Patent Publication Number: US-7714807-B2

Title: Plasma display apparatus and method of driving the same

Description:
This Nonprovisional application claims priority under 35 U.S.C. § 119(a) on Patent Application No. 10-2006-0001136 filed in Korea on Jan. 4, 2006 the entire contents of which are hereby incorporated by reference. 
   BACKGROUND 
   1. Field 
   This document relates to a display apparatus, and more particularly, to a plasma display apparatus and a method of driving the same. 
   2. Description of the Related Art 
   Out of display apparatuses, a plasma display apparatus comprises a plasma display panel and a driver for driving the plasma display panel. 
   The plasma display panel has the structure in which barrier ribs formed between a front panel and a rear panel forms unit discharge cell or discharge cells. Each discharge cell is filled with an inert gas containing a main discharge gas such as neon (Ne), helium (He) and a mixture of Ne and He, and a small amount of xenon (Xe). The plurality of discharge cells form one pixel. For example, a red (R) discharge cell, a green (G) discharge cell, and a blue (B) discharge cell form one pixel. 
   When the plasma display panel is discharged by a high frequency voltage, the inert gas generates vacuum ultraviolet rays, which thereby cause phosphors formed between the barrier ribs to emit light, thus displaying an image. Since the plasma display panel can be manufactured to be thin and light, it has attracted attention as a next generation display device. 
   A driving voltage is supplied to the plasma display panel, thereby generating a reset discharge, an address discharge, and a sustain discharge. Accordingly, an image is displayed on the plasma display panel. 
   In a case where an image having the same pattern is displayed for a predetermined period of time in the related art plasma display apparatus, a state of wall charges distributed inside the discharge cell may be fixed. 
   For example, in a case where an image with a window pattern is displayed on the screen for a predetermined period of time, a state of wall charges distributed inside the discharge cell is maintained and fixed corresponding to the window pattern. 
   Accordingly, if another image other than the window pattern image is to be displayed on the screen, the window pattern image is not removed and remains on the screen, and thus image retention is generated. 
   SUMMARY 
   In one aspect, a plasma display apparatus comprises a plasma display panel including a scan electrode and a sustain electrode, and a driver supplying a first signal and a second signal to the scan electrode during a reset period of at least one of a plurality of subfields of a frame, wherein the first signal gradually rises from a first voltage to a second voltage with a first slope, and then falls from the second voltage to a third voltage with a second slope, and the second signal rises from the third voltage to a fourth voltage, and then gradually rises from the fourth voltage to a fifth voltage with a third slope. 
   A magnitude of the first voltage may be substantially equal to a magnitude of the third voltage. 
   The first voltage may be substantially equal to a ground level voltage. 
   The driver may supply a first sustain bias voltage to the sustain electrode during the supplying of the first signal and the second signal to the scan electrode, and the first sustain bias voltage may be lower than a second sustain bias voltage supplied to the sustain electrode during an address period. 
   The first sustain bias voltage may be substantially equal to a ground level voltage. 
   The first slope may be substantially equal to the third slope. 
   A magnitude of the second voltage may be substantially equal to or more than a magnitude of the fourth voltage. 
   A magnitude of the fifth voltage may be more than, and equal to or less than three times a magnitude of the second voltage. 
   The second slope may be substantially equal to a rising slope of a sustain signal supplied to the scan electrode and/or the sustain electrode during a sustain period. 
   A gray level of a subfield where the first signal and the second signal are supplied may be less than a gray level of another subfield where only the second signal is supplied, wherein the subfields each may be one of the plurality of subfields of the frame. 
   The highest voltage level of the second signal supplied in a low gray level subfield of the plurality of subfields of the frame may be more than the highest voltage level of the second signal supplied in a high gray level subfield of the plurality of subfields of the frame. 
   A width of the second signal in a subfield where the first signal and the second signal are supplied may be less than a width of the second signal in another subfield where only the second signal is supplied, wherein the subfields each may be one of the plurality of subfields of the frame. 
   A width of the second signal in a low gray level subfield among subfields where the first signal and the second signal are supplied may be more than a width of the second signal in a high gray level subfield among the subfields where the first signal and the second signal are supplied. 
   Before supplying the first signal, the driver may supply a falling signal with a gradually falling voltage to the scan electrode in at least one subfield where the first signal and the second signal are supplied. 
