Patent Publication Number: US-7583240-B2

Title: Method of driving plasma display panel

Description:
THIS APPLICATION IS A U.S. NATIONAL PHASE APPLICATION OF PCT INTERNATIONAL APPLICATION PCT/JP2005/001436. 
     TECHNICAL FIELD 
     The present invention relates to a method of driving a plasma display panel. 
     BACKGROUND ART 
     An alternating current surface-discharging panel representing a plasma display panel (hereinafter abbreviated as a panel) has a plurality of discharge cells that are formed between a front panel and rear panel facing with each other. In the front panel, a plurality of display electrodes, each formed of a pair of scan electrode and sustain electrode, are formed on a front glass substrate in parallel with each other. A dielectric layer and a protective layer are formed to cover these display electrodes. On the other hand, in the rear panel, a plurality of data electrodes is formed in parallel with each other on a rear glass substrate. A dielectric layer is formed on the data electrodes to cover them. Further, a plurality of barrier ribs are formed on the dielectric layer in parallel with the data electrodes. Phosphor layers are formed on the surface of the dielectric layer and the side faces of the barrier ribs. Then, the front panel and the rear panel are faced with each other and hermetically sealed together so that the display electrodes and data electrodes intersect with each other and a discharge gas is filled into an internal discharge space formed therebetween. A discharge cell is formed at a part where a display electrode is faced with a corresponding data electrode. In a panel structured as above, ultraviolet light is generated by gas discharge in each discharge cell. This ultraviolet light excites respective phosphors to emit R, G, or B color, for color display. 
     A general method of driving a panel is a so-called sub-field method: one field period is divided into a plurality of sub-fields and combination of light-emitting sub-fields provides gradation images for display. Among such sub-field methods, a novel driving method of minimizing light emission unrelated to gradation representation to improve a contrast ratio is disclosed in Japanese Patent Unexamined Publication No. 2000-242224. 
       FIG. 8  shows an example of driving waveforms of the conventional plasma display disclosed in the above publication. These driving waveforms are described hereinafter. One filed period is composed of n sub-fields, each having an initializing period, writing period, and sustaining period. The sub-fields are abbreviated as a first SF, second SF, and so on to an n-th SF. As described below, in sub-fields except the first SF among these n sub-fields, initializing operation is performed only on discharge cells that have been lit during the sustaining period of the previous sub-field. 
     In the former half of the initializing period of the first SF, application of a gradually-increasing ramp voltage to scan electrodes causes weak discharge so that wall electric charge necessary for writing operation is formed on each electrode. At this time, in order to optimize the wall electric charge afterwards, excessive wall electric charge is formed. In the following latter half of the initializing period, application of a gradually-decreasing ramp voltage to the scan electrodes causes weak discharge again, to weaken the wall electric charge excessively stored on each electrode and adjust the wall electric charge to a value appropriate for each discharge cell. 
     In the writing period of the first SF, writing discharge is caused in discharge cells to be lit. In the sustaining period of the first SF, sustain pulses are applied to scan electrodes and sustain electrodes to cause sustaining discharge in the discharge cells in which writing discharge has occurred. Thus, the phosphors of the corresponding discharge cells emit light for image display. 
     In the following initializing period of the second SF, the same driving waveforms as the latter half of the initializing period of the first SF, i.e. a gradually-decreasing ramp voltage, is applied to the scan electrodes. This is because the wall charge necessary for writing operation is provided at the time of sustaining charge and thus the former half of the initializing period need not be provided independently. Therefore, weak discharge occurs in the discharge cells in which sustaining discharge has occurred in the first SF, to weaken the wall discharge excessively stored on each electrode and adjust the wall discharge to a value appropriate for each discharge cell. In discharge cells in which no sustaining discharge has occurred, the wall charge at the time of completion of the initializing period of the first SF is maintained. Thus, discharge does not occur. 
     As described above, the initializing operation in the first SF is all-cell initializing operation in which all the cells are discharged. The initializing operation in the second SF or after is selective initializing operation in which only discharge cells subjected to sustaining discharge are initialized. For this reason, light emission unrelated to display is weak discharge occurring in the initializing operation of the first SF only. Thus, images with a high contrast can be displayed. 
     With recent higher definition of a panel, the number of discharge cells is increasing and the period of time used for writing operation of one discharge cell is reducing. In addition, to improve image display quality, such as improvement of dynamic false contour, writing operation at higher speeds, such as discussion on a driving method for increasing the number of sub-fields, is required. 
     Now, the all-cell initializing operation for initializing all the discharge cells serves to form wall discharge necessary for writing operation, as described above. The all-cell initializing operation also serves to generate priming (priming=excited particles) to reduce discharge delay and stabilize writing discharge. Therefore, for stable high-speed writing operation, a method of increasing priming is effective. However, simply increasing the number of the all-cell initializing operations increases black picture level and decreases contrast, thus deteriorating image display quality. 
     The method of driving a plasma display panel of the present invention addresses the above problem, and aims to provide a method of driving a plasma display panel that enables stable high-speed writing operation and inhibits an increase in black picture level. 
     SUMMARY OF THE INVENTION 
     A method of driving a plasma display panel of the present invention, the plasma display panel including discharge cells, each formed at an intersection of a scan electrode and a sustain electrode, and a data electrode, the method comprising: dividing one field period into a plurality of sub-fields, each having an initializing period, writing period, and sustaining period; in the initializing periods of the plurality of sub-fields, performing one of all-cell initializing operation and selective initializing operation, wherein, in the all-cell initializing operation, initializing discharge is performed in all the discharge cells for displaying an image, and, in the selective initializing operation, initializing discharge is selectively performed only in the discharge cells subjected to sustaining discharge in the sub-field immediately before the sub-filed; and, according to a signal of an image to be displayed, determining the initializing operation in the initializing period of each sub-field to be one of the all-cell initializing operation and the selective initializing operation. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view illustrating an essential part of a panel for use in a first exemplary embodiment of the present invention. 
         FIG. 2  is a diagram illustrating an array of electrodes of the panel. 
         FIG. 3  is a circuit block diagram of a plasma display device for use in the method of driving a panel. 
         FIG. 4  is a diagram showing driving waveforms applied to respective electrodes of the panel. 
         FIG. 5  is a diagram illustrating a structure of sub-fields in the method of driving a panel. 
         FIG. 6  is a circuit block diagram of a plasma display device for use in a method of driving a panel in accordance with a second exemplary embodiment. 
         FIG. 7  is a diagram illustrating a structure of sub-fields in the method of driving a panel. 
         FIG. 8  is a diagram showing driving waveforms of a conventional panel. 
     
