Patent Publication Number: US-7589696-B2

Title: Plasma display panel apparatus performing image display drive using display method that includes write period and sustain period, and driving method for the same

Description:
TECHNICAL FIELD 
     The present invention relates to a plasma display panel (PDP) apparatus and a driving method for the same. The present invention particularly relates to a technique to enhance luminous efficiency while reducing an increase in cost of the apparatus. 
     BACKGROUND ART 
     PDP apparatuses have relative ease in increasing a screen size, when compared with CRT display apparatuses which are currently most common image display apparatuses. Therefore, PDP apparatuses attract attention as image display apparatuses suitable for high-definition broadcasting. Here, PDP apparatuses can be classified into alternating current (AC) and direct current (DC) types. At present, AC-type PDP apparatuses form a mainstream because of their superiority in a variety of aspects such as reliability and display quality. (Hereinafter, the term PDP apparatus refers to AC types.) 
     A PDP apparatus is constituted by a panel unit and a driving unit. The panel unit includes a front panel in which a plurality of pairs of a scan electrode and a sustain electrode are provided, and a back panel on which a plurality of data electrodes are provided. The front panel and the back panel are arranged so as to oppose each other with a space therebetween. Here, the front panel and the back panel are aligned so that the data electrodes intersect the scan electrodes and the sustain electrodes. The front panel and the back panel are sealed together at their peripheral portions. Furthermore, a rare gas such as Ne, Xe and He is enclosed in the space (a discharge space) between the front and back panels. In this way, discharge cells are formed at areas where the data electrodes intersect the scan and sustain electrodes. 
     This PDP apparatus is generally driven using a field timesharing gradation display method. According to this method, one field (one frame) is divided into a plurality of sub-fields each of which includes a write period and a sustain period. In this way, a duration of lighting is time-divided. Furthermore, images of the sub-fields are combined, to express a gray-scale image for the field. 
     Regarding such PDP apparatuses, there is a demand for a larger screen and higher definition. To meet this demand, it is required to further reduce degradation in display quality due to electric resistances of scan electrodes and sustain electrodes on a front panel. In detail, since the scan electrodes and the sustain electrodes are usually disposed so as to extend in a lengthwise direction of the front panel, an increase in size of the front panel particularly tends to cause an increase in resistance of the scan and sustain electrodes. Consequently, when electric currents are supplied to the scan and sustain electrodes to drive a PDP apparatus, a significant voltage drop occurs, and the display quality is degraded. This is particularly noticeable in a sustain period. In the sustain period, a discharge current E 0  flows in each discharge cell in a very short time period of approximately several hundred nanoseconds from a start of a discharge, as shown in  FIG. 11 . The sum of the amounts of discharge currents E 0  flowing in all of the discharge cells formed by the individual scan and sustain electrodes is equal to the amount of a current Et 0  flowing in the individual scan and sustain electrodes, as shown in  FIG. 12 . As a result, a noticeable voltage drop occurs in the scan and sustain electrodes. This results in lower display quality of the PDP apparatus. 
     To prevent such a voltage drop of scan and sustain electrodes in a sustain period, it has been considered and attempted to differentiate discharge cells in terms of discharge start timing. For example, Japanese patent application publication No. H11-149274 discloses a driving method in which a pulse is applied to data electrodes forming selected discharge cells in a sustain period. This pulse rises before pulses are applied to scan and sustain electrodes, and falls immediately after a discharge caused by the pulses applied to the scan and sustain electrodes is completed. According to this technique, a discharge starts at a different timing between in the selected discharge cells and remaining not-selected discharge cells. This prevents a large current from flowing into the scan and sustain electrodes in a short time, thereby reducing occurrence of a voltage drop. 
     In addition, Japanese patent application publication No. H10-133622 discloses the following driving method. In a sustain period, each data electrode is set to a different potential, or data electrodes are grouped so that each group of data electrodes is set at a different potential. According to this technique, a discharge starts at a different timing among discharge cells, or discharge cell groups corresponding to the data electrode groups. This lowers a peak value of discharge currents flowing into scan and sustain electrodes in the sustain period. 
     As described above, driving of a PDP apparatus is controlled, by means of two options of whether or not to apply the pulse to the data electrodes (Japanese patent application publication No. H11-149264), or by means of two options of whether to apply a pulse of high or low potential (Japanese patent application publication No. H10-133622). According to these techniques, discharge currents in the scan and sustain electrodes are divided into only two groups. Therefore, only little effect is achieved by differentiating discharge currents. The effect can possibly be improved by increasing the number of potential levels for pulses applied to data electrodes, based on the technical idea disclosed in the latter patent application publication. However, an increase in number of potential levels causes an increase in number of necessary power sources. This increase leads to a higher manufacturing cost of a driving unit and unevenness of luminance among discharge cells. For this reason, this alternative method is hardly realistic. 
     DISCLOSURE OF THE INVENTION 
     In light of the above-described problems, an objective of the present invention is to provide a PDP apparatus and a driving method for the same which attain enhanced display quality by lowering a peak value of discharge currents flowing in scan and sustain electrodes in a sustain period, without increasing a manufacturing cost of the apparatus. 
     To achieve this objective, the present invention has the following characteristics. 
     (1) A PDP apparatus comprising a panel unit and a driving unit, the panel unit including a first substrate on which a plurality of pairs of first and second electrodes are formed and a second substrate on which a plurality of third electrodes are formed, the first substrate and the second substrate being opposed to each other with a discharge space therebetween so as to form discharge cells at areas where the plurality of pairs of first and second electrodes intersect the plurality of third electrodes, the driving unit driving the panel unit to display an image according to a display method that includes a write period and a sustain period, by, in the sustain period, applying a voltage to the plurality of pairs of first and second electrodes and applying a voltage to the plurality of third electrodes, the PDP apparatus being characterized in that in the sustain period, voltage waveforms applied to the plurality of third electrodes differ in terms of a rise start timing which is set relative to a time at which the voltage applied to the plurality of pairs of first and second electrodes reaches a predetermined level. 
     According to this PDP apparatus, the voltage waveforms differ in terms of rise start timing, among the plurality of third electrodes. This can differentiate a sustain discharge in terms of start timing, among the third electrodes. Thus, currents flowing in the first and second electrodes can differ in terms of peak time in the sustain period. As a result, occurrence of a voltage drop in the first and second electrodes can be prevented. 
     According to this PDP apparatus, in addition, the voltage waveforms differ among the plurality of third electrodes in terms of rise start timing. This can cause sustain discharges to occur at different timings. Therefore, discharge currents can differ at many levels in terms of peak time without increasing the number of power sources. 
     As a consequence, the PDP apparatus can reduce the voltage drop, by lowering a peak value of the discharge currents flowing in the first and second electrodes in the sustain period, thereby attaining high display quality without an increase in cost. 
     Here, the voltage is not necessarily applied to all of the plurality of third electrodes in the sustain period, but may be applied to selected ones of the plurality of third electrodes. Moreover, the voltage waveforms applied in the sustain period may differ in terms of rise start timing, among all of the third electrodes, or between a group of selected electrodes and a group of remaining not-selected electrodes. 
     (2) The PDP apparatus of (1), wherein the plurality of third electrodes are divided into a plurality of groups each of which includes two or more third electrodes, and in the sustain period, the driving unit controls the rise start timing in units of groups.
 