   The driver may supply a third sustain bias voltage to the sustain electrode during the supplying of the falling signal to the scan electrode, and the third sustain bias voltage may be higher than the second sustain bias voltage. 
   The third sustain bias voltage may be substantially equal to a voltage level of a sustain signal supplied to the scan electrode and/or the sustain electrode during a sustain period. 
   In another aspect, a method of driving a plasma display apparatus displaying an image during a frame including a plurality of subfields, the method comprises supplying a first signal to a scan electrode during a reset period of at least one of the plurality of subfields, wherein the first signal gradually rises from a first voltage to a second voltage with a first slope, and then falls from the second voltage to a third voltage with a second slope, and after supplying the first signal, supplying a second signal to the scan electrode, wherein the second signal rises from the third voltage to a fourth voltage, and then gradually rises from the fourth voltage to a fifth voltage with a third slope. 
   A magnitude of the first voltage may be substantially equal to a magnitude of the third voltage, a magnitude of the second voltage may be substantially equal to or more than a magnitude of the fourth voltage, and a magnitude of the fifth voltage may be more than, and equal to or less than three times a magnitude of the second voltage. 
   A gray level of a subfield where the first signal and the second signal are supplied may be less than a gray level of another subfield where only the second signal is supplied, wherein the subfields each may be one of the plurality of subfields of the frame. 
   The highest voltage level of the second signal supplied in a low gray level subfield of the plurality of subfields of the frame may be more than the highest voltage level of the second signal supplied in a high gray level subfield of the plurality of subfields of the frame. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The accompany drawings, which are included to provide a further understanding of the invention and are incorporated on and constitute a part of this specification illustrate embodiments of the invention and together with the description serve to explain the principles of the invention. 
       FIG. 1  illustrates a plasma display apparatus according to one embodiment; 
       FIGS. 2   a  and  2   b  illustrate one example of a plasma display panel of the plasma display apparatus according to one embodiment; 
       FIG. 3  illustrates one example of an operation of the plasma display apparatus according to one embodiment; 
       FIG. 4  illustrates a first signal and a second signal; 
       FIGS. 5   a  and  5   b  illustrate a falling slope of a first signal; 
       FIGS. 6   a  and  6   b  illustrate one example of a driver of the plasma display apparatus according to one embodiment; 
       FIGS. 7   a  and  7   b  illustrate an operation of a scan reference voltage supply controller; 
       FIG. 8  illustrates one example of an operation of a driver of the plasma display apparatus according to one embodiment; 
       FIGS. 9   a  and  9   b  illustrate one example of a method of using a first signal and a second signal during a predetermined subfield of a plurality of subfields of a frame; and 
       FIG. 10  illustrates one example of a method for supplying a falling signal prior to the supplying of a first signal to a scan electrode during at least one subfield where the first signal and a second signal are supplied to the scan electrode. 
   

   DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
   Reference will now be made in detail embodiments of the invention examples of which are illustrated in the accompanying drawings. 
     FIG. 1  illustrates a plasma display apparatus according to one embodiment. 
   Referring to  FIG. 1 , the plasma display apparatus according to one embodiment includes a plasma display panel  100  and a driver  101 . 
   While one driver  101  is illustrated in  FIG. 1 , the number of drivers may be plural depending on electrodes formed in the plasma display panel  100 . 
   For example, in a case where the plasma display panel  100  includes address electrodes X 1 -Xm, scan electrodes Y 1 -Yn, and sustain electrodes Z 1 -Zn, a data driver, a scan driver, and a sustain driver may be formed. 
     FIGS. 2   a  and  2   b  illustrate one example of a plasma display panel of the plasma display apparatus according to one embodiment. 
   As illustrated in  FIG. 2   a , the plasma display panel  100  of the plasma display apparatus according to one embodiment includes a front panel  200  and a rear panel  210  which are coupled in parallel to oppose to each other at a given distance therebetween. The front panel  200  includes a front substrate  201  being a display surface on which an image is displayed. The rear panel  210  includes a rear substrate  211  constituting a rear surface. A plurality of scan electrodes  202  and a plurality of sustain electrodes  203  are formed on the front substrate  201 . A plurality of address electrodes  213  are arranged on the rear substrate  211  to intersect the scan electrodes  202  and the sustain electrodes  203 . 