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     Methods of driving a panel in accordance with exemplary embodiments of the present invention are described hereinafter with reference to the accompanying drawings. 
     FIRST EXEMPLARY EMBODIMENT 
       FIG. 1  is a perspective view illustrating an essential part of a panel for use in the first exemplary embodiment of the present invention. Panel  1  is composed of front substrate  2  and rear substrate  3  that are made of glass and faced with each other so as to form a discharge space therebetween. On front substrate  2 , a plurality of display electrodes, each formed of a pair of scan electrode  4  and sustain electrode  5 , is formed in parallel with each other. Dielectric layer  6  is formed to cover scan electrodes  4  and sustain electrodes  5 . On dielectric layer  6 , protective layer  7  is formed. On the other hand, on rear substrate  3 , a plurality of data electrodes  9  covered with insulating layer  8  is provided. Barrier ribs  10  are provided on insulating layer  8  between data electrodes  9  in parallel therewith. Also, phosphor layers  11  are provided on the surface of insulating layer  8  and the side faces of barrier ribs  10 . Front substrate  2  and rear substrate  3  are faced with each other in a direction in which scan electrodes  4  and sustain electrodes  5  intersect with data electrodes  9 . In a discharge space formed therebetween, a mix gas, e.g. neon-xenon, is filled as a discharge gas. 
       FIG. 2  is a diagram showing an array of electrodes of the panel for use in the first exemplary embodiment of the present invention. N scan electrodes SCN  1  to SCNn (scan electrodes  4  in  FIG. 1 ) and n sustain electrodes SUS  1  to SUSn (sustain electrodes  5  in  FIG. 1 ) are alternately disposed in a row direction. M data electrodes D 1  to Dm (data electrodes  9  in  FIG. 1 ) are disposed in a column direction. A discharge cell is formed at a portion in which a pair of scan electrode SCNi and sustain electrode SUSi (i=1 to n) intersect with one data electrode Dj (j=1 to m). Thus, m×n discharge cells are formed in the discharge space. 
       FIG. 3  is a circuit diagram of a plasma display device for use in the method of driving a panel in accordance with the first exemplary embodiment. The plasma display panel device includes panel  1 , data electrodes driver circuit  12 , scan electrodes driver circuit  13 , sustain electrodes driver circuit  14 , timing-generating circuit  15 , analog-to-digital (A/D) converter  18 , line number converter  19 , and sub-field converter  20 , average picture level (APL) detector  30 , and power supply circuits (not shown). 
     With reference to  FIG. 3 , image signal VD is fed into A/D converter  18 . Horizontal synchronizing signal H and vertical synchronizing signal V are fed into timing-generating circuit  15 , A/D converter, line number converter  19 , and sub-field converter  20 . A/D converter  18  converts image signal VD into image data of digital signals, and feeds the digital image data into line number converter  19  and APL detector  30 . APL detector  30  detects an average picture level of the image data. Line number converter  19  converts the image data into image data corresponding to the number of pixels of panel  1 , and feeds the image data to sub-field converter  20 . Sub-field converter  20  divides the image data of respective pixels into a plurality of bits corresponding to a plurality of sub-fields. The image data per sub-field is fed into data electrodes driver circuit  12 . Data electrodes driver circuit  12  converts the image data per sub-field into signals corresponding to respective data electrodes D 1  to Dm, and drives respective data electrodes D 1  to Dm. 
     Timing-generating circuit  15  generates timing signals based on horizontal synchronizing signal H and vertical synchronizing signal V, and feeds the timing signals to scan electrodes driver circuit  13  and sustain electrodes driver circuit  14 , respectively. Responsive to the timing signals, scan electrodes driver circuit  13  feeds driving waveforms to scan electrodes SCN 1  to SCNn. Responsive to the timing signals, sustain electrodes driver circuit  14  feeds driving waveforms to sustain electrodes SUS 1  to SUSn. At this time, timing-generating circuit  15  controls the driving waveforms, according to an APL supplied from APL detector  30 . Specifically, as described later, according to the APL, timing-generating circuit  15  determines to perform one of all-cell initializing operation and selective initializing operation in each of the sub-fields comprising one field and, controls the number of the all-cell initializing operations in one field. 
