Abstract:
Disclosed herein is an apparatus and method for driving a plasma display panel, wherein electromagnetic interference is minimized and stability is improved. According to the present invention, the apparatus for driving a PDP includes a plurality of scan electrodes and sustain electrodes, which are formed parallel to each other, and a scan driving unit for alternately supplying sustain pulses of the positive polarity and the negative polarity to the scan electrodes during a sustain period, wherein the sustain electrodes are connected to a ground voltage source, and thus always keep a ground voltage.

Description:
CROSS-REFERENCES TO RELATED APPLICATIONS  
       [0001]     This Nonprovisional application claims priority under  35  U.S.C. § 119(a) on Patent Application No.  10-2004-0015057  filed in Korea on Mar. 5, 2004, the entire contents of which are hereby incorporated by reference.  
       FIELD OF THE INVENTION  
       [0002]     The present invention relates to an apparatus and method for driving a plasma display panel, and more particularly, to an apparatus and method for driving a plasma display panel, wherein electromagnetic interference is minimized and stability is improved.  
       BACKGROUND OF THE RELATED ART  
       [0003]     A plasma display panel (hereinafter, referred to as a ‘PDP’) is adapted to display an image including characters or graphics by light-emitting phosphors with ultraviolet of 147 nm generated during the discharge of a gas such as He+Xe, Ne+Xe or He+Ne+Xe. This PDP can be easily made thin and large, and it can provide greatly increased image quality with the recent development of the relevant technology. Particularly, a three-electrode AC surface discharge type PDP has advantages of lower driving voltage and longer product lifespan as a voltage necessary for discharging is lowered by wall charges accumulated on a surface upon discharging and electrodes are protected from sputtering caused by discharging.  
         [0004]     FIG. 1  is a perspective view illustrating the structure of a discharge cell of a conventional three-electrode AC surface discharge type PDP.  
         [0005]     Referring now to  FIG. 1 , a discharge cell of a three-electrode AC surface discharge type PDP includes a scan electrodes Y and a sustain electrode Z which are formed on the bottom surface of an upper substrate  10 , and an address electrode X formed on a lower substrate  18 . The scan electrodes Y includes a transparent electrode  12 Y, and a metal bus electrode  13  which has a line width smaller than that of the transparent electrode  12 Y and is disposed at one side edge of the transparent electrode. Further, the sustain electrode Z includes a transparent electrode  12 Z, and a metal bus electrode  13 Z which has a line width smaller than that of the transparent electrode  12 Z and is disposed at one side edge of the transparent electrode.  
         [0006]     The transparent electrodes  12 Y and  12 Z, which are generally made of ITO (indium tin oxide), are formed on the bottom surface of the upper substrate  10 . The metal bus electrodes  13 Y and  13 Z are generally formed on the transparent electrodes  12 Y and  12 Z made of metal such as chromium (Cr), and serves to reduce a voltage drop caused by the transparent electrodes  12 Y and  12 Z having high resistance. On the bottom surface of the upper substrate  10  in which the scan electrodes Y and the sustain electrode Z are placed parallel to each other is laminated an upper dielectric layer  14  and a protective layer  16 . The upper dielectric layer  14  is accumulated with a wall charge generated during plasma discharging. The protective layer  16  is adapted to prevent damages of the upper dielectric layer  14  due to sputtering caused during plasma discharging, and improve efficiency of secondary electron emission. As the protective layer  16 , magnesium oxide (MgO) is generally used.  
         [0007]     A lower dielectric layer  22  and barrier ribs  24  are formed on the lower substrate  18  in which the address electrode X is formed. A phosphor layer  26  is applied to the surfaces of both the lower dielectric layer  22  and the barrier ribs  24 . The address electrode X is formed on the lower substrate  18  in the direction in which the scan electrodes Y and the sustain electrode Z intersect with each other. The barrier ribs  24  are in the form of stripe or lattice to prevent leakage of an ultraviolet and a visible light generated by discharging to an adjacent discharge cell. The phosphor layer  26  is excited with an ultraviolet generated during the plasma discharging to generate any one visible light of red, green and blue lights. An inert mixed gas is injected into the discharge spaces defined between the upper substrate  10  and the barrier ribs  24  and between the lower substrate  18  and the barrier ribs  24 .  
