on the upper surface of the rear dielectric layer over the address electrodes. Each phosphor layer includes a red-emitting phosphor layer, a green-emitting phosphor layer, and a blue-emitting phosphor layer which are sequentially arranged.  
      The sustain electrodes and the scan electrodes are formed in a pattern on the rear surface of the front substrate in such a manner as to intersect the address electrodes. Each of the sustain electrodes and the scan electrodes is formed by coupling a transparent electrode line made of a transparent conductive material such as Indium Tin Oxide (ITO) with a metal electrode line (a bus electrode) for increasing conductivity. The front dielectric layer is formed in such a manner as to entirely cover the rear surfaces of the sustain electrodes and the scan electrodes. The protection layer for protecting the plasma display panel from a strong electric field, for example, a MgO layer is entirely formed on the surface of the front dielectric layer. A plasma forming gas is filled in the discharge spaces. The plasma display panel as described above is an example, and the present invention is not limited to this. That is, an arbitrary structure where scan electrodes and sustain electrodes parallel to each other intersect address electrodes is possible.  
       FIG. 4  is a diagram illustrating an address display mixing (ADM) driving method according to an embodiment.  
      In this embodiment, the plasma display panel is driven using an address display mixing (ADM) driving method, instead of the address display separation (ADS) driving method illustrated in  FIG. 1 .  
      Hereinafter, the ADM driving method will be described with reference to  FIGS. 3 and 4 .  
      In the ADM driving method, discharge cells are divided into a plurality of groups sequentially from the upper portion of the plasma display panel toward the lower portion thereof, addressing is performed for each group, and a number of sustain discharge operations is performed in groups where addressing has been performed. The ADM driving method is aimed at improving a problem where a sustain discharge is not uniformly performed between the upper and lower portions of a plasma display panel because addressing is performed on the entire plasma display panel in the ADS driving method.  
      The ADM driving method divides a unit frame into reset periods R 1  through R 8 , mixing driving periods M 1  through M 8 , and correction sustain periods C 1  through C 8 , as shown in  FIG. 4 . In the reset periods R 1  through R 8 , a reset pulse, such as that shown in  FIG. 2 , consisting of a rising pulse and a falling pulse is applied to all scan electrodes Y 1 , . . . , Y n , so that all discharge cells are initialized. Each of the mixing driving periods M 1  through M 8  is divided into a group address period, during which discharge cells of the group to be turned on are selected, and a group sustain period which occurs between group address periods and performs a number of sustain discharge operations in the selected discharge cells. The correction sustain periods C 1  through C 8  are divided into selection sustain periods AS 1  through AS 8  for selectively performing a sustain discharge in the discharge cell groups and for correcting differences in the numbers of sustain discharge operations between respective groups, and common sustain periods CS 1  through CS 8  for performing sustain discharge operations in such a manner that the number of sustain discharge operations corresponding to a gray scale weight allocated to each sub-field is performed in the sub-field such that the same number of sustain discharge operations are performed for each of the groups.  
      The plurality of groups can be variously set. For example, the discharge cells can be divided into two groups as illustrated in  FIG. 4 . Also, the sustain discharge may be once performed in the group sustain period, however, the present invention is not limited to this.  
      The ADM driving method will be described with reference to  FIGS. 5 and 6 , below.  
       FIG. 5  is a diagram illustrating a driving operation of a first sub-field SF 1  illustrated in  FIG. 4 .  
      First, in a reset period R 1 , a reset pulse, such as that illustrated in  FIG. 2 , consisting of a rising pulse and a falling pulse is applied to all scan electrodes and a bias voltage is applied to all sustain electrodes from when the falling pulse is applied, so that a reset discharge is performed. Thus, after the reset period R 1  is terminated, the state of wall charges in all discharge cells is uniformly initialized.  
      Then, in a mixing driving period M 1 , addressing, that is, an addressing discharge period A G1  is performed in a first discharge cell group G 1  during a first group address period P A1 . Then, in a first group sustain period P S1 , a sustain discharge period S 11  is performed in the first discharge cell group G 1  in which addressing has been performed. Successively, in a second group address period P A2 , an address discharge period A G2  is performed in a second discharge cell group G 2 .  