(3) The PDP apparatus of (2), wherein the driving unit includes: a plurality of voltage applying circuit units which apply the voltage to the plurality of third electrodes in the sustain period; and a timing signal generation unit that outputs a signal indicating the rise start timing, in the sustain period, to each of the plurality of voltage applying circuit units.
 
(4) The PDP apparatus of (1), wherein in the sustain period, the driving unit controls the voltage waveforms applied to the plurality of third electrodes so as to start rising within a time period shorter than a half cycle of a waveform of the voltage applied to the plurality of pairs of first and second electrodes.
 
(5) The PDP apparatus of (4), wherein in the sustain period, the driving unit controls the voltage waveforms applied to the plurality of third electrodes so as to start rising, after a time at which the voltage applied to the plurality of pairs of first and second electrodes reaches a predetermined level, but before a time at which a discharge is generated by the voltage applied to the plurality of pairs of first and second electrodes when the voltage is assumed not to be applied to the plurality of third electrodes.
 
(6) The PDP apparatus of (5), wherein in the sustain period, a voltage waveform applied to a first electrode and a voltage waveform applied to a second electrode paired with the first electrode have a same cycle, but are different from each other in terms of a timing of application, by half the cycle.
 
(7) The PDP apparatus of (1), wherein in the sustain period, a voltage waveform applied to at least one of the plurality of third electrodes starts to fall at a different timing, from a voltage waveform applied to an adjacent third electrode, which is set relative to a time at which the voltage applied to the plurality of pairs of first and second electrodes reaches a predetermined level.
 
(8) The PDP apparatus of (7), wherein in the sustain period, the driving unit controls the voltage waveforms applied to the plurality of third electrodes so as to start falling within a time period shorter than a half cycle of a waveform of the voltage applied to the plurality of pairs of first and second electrodes.
 
(9) The PDP apparatus of (1), wherein when the voltage waveforms applied to the plurality of third electrodes in the sustain period are expressed using a time axis and a voltage axis, at least one of a rising portion and a falling portion of each of the voltage waveforms has a gradient, and a voltage waveform applied to at least one of the plurality of third electrodes has a different gradient for at least one of a rising portion and a falling portion, from a waveform applied to an adjacent third electrode.
 
(10) The PDP apparatus of (9), wherein a duration of at least one of the rising portion and the falling portion of the voltage waveform is shorter than a half cycle of a waveform of the voltage applied to the plurality of pairs of first and second electrodes.
 
(11) The PDP apparatus of (1), wherein each of the voltage waveforms applied the plurality of third electrodes in the sustain period is a pulse waveform of a substantially same width.
 
(12) The PDP apparatus of (1), wherein the driving unit drives the panel unit by repeating a sub-field including the write period and the sustain period, and the driving unit controls the rise start timing in units of sub-fields.
 
(13) The PDP apparatus of (12), wherein two or more sub-fields constitute a sub-field group, and the driving unit controls the rise start timing in units of sub-field groups.
 
(14) The PDP apparatus of (1), wherein the driving unit drives the panel unit by repeating a sub-field including the write period and the sustain period, and a plurality of sub-fields constitute a field, and the driving unit controls the rise start timing in units of fields.
 
(15) The PDP apparatus of (14), wherein two or more fields constitute a field group, and the driving unit controls the rise start timing in units of field groups.
 
(16) The PDP apparatus of (1), wherein the write period and the sustain period constitute a sub-field, and a plurality of sub-fields constitute a field, and for each of the voltage waveforms applied to the plurality of third electrodes, an average time period, in each sub-field or field, from a time at which the voltage applied to the plurality of pairs of first and second electrodes reaches a predetermined level to a time at which the voltage applied to the plurality of third electrodes starts to rise is substantially same.
 
(17) The PDP apparatus of (1), wherein in the sustain period, a cycle of the voltage waveforms applied to the plurality of third electrodes is equal to a half cycle of a waveform of the voltage applied to the plurality of pairs of first and second electrodes.
 
(18) The PDP apparatus of (1), wherein in the sustain period, a cycle of the voltage waveforms applied to the plurality of third electrodes is equal to a cycle of a waveform of the voltage applied to the plurality of pairs of first and second electrodes.
 
(19) The PDP apparatus of (1), wherein in the sustain period, a cycle of the voltage waveforms applied to the plurality of third electrodes is equal to an integral multiple of a cycle of a waveform of the voltage applied to the plurality of pairs of first and second electrodes.
 
(20) A driving method for a PDP apparatus including a panel unit including a first substrate on which a plurality of pairs of first and second electrodes are formed and a second substrate on which a plurality of third electrodes are formed, the first substrate and the second substrate being opposed to each other with a discharge space therebetween so as to form discharge cells at areas where the plurality of pairs of first and second electrodes intersect the plurality of third electrodes, the driving method including a write period and a sustain period, and being used to display an image, by, in the sustain period, applying a voltage to the plurality of pairs of first and second electrodes and applying a voltage to the plurality of third electrodes, the driving method being characterized in that in the sustain period, voltage waveforms applied to the plurality of third electrodes differ in terms of a rise start timing which is set relative to a time at which the voltage applied to the plurality of pairs of first and second electrodes reaches a predetermined level.
 
     According to this driving method, the voltage drop can be reduced, by lowering a peak value of the discharge currents flowing in the first and second electrodes in the sustain period, thereby attaining high display quality without an increase in cost of the PDP apparatus. 
     (21) The driving method of (20), wherein the plurality of third electrodes are divided into a plurality of groups each of which includes two or more third electrodes, and in the sustain period, the rise start timing is controlled in units of groups. 
     (22) The driving method of (21), wherein a voltage applying circuit that applies a voltage is connected to each of the plurality of groups of third electrodes, and in the sustain period, the rise start timing is controlled in such a manner that a signal indicating the rise start timing is input into the voltage applying circuit.
 