         [0008]     This PDP is driven with one frame being time-divided into a plurality of sub-fields having a different number of emission in order to implement the gray scale of an image. Each of the sub fields is divided into an initialization period for initializing the entire screen, an address period for selecting a scan line and selecting a cell from the selected scan line, and a sustain period for implementing gray scales according to the number of discharging.  
         [0009]     In this time, the initialization period is divided into a set-up period where a ramp-up waveform is applied, and a set-down period where a ramp-down waveform is applied. If it is desired to display an image with 256 gray scales, a frame period (16.67 ms) corresponding to 1/60 seconds is divided into eight sub-fields SF 1  to SF 8 , as shown in  FIG. 2 . Each of the sub-fields SF 1  to SF 8  is subdivided into the initialization period, the address period and the sustain period, as described above. The initialization period and the address period of each of the sub-fields SF 1  to SF 8  are the same every sub-field, whereas the sustain period increases in the ratio of 2 n  (where, n=0,1,2,3,4,5,6,7) in each sub-field.  
         [0010]      FIG. 3  is a block diagram of an apparatus for driving a PDP in the prior art.  
         [0011]     Referring to  FIG. 3 , the conventional apparatus for driving the PDP includes an address driving unit  32  for driving address electrodes X 1  to Xm disposed in a panel  30 , a scan driving unit  34  for driving scan electrodes Y 1  to Yn disposed in the panel  30 , a sustain driving unit  36  for driving sustain electrodes Z 1  to Zn disposed in the panel  30 , a driving voltage generator  40  for supplying driving voltages to the driving units  32 ,  34  and  36 , and a timing controller  38  for supplying control signals SCS 1  to SCS 3  to the driving units  32 ,  34  and  36 .  
         [0012]     The driving voltage generator  40  generates a variety of driving voltages so that a driving waveform as shown in  FIG. 4  can be generated, and supplies the generated voltages to the address driving unit  32 , the scan driving unit  34  and the sustain driving unit  36 . For example, the driving voltage generator  40  generates voltages, such as Vsetup, −Vw, Vr and Vs, and supplies the voltages to the scan driving unit  34 . It generates a voltage Vs, and provides the voltage to the sustain driving unit  36 . Furthermore, the driving voltage generator  40  generates a voltage Va, and provides it to the address driving unit  32 .  
         [0013]     The timing controller  38  generates a variety of the switching control signals so that the driving waveform as shown in  FIG. 4  can be generated, and supplies the generated switching control signals to the address driving unit  32 , the scan driving unit  34  and the sustain driving unit  36 . For example, the timing controller  38  generates a first switching control signal SCS 1  and a second switching control signal SCS 2 , and supplies the signals to the scan driving unit  34  and the sustain driving unit  36 , respectively. Also, the timing controller  38  generates a third switching control signal SCS 3  and a data clock DCLK, and supplies them to the address driving unit  32 .  
         [0014]     The address driving unit  32  serves to supply image data data, which are received from the outside, to the address electrodes X 1  to Xm, under the control of the data clock DCLK and the third switching control signal SCS 3 , both of which are supplied from the timing controller  38 .  
         [0015]     The scan driving unit  34  supplies a reset pulse, a scan pulse scan and a sustain pulse sus to the scan electrodes Y 1  to Ym, under the control of the first switching control signal SCS 1  outputted from the timing controller  38 .  
         [0016]     The sustain driving unit  36  supplies a positive polarity voltage (Vs), the sustain pulse sus and an erase pulse erase to the sustain electrodes Z 1  to Zn, under the control of the second switching control signal SCS 2  outputted from the timing controller  38 .  
         [0017]     The driving waveform applied to the electrodes will now be described in detail with reference to  FIG. 4 . In a set-up period of the initialization period, a ramp-up waveform Ramp-up is applied to all the scan electrodes Y at the same time. A weak discharge is generated within cells of the entire screen by the ramp-up waveform Ramp-up, thus generating wall charges within the cells. In the set-down period, after the ramp-up waveform Ramp-up is applied, a ramp-down waveform Ramp-down, which falls from a voltage of the positive polarity that is lower than the peak voltage of the ramp-up waveform Ramp-up, is applied to the scan electrodes Y at the same time. The ramp-down waveform Ramp-down generates a weak erase discharge within the cells to erase the wall charges generated by a set-up discharge and unnecessary charges among space charges and also to allow the wall charges necessary for an address discharge to uniformly remain within the cells of the entire screen.  