     Next, driving waveforms for driving the panel and their operation are described.  FIG. 4  is a diagram showing driving waveforms applied to respective electrodes of the panel in accordance with the first exemplary embodiment of the present invention The diagram shows waveforms of a sub-field having an initializing period in which all-cell initializing operation is performed (hereinafter abbreviated as “all-cell initializing sub-field”) and a sub-field having an initializing period in which selective initializing operation is performed (hereinafter abbreviated as “selective initializing sub-field”). In  FIG. 4 , for simple description, the first sub-field is shown as an all-cell initializing sub-field, and the second sub-field is shown as a selective initializing sub-field. 
     First, the driving waveforms and operation of the all-cell initializing sub-field are described. 
     In the initializing period, while data electrodes D 1  to Dm and sustain electrodes SUS 1  to SUSn are kept at 0V, a ramp voltage gradually increasing from voltage Vp (V) not higher than a discharge-starting voltage to voltage Vr (V) exceeding the discharge-starting voltage is applied to scan electrodes SCN 1  to SCNn. This causes a first weak initializing discharge in all the discharge cells. Thus, negative wall voltage accumulates on scan electrodes SCN 1  to SCNn and positive wall voltage accumulates on sustain electrodes SUS 1  to SUSn and data electrodes D 1  to Dm. Now, the wall voltage on electrodes indicates a voltage generated by wall electric charge that has accumulated on the dielectric layers or phosphor layers covering the electrodes. Thereafter, sustain electrodes SUS 1  to SUSn are kept at positive voltage Vh (V), and a ramp voltage gradually decreasing from voltage Vg (V) to voltage Va(V) is applied to scan electrodes SCN 1  to SCNn. This causes a second weak initializing discharge in all the discharge cells. The wall voltage on scan electrodes SCN 1  to SCNn and the wall voltage on sustain electrodes SUS 1  to SUSn are weakened, and the wall voltage on data electrodes D 1  to Dm are adjusted to a value appropriate for writing operation. In this manner, the initializing operation in the all-cell initializing sub-field is all-cell initializing operation in which initializing discharge is performed in all the discharge cells. 
     In the subsequent writing period, scan electrodes SCN 1  to SCNn are held at voltage Vs (V) once. Next, positive write pulse voltage Vw (V) is applied to data electrode Dk of discharge cells to be lit in the first row among data electrodes D 1  to Dm, and scan pulse voltage Vb (V) is applied to scan electrode SCN 1  in the first row. At this time, the voltage at the intersection between data electrode Dk and scan electrode SCN 1  is addition of the wall voltage on data electrode Dk and the wall voltage on scan electrode SCN 1  to externally applied voltage (Vw-Vb) (V), thus exceeding the discharge-starting voltage. This causes writing discharge between data electrode Dk and scan electrode SCN 1 , and between sustain electrode SUS 1  and scan electrode SCN 1 . Thus, positive wall voltage accumulates on scan electrode SCN 1 , negative wall voltage accumulates on sustain electrode SUS 1 , and negative wall voltage also accumulates on data electrode Dk in this discharge cell. Thus, writing operation is performed in the discharge cells to be lit in the first row to accumulate wall voltage on respective electrodes. On the other hand, the intersection of a data electrode to which positive write pulse voltage Vw (V) is not applied, and scan electrode SCN 1  does not exceed the discharge-starting voltage. Thus, no writing discharge occurs in this intersection. Such writing operation is sequentially performed on the cells in the second row to the n-th row, and the writing period is completed. 
     In the subsequent sustaining period, first, sustain electrodes SUS 1  to SUSn are reset to 0V, and positive sustain pulse voltage Vm (V) is applied to scan electrodes SCN 1  to SCNn. At this time, in the discharge cells in which writing discharge has occurred, the voltage across scan electrode SCNi and sustain electrode SUSi amounts to addition of the wall voltage on scan electrode SCNi and the wall voltage on sustain electrode SUSi to sustain pulse voltage Vm (V), thus exceeding the discharge-starting voltage. This causes sustaining discharge between scan electrode SCNi and sustain electrode SUSi. Thus, negative wall voltage accumulates on scan electrode SCNi, and positive wall voltage accumulates on sustain electrode SUSi. At this time, positive wall voltage also accumulates on data electrode Dk. Incidentally, in the discharge cells in which no writing discharge has occurred in the writing period, no sustaining discharge occurs, and the state of the wall voltage at the time of completion of the initializing period is maintained. Sequentially, scan electrodes SCN 1  to SCNn are reset to 0V, and positive sustain pulse voltage Vm (V) is applied to sustain