   The scan electrode  202  and the sustain electrode  203  generate a mutual discharge therebetween in one discharge cell, and maintain light-emissions of the discharge cells. 
   The scan electrode  202  and the sustain electrode  203  are covered with one or more upper dielectric layers  204  for limiting a discharge current and providing insulation between the scan electrode  202  and the sustain electrode  203 . A protective layer  205  is formed on an upper surface of the upper dielectric layer  204  to facilitate discharge conditions. 
   The protective layer  205  is formed by depositing a material such as magnesium oxide (MgO) on the upper surface of the upper dielectric layer  204 . 
   A plurality of stripe-type (or well-type) barrier ribs  212  are arranged in parallel on the rear substrate  211  of the rear panel  210  to form a plurality of discharge spaces (i.e., a plurality of discharge cells). The plurality of address electrodes  213  supplied with a data signal are arranged in parallel to the barrier ribs  212 . 
   An upper surface of the rear panel  210  is coated with Red (R), green (G) and blue (B) phosphors  214  for emitting visible light for an image display when the address discharge is performed. 
   A lower dielectric layer  215  is formed between the address electrodes  213  and the phosphors  214  to protect the address electrodes  213 . 
   The scan electrode  202  and the sustain electrode  203  may be formed of a conductive metal material. For example, silver (Ag) or indium-tin-oxide (ITO) may be used. 
   Considering light transmissivity and electrical conductivity, the scan electrode  202  and the sustain electrode  203  each may include a bus electrode made of Ag and a transparent electrode made of ITO. This will be described with reference to  FIG. 2   b.    
   Referring to  FIG. 2   b , the scan electrode  202  and the sustain electrode  203  for generating a surface discharge therebetween each include transparent electrodes  202   a  and  203   a  made of ITO and bus electrodes  202   b  and  203   b  made of an opaque metal material, thereby emitting light generated within the discharge cell to the outside of the plasma display panel and securing the driving efficiency. 
   As above, since the scan electrode  202  and the sustain electrode  203  each include the transparent electrodes  202   a  and  203   a , visible light generated within the discharge cell is effectively emitted to the outside of the plasma display panel. 
   Furthermore, in a case where the scan electrode  202  and the sustain electrode  203  each include only the transparent electrodes  202   a  and  203   a , electrical conductivity of the transparent electrodes  202   a  and  203   a  is relatively low, thereby reducing the driving efficiency. However, since the scan electrode  202  and the sustain electrode  203  further include the bus electrodes  202   b  and  203   b , the low electrical conductivity of the transparent electrodes  202   a  and  203   a  causing a reduction in the driving efficiency is compensated. 
   Although  FIGS. 2   a  and  2   b  have illustrated and described only one example of the plasma display panel of the plasma display apparatus according to one embodiment, the embodiment is not limited to the plasma display panel illustrated in  FIGS. 2   a  and  2   b.    
   For instance, although the above description illustrates a case where the upper dielectric layer  204  and the lower dielectric layer  215  each are formed in the form of a single layer, at least one of the upper dielectric layer  204  and the lower dielectric layer  215  may be formed in the form of a plurality of layers. 
   The plasma display panel applicable to one embodiment has only to comprise the scan electrode  202  and the sustain electrode  203 . Accordingly, the plasma display panel  100  may have various structures except the above-described structural characteristic. 
   Referring again to  FIG. 1 , the driver  101  supplies a first signal and a second signal to the scan electrode Y during a reset period of at least one of a plurality of subfields of a frame. The first signal gradually rises from a first voltage V 1  to a second voltage V 2  with a first slope, and then falls from the second voltage V 2  to a third voltage V 3  with a second slope. The second signal sharply rises from the third voltage V 3  to a fourth voltage V 4 , and then gradually rises from the fourth voltage V 4  to a fifth voltage V 5  with a third slope. 
   The driver  101  supplies a data signal having a data voltage Vd to the address electrode X. 
   The driver  101  supplies a scan signal of a negative polarity and a sustain signal having a sustain voltage Vs to the scan electrode Y. 
   The driver  101  supplies a sustain bias voltage and a sustain signal having the sustain voltage Vs to the sustain electrode Y. 