         [0018]     In the address period, simultaneous when the scan pulse scan of the negative polarity is sequentially applied to the scan electrodes Y, the data pulse data of the positive polarity is applied to the address electrodes X. As a voltage difference between the scan pulse scan and the data pulse data and the wall voltage generated in the initialization period are added, the address discharge is generated within cells to which the data pulse data is applied. The wall charges are generated within cells selected by the address discharge.  
         [0019]     Meanwhile, during the set-down period and the address period, a positive DC voltage of the sustain voltage level (Vs) is applied to the sustain electrodes Z.  
         [0020]     In the sustain period, the sustain pulse sus is alternately applied to the scan electrodes Y and the sustain electrodes Z. Then, in cells selected by the address discharge, a sustain discharge is generated in the form of a surface discharge between the scan electrodes Y and the sustain electrodes Z whenever every sustain pulse sus is applied as wall voltages within the cells and the sustain pulse sus are added. After the sustain discharge is completed, an erase ramp waveform erase having a small pulse width is applied to the sustain electrodes Z to erase the wall charges within the cells.  
         [0021]     In such a conventional PDP, during the sustain period, the scan electrodes Y and the sustain electrodes Z are alternately applied with the sustain pulse sus. At this time, when the sustain pulse sus is supplied to the scan electrodes Y, the sustain electrodes Z is supplied with the ground voltage GND. When the sustain pulse sus is provided to the sustain electrodes Y, the scan electrodes Z is supplied with the ground voltage GND. That is, since a high current flows when the sustain pulse sus is provided to a given electrodes Y or Z, the remaining electrode to which the sustain pulse sus is not supplied is connected to the ground voltage GND, so that the operation is stabilized. However, during the sustain period, in order for the scan electrodes Y and the sustain electrodes Z to be connected to the sustain pulse sus and the ground voltage GND in an alternate way, switching means included in the scan driving unit  34  and the sustain driving unit  36  perform lots of switching operations. Accordingly, there is a problem in that high EMI is generated. Furthermore, in the prior art, since lots of switching means (i.e., line is long) are needed in order for the scan electrodes Y and the sustain electrodes Z to be connected to the ground voltage GND, there is a problem in that additional noise is generated.  
         [0022]     Generally, in order to stabilize the operation of a PDP, any one of the scan electrodes Y and the sustain electrodes Z has to be connected to the ground voltage GND so that a voltage level can be stabilized. Practically, however, if any one of the scan electrodes Y and the sustain electrodes Z is connected to the ground voltage GND, introduction of external noise, generation of EMI, etc. can be minimized. In the prior art, however, since a variety of driving waveforms are supplied to the scan electrodes Y and the sustain electrodes Z, it is difficult to secure the stability of a PDP.  
         [0023]     Moreover, in the prior art, the scan driving unit  34  and the sustain driving unit  36  include switching means which are connected to the scan electrodes Y and the sustain electrodes Z, respectively, in a push-pull type. If the switching means are connected in the push-pull type as such, lots of the switching means are needed. As a result, there are problems in that the manufacture cost is increased, leakage current is generated, etc.  
       SUMMARY OF THE INVENTION  
       [0024]     Accordingly, the present invention has been made in view of the above problems occurring in the prior art, and it is an object of the present invention to provide an apparatus and method for driving a plasma display panel, wherein electromagnetic interference can be minimized and stability can be also improved.  
         [0025]     To achieve the above object, according to the present invention, there is provided an apparatus for driving a PDP, including a plurality of scan electrodes and sustain electrodes, which are formed parallel to each other, and a scan driving unit for alternately supplying sustain pulses of the positive polarity and the negative polarity to the scan electrodes during a sustain period, wherein the sustain electrodes are connected to a ground voltage source, and thus always keep a ground voltage.  