      Then, in a correction sustain period C 1 , that is, in a selection sustain period AS 1 , a sustain discharge period S 21  is performed in the second discharge cell group G 2  for which addressing has been performed in the second group address period P A2 . When a gray scale weight of the first sub-field SF 1  is 1, it is sufficient if the sustain discharge is once performed over the first sub-field SF 1 . However, since the first group sustain period P S1  is performed in the first discharge cell group G 1  and the selection sustain period AS 1  is performed in the second group discharge cell group G 2 , no common sustain period is needed.  
       FIG. 6  is a diagram illustrating a driving operation of a fourth sub-field SF 4  illustrated in  FIG. 4 .  
      First, in a reset period R 4 , a reset pulse, such as that illustrated in  FIG. 2 , consisting of a rising pulse and a falling pulse is applied to all the scan electrodes and a bias voltage is applied to all sustain electrodes from when the falling pulse is applied, so that a reset discharge is performed. Thus, the state of wall charges in the entire discharge cells is uniformly initialized.  
      Then, in a mixing driving period M 4 , an address discharge period A G1  is performed in the first discharge cell group G 1  during a first group address period P A1 . Then, a sustain discharge period S 11  is performed in the first discharge cell group G 1  in which addressing has been performed, in a first group sustain period P S1 . Subsequently, in a second group address period P A2 , an address discharge period A G2  is performed in the second discharge cell group G 2 .  
      In a correction sustain period C 4 , during a selection sustain period AS 4 , a sustain discharge period S 21  is performed only in the second discharge cell group G 2  for which addressing has been performed in the second group address period P A2.  If, for example, a gray scale weight of the fourth sub-field SF 4  is 8, a sustain discharge must be performed 8 times for the fourth sub-field SF 4 . Thus, in a common sustain period CS 4 , 7 sustain discharge periods S 12  through S 18  are performed in the first discharge cell group G 1 , and 7 sustain discharge periods S 22  through S 28  are performed in the second discharge cell group G 2 , one sustain discharge having been previously performed in each of the first and second discharge cell groups G 1  and G 2 .  
      Sub-fields other than the fourth sub-field SF 4  are also driven in the same manner as described above.  
       FIG. 7  is a timing diagram of driving signals in the fourth sub-field SF 4  illustrated in  FIG. 6 , according to an embodiment.  
      In this embodiment, discharge cells are divided into two groups of a first discharge cell group G 1  and a second discharge cell group G 2 , in a up and down direction of a plasma display panel, that is, in a direction in which address electrodes extend. Hereinafter, scan electrodes belonging to the first discharge cell group G 1  are referred to as a first scan electrode group Y 1 , . . . , Y n/2 , and scan electrodes belonging to the second discharge cell group G 2  are referred to as a second scan electrode group Y n/2+1 , . . . , Y n .  
      First, in a reset period R 4 , the same reset pulse is applied to all the scan electrodes Y 1 , . . . , Y n  so that wall charges in all the discharge cells are uniformly distributed. Accordingly, a reset pulse consisting of a rising pulse rising by a ninth voltage V set  from a first voltage V s  as a sustain discharge voltage and finally reaching a tenth voltage V set +V s  and a falling pulse falling from the first voltage V s  and finally reaching an eleventh voltage V nf , is applied to all the scan electrodes Y 1 , . . . , Y n . A seventh voltage V b  which is a bias voltage is applied to all sustain electrodes X 1 , . . . , X n  from when the falling pulse is applied, and a third voltage V g  is applied to all address electrodes A 1 , . . . , A m . Here, the seventh voltage V b  may be equal to the first voltage V s . In some embodiments, V g  is a ground voltage.  