     FIG. 3  illustrates one example of an operation of the plasma display apparatus according to one embodiment. 
   In  FIG. 3 , a driving waveform generated during one subfield is illustrated. 
   During a reset period, the first signal and the second signal are supplied to the scan electrode Y, thereby generating a weak dark discharge within the discharge cell. The weak dark discharge accumulates a proper amount of wall charges inside the discharge cell, and then a portion of wall charges is erased. The remaining wall charges are uniform inside the discharge cell to the extent that an address discharge can be stably performed. During the reset period, a state of the wall charges distributed inside the discharge cell is uniform. 
   By supplying the first signal and the second signal to the scan electrode Y during the reset period, the generation of image retention is prevented. 
   More specifically, in a case where the plasma display apparatus displays an image having the same pattern for a predetermined period of time, a state of wall charges distributed inside the discharge cell may be fixed. 
   For example, in a case where an image with a window pattern is displayed on the screen for a predetermined period of time, a state of wall charges distributed inside the discharge cell is maintained and fixed corresponding to the window pattern. 
   In this case, the first signal and the second signal are sequentially supplied. The first signal causes fluctuation in the state of the fixed wall charges inside the discharge cell. The second signal supplied subsequent to the first signal uniformizes the state of the wall charges. 
   Accordingly, although after images having a specific pattern are successively displayed for a predetermined period of time, another image is displayed on the screen, the generation of image retention, in which the specific pattern image is not removed and remains on the screen, is prevented. 
   During the supplying of the first signal and the second signal to the scan electrode Y, a first sustain bias voltage Vz 1  is supplied to the sustain electrode Z. The first sustain bias voltage Vz 1  is lower than a second sustain bias voltage Vz 2  supplied to the sustain electrode Z during an address period. As a result, a voltage difference between the scan electrode Y and the sustain electrode Z is provided, thereby generating a reset discharge between the scan electrode Y and the sustain electrode Z. 
   The first sustain bias voltage Vz 1  may be substantially equal to a ground level voltage GND. 
   During the address period, a scan reference voltage Vsc and a scan voltage −Vy of a scan signal (Scan) of a negative polarity falling from scan reference voltage Vsc are supplied to the scan electrode Y. A data voltage Vd of a data signal (Data) corresponding to the scan signal (Scan) is supplied to the address electrode X. 
   During the address period, the second sustain bias voltage Vz 2  is supplied to the sustain electrode Z, thereby preventing the generation of an erroneous discharge caused by interference of the sustain electrode Z. 
   As a difference between the negative scan voltage −Vy and the data voltage Vd is added to the wall voltage generated during the reset period, the address discharge is generated within the discharge cells to which the data voltage Vd is supplied. Wall charges are formed inside the discharge cells selected by performing the address discharge such that when a sustain voltage Vs of a sustain signal (Sus) is supplied a discharge occurs. 
   During a sustain period, the sustain signal (Sus) is supplied to the scan electrode Y and/or the sustain electrode Z. As the wall voltage within the discharge cells selected by performing the address discharge is added to the sustain voltage Vs of the sustain signal (Sus), every time the sustain signal (Sus) is supplied, a sustain discharge, i.e., a display discharge is generated between the scan electrode Y and the sustain electrode Z. Accordingly, an image is displayed on the plasma display panel. 
   The following is a detailed description of the first signal and the second signal supplied to the scan electrode Y with reference to  FIG. 4 . 
   Referring to  FIG. 4 , the first signal gradually rises from the first voltage V 1  to the second voltage V 2  with the first slope, and then falls from the second voltage V 2  to the third voltage V 3  with the second slope. 
   The second signal sharply rises from the third voltage V 3  to the fourth voltage V 4 , and then gradually rises from the fourth voltage V 4  to the fifth voltage V 5  with the third slope. 
   The second signal gradually rises to the fifth voltage V 5 , falls to the first voltage V 1 , and gradually falls with a predetermined slope. 
   The first slope of the first signal may be substantially equal to the third slope of the second signal. As a result, the first signal having the first slope and the second signal having the third slope are generated using the same circuit such that an increase in the manufacturing cost is prevented. 
   The second voltage V 2  may be equal to or higher than the fourth voltage V 4 . As a result, the efficiency of an initialization operation obtained by the supplying of the first signal increases, and an excessive increase in an intensity of the dark discharge generated by the second signal is prevented. 