(23) The driving method of (20), wherein in the sustain period, the voltage waveforms applied to the plurality of third electrodes are controlled so as to start rising within a time period shorter than a half cycle of a waveform of the voltage applied to the plurality of pairs of first and second electrodes.
 
(24) The driving method of (23), wherein in the sustain period, the voltage waveforms applied to the plurality of third electrodes are controlled so as to start rising, after a time at which the voltage applied to the plurality of pairs of first and second electrodes reaches a predetermined level, but before a time at which a discharge is generated by the voltage applied to the plurality of pairs of first and second electrodes when the voltage is assumed not to be applied to the plurality of third electrodes.
 
(25) The driving method of (24), wherein in the sustain period, a voltage waveform applied to a first electrode and a voltage waveform applied to a second electrode paired with the first electrode have a same cycle, but are different from each other in terms of a timing of application, by half the cycle.
 
(26) The driving method of (20), wherein in the sustain period, a voltage waveform applied to at least one of the plurality of third electrodes starts to fall at a different timing, from a voltage waveform applied to an adjacent third electrode, which is set relative to a time at which the voltage applied to the plurality of pairs of first and second electrodes reaches a predetermined level.
 
(27) The driving method of (26), wherein in the sustain period, the voltage waveforms applied to the plurality of third electrodes are controlled so as to start falling within a time period shorter than a half cycle of a waveform of the voltage applied to the plurality of pairs of first and second electrodes.
 
(28) The driving method of (20), wherein when the voltage waveforms applied to the plurality of third electrodes in the sustain period are expressed using a time axis and a voltage axis, at least one of a rising portion and a falling portion of each of the voltage waveforms has a gradient, and a voltage waveform applied to at least one of the plurality of third electrodes has a different gradient for at least one of a rising portion and a falling portion, from a waveform applied to an adjacent third electrode.
 
(29) The driving method of (28), wherein a duration of at least one of the rising portion and the falling portion of the voltage waveform is shorter than a half cycle of a waveform of the voltage applied to the plurality of pairs of first and second electrodes.
 
(30) The driving method of (20), wherein each of the voltage waveforms applied the plurality of third electrodes in the sustain period is a pulse waveform of a substantially same width.
 
(31) The driving method of (20), wherein the panel unit is driven by repeating a sub-field including the write period and the sustain period, and the rise start timing is controlled in units of sub-fields.
 
(32) The driving method of (31), wherein two or more sub-fields constitute a sub-field group, and the rise start timing is controlled in units of sub-field groups.
 
(33) The driving method of (20), wherein the panel unit is driven by repeating a sub-field including the write period and the sustain period, and a plurality of sub-fields constitute a field, and the rise start timing is controlled in units of fields.
 
(34) The driving method of (33), wherein two or more fields constitute a field group, and the rise start timing is controlled in units of field groups.
 
(35) The driving method of (20), wherein the write period and the sustain period constitute a sub-field, and a plurality of sub-fields constitute a field, and for each of the voltage waveforms applied to the plurality of third electrodes, an average time period, in each sub-field or field, from a time at which the voltage applied to the plurality of pairs of first and second electrodes reaches a predetermined level to a time at which the voltage applied to the plurality of third electrodes starts to rise is substantially same.
 
(36) The driving method of (20), wherein in the sustain period, a cycle of the voltage waveforms applied to the plurality of third electrodes is equal to a half cycle of a waveform of the voltage applied to the plurality of pairs of first and second electrodes.
 
(37) The driving method of (20), wherein in the sustain period, a cycle of the voltage waveforms applied to the plurality of third electrodes is equal to a cycle of a waveform of the voltage applied to the plurality of pairs of first and second electrodes.
 
(38) The driving method of (20), wherein in the sustain period, a cycle of the voltage waveforms applied to the plurality of third electrodes is equal to an integral multiple of a cycle of a waveform of the voltage applied to the plurality of pairs of first and second electrodes.
 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view illustrating (partly illustrating a cross-section of) a main part of a panel unit  10  of a PDP apparatus  1  relating to a first embodiment. 
         FIG. 2  is a block diagram illustrating a circuit structure of the PDP apparatus  1  relating to the first embodiment. 
         FIG. 3  is a block diagram illustrating, in detail, a circuit structure of a part of the PDP apparatus  1  which includes a data driver shown in  FIG. 2 . 
         FIG. 4  illustrates a waveform of a voltage applied to each type of electrodes to drive the PDP apparatus  1 . 
         FIG. 5  illustrates a waveform of a voltage applied to each type of electrodes in a sustain period to drive the PDP apparatus  1 . 
         FIG. 6  is a schematic diagram illustrating discharge currents flowing into a scan electrode and a sustain electrode when driving the PDP apparatus  1 . 
         FIG. 7  illustrates how a time period from application of a sustain pulse to application of a sustain data pulse is related to a time period from application of a sustain pulse to generation of a sustain discharge. 
         FIG. 8  illustrates a waveform of a voltage applied to each type of electrodes in a sustain period to drive a PDP apparatus  2  relating to a second embodiment. 
         FIG. 9  illustrates a waveform of a voltage applied to each type of electrodes in a sustain period to drive a PDP apparatus  3  relating to a third embodiment. 
         FIG. 10  illustrates a waveform of a voltage applied to each type of electrodes in a sustain period to drive a PDP apparatus  4  relating to a fourth embodiment. 
         FIG. 11  is a schematic diagram illustrating a discharge current flowing into one discharge cell when driving a conventional PDP apparatus. 
         FIG. 12  is a schematic diagram illustrating discharge currents flowing into a scan electrode and a sustain electrode in the conventional PDP apparatus. 
     