      In the reset period R 4 , while the rising pulse is applied, a weak discharge occurs in the discharge cells, negative wall charges are accumulated near the scan electrodes Y 1 , . . . , Y n , and positive wall charges are accumulated near the sustain electrodes X 1 , . . . , X m  and the address electrodes A 1 , . . . , A m . While the falling pulse is applied, a weak discharge occurs in the discharge cells, the negative wall charges accumulated near the scan electrodes Y 1 , . . . , Y n  are erased, and thus the positive wall charges accumulated near the sustain electrodes X 1 , . . . , X n  and the address electrodes A 1 , . . . , A m  are also erased. Accordingly, wall charges in the entire discharge cells are uniformly distributed and initialized.  
      Then, in a mixing driving period M 4 , an address discharge and a sustain discharge are both performed.  
      First, in a first group address period P A1 , an address discharge is performed in the first discharge cell group G 1 . That is, a scan pulse sequentially having a fifth voltage V sch  which is a scan high voltage and a sixth voltage V sc1  which is a scan low voltage, is applied to the first scan electrode group Y 1 , . . . , Y n/2 . At this time, a display data signal having an eighth positive voltage V a  is applied to the address electrodes A 1 , . . . , A m  in synchronization with the scan pulse, and a seventh voltage V b  is continuously applied to the sustain electrodes X 1 , . . . , X n . The seventh voltage V b  may be equal to the first voltage V s . By applying the display data signal and the scan pulse, an address discharge is performed between the address electrodes A 1 , . . . , A m  and the scan electrodes Y 1 , . . . , Y n/2  in the discharge cells. Accordingly, negative wall charges are accumulated near the sustain electrodes X 1 , . . . , X n  and positive wall charges are accumulated near the scan electrodes Y 1 , . . . , Y n . Meanwhile, a third voltage V g  is applied to the second scan electrode group Y n/2+1 , . . . , Y n .  
      Then, in a first group sustain period P S1 , a sustain discharge is performed in the first discharge cell group G 1 . First, while the first voltage V s  and the third voltage V g  are sequentially applied to all the scan electrodes Y 1 , . . . , Y n , the third voltage V g  and the first voltage V s  are sequentially applied to all the sustain electrodes X 1 , . . . , X n .  
      If the first voltage V s  is applied to the scan electrodes Y 1 , . . . , Y n  and the third voltage V g  is applied to the sustain electrodes X 1 , . . . , X n , since positive wall charges are accumulated near scan electrodes and negative wall charges are accumulated near sustain electrodes, in discharge cells in which an address discharge has been performed, that is, in the first discharge cell group G 2  in which an address discharge has been performed in the first group address period P A1 , a sustain discharge is performed by the first voltage V s  applied to the scan electrodes Y 1 , . . . , Y n  and the third voltage V g  applied to the sustain electrodes X 1 , . . . , X n .  
      After the sustain discharge is performed, negative wall charges are accumulated near the scan electrodes and positive wall charges are accumulated near the sustain electrodes. Meanwhile, since no wall charge is accumulated near scan electrodes and sustain electrodes of discharge cells in which no address discharge has been performed, that is, near scan electrodes and sustain electrodes of discharge cells belonging to the second discharge cell group G 2 , a discharge start voltage is not created and no sustain discharge is performed even when the first voltage V s  is applied to the scan electrodes Y 1 , . . . , Y n  and the third voltage V g  is applied to the sustain electrodes X 1 , . . . , X n . Thus, the state of wall charges in the discharge cells belonging to the second discharge cell group G 2  is maintained at the state of wall charges initialized in the reset period R 4 .  
      Then, if the third voltage V g  is applied to the scan electrodes Y 1 , . . . , Y n  and the first voltage V s  is applied to the sustain electrodes X 1 , . . . , X n , a sustain discharge is performed in the discharge cells belonging to the first discharge cell group G 1 . After the sustain discharge is performed, negative wall charges are accumulated near the sustain electrodes and positive wall charges are accumulated near the scan electrodes. Meanwhile, in the discharge cells belonging to the second discharge cell group G 2 , no sustain discharge is performed even when the third voltage V g  and the first voltage V s  are respectively applied to the scan electrodes Y 1 , . . . , Y n  and the sustain electrodes X 1 , . . . , X n .  