electrodes SUS 1  to SUSn. In the discharge cells in which sustaining discharge has occurred, the voltage across sustain electrode SUSi and scan electrode SCNi exceeds the discharge-starting voltage. This causes sustaining discharge between sustain electrode SUSi and scan electrode SCNi again. Thus, negative wall voltage accumulates on sustain electrode SUSi, and positive wall voltage accumulates on scan electrode SCNi. Applying sustain pulse alternately across scan electrodes SCN 1  to SCNn and sustain electrodes SUS 1  to SUSn in a similar manner can continue sustaining discharge in the discharge cells in which writing discharge has occurred in the writing period. Incidentally, at the end of the sustaining period, the wall voltage on sustain electrodes SCN 1  to SCNn and sustain electrodes SUS 1  to SUSn are erased by applying a so-called thin pulse across scan electrodes SCN 1  to SCNn and sustain electrodes SUS 1  to SUSn while leaving the positive wall voltage on data Dk. Thus, the sustaining operation in the sustaining period is completed. 
     Next, the driving waveforms of the selective sub-field and their operation are described. 
     In the initializing period, sustain electrodes SUS 1  to SUSn are kept at voltage Vh (V), data electrodes D 1  to Dm are kept at 0V, and a ramp voltage gradually decreasing from voltage Vq (V) to voltage Va(V) is applied to scan electrodes SCN 1  to SCNn. This causes weak initializing discharge in the discharge cells in which sustaining discharge has occurred in the sustaining period of the previous sub-field. The wall voltage on scan electrode SCNi and the wall voltage on sustain electrode SUSi are weakened, and the wall voltage on data electrode Dk is adjusted to a value appropriate for writing operation. On the other hand, in the discharge cells in which writing discharge or sustaining discharge has not occurred in the previous sub-field, no discharge occurs and the state of the wall charge at the time of completion of the initializing period of the previous sub-field is maintained. In this manner, in the initializing period of the selective initializing sub-field is selective initializing operation in which initializing discharge occurs in the discharge cells subjected to sustaining discharge in the previous sub-field. 
     The writing period and sustaining period are the same as those of the all-cell initializing sub-field. Thus, the description is omitted. 
     Next, a description is provided of a structure of the sub-fields in the method of driving a panel of this embodiment. In this embodiment, one field is composed of 11 sub-fields. In the description, respective sub-fields have a brightness weight of 1, 2, 3, 7, 11, 14, 23, 37, 39, 57, or 61. However, the number of sub-fields or the brightness weight of each sub-field is not limited to the above values. 
       FIG. 5  is a diagram illustrating a structure of each sub-field (SF) in the method of driving a panel of the first exemplary embodiment. The sub-field structure is changed according to the APL of the signal of an image to be displayed.  FIG. 5A  shows a structure to be used for an image signal having an APL ranging from 0 to 1.5%. In this SF structure, all-cell initializing operation is performed only in the initializing period of the first SF, and selective initializing operation is performed in the initializing periods of the second to 11th SFs.  FIG. 5B  shows a structure to be used for an image signal having an APL ranging from 1.5 to 5%. In this SF structure, all-cell initializing operation is performed in the initializing periods of the first and 10th SFs, and selective initializing operation is performed in the initializing periods of the second to ninth, and 11th SFs.  FIG. 5C  shows a structure to be used for an image signal having an APL ranging from 5 to 10%. In this SF structure, all-cell initializing operation is performed in the initializing periods of the first, fourth and 10th SFs, and selective initializing operation is performed in the second, third, fifth to ninth, and 11th SFs.  FIG. 5D  shows a structure to be used for an image signal having an APL ranging from 10 to 15%. In this SF structure, all-cell initializing operations is performed in the initializing periods of the first, fourth, eighth and 10th SFs, and selective initializing operation is performed in the initializing periods of the second, third, fifth to seventh, ninth and 11th SFs.  FIG. 5E  shows a structure to be used for an image signal having an APL ranging from 15 to 100%. In this SF structure, all-cell initializing operation is performed in the initializing periods of the first, fourth, sixth, eighth and 10th SFs, and selective initializing operation is performed in the initializing periods of the second, third, fifth, seventh, ninth and 11th SFs. Table 1 shows a relation between the above SF structure and APL. 
     