         [0026]     The scan driving unit includes a first switching means disposed between a sustain voltage source of the positive polarity and the scan electrodes, a second switching means disposed between a sustain voltage source of the negative polarity and the scan electrodes, a third switching means disposed between the ground voltage source and the scan electrodes, and fourth switching means and diodes, which are connected between a common terminal of the first to third switching means and the scan electrodes, respectively, in a parallel manner.  
         [0027]     If the first switching means is turned on, the voltage of the positive polarity of the sustain voltage source is applied to the scan electrodes as the sustain pulse of the positive polarity through the first switching means and the diodes.  
         [0028]     If the second switching means and the fourth switching means are turned on, the sustain pulse of the negative polarity is applied to the scan electrodes.  
         [0029]     After the sustain pulse of the positive polarity is applied, the third switching means and the fourth switching means are turned on, and after the sustain pulse of the negative polarity is applied, the third switching means are turned on. Thus, the voltage of the ground voltage source is applied to the scan electrodes.  
         [0030]     The scan driving unit includes a first switching means disposed between a sustain voltage source of the positive polarity and the scan electrodes, a second switching means disposed between a sustain voltage source of the negative polarity and the scan electrodes, a third switching means disposed between the ground voltage source and the scan electrodes, fourth switching means respectively disposed between the second switching means and the scan electrodes, and fifth switching means and diodes, which are connected between a common terminal of the first and third switching means and the scan electrodes, respectively, in a parallel manner.  
         [0031]     If the first switching means is turned on, the voltage of the positive polarity of the sustain voltage source is applied to the scan electrodes as the sustain pulse of the positive polarity through the first switching means and the diodes.  
         [0032]     If the second switching means and the fourth switching means are turned on, the sustain pulse of the negative polarity is applied to the scan electrodes.  
         [0033]     After the sustain pulse of the positive polarity is applied, the third switching means and the fifth switching means are turned on, and after the sustain pulse of the negative polarity is applied, the third switching means are turned on. Thus, the voltage of the ground voltage source is applied to the scan electrodes.  
         [0034]     According to the present invention, there is provided a method of driving a PDP, including the steps of alternately supplying sustain pulses of the positive polarity and the negative polarity to scan electrodes during a sustain period of sub-fields, and supplying a ground voltage to sustain electrodes, which are formed parallel to scan electrodes, during a sub-field period.  
         [0035]     In the present invention, since sustain electrodes always keep a ground voltage, introduction of external noise, generation of EMI, etc. can be minimized. Furthermore, in the present invention, sustain electrodes are always kept to a ground voltage, i.e., the flow path of current shortens. Due to this, generation of additional noise can be prevented, and the stability of a PDP can be thus secured. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0036]     Further objects and advantages of the invention can be more fully understood from the following detailed description taken in conjunction with the accompanying drawings in which:  
         [0037]      FIG. 1  is a perspective view illustrating the structure of a discharge cell of a conventional three-electrode AC surface discharge type PDP;  
         [0038]      FIG. 2  shows one frame of a PDP;  
         [0039]      FIG. 3  is a block diagram of an apparatus for driving a conventional PDP;  
         [0040]      FIG. 4  is a waveform showing a method of driving a conventional PDP;  
         [0041]      FIG. 5  is a block diagram showing an apparatus for driving a PDP according to an embodiment of the present invention;  
         [0042]      FIG. 6  is a detailed circuit diagram of the scan driving unit shown in  FIG. 5 ;  
         [0043]      FIG. 7  shows sustain pulses supplied to scan electrodes corresponding to the timing diagram of the switches shown in  FIG. 6 ;  
         [0044]      FIG. 8  is another detailed circuit diagram of the scan driving unit shown in  FIG. 5 ; and  
         [0045]      FIG. 9  shows sustain pulses supplied to scan electrodes corresponding to the timing diagram of the switches shown in  FIG. 8 . 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0046]     Preferred embodiments of the present invention will be described in more detail with reference to the drawings.  
         [0047]      FIG. 5  is a block diagram showing an apparatus for driving a PDP according to an embodiment of the present invention.  