      The sustain discharge which is performed as described above, includes a sustain discharge in which the first voltage V s  is applied to the scan electrodes Y 1 , . . . , Y n  and the third voltage V g  is applied to the sustain electrodes X 1 , . . . , X n , and a sustain discharge in which the third voltage V g  is applied to the scan electrodes Y 1 , . . . , Y n  and the first voltage V s  is applied to the sustain electrodes X 1 , . . . , X n .  
      Then, in a second group address period P A2 , an address discharge is performed sequentially in the second discharge cell group G 2 . That is, a scan pulse sequentially having a fifth voltage V sch  which is a scan high voltage and a sixth voltage V sc1  which is a scan low voltage, is applied to the second scan electrode group Y n/2+1 , . . . , Y n . At this time, a display data signal having an eighth voltage V a  which is an address voltage is applied to the address electrodes A 1 , . . . , A m  in synchronization with the scan pulse, and a seventh voltage V b  is applied to the sustain electrodes X 1 , . . . , X n . By applying the display data signal and the scan pulse, an address discharge is performed between the address electrodes A 1 , . . . , A m  and the scan electrodes Y 1 , . . . , Y n , so that negative wall charges are accumulated near the sustain electrodes in the discharge cells belonging to the second discharge cell group G 2  and positive wall charges are accumulated near the scan electrodes in the discharge cells. Meanwhile, the third voltage V g  is applied to the first scan electrode group Y 1 , . . . , Y n/2 .  
      Then, a correction sustain period C 4  including a selection sustain period AS 4  and a common sustain period CS 4  is performed. Referring to  FIG. 8 , in the selection sustain period AS 4 , a sustain discharge is selectively performed in the first discharge cell group G 1  and the second discharge cell group G 2 . Since the sustain discharge is once performed in the first discharge cell group G 1  and no sustain discharge is performed in the second discharge cell group G 2  in the mixing driving period M 4 , the sustain discharge is selectively performed for each discharge cell group in the selection sustain period AS 4 . Thus, the first voltage V s  and a second voltage V m  lower than the first voltage V s  are sequentially applied to the first scan electrode group Y 1 , . . . , Y n/2 , and the first voltage V s  and the third voltage V g  are sequentially applied to the second scan electrode group Y n/2+1 , . . . , Y n . In some embodiments, a period T 2  in which the first voltage V s  is applied to the second scan electrode group Y n/2+1 , . . . , Y n  is longer than a period T 1  in which the first voltage V s  is applied to the first scan electrode group Y 1 , . . . , Y n/2 . For example, the period T 1  is half of the period T 2 . Meanwhile, the third voltage V g  and the first voltage V s  are sequentially applied to all the sustain electrodes X 1 , . . . , X n . As illustrated in the drawing, if the third voltage V g  is applied to the sustain electrodes X 1 , . . . , X n  and the first scan electrode group Y 1 , . . . , Y n/2  and the first voltage V s  is applied to the second scan electrode group Y n/2+1 , . . . , Y n , no sustain discharge is performed in the discharge cells belonging to the first discharge cell group G 1 , while a sustain discharge is performed in the discharge cells belonging to the second discharge cell group G 2 . Thus, in the discharge cells belonging to the first discharge cell group G 1 , the positive wall charges formed in the first group sustain period P A1  are accumulated near scan electrodes and negative wall charges are accumulated near sustain electrodes. In the discharge cells belonging to the second discharge cell group G 2 , negative wall charges are accumulated near scan electrodes and positive wall charges are formed near sustain electrodes.  
      Then, when the third voltage V g  is applied to the sustain electrodes X 1 , . . . , X n , the first voltage V s  is applied to the first scan electrode group Y 1 , . . . , Y n/2 , and the first voltage V s  is applied to the second sustain electrode group Y n/2+1 , . . . , Y n , a sustain discharge is performed in the discharge cells belonging to the first discharge cell group G 1 . Meanwhile, due to the sustain discharge of the first discharge cell group G 1 , negative wall charges are accumulated near the scan electrodes of the discharge cells belonging to the first discharge cell group G 1  and positive wall charges are accumulated near the sustain electrodes of the discharge cells belonging to the first discharge cell group G 1 . Meanwhile, since the third voltage V g  is continuously applied to the sustain electrodes of the second discharge cell group G 2  and the first voltage V s  is continuously applied to the scan electrodes of the second discharge cell group G 2 , more positive wall charges are accumulated in addition to positive wall charges previously accumulated, near the sustain electrodes of the second discharge cell group G 2 , and more negative wall charges are accumulated in addition to negative wall charges previously accumulated, near the scan electrodes of the second discharge cell group G 2 .  
