Patent Publication Number: US-6667728-B2

Title: Plasma display panel and method of driving the same capable of increasing gradation display performance

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a technique of driving a plasma display panel and, more particularly, to a plasma display panel of an ALIS system and a method of driving this plasma display panel. 
     2. Description of the Related Art 
     Recently, as a plasma display panel (PDP) that is capable of obtaining a high definition and a high aperture ratio, there has been proposed a PDP of an ALIS (Alternate Lighting of Surfaces) system. In such a PDP of the ALIS system, there has been a high demand for increasing the gradation display performance by avoiding a distortion in the brightness that is generated depending on a lighting pattern and by preventing the occurrence of an abnormal discharge. 
     Specifically, the conventional PDP of the ALIS system has a problem in that the linearity of the gradation fails depending on the display pattern. This problem is not limited to a PDP of the ALIS system. A similar problem also exists in a PDP in which there is a short interval between the discharged display lines, and the pitches of the cells are short so that the discharge in the adjacent cells is partially superimposed. 
     The prior art and the problems associated with the prior art will be described later, in detail, with reference to accompanying drawings. 
     SUMMARY OF THE INVENTION 
     An object of the present invention is to provide a plasma display panel and a method of driving the same capable of increasing the gradation display performance by avoiding distortion in the brightness that is generated depending on a lighting pattern. It is another object of the present invention to provide a plasma display panel and a method of driving the same capable of preventing an occurrence of an abnormal discharge in the PDP. 
     According to the present invention, there is provided a method of driving a plasma display panel having a plurality of first electrodes and a plurality of second electrodes adjacently disposed alternately, first display lines being formed between the first electrodes and the second electrodes adjacent to one side of the first electrodes, second display lines being formed between the first electrodes and the second electrodes adjacent to the other side of the first electrodes, the first and second display lines alternately lighting or only one of the first and second display lines lighting, and an image being displayed on the plasma display panel by dividing a frame or a field into a plurality of sub-fields for a gradation display, comprising the steps of carrying out a sustain discharge in a sustain discharge period cells when are lighted on the adjacent first display lines or on the adjacent second display lines in a direction crossing the first and second electrodes; and carrying out a compensation sustain discharge a plurality of times on the second display lines or on the first display lines positioned between the adjacent first display lines or between the adjacent second display lines. 
     The first electrodes and the second electrodes may be disposed alternately in parallel with each other, and cells that are lighted on the adjacent first display lines or on the adjacent second display lines may be cells on the first display lines or the second display lines that are adjacent to each other in a direction orthogonal with the first and second electrodes. The compensation sustain discharge may be carried out in at least sub-fields in which a sustain discharge is carried out most. The number times of carrying out the compensation sustain discharge is carried out in each sub-field may be allocated in a ratio approximately proportional to the number of sustain discharge. A width of a pulse discharged at the beginning may be set large among the widths of the compensation sustain discharge pulses. 
     The method may comprise the steps of applying a sustain discharge pulse to cancel the voltage of the second display lines when a sustain discharge is carried out on the first display lines, or, of applying a sustain discharge pulse to cancel the voltage of the first display lines when a sustain discharge is carried out on the second display lines; inverting wall charges of cells where the sustain discharge is carried out by applying an inverted pulse necessary for a discharge only between pairs of electrodes of either odd display lines or even display lines among the first display lines; and carrying out a compensation sustain discharge a predetermined number of times, by applying compensation sustain discharge pulses such that a voltage is generated between electrodes that form display lines where the sustain discharge was not carried out during the sustain discharge period immediately before, and that a voltage is not generated between electrodes that form display lines where the sustain discharge was carried out during the sustain discharge period immediately before. 
     The width of the inverted pulse may be set larger than the width of the sustain discharge pulse. The voltage of the inverted pulse may be set higher than the voltage of the sustain discharge pulse. A voltage of a pulse discharged at the beginning may be set high among voltages of the compensation sustain discharge pulses. The method of driving the plasma display panel may further comprise the step of applying a voltage pulse necessary for a discharge to only pairs of electrodes of odd or even display lines among the first or second display lines where the compensation sustain discharge is carried out, thereby wall charges of cells where the compensation sustain discharge is carried out is inverted and polarities of wall charges formed on the first electrodes and on the second electrodes are matched on the respective electrodes. 
     Further, according to the present invention, there is also provided a plasma display panel comprising a plurality of first electrodes; a plurality of second electrodes adjacently disposed alternately with the first electrodes; first display lines formed between the first electrodes and the second electrodes adjacent to one side of the first electrodes; second display lines formed between the first electrodes and the second electrodes adjacent to the other side of the first electrodes; and a control circuit for alternately lighting the first and second display lines or lighting only one of the first and second display lines, and for displaying an image on the plasma display panel by dividing a frame or a field into a plurality of sub-fields for a gradation display, wherein when cells are lighted on the adjacent first display lines or on the adjacent second display lines in a direction crossing the first and second electrodes, a compensation sustain discharge is carried out by a plurality of times on the second display lines or on the first display lines positioned between the adjacent first display lines or between the adjacent second display lines, after a sustain discharge period on the first or second display lines is finished. 