    
    
     BEST MODE FOR CARRYING OUT THE INVENTION 
     First Embodiment 
     1-1 Construction of Panel Unit  10   
     The following describes a PDP apparatus  1  relating to a first embodiment. To start with, a construction of a panel unit  10  in the PDP apparatus  1  is described with reference to FIG.  1 . It should be noted that the PDP apparatus  1  is AC-type. 
     As shown in  FIG. 1 , the panel unit  10  is constituted by a front panel  11  and a back panel  12  which are placed so as to oppose each other with a space therebetween. A plurality of scan electrodes SCN and a plurality of sustain electrodes SUS are alternately arranged in stripes on a front substrate  111  in the front panel  11 . Note that the scan electrodes SCN and the sustain electrodes SUS may be sometimes collectively referred to as display electrodes hereinafter. A dielectric layer  112  is formed on the entire surface of the front substrate  111  on which the display electrodes SCN and SUS are formed. A protective layer  113  is formed on the dielectric layer  112 . 
     On the other hand, a plurality of data electrodes D are arranged in stripes on a back substrate  121  in the back panel  12 . A dielectric layer  122  is formed on a surface of the back substrate  121  on which the data electrodes D are formed. A plurality of barrier ribs  123  are provided so as to protrude between adjacent data electrodes D, in parallel to the data electrodes D, on the dielectric layer  122 . A red phosphor layer  124 R, a green phosphor layer  124 G and a blue phosphor layer  124 B are formed on the Walls and bottom of grooves defined by the dielectric layer  122  and adjacent barrier ribs  123 . 
     The front panel  11  and the back panel  12  are opposed to each other in such a manner that the protective layer  113  is faced to the phosphor layers  124 R,  124 G and  124 B, and so that the display electrodes SCN and SUS intersect the data electrodes D in the panel unit  10 . Furthermore, the front panel  11  and the back panel  12  are sealed at their peripheral portions using a glass frit. A discharge gas including inert gas components such as helium (He), xenon (Xe) and neon (Ne) is enclosed in the space (a discharge space) between the front panel  11  and the back panel  12 , at a predetermined pressure of approximately 53.2 kPa to 79.8 kPa. 
     In this panel unit  10 , an area where a scan electrode SCN and a sustain electrode SUS intersect a data electrode D forms each discharge cell in relation to image display. 
     Since a typical material is used to form each constituent of the panel unit  10  in the PDP apparatus  1  relating to the first embodiment, a material for each constituent is not explained. There is not particular limitation to the size of the panel unit  10 , but an example size is provided in the following. To realize a VGA in the 40-inch range using the panel unit  10 , a cell pitch of 1080 μm and a cell pitch of 360 μm are required, and the size of one pixel composed of adjacent red, green and blue discharge cells is required to be 1080 μm×1080 μm. 
     1-2 Construction of the PDP Apparatus  1   
     The following describes a construction of the PDP apparatus  1  including the panel unit  10 , with reference to  FIG. 2  which is a block diagram illustrating the construction of the PDP apparatus  1 . 
     As shown in  FIG. 2 , the PDP apparatus  1  relating to the first embodiment is constituted by the panel unit  10  and a driving unit  20 . The driving unit  20  drives the panel unit  10  using a field timesharing gradation display method, to display a gray-scale image. 
     The driving unit  20  is constituted by a preprocessor  21 , a frame memory  22 , a timing generation unit  23  for a synchronizing pulse, a scan driver  24 , a sustain driver  25 , a timing generation unit  26  for a sustain data pulse, and a data driver  27 . 
     The preprocessor  21  extracts image data for each field (field data) from image data input thereto, and generates image data for each sub-field (sub-field data) from the extracted field data. The preprocessor  21  stores the generated sub-field data in the frame memory  22 . Also, the preprocessor  21  extracts line-by-line data from current sub-field data stored in the frame memory  22 , and outputs the extracted data to the data driver  27 . Furthermore, the preprocessor  21  extracts a synchronizing signal such as a horizontal synchronizing signal and a vertical synchronizing signal from image data input thereto, and sends a timing signal, for each field or sub-field, to the timing generation unit  23 . 
     The frame memory  22  is a two-port frame memory including two memory areas each of which can store one piece of field data (for example, eight pieces of sub-field data). In this way, while sub-filed data is being written into one of the memory areas, sub-field data written in the other memory area is being read. Here, writing and reading operations alternate in each of the memory areas. 
     The timing generation unit  23  generates a timing signal to raise each of a set-up pulse, a scan pulse and a sustain pulse, based on the timing signal received from the preprocessor  21 . The timing generation unit  23  sends the generated timing signal to a corresponding one or more of the scan driver  24 , the sustain driver  25  and the data driver  27 . Furthermore, the timing generation unit  23  sends a timing signal to the timing generation unit  26  which generates and sends a timing signal for pulse application, to the data driver  27  in a sustain period. 
     The scan driver  24  is constituted by a driving circuit formed using a publicly-known driver IC. In response to a timing signal from the timing generation unit  23 , the scan driver  24  generates and applies a set-up pulse and a scan pulse to the scan electrodes SCN 1  to SCNk included in the panel unit  10 . 
     The sustain driver  25  is constituted by a driving circuit formed using a publicly-known driver IC. In response to a timing signal from the timing generation unit  23 , the sustain driver  25  generates and applies a set-up pulse and a sustain pulse to the sustain electrodes SUS 1  to SUSk included in the panel unit  10 . 
     The data driver  27  is constituted by a driving circuit formed using a publicly-known driver IC. In a write period, the data driver  27  selectively applies a write pulse to the data electrodes D 1  to Dn, based on sub-field data from the preprocessor  21  and a timing signal sent from the timing generation unit  23 . In a sustain period, each driving circuit built in the data driver  27  applies a pulse (hereinafter referred to as a sustain data pulse) to one or more corresponding data electrodes D, based on a timing signal sent from the timing generation unit  26 . A method to control application of the sustain data pulse is described later. 
     1-3 Construction of the Data Driver  27   
     The following describes the data driver  27  and constituents of the driving unit  20  relevant to the data driver  27  in detail, with reference to  FIG. 3 . 
     As shown in  FIG. 3 , the data driver  27  can receive a signal from the preprocessor  21 , the timing generation unit  23 , and the timing generation unit  26 . Also, the data driver  27  is configured to be able to apply a write pulse and a sustain data pulse to the data electrodes D 1  to Dn. Here, the data driver  27  has M driving circuits  271  to  27   m  built-in, and each of the driving circuits  271  to  27   m  is connected to a predetermined number of data electrodes D. In the first embodiment, as an example, each driving circuit is connected to four data electrodes D. In other words, the data electrodes D 1  to Dn are divided into a plurality of groups of four data electrodes D. The driving circuits  271  to  27   m  are provided in a one-to-one correspondence with the groups of four data electrodes D. 