      Then, while the third voltage V g  is applied to the sustain electrodes X 1 , . . . , X n , a second voltage V m  which is an intermediate voltage between the first voltage V s  and the third voltage V g  is applied to the first scan electrode group Y 1 , . . . , Y n/2  and the first voltage V s  is applied to the second scan electrode group Y n/2+1 , . . . , Y n . That is, since the second voltage V m  lower than the first voltage V s  is applied to the first scan electrode group Y 1 , . . . , Y n/2 , a discharge start voltage is not created and no sustain discharge is performed in the first scan electrode group Y 1 , . . . , Y n/2 . However, since the first voltage V s  is applied to the second scan electrode group Y n/2+1 , . . . , Y n , a sustain discharge is performed in the second scan electrode group Y n/2+1 , . . . , Y n . After the selection sustain period AS 4  is terminated, more negative wall charges are accumulated in addition to negative wall charges previously accumulated near the scan electrodes and more positive wall charges are accumulated near the sustain electrodes, due to the application of the second positive voltage V m  to the scan electrodes. Meanwhile, since the sustain charge is performed in the discharge cells of the second discharge cell group G 2 , positive wall charges are accumulated near the scan electrodes in the discharge cells and negative wall charge are accumulated near the sustain electrodes in the discharge cells. Here, since the period T 2  in which the first voltage V s  was applied to the second discharge cell group G 2  is longer than the period T 1  in which the first voltage V s  was applied to the first discharge cell group G 1 , wall charges are further accumulated by the increased amount of wall charges due to the application of the second voltage V m  to the first discharge cell group G 1 .  
      As a result, the sustain discharge is once performed only in the second discharge cell group G 2 .  
      Then, in the common sustain period CS 4 , a sustain discharge is performed in both the first discharge cell group G 1  and the second discharge cell group G 2 .  
      The number of total sustain discharge operations occurring before the common sustain period CS 4  is 1 for the each of the first discharge cell group G 1  and the second discharge cell group G 2 . If a gray scale weight of the fourth sub-field SF 4  is  8 ,  7  sustain discharge operations must be additionally performed in the common sustain period CS 4 .  
      A sustain pulse sequentially having the first voltage V s  and the third voltage V g  is repeatedly applied to all the scan electrodes Y 1 , . . . , Y n , and a sustain pulse sequentially having the third voltage V g  and the first voltage V s  is repeatedly applied to all the sustain electrodes X 1 , . . . , X n . The third voltage V g  is applied to the address electrodes A 1 , . . . , A m .  
      When the common sustain period CS 4  is started, negative wall charges are formed near the scan electrodes of the first discharge cell group G 1 , positive wall charges are formed near the sustain electrodes of the first discharge cell group G 1 , positive wall charges are formed near the scan electrodes of the second discharge cell group G 2 , and negative wall charges are formed near the sustain electrodes of the second discharge cell group G 2 .  
      When the first voltage V s  is first applied to all the scan electrodes Y 1 , . . . , Y n  in the common sustain period CS 4 , no sustain discharge is performed in the first discharge cell group G 1  and a sustain discharge is performed in the second discharge cell group G 2  according to the state of wall charges previously formed in the discharge cells, so that negative wall charges are performed near the scan electrodes of the second discharge cell group G 2  and positive wall charges are formed near the sustain electrodes of the second discharge cell group G 2 . When the third voltage V g  is applied to all the scan electrodes Y 1 , . . . , Y n , a sustain discharge is performed in all the discharge cells in the state where wall charges have been formed. Thereafter, if a sustain pulse is continuously and repeatedly applied, the sustain discharge is repeatedly performed in all the discharge cells.  