         [0048]     Referring to  FIG. 5 , the apparatus for driving the PDP according to an embodiment of the present invention includes a address driving unit  52  for driving address electrodes X 1  to Xm disposed in a panel  50 , a scan driving unit  54  for driving scan electrodes Y 1  to Yn disposed in the panel  50 , a driving voltage generator  58  for applying a driving voltage to the driving units  52 ,  54 , and a timing controller  56  for applying control signals SCS 1 , SCS 2  to the driving units  52 ,  54 . At this time, sustain electrodes Z 1  to Zn (omitted) disposed in the panel  50  are connected to a ground voltage GND.  
         [0049]     The driving voltage generator  58  generates a variety of driving voltages, and supplies the generated voltages to the address driving unit  52  and the scan driving unit  54  so that a predetermined driving waveform can be generated.  
         [0050]     The timing controller  56  generates various switching control signals, and applies them to the address driving unit  52  and the scan driving unit  54  so that a predetermined driving waveform can be generated. For example, the timing controller  56  generates a first switching control signal SCS 1 , and applies it to the scan driving unit  54 . It also generates a second switching control signal SCS 2  and a data clock DCLK, and applies them to the address driving unit  52 .  
         [0051]     The address driving unit  52  supplies image data data, which are supplied from the outside, to the address electrodes X 1  to Xm according to the data clock DCLK and the second switching control signal SCS 2 , both of which are supplied from the timing controller  56 .  
         [0052]     The scan driving unit  54  applies a reset pulse, a scan pulse, and sustain pulses of the negative polarity and the positive polarity to the scan electrodes Y 1  to Ym, according to the first switching control signal SCS 1  that is supplied from the timing controller  56 . At this time, the scan driving unit  5  supplies the sustain pulses, which switch from the negative polarity and the positive polarity, and vice versa, to the scan electrodes Y 1  to Ym in order to generate a sustain discharge together with the sustain electrodes Z 1  to Zn to which the ground voltage GND is always applied.  
         [0053]      FIG. 6  is a detailed circuit diagram of the scan driving unit shown in  FIG. 5 .  
         [0054]     Referring to  FIG. 6 , the scan driving unit  54  includes a driving voltage supply unit  60 , and fourth switches S 4  connected to the scan electrodes Y 1  to Ym, respectively. The fourth switches S 4  are disposed between the driving voltage supply unit  60  and the scan electrodes Y, and supply the driving voltage received from the driving voltage supply unit  60  to the scan electrodes Y. At this time, the fourth switches S 4  are connected in the open drain manner.  
         [0055]     In this case, the switches according to the present invention can be implemented using MOS TR, FET, IGBT, SCR, and the like. If the fourth switches S 4  are connected in the open drain manner, leakage current between the scan electrodes Y 1  to Yn, etc. can be prevented from occurring. Since the fourth switches S 4  are also disposed in the scan electrodes Y one by one, the number of components mounted in the scan driving unit  54  can be minimized. Further, fourth diodes D 4 , which are respectively connected to the fourth switches S 4  in a parallel manner, are further disposed between the driving voltage supply unit  60  and the scan electrodes Y (where, the fourth diodes D 4  can be diodes within the fourth switches S 4  or external diodes additionally disposed). The fourth diodes D 4  serve to supply the driving voltage, which is supplied from the driving voltage supply unit  60 , to the scan electrodes Y, and also to prevent the driving voltage from the scan electrodes Y from being supplied to the driving voltage supply unit  60 .  
         [0056]     The driving voltage supply unit  60  includes a first switch S 1  connected between a sustain voltage source +Vs of the positive polarity and the fourth switches S 4 , a second switch S 2  connected between a sustain voltage source −Vs of the negative polarity and the fourth switches S 4 , and a third switch S 3  connected between a ground voltage GND and the fourth switches S 4 . The first to third switches S 1  to S 3  are turned on and off under the control of the timing controller  56 .  
         [0057]      FIG. 7  shows sustain pulses supplied to the scan electrodes corresponding to the timing diagram of the switches shown in  FIG. 6 .  
         [0058]     The process where the sustain pulses are supplied from the scan driving unit  54  will now be described in detail with reference to  FIG. 7 . As shown in  FIG. 7 , according to the present invention, during a sustain period, the sustain electrodes Z are kept to the ground voltage GND, and the scan electrodes Y are alternately supplied with the sustain pulse sus+ of the positive polarity and the sustain pulse sus- of the negative polarity (actually, the ground voltage GND is provided between the voltage +Vs, −Vs of the positive polarity and the negative polarity for a predetermined time). Then, as a wall voltage within cells that are selected in a previous address period, and voltage values of the sustain pulse sus+ or sus− of the positive polarity or the negative polarity are added, a sustain discharge is generated in the form of surface discharge between the scan electrodes Y and the sustain electrodes Z whenever the sustain pulses sus+, sus− are applied.  