     The timing generation unit  26  inputs timing signals Sig.  1  to Sig. m to the driving circuits  271  to  27   m  respectively. 
     The preprocessor  21  and the timing generation unit  23  respectively input sub-field data and a timing signal to the data driver  27  in the same manner as their counterparts of a conventional PDP apparatus. 
     1-4 Driving Method for the PDP Apparatus  1   
     The following describes a driving method for the PDP apparatus  1  with reference to  FIG. 4 .  FIG. 4  illustrates a method to drive the PDP apparatus  1  using a field timesharing gradation display method. As an example, one field is divided into eight sub-fields SF 1  to SF 8  to express 256 gray levels. In  FIG. 4 , time is plotted along the horizontal axis, and each rectangular area crossed by a line indicates a write period. 
     As shown in  FIG. 4 , the PDP apparatus  1  relating to the first embodiment is driven in such a manner that one field is divided into eight sub-fields SF 1  to SF 8 . The number of sustain pulses applied in each of the sub-fields SF 1  to SF 8  is set so that the relative luminance ratio of the eight sub-fields is 1:2:4:8:16:32:64:128. Here, lit/unlit states in the sub-fields SF 1  to SF 8  are controlled in accordance with data relating to display luminance. In this way, 256 gray levels can be expressed by various combinations of the sub-fields SF 1  to SF 8 . According to the first embodiment, an image is displayed in 256 gray levels, but the present invention is not limited to such. 
     The sub-fields SF 1  to SF 8  are each constituted by a set-up period T 1 , a write period T 2 , and a sustain period T 3 . The set-up period T 1  and the write period T 2  each have a predetermined duration, but the sustain period T 3  has a duration determined in accordance with a relative luminance ratio of a corresponding sub-field. The panel unit  10  is, for example, driven in the following manner to display an image. To start with, in the set-up period T 1 , a set-up discharge is caused in all of the discharge cells in the panel unit  10 . This eliminates an effect of a discharge generated in a previous sub-field, and absorbs unevenness in discharge properties. 
     In the write period T 2 , the scan electrodes SCN 1  to SCNk are scanned line by line in this order based on sub-field data. Thus, a weak discharge is generated between scan electrodes SCN and data electrodes D in discharge cells in which a sustain discharge needs to be performed in a current sub-field. As a result of the weak discharge, a wall charge accumulates in the discharge cells, on a surface of the protective layer  113  of the front panel  11 . 
     In the sustain period T 3 , sustain pulses  300  and  310  having a rectangular waveform are respectively applied to the sustain electrodes SUS and the scan electrodes SCN. The sustain pulses  300  and  310  each have a predetermined voltage and a predetermined cycle (for example, 2.5 μsec). The sustain pulse  300  applied to the sustain electrodes SUS and the sustain pulse  310  applied to the scan electrodes SCN have the same cycle, but are out of phase by half a cycle. The sustain pulses  300  and  310  are simultaneously applied to all of the discharge cells in the panel unit  10 . 
     In addition, a pulse having a rectangular waveform (a sustain data pulse)  320  is applied to the data electrodes D in the sustain period T 3 , according to the driving method for the PDP apparatus  1  relating to the first embodiment, as shown in  FIG. 4 . 
     1-5 Application of the Sustain Data Pulse  320   
     The following describes a manner of applying the sustain data pulse  320  to the data electrodes D in the sustain period T 3 , with reference to  FIG. 5  which illustrates the sustain period T 3  shown in the driving chart of  FIG. 4  in detail. 
     As seen from  FIG. 5 , the sustain pulses  300  and  310  are applied to the sustain electrodes SUS and the scan electrodes SCN in the sustain period T 3  so as to be out of phase by half a cycle as mentioned above. Furthermore, the sustain data pulses  320  are applied to the data electrodes D 1  to Dn in the sustain period T 3  according to the first embodiment, as mentioned above. The first embodiment is characterized in that the sustain data pulses  320  differ in terms of timing of application among the data electrodes D. 
     To be specific, sustain data pulses  320 ( 1 ) to  320 ( 4 ) are respectively applied to data electrodes D 1  to D 4 . Here, rectangular waveforms P 11 , P 12  and P 13  of the sustain data pulse  320 ( 1 ) start to rise at timings t 11 , t 12  and t 13  (rise start timings) respectively. The same is true about rectangular waveforms P 21  to P 23  of the sustain data pulse  320 ( 2 ), P 31  to P 33  of the sustain data pulse  320 ( 3 ), and P 41  to P 43  of the sustain data pulse  320 ( 4 ). On the other hand, the sustain pulse  300  applied to the sustain electrodes SUS starts to rise at a timing t 2  (a rising portion of  302   a ), and the sustain pulse  310  applied to the scan electrodes SCN starts to rise at timings t 1  and t 3  (rising portions of  311   a  and  313   a ). Here, the rise start timings t 11 , t 12  and t 13  are substantially the same as the rise start timings t 1 , t 2  and t 3 . In other words, when receiving a timing signal Sig.  1  from the timing generation unit  26 , a driving circuit  1  ( 271 ) to which the data electrodes D 1  to D 4  are connected applies the sustain data pulses  320 ( 1 ) to  320 ( 4 ) to the data electrodes D 1  to D 4 . 
     Rectangular pulses P 51  to P 53 , P 61  to P 63 , P 71  to P 73 , and P 81  to P 83  which are applied to data electrodes D 5 , D 6 , D 7  and D 8  start to rise at timings t 51 , t 52  and t 53 . Here, there is a slight time lag from the rise start timings t 1 , t 2  and t 3  of the sustain pulses  300  and  310  to the rise start timings t 51 , t 52  and t 53 . The time lag is set in accordance with a clock pulse  330  shown in the bottom of  FIG. 5 . 
     As shown in  FIG. 5 , when driving the PDP apparatus  1 , the sustain data pulses  320 ( 1 ) to  320 ( n ) are applied to the data electrodes D 1  to Dn in the sustain period T 3 , in such a manner that each of the driving circuits  271  to  27   m  raises rectangular pulses at a different timing. 
     As seen from  FIG. 5 , a potential of each rectangular pulse of the sustain data pulses  320 ( 1 ) to  320 ( n ) applied to the data electrodes D 1  to Dn in the sustain period T 3  is uniform. Here, strictly speaking, the sustain pulses  300  and  310  and the sustain data pulse  320  do not have a completely rectangular waveform shown in  FIG. 5 . Which is to say, the rising portion  311   a  of the sustain pulse  310  applied to the scan electrodes SCN has a gradient. In other words, there is a time lag (for example, 250 nsec) between the rise start timing t 1  and a timing at which a predetermined potential is achieved. Taking this into account, the sustain data pulses  320 ( 1 ) to  320 ( n ) are applied at timings that are determined with respect to timings at which the voltage of the sustain pulses  300  and  310  reaches a predetermined level after a certain time period (for example, 250 nsec.) has elapsed from the rise start timings t 1 , t 2 , . . . . 
     1-6 Advantages of the PDP Apparatus  1   