     The plasma display panel may further comprise a memory for storing the number of times carrying out a sustain discharge on cells that are lighted on the adjacent first display lines or on the adjacent second display lines, and controls the number times of carrying out a compensation sustain discharge on the second display lines positioned between the adjacent first display lines or on the first display lines positioned between the adjacent second display lines, according to the number of times carrying out the sustain discharge stored in the memory. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The present invention will be more clearly understood from the description of the preferred embodiments as set forth below with reference to the accompanying drawings, wherein: 
     FIG.  1 A and FIG. 1B are diagrams showing a comparison between a plasma display panel (PDP) of the ALIS system to which the present invention is applied and a conventional plasma display panel; 
     FIG. 2 is a diagram for explaining a method of displaying on a PDP of the ALIS system; 
     FIG.  3 A and FIG. 3B are diagrams for explaining the operation principle of a PDP of the ALIS system; 
     FIG. 4 is a diagram showing one example of a display sequence of a PDP of the ALIS system; 
     FIG. 5 is a diagram (an odd field) showing one example of a driving waveform according to the ALIS system; 
     FIG. 6 is a diagram (an even field) showing one example of a driving waveform according to the ALIS system; 
     FIG. 7 is a circuit block diagram showing one example of a PDP of the ALIS system to which the present invention is applied; 
     FIG. 8 is a diagram showing one example of a panel structure of a PDP of the ALIS system; 
     FIG. 9 is a diagram showing a relationship between the gradation of first group cells and a lighting sub-field; 
     FIG. 10 is a diagram showing a relationship between the gradation of second group cells and a lighting sub-field; 
     FIG.  11 A and FIG. 11B are diagrams showing an example of a lighting pattern of two sub-fields; 
     FIG. 12 is a diagram showing one example of a lighting pattern in a PDP of the ALIS system; 
     FIG. 13 is a diagram showing another example of a lighting pattern in a PDP of the ALIS system; 
     FIG.  14 A and FIG. 14B are diagrams for explaining the principle of a method of driving a plasma display panel (PDP) relating to the present invention; 
     FIG. 15 is a diagram showing a driving waveform according to a first embodiment of a method of driving a PDP relating to the present invention; 
     FIG. 16 is a diagram (part 1) for explaining the operation of the method of driving a PDP relating to the present invention shown in FIG. 15; 
     FIG. 17 is a diagram (part 2) for explaining the operation of the method of driving a PDP relating to the present invention shown in FIG. 15; 
     FIG. 18 is a diagram showing a driving waveform according to another embodiment of a method of driving a PDP relating to the present invention; 
     FIG. 19 is a diagram showing one example of a lighting sequence according to a method of driving a PDP relating to the present invention; 
     FIG. 20 is a diagram showing one example of a lighting state according to a method of driving a PDP relating to the present invention; 
     FIG. 21 is a diagram (part 1) for explaining a problem of a fixed display in a PDP of the ALIS system; 
     FIG.  22 A and FIG. 22B are diagrams (part 2) for explaining a problem of a fixed display in a PDP of the ALIS system; and 
     FIG. 23 is a diagram for explaining a work effect of a method of driving a PDP relating to the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Before making a detailed description of the present invention, there will be first explained a conventional plasma display panel, a conventional method of driving the plasma display panel, and problems in the conventional techniques, with reference to the drawings. 
     FIG.  1 A and FIG. 1B are diagrams showing a comparison between a plasma display panel (PDP) of the ALIS system to which the present invention is applied and a conventional plasma display panel. FIG. 1A shows a conventional PDP (for example, a VGA type having 480 display lines), and FIG. 1B shows a PDP of the ALIS system (for example, having 1,024 display lines). 
     As shown in FIG. 1A, the conventional PDP has two display electrodes disposed in parallel. In order to carry out a display discharge between these electrodes, it is necessary to provide twice as many display electrodes (also called a sustain electrode) as the number of display lines. For example, in the case of a VGA having 480 display lines, 480×2=960 display electrodes are necessary. 
     On the other hand, in the case of the PDP of the ALIS system, a display is carried out by generating a discharge between all the adjacent electrodes as disclosed in, for example, Japanese Patent Publication No. 2801893 (Japanese Patent Application Laid-open Publication No. Hei 9-160525: corresponding to EP 0762373-A2), and as shown in FIG.  1 B. According to this system, the required number of display electrodes is the number of display lines plus one. For example, when there are 1,024 display lines, the required number of electrodes is 1,024+1=1,025. 
     In other words, according to the PDP of the ALIS system, it is possible to achieve a high definition of two times that achieved by the conventional system, by using a number of electrodes similar to that of the conventional system. Further, according to the PDP of the ALIS system, it is possible to minimize the shielding of light beams due to electrodes, based on an efficient use of discharging space, without waste. As a result, a high aperture ratio can be obtained, and a high brightness can be realized. 
     FIG. 2 is a diagram for explaining a method of displaying on a PDP of the ALIS system. This shows an example of displaying a character “A”. In FIG. 2, X-electrodes X 1 , X 2 , - - - , and Y-electrodes Y 1 , Y 2 , - - - are display electrodes (sustain electrodes). A 1 , A 2 , - - - are address electrodes. 
     As shown in FIG. 2, according to the display method of the ALIS system, the display of an image is divided into odd lines and even lines in time order. For example, a display is made on odd lines (display lines &lt; 1 &gt;, &lt; 3 &gt;, &lt; 5 &gt;, - - - ) based on the discharge between the X-electrodes electrodes(X 1 , X 2 , - - - ) and the Y-electrodes (Y 1 , Y 2 , - - - ) below these X-electrodes. Also, a display is made on even lines (display lines &lt; 2 &gt;, &lt; 4 &gt;, &lt; 6 &gt;, - - - ) based on the discharge between the Y-electrodes (Y 1 , Y 2 , - - - ) and the X-electrodes (X 2 , X 3 , - - - ) below these Y-electrodes. These two sets of displays are combined together to make a display of a whole image. This display method is very similar to that of interlaced scanning of a picture tube. 