       
         
           
               
               
               
               
             
               
                   
                 TABLE 1 
               
               
                   
                   
               
               
                   
                   
                 Number of all-cell 
                   
               
               
                   
                   
                 initializing 
                 All-cell initializing 
               
               
                   
                 APL (%) 
                 operations (times) 
                 SFs 
               
               
                   
                   
               
             
            
               
                   
                   0 to 1.5 
                 1 
                 1 
               
               
                   
                 1.5 to 5   
                 2 
                 1,       10 
               
               
                   
                  5 to 10 
                 3 
                 1,4,     10 
               
               
                   
                 10 to 15 
                 4 
                 1,4,    8,10 
               
               
                   
                  15 to 100 
                 5 
                 1,4,6,  8,10 
               
               
                   
                   
               
            
           
         
       
     
     In this manner, in the method of driving a panel of the first exemplary embodiment, the structure of SFs is controlled so that the number of all-cell initializing operations is reduced at a lower APL. Although the number of all-cell initializing operations per field is determined depending on the APL, many forms can be considered for the determination of the position of the sub-fields in which all-cell initializing operation is performed. However, in consideration of the effect of the all-cell initializing operation, i.e. formation of wall voltage for writing operation and generation of priming, it is desirable to distribute the SFs having all-cell initializing periods. It is especially desirable that these SFs are not disposed successively. The reason why the all-cell initializing period is placed not in the 11th SF but in the 10th SF in Table 1 is to avoid successive placement of the all-cell initializing periods, i.e. the 11th SF and the first SF. 
     Additionally, in the first exemplary embodiment, the SFs having initializing periods subjected to all-cell initializing operation are preferentially placed at the former part or latter part of one field period rather than the middle part of one field. In other words, when the number of all-cell initializing operations are sequentially reduced from 5 to 1, the all-cell initializing SF is eliminated from the 6th SF in the middle part first, and then sequentially eliminated from the 8th, 4th, and 10th in order. The all-cell initializing periods should be eliminated from those least affecting the image display quality. This depends on the brightness weights of respective SFs or coding methods (how to assign sub-fields having brightness weights to respective gradation levels). Experiments have validated that elimination of all-cell initializing periods in the middle part of one field less affects the image quality when the weighting is made in an increasing order and the employed coding method is to express brightness using sub-fields in time order, like the first exemplary embodiment. Further, the all-cell initializing operation in the first SF largely affects the image display quality. This is because writing operation should securely be performed from the top SF, and priming for this writing operation is important when a dark image is displayed. The all-cell initializing operation in the SFs in the latter part is also important. This is because it is considered that excessive priming neutralizes the wall discharge on unlit discharge cells and thus destabilizes the writing operation in the following SFs when the discharge cells adjacent to the unlit cell light in a sub-filed having a large brightness weight. 
     As described above, in the first exemplary embodiment, because it is considered that there is no or a small area displaying a black picture when an image having a large APL is displayed, the number of all-cell initializing operations and thus priming are increased to stabilize discharge. In contrast, when an image having a low APL is displayed, it is considered that there is a large area displaying a black picture. Thus, the number of all-cell initializing operations is reduced to improve black display quality. Therefore, at a low APL, luminance in an area displaying black picture is low, and an image having high contrast can be displayed even when the image has areas having high luminance. 
     In the first exemplary embodiment, one field is composed of 11 SFs and the number of all-cell initializing operations is controlled to one to five times, as an example. However, the present invention is not limited to this example. Tables 2 and 3 show another example. 
     