     The following describes advantages of the PDP apparatus  1  relating to the first embodiment, with reference to  FIG. 6 .  FIG. 6  is a schematic view illustrating discharge currents flowing in the scan electrodes SCN and the sustain electrodes SUS in the sustain period T 3 . 
     As shown in  FIG. 6 , discharge currents E 1 , E 2 , E 3  and E 4  flowing in the scan electrodes SCN and the sustain electrodes SUS in the sustain period T 3  respectively peak at times t 501 , t 502 , t 503  and t 504 , which are different from each other. According to the first embodiment, each of the driving circuits  271  to  27   m  applies a set of sustain data pulses  320  at a different timing in the sustain period T 3 , as presented in  FIG. 5 . This can make a difference in time period from the application of the sustain pulses  300  and  310  to occurrence of a sustain discharge. Hence, the discharge currents E 1 , E 2 , E 3  and E 4  each peak at a different time in the PDP apparatus  1  as shown in  FIG. 6 . As a consequence, a total discharge current Et flowing in the sustain period T 3  observed when driving the PDP apparatus  1  can be reduced, when compared with a total discharge current Et 0  (shown in  FIG. 12 ) observed when driving a conventional PDP apparatus. 
     As explained above, each of the driving circuits  271  to  27   m  applies a set of sustain data pulses  320  at a different timing in the sustain period T 3  when driving the PDP apparatus  1 . This means that a sustain discharge starts at three or more different timings in the sustain period T 3 . Therefore, the first embodiment of the present invention is superior to the technique disclosed in Japanese patent application publication No. H11-149274, from the aspect of enhancement of display quality. 
     Moreover, discharge currents generated in the sustain period T 3  differ in terms of peak time without increasing the number of power sources in the PDP apparatus  1 . Therefore, the first embodiment of the present invention is superior to the technique disclosed in the Japanese patent application publication No. H10-133622, from the aspect of a manufacturing cost. 
     In the PDP apparatus  1 , since a voltage drop caused by the discharge currents in the sustain period T 3  can be reduced, high display quality is maintained. Here, a current drive power required for the driving unit  20  is determined by a peak value of a total discharge current. In the PDP apparatus  1 , since the sustain data pulses  320  differ in terms of timing of application, a peak value of the total discharge current Et can be made lower than in the related art. This means that the driving unit  20  is required to have only a relatively small current drive power. Therefore, an inexpensive driving circuit can be used for the PDP apparatus  1  relating to the first embodiment. This reduces the manufacturing cost of the PDP apparatus  1 . 
     If possible in terms of manufacturing cost, two or more power sources which each have a different voltage value may be used. Thus, the sustain data pulses  320  differ with respect to not only timing of application, but also potential. This can differentiate the discharge currents more minutely in terms of peak time in the sustain period T 3 , and therefore achieves a better result in lowering the peak value of the total discharge current Et. However, it should be taken into consideration that an excessively large difference in potential causes enormous unevenness in luminance among the discharge cells. In this case, display quality is adversely degraded. 
     According to the above description, each driving circuit in the data driver  27  applies a pulse to four data electrodes D in the first embodiment. However, the present invention is not limited to such. The most distinctive feature of the first embodiment is that each driving circuit in the data driver  27  applies a set of sustain data pulses  320  at a different timing. Thus, a sustain discharge differs with respect to timing of generation. This produces an effect of lowering a peak value of a total discharge current in the scan electrodes SCN and the sustain electrodes SUS. 
     1-7 Confirmation Data 
     The following describes how a time difference from application of the sustain pulse  300  or  310  to application of the sustain data pulse  320  (an application timing) is related to a time difference from application of the sustain pulses  300  and  310  to occurrence of a sustain discharge (a discharge start timing), with reference to  FIG. 7 .  FIG. 7  is a characteristic diagram illustrating the relation between the application timing and the discharge start timing, when the sustain pulses  300  and  310  rising in 0.5 μsec are applied to the sustain electrodes SUS and the scan electrodes SCN. 
     As shown in  FIG. 7 , when the application timing is within a range from 0 μsec to 0.3 μsec, the discharge start timing is constant at approximately 0.73 μsec. Similarly, when the application timing is 0.7 μsec or more, the discharge start timing is constant at approximately 0.73 μsec. This is because the sustain data pulses  320  are applied to the data electrodes D before the voltage of the sustain pulses  300  and  310  applied to the sustain electrodes SUS and the scan electrodes SCN rises to a predetermined level. Specifically speaking, the sustain data pulses  320  are applied too early, and therefore make no difference in discharge start timing. 
     The predetermined level of the voltage is equal to approximately 60% of a voltage value V SUS  which is achieved at the end of the rising portions of the sustain pulses  300  and  310 . This percentage is calculated as follows.  FIG. 7  shows that, when the application timing is 0.3 μsec or more, the discharge start timing varies. Based on this, 0.3/0.5=0.6. Thus, the predetermined level of the voltage can be calculated based on this percentage. However, it should be noted that the predetermined level is determined in accordance with a gradient of increase in voltage in the rising portions, if the sustain pulses  300  and  310  do not rise linearly. 
     When the application timing is 0.7 μsec or more, application of the sustain data pulses  320  makes no difference in discharge start timing of a sustain discharge. This is because the sustain data pulses  320  are applied after a time at which a sustain discharge is generated by the sustain pulses  300  and  310  when the sustain data pulses  320  are assumed not to be applied. 
     As seen from  FIG. 7 , when the application timing is in a range from 0.3 μsec to 0.7 μsec, the discharge start timing takes the smallest value of 0.43 μsec at the application timing of 0.4 μsec. Furthermore, when the application timing is changed within a range from 0.4 μsec to 0.7 μsec, the discharge start timing varies substantially linearly. 
     1-8 Modifications of the First Embodiment 
     According to the first embodiment, each of the driving circuits  271  to  27   m  in the data driver  27  applies a voltage to four data electrodes D. However, the present invention is not limited to such. 
     Furthermore, the cycle of the sustain data pulses  320  applied to the data electrodes D is equal to a half cycle of the sustain pulses  300  and  310 , as shown in  FIG. 5 . However, the present invention is not limited to such. As an alternative example, the cycle of the sustain data pulses  320  may be equal to the cycle of the sustain pulses  300  and  310 . Which is to say, while the sustain data pulse  320  is applied to each of the data electrodes D 1  to Dn once, a sustain discharge may be generated twice. Moreover, the cycle of the sustain data pulses  320  may be equal to an integral multiple of the cycle of the sustain pulses  300  and  310 . In other words, while the sustain data pulse  320  is applied to each of the data electrodes D 1  to Dn once, a sustain discharge may be generated four or more times. According to these modifications, the sustain data pulses  320  can also produce an effect of reducing a voltage drop, differently from a conventional driving method where the sustain data pulses  320  are not applied. 