     FIG.  3 A and FIG. 3B are diagrams for explaining the operation principle of a PDP of the ALIS system. FIG. 3A shows the operation during a discharge (display) of the odd lines, and FIG. 3B shows the operation during a discharge (display) of the even lines. 
     As shown in FIG. 3A, in order to make a stable discharge on the odd display lines (display lines &lt; 1 &gt;, &lt; 3 &gt;, - - - ), for example, the odd X-electrodes X 1 , X 3 , - - - are grounded (for example, zero volt), a voltage Vs is applied to the odd Y-electrodes Y 1 , Y 3 , - - - , a voltage Vs is applied to the even X-electrodes X 2 , X 4 , - - - , and the even Y-electrodes Y 2 , Y 4 , - - - are grounded. Based on this arrangement, a current is discharged to the odd display lines &lt; 1 &gt;, &lt; 3 &gt;, - - - , and a current is not discharged to the even lines &lt; 2 &gt;, &lt; 4 &gt;, - - - . In other words, a current is discharged to the first display line &lt; 1 &gt; based on a voltage (Vs) generated between the grounded first X-electrode X 1  and the first Y-electrode Y 1  to which the voltage Vs has been applied. Further, a current is discharged to the third display line &lt; 3 &gt; based on a voltage (Vs) generated between the second X-electrode X 2  to which the voltage Vs has been applied and the grounded second Y-electrode Y 2 . In this case, a current is not discharged to the second display line &lt; 2 &gt; as there occurs no potential difference between the first Y-electrode Y 1  to which the voltage Vs has been applied and the second X-electrode X 2  to which the voltage Vs has been applied. Further, a current is not discharged to the fourth display line &lt; 4 &gt; as there occurs no potential difference between the grounded second Y-electrode Y 2  and the grounded third X-electrode X 3 . 
     On the other hand, as shown in FIG. 3B, in order to make a stable discharge on the even display lines (display lines &lt; 2 &gt;, &lt; 4 &gt;, - - - ), for example, a voltage Vs is applied to the odd X-electrodes X 1 , X 3 , - - - and to the odd Y-electrodes Y 1 , Y 3 , - - - , and the even X-electrodes X 2 , X 4 , - - - , and the even Y-electrodes Y 2 , Y 4 , - - - are grounded. Based on this arrangement, a current is discharged to the even display lines &lt; 2 &gt;, &lt; 4 &gt;, - - - , and a current is not discharged to the odd lines &lt; 1 &gt;, &lt; 3 &gt;, - - - . In other words, a current is discharged to the second display line &lt; 2 &gt; based on a voltage (Vs) generated between the first Y-electrode Y 1  to which the voltage Vs has been applied and the grounded second X-electrode X 2 . Further, a current is discharged to the fourth display line &lt; 4 &gt; based on a voltage (Vs) generated between the grounded second Y-electrode Y 2  and the third X-electrode X 3  to which the voltage Vs has been applied. In this case, a current is not discharged to the first display line &lt; 1 &gt; as there occurs no potential difference between the first X-electrode X 1  to which the voltage Vs has been applied and the first Y-electrode Y 1  to which the voltage Vs has been applied. Further, a current is not discharged to the third display line &lt; 3 &gt; as there occurs no potential difference between the grounded second X-electrode X 2  and the grounded second Y-electrode Y 2 . 
     By alternately repeating the discharge on the odd lines shown in FIG.  3 A and the discharge on the even lines shown in FIG. 3B, the discharge of the odd lines and the discharge of the even lines are combined together. As a result, a total image is displayed. 
     FIG. 4 is a diagram showing one example of a display sequence of a PDP of the ALIS system. 
     As explained above, according to the PDP of the ALIS system, a display of a total screen is carried out by dividing the display into a display (discharge) of the odd lines and a display of the even lines. Therefore, one frame is divided into an odd field and an even field as shown in FIG.  4 . Each of these odd and even fields is further divided into a plurality of sub-fields ( 1 SF to nSF). It is necessary to divide each field into the plurality of sub-fields in order to carry out a gradation display. Usually, in order to realize a graduation of about 50 to 300, each field is divided into about eight to twelve sub-fields (SF). 
     Each sub-field ( 4 SF to nSF) is further divided into a reset period (not shown in FIG.  4 : positioned before an address period) for initializing a state of the discharge cell, an address period for writing into a lighting cell according to a display data, and a display period (a sustain period) for making a display using a cell selected during the address period. During the display period, a discharge is carried out repeatedly (a sustain discharge). The weight of the brightness of each sub-field is determined based on the number of this repetition. 
     FIG. 5 is a diagram (part 1: an odd field) showing one example of a driving waveform according to the ALIS system, and FIG. 6 is a diagram (part 2: an even field) showing one example of a driving waveform according to the ALIS system. Each drawing shows a driving waveform of one sub-field. 
     As shown in FIG. 5, in the driving waveform of one sub-field in the odd field, a voltage pulse is applied to between all the adjacent X-electrodes X 1 , X 2 , - - - and Y-electrodes Y 1 , Y 2 , - - - , thereby to carry out an initial discharge (a reset discharge), during the reset period. During the address period, a selective pulse (a scan pulse) is sequentially applied to the Y-electrodes Y 1 , Y 2 , - - - , and an address pulse is applied to the address electrode (A 1 , A 2 , - - - ) corresponding to a selective cell, thereby executing a write discharge (an address discharge). After executing the reset discharge and the write discharge to the whole screen, a sustain pulse is applied alternately to the X-electrodes and the Y-electrodes, thereby executing a sustain discharge (a sustain discharge). FIG. 5 shows a driving waveform of the odd field for carrying out a display of the odd lines (odd display lines &lt; 1 &gt;, &lt; 3 &gt;, - - - ). In FIG. 5, the address discharge and the sustain discharge are generated to only the odd display lines. 