       
         
           
               
               
               
               
             
               
                   
                 TABLE 2 
               
               
                   
                   
               
               
                   
                   
                 Number of all-cell 
                   
               
               
                   
                   
                 initializing 
                 All-cell initializing 
               
               
                   
                 APL (%) 
                 operations (times) 
                 SFs 
               
               
                   
                   
               
             
            
               
                   
                 0.0 to 1.5 
                 1 
                 1 
               
               
                   
                 1.5 to 5   
                 2 
                 1,     9  
               
               
                   
                  5 to 10 
                 3 
                 1,4,    9  
               
               
                   
                  10 to 100 
                 4 
                 1,4,  8, 10 
               
               
                   
                   
               
            
           
         
       
     
     
       
         
           
               
               
               
               
             
               
                   
                 TABLE 3 
               
               
                   
                   
               
               
                   
                   
                 Number of all-cell 
                   
               
               
                   
                   
                 initializing 
                 All-cell initializing 
               
               
                   
                 APL (%) 
                 operations (times) 
                 SFs 
               
               
                   
                   
               
             
            
               
                   
                 0.0 to 1.5 
                 1 
                 1 
               
               
                   
                 1.5 to 5   
                 2 
                 1,4 
               
               
                   
                  5 to 100 
                 3 
                 1,4,6 
               
               
                   
                   
               
            
           
         
       
     
     In Table 2, the number of all-cell initializing operations is controlled to one to four times, and the SFs in which all-cell initializing operation is performed are changed, as an example. In Table 3, the number of all-cell initializing operations is controlled to one to three times, and the SFs near the top part are initialized preferentially, as an example. 
     As described above, at a low APL, reducing the number of SFs each having an initializing period subjected to all-cell initializing operation, and, at a higher APL, increasing the number of SFs each having an initializing period subjected to all-cell initializing operation can achieve a method of driving a panel that enables stable high-speed writing and inhibits an increase in black picture level. 
     SECOND EXEMPLARY EMBODIMENT 
     The essential part of a panel and the array of electrodes for use in the second exemplary embodiment are similar to those of the first exemplary embodiment. Thus, the description thereof is omitted.  FIG. 6  is a circuit block diagram of a plasma display device for use in a method of driving a panel in accordance with the second exemplary embodiment. The same elements used in the first exemplary embodiment are denoted with the same reference marks and the description thereof is omitted. 
     Sub-field converter  20  divides image data of each pixel into a plurality of bits corresponding to a plurality of sub-fields (SFs), and supplies the image data per SF to data electrodes driving circuit  12  and light-emitting rate detector  31 . Light-emitting rate detector  31  detects a light-emitting rate of a predetermined SF, i.e. the light-emitting rate of the 10th SF in this secondary exemplary embodiment. 
     Timing-generating circuit  15  generates timing signals based on horizontal synchronizing signal H and horizontal synchronizing signal V, and supplies them to scan electrodes driving circuit  13  and sustain electrodes driving circuit  14 . Now, timing-generating circuit  15  controls a driving waveform according to an APL supplied from APL detector  30  and a light-emitting rate supplied from light-emitting rate detector  31 . Specifically, as described later, timing-generating circuit  15  determines the initializing operation in respective SFs constituting one field to be all-cell initializing or selective initializing, and controls the positions and number of all-cell initializing operations in one field. 
       FIG. 7  is a diagram illustrating a structure of SFs in the method of driving a panel in accordance with the second exemplary embodiment. The SF structure is changed according to an APL of an image to be displayed and a light-emitting rate of the 10th SF.  FIG. 7A  shows a structure to be used for an image signal having an APL ranging from 0 to 1.5%. In this SF structure, all-cell initializing operation is performed in the initializing period of the first SF only, irrelevant to the light-emitting rate of the 10th SF, and selective initializing operation is performed in the initializing periods of the second to 11th SFs.  7 B shows a structure to be used for an image signal having an APL ranging from 1.5 to 5%, and a light-emitting rate ranging from 0 to 1%. In this SF structure, all-cell initializing operation is performed in the initializing periods of the first and fourth SFs, and the selective initializing operation is performed in the initializing periods of the second, third, and fifth to 11th SFs.  7 C shows a structure to be used for an image signal having an APL ranging from 1.5 to 5% and a light-emitting rate of at least 1%. In this SF structure, all-cell initializing operation is performed in the initializing periods of the first and 10th SFs, and selective initializing operation is performed in the initializing periods of the second to ninth, and 11th SFs.  7 D shows a structure to be used for an image signal having an APL ranging from 15 to 100%. In this SF structure, all-cell initializing operation is performed in the initializing periods of the first, fourth, sixth, eighth, and 10th SFs, and selective initializing operation is performed in the initializing periods of the second, third, fifth, seventh, ninth, and 11th SFs, irrelevant to the light-emitting rate of the 10th SF. The structure used for an image signal having an APL ranging from 5 to 15% is not shown. Its SF structure is different from those described above. Table 4 shows a relation between a SF structure, APL, and light-emitting rate. 
     