         [0059]     This will be described in more detail. When the sustain pulse sus+ of the positive polarity is applied, the first switch S 1  is turned on. If the first switch S 1  is turned on, a voltage of the sustain voltage source +Vs of the positive polarity is supplied to the scan electrodes Y 1  to Yn through the first switch S 1  and the fourth diodes D 4 . At this time, the scan electrodes Y 1  to Yn are supplied with the sustain pulse sus+ of the positive polarity.  
         [0060]     After the sustain pulse sus+ of the positive polarity is supplied to the scan electrodes Y 1  to Yn, the third and fourth switches S 3 , S 4  are turned on. If the third switch S 3  is turned on, the ground voltage GND is applied to the scan electrodes Y 1  to Yn through the third and fourth switches S 3 , S 4 .  
         [0061]     After the ground voltage GND is applied to the scan electrodes Y 1  to Yn, the third switch S 3  is turned off and the second switch S 2  is turned on. If the second switch S 2  is turned on, the voltage of the sustain voltage source −Vs of the negative polarity is applied to the scan electrodes Y 1  to Yn through the second and fourth switches S 2 , S 4 . At this time, the scan electrodes Y 1  to Yn are supplied with the sustain pulse sus- of the negative polarity.  
         [0062]     After the scan electrodes Y 1  to Yn are supplied with the sustain pulse sus− of the negative polarity, the third switch S 3  is turned on, and the second and fourth switches S 2 , S 4  are also turned off. If the third switch S 3  is turned on, the ground voltage GND is applied to the scan electrodes Y 1  to Yn via the third switch S 3  and the fourth diodes D 4 . Practically, in the present invention, while this process is repeatedly performed, the sustain pulses sus+, sus− of the positive polarity and the negative polarity are alternately supplied to the scan electrodes Y 1  to Yn.  
         [0063]     On the other hand, in an address period, the second switch S 2  keeps turned on. Further, when the second switch S 2  keeps turned on, the fourth switches S 4  are sequentially turned on to supply the scan pulse scan to the scan electrodes Y. At this time, the address driving unit  52  supplies the data pulse, which is synchronized to the scan pulse scan, to the data lines X 1  to Xm.  
         [0064]     As described above, in the present invention, the sustain electrodes Z are always (during one sub-field period) supplied with the ground voltage GND. If the ground voltage GND is always supplied to the sustain electrodes Z as such, introduction of external noise, generation of EMI, etc., can be minimized, and the stability of a PDP can be improved accordingly.  
         [0065]     Further, in the present invention, the sustain electrodes Z are always connected to the ground voltage GND. Thus, a sustain driving unit as in the prior art can be omitted, and EMI, etc., which is generated due to driving of the sustain driving unit, can be prevented. In addition, in the present invention, since the sustain electrodes Z are directly connected to the ground voltage GND, additional generation of noise can be prevented. Moreover, in the present invention, only one switching means S 4  is connected to each of the scan electrodes Y in the off drain mode. Therefore, the number of components can be minimized, the manufacture const can be reduced, and leakage current between electrodes can be thus prevented.  
         [0066]     Meanwhile, in the present invention, the scan driving unit  54  can be constructed in various forms. For example, according to the present invention, the scan driving unit  54  can be constructed, as shown in  FIG. 8 .  
         [0067]      FIG. 8  is another detailed circuit diagram of the scan driving unit shown in  FIG. 5 .  
         [0068]     Referring to  FIG. 8 , the scan driving unit  54  according to the present invention includes a driving voltage supply unit  64 , and fourth switches S 4  and fifth switches S 5 , which are disposed between scan electrodes Y 1  to Ym respectively.  
         [0069]     The driving voltage supply unit  64  includes a first switch S 1  connected to a sustain voltage source +Vs of the positive polarity, a third switch S 3  connected to the ground voltage GND, and a second switch S 2  connected to a sustain voltage source −Vs of the negative polarity. The first to third switches S 1  to S 3  are turned on and off under the control of the timing controller  56 .  