     FIG. 6 shows a driving waveform of the even field for displaying the even lines (the even display lines &lt; 2 &gt;, &lt; 4 &gt;, - - - ). This corresponds to the driving waveform in the odd field shown in FIG.  5 . In FIG. 6, the address discharge and the sustain discharge are generated at only the even display lines. 
     FIG. 7 is a circuit block diagram showing one example of a PDP (a PDP apparatus) of the ALIS system to which the present invention is applied. In FIG. 7, a reference symbol  101  denotes a control circuit,  121  denotes a sustaining circuit for odd X-electrodes (PX 1 ),  122  denotes a sustaining circuit for even X-electrodes (PX 2 ),  131  denotes a sustaining circuit for odd Y-electrodes (PY 1 ),  132  denotes a sustaining circuit for even Y-electrodes (PY 2 ),  104  denotes an address circuit (an address driver),  105  denotes a scanning circuit (a scan driver), and  106  denotes a display panel (PDP). 
     The control circuit  101  converts display data DATA supplied from the outside into data for the display panel  106 , and supplies the converted data to the address circuit  104 . The control circuit  101  further generates various control signals according to a clock CLK, a vertical synchronization signal VSYNC, and a horizontal synchronization signal HSYNC, and controls the circuits  121 ,  122 ,  131 ,  132 ,  104 , and  105 . In order to apply the voltage waveforms shown in FIG.  5  and FIG. 6 to the electrodes, a power source (not shown) supplies predetermined voltages to the sustaining circuit for odd X-electrodes  121 , the sustaining circuit for even X-electrodes  122 , the sustaining circuit for odd Y-electrodes  131 , the sustaining circuit for even Y-electrodes  132 , the address circuit  104 , and the scanning circuit  105 , respectively. 
     FIG. 8 is a diagram showing one example of a panel structure of a PDP of the ALIS system. The display panel  106  includes a color type and a monochromatic type. FIG. 8 shows a case of the color display panel. 
     As shown in FIG. 8, on a front glass substrate  161 , there are alternately formed in parallel the X-electrodes and Y-electrodes X 1 , Y 1 , X 2 , - - - that are structured by transparent electrodes like IT 0  films  1631 ,  1632 ,  1633 , - - - and metal electrodes like copper electrodes  1641 ,  1642 ,  1643 , - - - . In this case, in the X-electrode X 1 , for example, the metal electrode  1641  is provided along a longitudinal direction of its transparent electrode  1631  in order to decrease a reduction in the voltage due to the transparent electrode  1631 . A dielectric for holding a wall charge and a protection film like an MgO film (not shown) are provided over the whole surface of the transparent electrodes  1631 ,  1632 ,  1633 , - - - and the metal electrodes  1641 ,  1642 ,  1643 , - - - that constitute the X-electrodes and Y-electrodes X 1 , Y 1 , X 2 , - - - , and over the whole inner surface of the front glass substrate  161 . 
     On a rear glass substrate  162 , there are formed the address electrodes A 1 , A 2 , A 3 , - - - and partitions  1650  surrounding these address electrodes, in a direction orthogonal with the X-electrodes and the Y-electrodes X 1 , Y 1 , X 2 , - - - , on the surface opposite to the MgO protection film of the front glass substrate  161 . Phosphors  1651 ,  1652 ,  1653 , - - - that emit various colors (a red color R, a green color G, and a blue color B) based on an incidence of ultraviolet rays generated by a discharge are coated on the address electrodes A 1 , A 2 , A 3 , - - - that are surrounded by the partitions  1650 . A Penning mixed gas of Ne+Xe is sealed into a discharge space formed between the MgO protection film (the inner surface) of the front glass substrate  161  and the phosphors (the inner surface) of the rear glass substrate  162 . 
     The odd X-electrodes X 1  (X 3 , X 5 , - - - ) of the front glass substrate  161  are connected to the sustaining circuit for odd X-electrodes  121  shown in FIG. 7, and the even X-electrodes X 2  (X 4 , X 6 , - - - ) are connected to the sustaining circuit for even X-electrodes  122 . The odd Y-electrodes Y 1  (Y 3 , Y 5 , - - - ) are connected to the sustaining circuit for odd Y-electrodes  131  via the scanning circuit  105  (the IC for scan driving)  105 , and the even Y-electrodes Y 2  (Y 4 , Y 6 , - - - ) are connected to the sustaining circuit for even Y-electrodes  132  via the scanning circuit  105 . Based on this arrangement, the above-described driving of the ALIS system is carried out. 
     FIG. 9 is a diagram showing a relationship between the gradation of first group cells and a lighting sub-field, and FIG. 10 is a diagram showing a relationship between the gradation of second group cells and a lighting sub-field. FIG.  9  and FIG. 10 are examples of a case of showing sixty gradations. Reference symbols SF 1  to SF 8  denote sub-fields. Sub-fields SF 1  and SF 8  have a brightness weight of 16 respectively. Sub-fields SF 2  and SF 7  have a brightness weight of 8 respectively, and sub-fields SF 3  and SF 6  have a brightness weight of 4 respectively. 