       
         
           
               
               
               
               
             
               
                   
                 TABLE 4 
               
             
            
               
                   
                   
               
               
                   
                 Number of 
                   
                   
               
               
                   
                 all-cell 
                 Light-emitting rate 
               
               
                   
                 initializing 
                 of 10th SF 
               
            
           
           
               
               
               
               
               
               
            
               
                   
                 APL (%) 
                 operations 
                 0~1 
                 1~20 
                 20~100 
               
               
                   
                   
               
            
           
           
               
               
               
               
               
            
               
                   
                   0~1.5 
                 1 
                 1 
                   
               
            
           
           
               
               
               
               
               
            
               
                   
                 1.5~5   
                 2 
                 1,4 
                 1,  10 
               
            
           
           
               
               
               
               
               
               
            
               
                   
                  5~10 
                 3 
                 1,4,6 
                 1,4,    10 
                 1, 
               
               
                   
                   
                   
                   
                   
                 8,10 
               
               
                   
                 10~15 
                 4 
                 1,4,6,8 
                 1,4,  8,10 
                 1, 
               
               
                   
                   
                   
                   
                   
                 6,8,10 
               
            
           
           
               
               
               
               
               
            
               
                   
                  15~100 
                 5 
                 1,4,6,8,10 
               
               
                   
                   
               
            
           
         
       