         [0070]     The fourth switches S 4  are connected between the second switch S 2  and the scan electrodes Y 1  to Ym, respectively, and are turned on and off under the control of the timing controller  56 . The fifth switches S 5  are connected between a common terminal of the first and third switches S 1 , S 3  and the scan electrodes Y 1  to Ym, respectively, and are turned on and off under the control of the timing controller  56 . In this case, the fourth switches S 4  are connected to the fourth diodes D 4  in a parallel manner, and the fifth switches S 5  are connected to the fifth diodes D 5  in a parallel manner. The fourth and fifth diodes D 4  and D 5  serve to prevent a driving voltage, which is supplied from the scan electrodes Y 1 , from being applied to the driving voltage supply unit  64 .  
         [0071]     The process in which the sustain pulse is supplied from the scan driving unit  54  will now be described in detail with reference to  FIG. 9 .  
         [0072]     Referring to  FIG. 9 , the first switch S 1  is turned on. If the first switch S 1  is turned on, the voltage of the sustain voltage source +Vs of the positive polarity is applied to the scan electrodes Y 1  to Yn via the first switch S 1  and the fifth diode D 5 . At this time, the scan electrodes Y 1  to Yn are supplied with the sustain pulse sus+ of the positive polarity.  
         [0073]     After the scan electrodes Y 1  to Yn are supplied with the sustain pulse sus+ of the positive polarity, the first switch S 1  is turned off, and the third and fifth switches S 3  and S 5  are also turned on. If the third and fifth switches S 3  and S 5  are turned on, the ground voltage GND is applied to the scan electrodes Y 1  to Yn through the third and fifth switches S 3  and S 5 .  
         [0074]     After the ground voltage GND is applied to the scan electrodes Y 1  to Yn, the third and fifth switches S 3 , S 5  are turned off, and the second and fourth switches S 2 , S 4  are also turned on. If the second and fourth switches S 2 , S 4  are turned on, the voltage of the negative polarity of the sustain voltage source −Vs is applied to the scan electrodes Y 1  to Yn through the second switch S 2  and the fourth switch S 4 . At this time, the scan electrodes Y 1  to Yn are supplied with the sustain pulse sus- of the negative polarity.  
         [0075]     After the sustain pulse sus- of the negative polarity is applied to the scan electrodes Y 1  to Yn, the second and fourth switches S 2 , S 4  are turned off, and the third switch S 3  is also turned on. If the third switch S 3  is turned on, the ground voltage GND is applied to the scan electrodes Y 1  to Yn through the third switch S 3  and the fifth diode D 5 . Practically, in the present invention, while this process is repeatedly performed, the sustain pulses sus+, sus− of the positive polarity and the negative polarity are alternately applied to the scan electrodes Y 1  to Yn.  
         [0076]     On the other hand, in an address period, the second switch S 2  keeps turned on. Further, when the second switch S 2  keeps turned on, the fourth switches S 4  are sequentially turned on to sequentially apply scan pulses scan to the scan electrodes Y. At this time, the address driving unit  52  applies the data pulse, which is synchronized to the scan pulse scan, to the data lines X 1  to Xm.  
         [0077]     As such, in the present invention, the sustain electrodes Z are always (during one sub-field period) supplied with the ground voltage GND. If the ground voltage GND is always applied to the sustain electrodes Z as such, introduction of external noise, generation of EMI, etc. can be minimized, and the stability of a PDP can be improved accordingly.  
         [0078]     Furthermore, in the present invention, since the sustain electrodes Z are always connected to the ground voltage GND, a sustain driving unit as in the prior art can be omitted. Generation of EMI, which is generated due to driving of the sustain driving unit, can be also prevented. Moreover, in the present invention, since the sustain electrodes Z are directly connected to the ground voltage GND, additional generation of noise can be prevented.  
         [0079]     While the present invention has been described with reference to the particular illustrative embodiments, it is not to be restricted by the embodiments but only by the appended claims. It is to be appreciated that those skilled in the art can change or modify the embodiments without departing from the scope and spirit of the present invention.