     It is generally true that a PDP has a plurality of sub-fields (SF 1  to SF 8 ) with different brightness weights for carrying out a gradation display. In this case, depending on a state of a sub-field to be lighted, there arises a problem of a pseud outline in a dynamic image. This is a unique phenomenon of a PDP that does not occur in a picture tube. How to solve this phenomenon has been an important theme from the viewpoint of improving the picture quality of the PDP. In order to solve this problem of a pseud outline in the dynamic image, there has been known a method of dispersing a lighting field, and making a predetermined gradation display in first group cells and second group cells by using mutually different lighting sub-fields, as shown in FIG.  9  and FIG.  10 . 
     Specifically, in the case of expressing 30 gradations, for example, the sub-fields SF 2 , SF 4 , SF 6  and SF 8  are lighted as shown in FIG.  9 . The gradation of 30 can also be obtained when all the sub-fields from SF 1  to SF 4 , for example, are lighted. However, when the lighted sub-fields are concentrated at one portion, a flickering and a pseud outline become conspicuous in the dynamic image, which lowers the picture quality. In order to prevent the occurrence of this phenomenon, the sub-fields SF 2 , SF 4 , SF 6  and SF 8  are lighted to express the gradation of 30. The weights of the brightness of these sub-fields SF 2 , SF 4 , SF 6  and SF 8  are 8, 2, 4 and 6 respectively, and they add up to 30 in total. By dispersing the lighted sub-fields in the order of time like this, the lighting cycle becomes short. As a result, flickering and a pseud outline in the dynamic images are not seen by an eye. 
     Further, the gradation of 30 can also be obtained when the sub-fields SF 1 , SF 3 , SF 4  and SF 7  are lighted as shown in FIG.  10 . The weights of the brightness of these sub-fields SF 1 , SF 3 , SF 4  and SF 7  are 16, 4, 2 and 8 respectively, and they add up to 30 in total. There has also been a measure for improving the state of a pseud outline in the dynamic image by alternately using the lighting sub-fields (SF 2 , SF 4 , SF 6  and SF 8 ) shown in FIG.  9  and the lighting sub-fields (SF 1 , SF 3 , SF 4  and SF 7 ) shown in FIG. 10 for each pixel (for example, R. G and B cells form one pixel). 
     In other words, when certain pixels (first group cells) have a lighting pattern of the sub-fields shown in FIG. 9, for example, the pixels (second group cells) that are adjacent to these pixels at above, below, left and right positions have a lighting pattern of the sub-fields shown in FIG.  10 . Therefore, in the case of displaying a gradation of 40, for example, the sub-fields SF 2 , SF 3 , SF 6 , SF 7  and SF 8  are lighted in the first group cells, and the sub-fields SF 1 , SF 2 , SF 3 , SF 6  and SF 7  are lighted in the second group cells. In other words, as the sub-field having the brightness weight 16, the sub-field SF 8  is used in the first group cells and the sub-field SF 1  is used in the second group cells. 
     FIG.  11 A and FIG. 11B are diagrams showing an example of a lighting pattern of two sub-fields. They show a state of displaying 40 gradations in all cells in the display of odd lines. 
     First, as is apparent from a comparison between FIG.  11 A and FIG. 11B, in the display of the odd lines, the first group cells and the second group cells are positioned alternately in up and down directions and in left and right directions. In the case of displaying 40 gradations, for example, the sub-field SF 8  is used as the sub-field having the brightness weight 16 in the first group cells. The sub-field SF 1  is used as the sub-field having the brightness weight of 16 in the second group cells. As explained above, when the lighting sub-fields are dispersed by changing them for each pixel even when the sub-fields have the same gradation weight, it is possible to mitigate the pseud outline in the dynamic image. This technique has been successfully applied to PDPS currently in practical use. As an example of literature relating to this technique, there is Japanese Patent Application Laid-open Publication No. Hei 7-271325. 
     FIG. 12 is a diagram showing one example of a lighting pattern in a PDP of the ALIS system, and FIG. 13 is a diagram showing another example of a lighting pattern in a PDP of the ALIS system. FIG. 12 shows portions of lighting each one line in the display of odd lines in a PDP of the ALIS system, and FIG. 13 shows portions of lighting in continuous odd lines in the display of odd lines. In FIG.  12  and FIG. 13, a reference symbol  161  denotes a front glass substrate,  162  denotes a rear glass substrate, and  165  denotes a phosphor (R: 1651, G: 1652, and B: 1653). 
     In the PDP of the ALIS system shown in FIG. 8, a light emitting area is relatively larger than the interval between the display lines. Therefore, a light emission range of the display line &lt; 1 &gt; formed by a pair of electrodes X 1  and Y 1  and a light emission range of the display line &lt; 5 &gt; formed by a pair of electrodes X 3  and Y 3  extend respectively to the area of the display line &lt; 3 &gt; formed by a pair of electrodes X 2  and Y 2 . 
     Therefore, in the display of the odd lines, there arise the following cases. As shown in FIG. 12, the light emission range of the display line &lt; 1 &gt; and the light emission range of the display line &lt; 5 &gt; are not superimposed with each other at portions where the lighting is carried out for each line (the display lines &lt; 1 &gt;, &lt; 5 &gt;, &lt; 9 &gt;, - - - ) in one sub-field. However, as shown in FIG. 13, the light emission range of the display line &lt; 1 &gt; and the light emission range of the display line &lt; 5 &gt; are superimposed with a part of the light emission range of the display line &lt; 3 &gt; at portions where the lighting is carried out in continuous odd lines (the display lines &lt; 1 &gt;, &lt; 3 &gt;, &lt; 5 &gt;, - - - ). In other words, as shown in FIG. 13, when the display lines &lt; 1 &gt;, &lt; 3 &gt; and &lt; 5 &gt; are lighted continuously in a certain sub-field, the light emission areas of the adjacent cells are partially superimposed on each other. It is needless to mention that this problem is not limited to the display of odd lines, but this occurs similarly in the display of even lines. 