     
     In this manner, the method of driving a panel of the second exemplary embodiment controls the SF structure to reduce the number of all-cell initializing operations at a lower APL. Further, even when the number of all-cell initializing operations is the same, attention is drawn to the light-emitting rate of the 10th SF. At a low light-emitting rate, all-cell initializing SFs are preferentially placed in the former part of one field period. At a high light-emitting rate, all-cell initializing SFs are preferentially placed at the latter part of one field period. However, even at a high light-emitting rate, the first SF is an all-cell initializing SF. 
     As described above, the number of all-cell initializing operations per field is determined depending on an APL, and the position of the SFs subjected to all-cell initializing operation is determined depending on a light-emitting rate. In consideration of the effect of the all-cell initializing operation, i.e. formation of wall voltage for writing operation and generation of priming, it is desirable to distribute the SFs having all-cell initializing periods. It is especially desirable that these SFs are not disposed successively. The reason why the all-cell initializing period is placed not in the 11th SF but in the 10th SF in Table 4 is to avoid successive placement of the all-cell initializing periods, i.e. 11th SF and the first SF. The reason why attention is drawn to a light-emitting rate of the 10th SF is that the 10th SF has the largest brightness weight in the SFs that can have all-cell initializing periods. Additionally, in the second exemplary embodiment, the SFs in which all-cell initializing operation is performed are preferentially placed in the former part or latter part of one field period rather than the middle part thereof. Then, at a low light-emitting rate of the 10th SF, all-cell initializing SFs are preferentially placed in the former part of one field period. At a high light-emitting rate of the 10th SF, all-cell initializing SFs are preferentially placed in the latter part of one field period. This is because, at a relatively low APL and a low light-emitting rate of the 10th SF, the entire screen is dark and writing operation must securely be performed from the top SF so that a dark image is displayed. Thus, priming for the writing operation is extremely important. On the other hand, at a relatively high light-emitting rate of the 10th SF, all-cell initializing operation in the SFs in the latter part is considered important. The reason is explained as follows. When sustaining discharge occurs in discharge cells adjacent to unlit discharge cells in the sustaining period, in a SF with a large brightness weight that is placed in the latter part of one field, charged particles generated by the sustaining discharge neutralize the wall charge on the unlit discharge cells, and the wall charge is insufficient for writing operation in the successive SF. The all-cell initializing operation in the SFs in the latter part can compensate this insufficient wall charge. 
     As described above, in the second exemplary embodiment, because it is considered that there is no or a small area displaying a black picture when an image having a large APL is displayed, the number of all-cell initializing operations and thus priming are increased to stabilize discharge. In contrast, when an image having a low APL is displayed, it is considered that there is a large area displaying a black picture, and thus the number of all-cell initializing operations is reduced to improve black display quality. Then, when an image having a low light-emitting rate in a predetermined SF (the 10th SF in the second exemplary embodiment) is displayed, all-cell initializing SFs are preferentially placed in the former part of one field period to ensure priming for writing from the top SF. In contrast, at a high light-emitting rate, all-cell initializing SFs are preferentially placed in the latter part of one field to form necessary wall charge again even if excessive priming neutralizes the wall charge on unlit discharge cells. Therefore, at a low APL, luminance in an area displaying black picture is low and an image having a high contrast ratio can be displayed even when the image has an area having high luminance. Further, placement of all-cell initializing SFs in most effective positions according to the light-emitting rate of a predetermined SF enables stable high-speed writing operation. 
     Also in the second exemplary embodiment, one field is composed of 11 SFs and the number of all-cell initializing operations is controlled to one to five times, as an example. However, the present invention is not limited to this example. 
     In the second exemplary embodiment, the 10th SF is used as a predetermined SF. However, any other field having a large brightness weight, such as the ninth or 11th, can be used. Further, a plurality of SFs having large brightness weights can be used in combination. 
     
       
         
           
               
               
               
               
             
               
                   
                 TABLE 5 
               
             
            
               
                   
                   
               
               
                   
                 Number of 
                   
                   
               
               
                   
                 all-cell 
                 Sum of light-emitting rates 
               
               
                   
                 initializing 
                 of 9th to 11th SFs 
               
            
           
           
               
               
               
               
               
            
               
                   
                 APL (%) 
                 operations 
                 Less than 3% 
                 3% or more 
               
               
                   
                   
               
            
           
           
               
               
               
               
               
            
               
                   
                  0~1.5 
                 1 
                 1 
                   
               
            
           
           
               
               
               
               
               
            
               
                   
                 1.5~5   
                 2 
                 1,4 
                 1,  9 
               
            
           
           
               
               
               
               
               
            
               
                   
                 5~10 
                 3 
                 1,4,    9 
                   
               
               
                   
                 10~100 
                 4 
                 1,4,  7,9 
               
               
                   
                   
               
            
           
         
       
     
     In Table 5, the number of all-cell initializing operations is controlled in the range of one to four times, and only when the number of all-cell initializing operations is two, the position of the all-cell initializing SFs is changed depending on the sum of the light-emitting rates of the ninth to 11th SFs, as an example. In this manner, at a high APL, the number of SFs having initializing periods subjected to all-cell initializing operation is increased. When an image having a low light-emitting rate of a SF with a large brightness weight is displayed, all-cell initializing SFs are preferentially placed in the former part of one field period. When an image having a high light-emitting rate of a SF with large brightness weight is displayed, all-cell initializing SFs are preferentially placed in the latter part of one field period. This method can provide a method of driving a panel that enables stable high-speed writing and inhibits an increase in black picture level. 
     The present invention can provide a method of driving a plasma display panel that enables stable high-speed writing and inhibits an increase in black picture level. 
     INDUSTRIAL APPLICABILITY 
     The method of driving a panel of this invention can drives a panel in such a manner that enables stable high-speed writing and inhibits an increase in black picture level. The present invention is useful as a display device using a panel.