     As shown in  FIG. 5  and the like, the sustain pulses  300  and  310  and the sustain data pulses  320  have a rectangular waveform. However, the pulses  300 ,  310  and  320  may have a waveform with gradient rising and falling portions. If such is the case, the time at which the sustain data pulses  320  are applied to the data electrodes D is varied between the time at which the voltage of the sustain pulses  300  and  310  rises to the predetermined level and the time at which a sustain discharge is generated by the sustain pulses  300  and  310  when the sustain data pulses  320  are assumed not to be applied, as stated in the section 1-7. 
     Furthermore, each of the sustain data pulses  320 ( 1 ) to  320 ( n ) preferably has the same pulse width. However, the present invention is not limited to such. Similarly, each of the sustain data pulses  320 ( 1 ) to  320 ( n ) preferably has the same voltage in order to reduce unevenness in luminance among the discharge cells. However, the sustain data pulses  320  may differ in terms of voltage at several levels. In this case, unevenness in luminance is observed. In addition, since the number of power sources needs to be increased, the problem of a higher manufacturing cost emerges. 
     Second Embodiment 
     The following describes a PDP apparatus  2  relating to a second embodiment and a driving method for the same, with reference to  FIG. 8 . 
     The PDP apparatus  2  has substantially the same construction as the PDP apparatus  1  shown in  FIG. 2 . Therefore, the PDP apparatus  2  is not illustrated in the drawings. The PDP apparatus  2  is different form the PDP apparatus  1  in that the timing generation unit  26  (shown in  FIG. 2 ) is configured to be able to specify a timing of applying a sustain data pulse  321  to each one of the data electrodes D 1  to Dn in the sustain period. This configuration of the timing generation unit  26  can be realized making use of the construction of the timing generation unit  23  which sends a timing signal for applying a pulse to each of the data electrode D 1  to Dn in the write period T 2 . 
     According to the driving method for the PDP apparatus  2 , the sustain data pulses  321 ( 1 ) to  321 ( n ) are respectively applied to the data electrodes D 1  to Dn in the sustain period T 3 , in such a manner that each of the sustain data pulses  321 ( 1 ) to  321 ( n ) is applied at a different timing, as presented in  FIG. 8 . To be more specific, a rectangular pulse Q 11  is applied to the data electrode D 1  at substantially the same timing (t 111 ) as the sustain pulses  300  and  310  (t 101 ). A rectangular pulse Q 21  is applied to the data electrode D 2  at a timing t 121  which is slightly later than the rise start timings t 101  and t 111 . In this way, each of the sustain data pulses  321 ( 1 ) to  321 ( n ) is applied at a different timing. 
     As well as in the first embodiment, rectangular pulses (Q 11 , Q 12 , . . . ) of the sustain data pulses  321  are set to start rising after the time at which the voltage of the sustain pulses  300  and  310  reaches a predetermined level in the rising portions  302   a  and  311   a , in the second embodiment. 
     As described above, each of the sustain data pulses  321 ( 1 ) to  321 ( n ) is applied at a different timing in the sustain period T 3  when driving the PDP apparatus  2 . In this way, a time period from the application of the sustain pulses  300  and  310  to generation of a sustain discharge differs, in accordance with a time lag from the application of the sustain pulses  300  and  310  to the application of the sustain data pulses  321 ( 1 ) to  321 ( n ), as in the first embodiment. This differentiates discharge currents in terms of peak time in the PDP apparatus  2 , as shown in  FIG. 6 . Consequently, the total discharge current Et in the sustain period T 3  can be reduced, when compared with the total discharge current Et 0  (see  FIG. 12 ) in the conventional PDP apparatus. Furthermore, the sustain data pulse  321  is controlled for (applied at a different timing to) each of the data electrodes D 1  to Dn according to the second embodiment. This can achieve a more favorable result regarding the differentiation of discharge currents than in the PDP apparatus  1  relating to the first embodiment. 
     For the reasons stated above, the second embodiment can reduce a voltage drop caused by the discharge currents in the sustain period T 3 , thereby maintaining high display quality. Furthermore, since the sustain data pulses  321  differ in terms of timing of application according to the second embodiment, the peak value of the total discharge current Et can be lowered. Therefore, an inexpensive driving circuit with a relatively small current drive power can be used to constitute the PDP apparatus  2 . Accordingly, the PDP apparatus  2  is superior to the conventional PDP apparatus from the aspect of manufacturing cost. 
     As well as the first embodiment, the second embodiment can be modified in various manners. Such modifications of the second embodiment can also produce the above-described effects. 
     Third Embodiment 
     The following describes a PDP apparatus  3  relating to a third embodiment and a driving method for the same, with reference to  FIG. 9 . 
     The PDP apparatus  3  is not illustrated in the drawings. As well as the PDP apparatus  2 , the timing generation unit  26  is configured to be able to specify a timing of applying a sustain data pulse  322  to each of the data electrodes D 1  to Dn in the sustain period T 3  in the PDP apparatus  3 . The third embodiment is different from the second embodiment in terms of the following feature of the driving method. 
     As shown in  FIG. 9 , sustain data pulses  322 ( 1 ) to  322 ( n ) are respectively applied to the data electrodes D 1  to Dn in the sustain period T 3 , when driving the PDP apparatus  3 . Here, rectangular pulses R 11 , R 21 , . . . , Rn 1  of the sustain data pulses  322 ( 1 ) to  322 ( n ) are respectively applied in the third embodiment, at the same timings as in the second embodiment (shown in FIG.  8 ), which are determined with respect to a timing t 201  at which the sustain pulse  300  falls ( 301   a ) and the sustain pulse  310  rises ( 311   a ). 
     Furthermore, rectangular pulses R 12 , R 22 , . . . , Rn 2  are respectively applied at timings t 212 , t 222 , t 232 , . . . , t 2   n   2 , which are determined with respect to a timing t 202  at which the sustain pulse  300  rises ( 302   a ) and the sustain pulse  310  falls ( 312   a ). 
     Here, the timings of applying the rectangular pulses are set so as to satisfy the following condition. For each of the data electrodes D 1  to Dn, an average time period from the time (t 201 , . . . ) at which the sustain pulse  300  or  310  is applied to the time (t 211 , . . . ) at which the rectangular pulse (R 11 , . . . ) is applied is substantially the same, for each sub-field or field. In short, the timings at which the sustain data pulses  322  are applied are determined based on the following formulas in the third embodiment.
 