     Assume that the brightness of the lighting pattern for each pixel as shown in FIG. 12 is 50. This brightness is not the brightness of only the light-emitting pixels but is an average brightness of a plane constant area including both light ON and OFF cells. This is an average value of the brightness of the ON cells embedded in the OFF cells. 
     Under this condition, when all the cells (the continuous cells of the odd lines &lt; 1 &gt;, &lt; 3 &gt;, &lt; 5 &gt;, - - - ) as shown in FIG. 13 are lighted, for example, the cells of two times the number of cells of the light emitting pattern of FIG. 12 are lighted. Therefore, in principle, the brightness of 100, which is two times the brightness of 50, can be obtained. However, in actual practice, the brightness of only about 90 is obtained due to the superimposition of the light emission areas. The PDP has such a characteristic that ultraviolet rays generated by a discharge excite the phosphors to generate a visible light, but there is a limit to a generation amount of the visible light. Thus, it is not possible to obtain visible light in excess of a constant level even if ultraviolet rays of more than a certain level are applied. In other words, there is a phenomenon that the output of a visible light is saturated for the input of ultraviolet rays of the phosphors. Therefore, depending on a display picture, it is not possible to obtain the brightness according to the number of sustain pulses determined by a specified gradation. 
     Viewed another way, in a case where all cells of a specific area are lighted in the lighting sub-fields shown in FIG.  9  and FIG. 10, for example, to display 59 gradations when all the sub-fields SF 1  to SF 8  are lighted, the brightness becomes 59. In the display of 40 gradations, the scheduled brightness is 40. However, the sub-fields SF 1  and SF 8  take the display pattern (there is no superimposition of light emission areas) as shown in FIG.  11 A and FIG.  11 B. Therefore, the brightness of these sub-fields becomes approximately 1.1 times. In other words, the sub-fields SF 1  and SF 8  that have the brightness of 16 in principle have the brightness of about 18. As a result, the actual brightness becomes 42 despite the intended brightness of 40. 
     As explained above, the conventional PDP of the ALIS system has a problem in that the linearity of the gradation fails depending on the display pattern. This problem is not limited to the PDP of the ALIS system. A similar problem also exists in a PDP in which there is a short interval between the discharged display lines, and the pitches of the cells are short so that the discharge in the adjacent cells is partially superimposed. 
     The principle of a method of driving a plasma display panel (PDP) relating to the present invention will be explained next. 
     FIG.  14 A and FIG. 14B are diagrams for explaining the principle of a method of driving a plasma display panel (PDP) relating to the present invention. FIG. 14A shows portions of a continuous lighting, and FIG. 14B shows portions of lighting in selected lines. 
     Looking at FIG. 13 again, when continuous lighting is carried out in the display of the odd lines (in a certain sub-field SFn), the brightness is low at portions between the adjacent cells that are in the lighted state (the cells of the odd display lines &lt; 1 &gt;, &lt; 3 &gt; and &lt; 5 &gt;). In other words, the brightness is low near the even display lines &lt; 2 &gt; and &lt; 4 &gt; (that is, the gap between the electrodes Y 1  and X 2 , and the gap between the electrodes Y 2  and X 3 ). 
     According to the present invention, as shown in FIG. 14A, in the display of the odd lines, a sustain discharge that has not conventionally been carried out in the display of the odd lines is carried out on the even lines at the continuous lighting portions where the light emission areas of the adjacent cells are partially superimposed. With this arrangement, brightness compensation is carried out in the areas where the brightness is low due to the superimposition of the light emission areas. In other words, according to the present invention, a compensation sustain period is provided after the sustain period, as shown in FIG.  14 A. During this compensation sustain period, a sustain discharge (a compensation sustain discharge) is additionally carried out for compensating for the brightness in the gaps (even lines) between the adjacent display lines (odd lines) above and below those that are emitting light. When the lighting cells are not adjacent above and below as shown in FIG. 14B, the compensation sustain discharge is not carried out during the compensation sustain period. 
     As explained above, according to the present invention, it is possible to increase the gradation display performance by avoiding the distortion in the brightness that is generated depending on the lighting pattern. Further, according to the present invention, it is also possible to prevent an occurrence of an abnormal discharge in the PDP as described later. 
     Embodiments of a plasma display panel (PDP) and a method of displaying the plasma display panel according to the present invention will be explained in detail with reference to the drawings. 
     FIG. 15 is a diagram showing a driving waveform according to a first embodiment of a method of driving a PDP relating to the present invention, and FIG.  16  and FIG. 17 are diagrams for explaining the operation of the method of driving a PDP shown in FIG.  15 . FIG. 15 to FIG. 17 show examples of a driving waveform in the display of the odd lines. 