      As illustrated in  FIGS. 7 and 8 , a sustain discharge period is performed for each discharge cell group just after addressing is performed for each discharge cell group, a wait period between an address discharge and a sustain discharge is reduced compared to the conventional technique. This stabilizes the discharge characteristic of the sustain discharge. Also, when the number of sustain discharge operations is corrected in the correction sustain period C 4 , the first voltage V s , the first voltage V s , and the third voltage V g  are sequentially applied to the scan electrodes of the second discharge cell group G 2 , while the third voltage V g , the first voltage V s , and the second voltage V m  are sequentially applied to the scan electrodes of the first discharge cell group G 1 . Thus, it is possible to compensate for higher quantities of negative wall charges accumulated near the scan electrodes of the first discharge cell group G 1  than near the scan electrodes of the second discharge cell group G 2 . Accordingly, the sustain discharge is uniformly performed in the common sustain period CS 4  so that the brightness of actual sustain light is substantially uniform.  
       FIG. 9  is a timing diagram of driving signals in the fourth sub-field SF 4  illustrated in  FIG. 6 , according to another embodiment.  
      The driving signals illustrated in  FIG. 9  are similar to the driving signals illustrated in  FIG. 7 , except for driving signals applied in the correction sustain period C 4 . Accordingly, a description only regarding the correction sustain period C 4  will be given below  
      The correction sustain period C 4  of  FIG. 9  will be described with reference to  FIG. 10 .  
      In the embodiment illustrated in  FIG. 7 , during the selection sustain period AS 4  in the correction sustain period C 4 , a period in which the first voltage V s  is applied to the second scan electrode group Y n/2+1 , . . . , Y n  is longer than a period in which the first voltage V s  is applied to the first scan electrode group Y 1 , . . . , Y n/2 . In the embodiment illustrated in  FIG. 9 , during the selection sustain period AS 4  in the correction sustain period C 4 , a fourth voltage V x  higher than the first voltage V s  is applied to the second scan electrode group Y n/2+1 , . . . , Y n  while the first voltage V s  is applied to the first scan electrode group Y 1 , . . . , Y n/2 .  
      That is, in the selection sustain period AS 4 , the third voltage V g , the fourth voltage V x  higher than the first voltage V s , and the third voltage V g  are sequentially applied to the second scan electrode group Y n/2+1 , . . . , Y n , while the third voltage V g , the first voltage V s , and the second voltage V m  lower than the first voltage V s  are sequentially applied to the first scan electrode group Y 1 , . . . , Y n/2 . Also, the third voltage V g  and the first voltage V s  are sequentially applied to all the sustain electrodes X 1 , . . . , X n .  
      Accordingly, in the common sustain period CS 4 , a sustain discharge is uniformly performed in each of the first discharge cell group G 1  and the second discharge cell group G 2 , so that the brightness of sustain light is substantially uniformly generated.  
      As described above, according to the present invention, the following effects can be obtained.  
      First, by grouping pairs of scan electrodes and sustain electrodes defining discharge cells and sequentially performing addressing and a sustain discharge on respective groups, a wait period between an address discharge and a sustain discharge is reduced compared to the conventional ADS technique. This results in more uniform accumulation of wall charges in the discharge cells and better stabilizing of the discharge characteristic of the sustain discharge.  
      Second, in order to mitigate for a difference in the states and quantity of wall charges between a first discharge cell group and a second discharge cell group caused by a second positive voltage applied to a first scan electrode group, a the sustain discharge for the first discharge cell group is less than the sustain discharge for the second discharge cell group. This is accomplished by, for example, a first positive voltage is applied to a second scan electrode group longer than to the first scan electrode group or a fourth positive voltage higher than the first voltage is applied to the second scan electrode group in a selection sustain period. Accordingly, a sustain discharge can be more uniformly performed.  
      While the present invention has been particularly shown and described with reference to certain embodiments thereof, it will be understood by those of ordinary skill in the art that various changes in form and details may be made therein without departing from the spirit and scope of the present invention.