 t 1 ave   =Ave (( t 211− t 201),( t 212− t 202), . . . )  (FORMULA 1)
 
 t 2 ave   =Ave (( t 221− t 201),( t 222− t 202), . . . )  (FORMULA 2)
 
 t 3 Ave   =Ave (( t 231− t 201),( t 232− t 202), . . . )  (FORMULA 3)
 
     This calculation is conducted for each of the data electrodes D 1  to Dn. It should be noted that such an average time period is obtained for each sub-field or field as mentioned above. 
     The sustain data pulses  322 ( 1 ) to  322 ( n ) are applied at timings which are determined so as to satisfy the following formula (4) that defines the relation between the average time periods calculated for the data electrodes D 1  to Dn.
 
t1 Ave =t2 Ave =t3 Ave = . . . =tn Ave   (Formula 4)
 
     The third embodiment described above can differentiate the discharge currents in terms of peak time in the sustain period T 3 , as well as the first and second embodiments. Therefore, the third embodiment can reduce a voltage drop caused by the discharge currents in the sustain period T 3 , thereby maintaining high display quality. Furthermore, since the sustain data pulses  322  differ in terms of timing of application, the peak value of the total discharge current Et can be lowered. This makes it possible to use an inexpensive driving circuit with a relatively small current drive power for the PDP apparatus  3 . Hence, the PDP apparatus  3  is superior to the conventional PDP apparatus from the aspect of manufacturing cost. 
     According to the third embodiment, in each of the sustain data pulses  322 ( 1 ) to  322 ( n ), a time difference between the application of each rectangular pulse and the application of a corresponding one of the sustain pulses  300  and  310  is not constant. This construction can reduce occurrence of unevenness in luminance among groups of discharge cells formed by the respective data electrodes D. According to the second embodiment, on the other hand, a time difference from the application of each rectangular pulse of the sustain data pulse  322 ( 1 ) to the data electrode D 1  to the application of the sustain pulse  300  or  301 , for example, is constant as shown in  FIG. 8 . To be specific, time differences (t 111 −t 101 ), (t 112 −t 102 ), . . . are of the same value in each sub-field or field. The same rule applies to the rest of the sustain data pulses  322 . This causes unevenness in luminance among the groups of discharge cells formed by the respective data electrodes D. 
     According to the PDP apparatus  3  relating to the third embodiment, such unevenness in luminance is less likely to be caused. This is because the average time difference is the same for each data electrode D, in each sub-field or field. 
     To sum up, the PDP apparatus  3  relating to the third embodiment can achieve less unevenness in luminance, in addition to the effects of the PDP apparatuses  1  and  2 . Therefore, the PDP apparatus  3  attains high display quality. 
     The third embodiment can be modified in various manners, as well as the first and second embodiments. Such modifications can also produce the above-described effects. 
     Fourth Embodiment 
     The following describes a driving method for a PDP apparatus  4  relating to a fourth embodiment, with reference to  FIG. 10 . In  FIG. 10 , a sustain period T 31  of a sub-field in a first field is shown on the left side, and a sustain period T 32  in a sub-field in a second field following the first field is shown on the right side. 
     As seen from  FIG. 10 , in the first field, rectangular pulses S 11 , S 12 , . . . are applied to the data electrodes D 1  to Dn at timings t 311 , t 312 , . . . . Here, the rise start timings t 311 , t 312 , . . . are set in the same manner as in the second embodiment. In more detail, a group of rectangular pulses (S 11 , S 12 , . . . ) applied to each of the data electrodes D 1  to Dn in the sustain period T 31  is slightly different in terms of timing of application. 
     The application of the rectangular pulses S 11 , S 12 , . . . comes after the timings t 301 , t 302 , . . . at which the sustain pulses  310  and  300  are applied, or, to be more specific, after the voltage of the sustain pulses  300  and  310  rises to a predetermined level in the rising portions  302   a  and  311   a , as in the first to third embodiments. 
     In the second field, on the other hand, rectangular pulses S 15 , S 16 , . . . are applied to the data electrodes D 1  to Dn at timings t 315 , t 316 , . . . . Here, the timings t 315 , t 316 , . . . are determined in the same manner as in the third embodiment as follows. A time difference is calculated from the timings t 305 , t 306 , . . . at which the sustain pulses  310  and  300  are applied to the timings t 315 , t 316 , . . . at which the rectangular pulses S 15 , S 16 , . . . are applied to the data electrodes D 1  to Dn in the sustain period T 32 . Furthermore, an average value of such time differences for each of the data electrodes D 1  to Dn is calculated, for each sub-field or field. Here, the average value is substantially the same for each of the data electrodes D 1  to Dn. This configuration is not further described here as it is described in the third embodiment. 
     According to the driving method relating to the fourth embodiment, discharge currents differ with respect to peak time in the sustain periods T 31  and T 32 , as in the first to third embodiments. Thus, the fourth embodiment can reduce a voltage drop caused by the discharge currents in the sustain periods T 31  and T 32 , thereby maintaining high display quality. In addition, since sustain data pulses  323  differ in terms of timing of application in a different manner for each field as shown in  FIG. 10 , the peak value of the total discharge current Et can be lowered. This makes it possible to use an inexpensive driving circuit with a relatively small current drive power for the PDP apparatus  4  relating to the fourth embodiment. Therefore, the PDP apparatus  4  is superior to the conventional PDP apparatus with respect to manufacturing cost. 
     The fourth embodiment can be modified in various manners, as well as the first and second embodiments. Such modifications can also produce the above-described effects. 
     Other Modifications for the First to Fourth Embodiments 
     According to the first to fourth embodiments, every sub-field in a field has the set-up period T 1 , the write period T 2 , and the sustain period T 3 , as shown in  FIG. 4 . However, the present invention is not limited to such. As an alternative example, a field may have a sub-field which has only the write period T 2  and the sustain period T 3 , or a sub-field made up only by the sustain period T 3 . 
     Furthermore, as briefly mentioned in the first to fourth embodiments, the sustain data pulses  320 ,  321 ,  322 , or  323  applied to each of the data electrodes D 1  to Dn in the sustain period T 3  may have a different voltage, if possible in terms of manufacturing cost. In this case, it should be noted that a difference in voltage needs to be set within a range that does not cause large unevenness in luminance. 
     INDUSTRIAL APPLICABILITY 
     The present invention can be utilized to realize a display apparatus for use in computers and televisions, especially a display apparatus with high display quality.