     As shown in FIG. 15, during the sustain period, the timing of applying the sustain pulse (for example, a pulse of 2 to 5 μs at 150 to 180 V) is controlled to generate a sustain discharge on the odd display lines &lt; 1 &gt;, &lt; 3 &gt;, &lt; 5 &gt;, - - - , as explained with reference to FIG.  3 B and FIG.  5 . In other words, a sustain discharge is generated on the odd display lines (for example, the display line &lt; 1 &gt;), by applying a high voltage between the electrode X 1  and the electrode Y 1  based on an application of an opposite-phase sustain pulse to these electrodes, and by superimposing this high voltage on the wall charge. On the other hand, a sustain discharge is not generated on the even display lines (for example, the display line &lt; 2 &gt;), by suppressing a potential difference between the electrode Y 1  and the electrode X 1  based on an application of an in-phase sustain pulse to these electrodes. Based on this arrangement, the odd lines are displayed in the PDP of the ALIS system. 
     As shown in FIG.  15  and FIG. 16, a potential difference (wall voltage) is generated between the electrode X 1  and the electrode Y 1  corresponding to the odd display line &lt; 1 &gt;, between the electrode X 2  and the electrode Y 2  corresponding to the odd display line &lt; 3 &gt;, and between the electrode X 3  and the electrode Y 3  corresponding to the odd display line &lt; 5 &gt;, at the end of the sustain period. As a result, a potential difference is not generated between the electrode Y 1  and the electrode X 2  corresponding to the even display line &lt; 2 &gt;, and between the electrode Y 2  and the electrode X 3  corresponding to the even display line &lt; 4 &gt;. 
     According to the present embodiment, an inverted pulse (for example, a pulse of 5 to 10 μs at 160 to 200 V) is applied to the electrode X 2  after the end of the sustain period, thereby to invert the charges of the electrode X 2  and the electrode Y 2 . Then, a voltage Vs is applied to the electrode Y 1 , and a zero voltage is applied to the electrode X 2 , at a first pulse during the compensation sustain period. The voltage of the wall charge is superimposed on this application voltage so that the application voltage becomes more than the discharge starting voltage. Then, a discharge (a compensation sustain discharge) starts on the even display line &lt; 2 &gt;. At this point of time, a voltage has already been applied to the even display line &lt; 4 &gt; between the electrode Y 2  and the electrode X 3 . However, as the wall voltage is in the opposite polarity, a discharge is not generated to lower the effective voltage within the cell. At a second wave during the compensation sustain period, the wall voltage is superimposed at a point of time when the compensation pulse in the opposite polarity (the same as the sustain pulse: for example, 2 to 5 μs at 150 to 180 V) has been applied, and thus a discharge is started. Thereafter, the compensation sustain discharge of a predetermined number sufficient enough to compensate for the brightness is carried out repeatedly on the even display lines &lt; 2 &gt;, &lt; 4 &gt;, - - - . Then, the compensation sustain period finishes. 
     As explained above, according to the present embodiment, after the end of a sustain period similar to that of the conventional sustain period, an inverted pulse and a compensation sustain pulse are applied to a discharge gap (a slit: an even line in the case of a display of odd lines) in which a sustain discharge is not carried out so that a potential difference is generated in this gap. In this case, a compensation sustain pulse is applied to the slit side (an odd line) in which a discharge has been carried out during the intrinsic sustain period so as not to generate a potential difference or not to carry out a discharge even if a potential difference has been generated. 
     In this case, it is preferable that the compensation sustain discharge is carried out in at least the sub-fields (for example, the sub-fields SF 1  and SF 8  in FIG. 9, FIG.  11 A and FIG. 11B) in which normal sustain discharge is carried out most. Further, the number of times of carrying out the compensation sustain discharge in each sub-field may be allocated in a ratio approximately proportional to the number of normal sustain discharge. It is preferable that the width of the inverted pulse is set larger than the width of the sustain discharge pulse to ensure the inversion of the charge. 
     Next, a description will be made of a case where each one line is lighted in the display of the odd lines as explained with reference to FIG.  12 . FIG. 17 shows a case where a sustain discharge is not carried out on the odd lines &lt; 1 &gt;, &lt; 5 &gt;, - - - and a sustain discharge is carried out on the odd lines &lt; 3 &gt;, &lt; 7 &gt;, 
     As shown in FIG. 17, in the display of the odd lines, an inverted pulse and a compensation sustain pulse are also applied for lighting each line, as explained with reference to FIG.  15  and FIG.  16 . However, in the case of lighting each line, when a compensation sustain pulse similar to that as shown in FIG. 15 has been applied after inverting the charges of the electrode X 2  and the electrode Y 2  based on the application of the inverted pulse, a discharge (a compensation sustain discharge) is not generated on the even display lines &lt; 2 &gt;, &lt; 4 &gt;, - - - . Thus, the operation becomes similar to that when an inverted pulse and a compensation sustain pulse are not applied based on the provision of the compensation sustain period. In the case of the slit (an even display line) in which the compensation sustain discharge is carried out, the wall charge exists at only one side. Therefore, the voltage in this slit does not exceed the discharge starting voltage even when the compensation sustain voltage has been applied to this slit. As a result, no compensation sustain discharge is generated in this slit. 
     Therefore, by carrying out a compensation sustain discharge, it is possible to compensate for low brightness only when the brightness is lowered due to a partial superimposition of the light emission areas of the adjacent cells. 
     A PDP to which the present invention can be applied has a structure as shown in FIG. 7, for example, with an additional provision of a memory  110  in the control circuit  101 . This memory  110  stores a number of sustain discharge carried out in the case of a superimposition of the light emission areas of the adjacent cells in each sub-frame SF. The control circuit  101  reads this number of the sustain discharge stored in this memory  110 , and calculates a number of compensation sustain discharge corresponding to the sustain discharge. Based on a result of this calculation, the control circuit  101  makes compensation sustain discharge executed by the calculated number on the display lines corresponding to the slits in which the light emission areas are superimposed. 
     FIG. 18 is a diagram showing a driving waveform according to another embodiment of a method of driving a PDP relating to the present invention. 
     As shown in FIG. 18, according to the present embodiment, a slightly high voltage (for example, 160 to 200 V) is set as the voltage of a sustain discharge restarting pulse that is applied for starting a compensation sustain discharge (for restarting a sustain discharge). With this arrangement, the compensation sustain discharge is securely implemented. 
     FIG. 19 is a diagram showing one example of a lighting sequence according to a method of driving a PDP relating to the present invention. FIG. 19 shows a lighting sequence of one field (an odd field or an even field) in a method of driving a PDP. One field consists of eight sub-fields SF 1  to SF 8 . 
     In the example shown in FIG. 19, a compensation sustain discharge is carried out by providing a compensation sustain period in only sub-field that have a large brightness weight. 
     In FIG. 19, sub-fields SF 1  and SF 8  both with a large brightness weight have a sustain cycle number  192  and have a compensation sustain cycle number  19 . Sub-fields SF 2  and SF 7  have a sustain cycle number  96  and have a compensation sustain cycle number  9 . Sub-fields SF 3  and SF 6  have a sustain cycle number  48  and have a compensation sustain cycle number  5 . 
     On the other hand, a sub-field SF 4  has a sustain cycle number  24 , and a sub-field SF 5  has a sustain cycle number  12 . However, these sub-fields have a small brightness weight, that is, a small sustain number. Therefore, a compensation sustain period is not provided in these sub-fields. 
     Numbers of compensation sustain cycles are different depending on discharge characteristics of panels and saturation characteristics of phosphors. Therefore, an optimum value that is suitable for each PDP is set as a compensation sustain cycle number at the time of designing the PDP. For example, the number of compensation sustain cycles in each sub-field SF can be set as about ten percent of the number of sustain cycles. However, when the superimposed portion of the light emission areas of the adjacent cells becomes large, the ratio of the compensation sustain cycle number to the sustain cycle number is set large. 
     FIG. 20 is a diagram showing one example of a lighting state according to a method of driving a PDP relating to the present invention. 
     In FIG. 20, one field consists of ten sub-fields from SF 1  to SF 10 . 
     The example of FIG. 20 can be realized based on a combination of the display panel shown in FIG.  8  and the driving circuit shown in FIG. 7, using the driving waveforms shown in FIG.  5  and FIG. 6 (however, one field consists of the sub-fields SF 1  to SF 10 ), with an addition of the compensation sustain period shown in FIG. 15 or FIG. 18 to the driving waveform. 
     According to the present invention, it is also possible prevent an occurrence of an abnormal discharge due to the accumulation of distorted charges, in addition to the achievement of the above-described compensation for the brightness. This will be explained below. 
     FIG. 21, FIG.  22 A and FIG. 22B are diagrams for explaining a problem of a fixed display in a PDP of the ALIS system. 
     As explained above, according to the PDP of the ALIS system, the odd lines and the even lines are lighted by separate fields, as shown in FIG.  4 . Therefore, as the display can be carried out using all slits (between the X-electrodes and the Y-electrodes), it is possible to obtain a high resolution of two times that obtained conventionally. 
     However, when a fine horizontal line is displayed, a flickering of a 30 Hz period, for example, may be sensed similar to the one sensed in the interlace display of a picture tube. Therefore, there has been a request for avoiding a flickering at the cost of a reduction in the resolution to a half in the display of information like characters. In the case of a display of information like characters, the display is carried out by always using, for example, only the odd lines, as shown in FIG.  21 . When only the odd lines, for example, are used for the display, the address discharge becomes always in the same direction as shown in FIG.  21 . When this driving (display) is repeated, a distortion in the electric charge occurs on the display panel as shown in FIG.  22 A. 
     When the distorted accumulation of charges as shown in FIG. 22A progresses, a large-scale abnormal discharge may occur over a substantially long distance exceeding the pairs of the X-electrodes and the Y-electrodes as shown in FIG.  22 B. This abnormal discharge can damage a normal operation thereafter, and can damage the circuit by breaking an insulation film with a large current. 
     According to the present invention, the discharge is carried out in the slits in which the discharge has not been conventionally carried out based on the prior-art technique. Therefore, there is an effect that it is possible to prevent an abnormal discharge in the display panel by avoiding the distortion of charges. 
     FIG. 23 is a diagram for explaining a work effect of a method of driving a PDP relating to the present invention. As is apparent from FIG. 23, when the present invention is applied, the discharge during the address period (the address discharge) and the discharge during the compensation sustain period (the compensation sustain discharge) face in the opposite directions on the display panel. Therefore, it is possible to avoid the accumulation of distorted charges on the display panel, and thus it becomes possible to prevent an abnormal discharge. 
     While a description has been made of a case where the present invention is applied to mainly a PDP of the ALIS system (particularly the display of the odd lines), the application of the present invention is not limited to the PDP of the ALIS system. It is also possible to widely apply the present invention to a PDP in which charges are superimposed in adjacent cells, with short pitches of the cells in which a discharge is carried out. 
     As explained above in detail, according to the present invention, it is possible to increase the gradation display performance by avoiding a distortion in the brightness that is generated depending on the lighting pattern. Further, according to the present invention, it is also possible to prevent an occurrence of an abnormal discharge in the PDP. 
     Many different embodiments of the present invention may be constructed without departing from the spirit and scope of the present invention, and it should be understood that the present invention is not limited to the specific embodiments described in this specification, except as defined in the appended claims.