   The fifth voltage V 5  of the second signal may be higher than and may be equal to or lower than three times the second voltage V 2 . As a result, a sufficient amount of wall charges remains inside the discharge cell. 
     FIGS. 5   a  and  5   b  illustrates a falling slope of a first signal. 
     FIG. 5   a  illustrates the first signal and the second signal, and  FIG. 5   b  illustrates the sustain signal supplied to the scan electrode Y and/or the sustain electrode Z during the sustain period. 
   Referring to  FIG. 5   a , the first signal falls with the second slope during the falling of the first signal from the second voltage V 2  to the third voltage V 3  (i.e., during a period d 1 ). 
   The second slope may be substantially equal to a slope of the sustain signal supplied during a voltage recovery period d 2  of the sustain period. As a result, the second slope and the slope of the sustain signal supplied during the voltage recovery period d 2  are generated using the same circuit. 
     FIGS. 6   a  and  6   b  illustrate one example of a driver of the plasma display apparatus according to one embodiment. 
   Referring to  FIG. 6   a , the a driver of the plasma display apparatus according to one embodiment includes a scan drive integrated circuit (IC)  670 , a scan reference voltage supply controller  640 , a scan and falling signal common supply controller  650 , and an energy recovery circuit  600 . 
   The driver further includes a sustain voltage supply controller  610 , a ground level voltage supply controller  620 , and a rising signal supply controller  630 . 
   The scan drive IC  670  includes a scan top switch S 9  and a scan bottom switch S 10 . The scan drive IC  670  supplies a predetermined voltage supplied to the scan drive IC  670  to the scan electrode Y through switching operations of the scan top switch S 9  and the scan bottom switch S 10 . 
   The scan drive IC  670  is connected to the scan electrode between the scan top switch S 9  and the scan bottom switch S 10 . 
   The scan reference voltage supply controller  640  controls the supplying of the scan reference voltage Vsc to the scan drive IC  670 . 
   The scan reference voltage supply controller  640  includes a resistor  641  and a reverse blocking unit  642 . 
   The resistor  641  reduces a noise generated in the scan reference voltage Vsc supplied to the scan drive IC  670 . 
   The reverse blocking unit  642  prevents an inverse current flowing from the scan drive IC  670  to a scan reference voltage source. 
   The resistor  641  and the reverse blocking unit  642  are in series disposed between the scan drive IC  670  and the scan reference voltage source. 
   The reverse blocking unit  642  includes a reverse blocking diode D 3 . An anode of the reverse blocking diode D 3  faces toward the scan reference voltage source, and a cathode faces toward the scan drive IC  670 . 
   The scan reference voltage supply controller  640  further includes a current path unit  643  and a fluctuation prevention unit  644 . 
   The fluctuation prevention unit  644  includes a fluctuation prevention capacitor C 2 . The fluctuation prevention capacitor C 2  reduces the fluctuation of the scan reference voltage Vsc supplied to the scan electrode Y. 
   One terminal of the fluctuation prevention capacitor C 2  is commonly connected to a current path diode D 4  of the current path unit  643  and the resistor  641 , and the other terminal is commonly connected to the scan bottom switch S 10  of the scan drive IC  670  and the scan and falling signal common supply controller  650 . 
   The current path unit  643  includes the current path diode D 4  connected in parallel to the resistor  641 . The current path diode D 4  passes a current flowing from the scan drive IC  670  to the fluctuation prevention unit  644 . 
   A cathode of the current path diode D 4  faces toward the fluctuation prevention capacitor C 2 , and an anode faces toward the scan top switch S 9  of the scan drive IC  670 . 
     FIGS. 7   a  and  7   b  illustrate an operation of a scan reference voltage supply controller. 
   Referring to  FIG. 7   a , the scan reference voltage Vsc is supplied to the scan electrode Y through the scan reference voltage source, the reverse blocking diode D 3 , the resistor  641 , and the scan top switch S 9 . 
   In this case, since the cathode of the current path diode D 4  faces toward the scan reference voltage source, the scan reference voltage Vsc does not pass the current path diode D 4 . Therefore, the scan reference voltage Vsc, in which a noise is reduced, is supplied to the scan electrode Y. 
   Referring to  FIG. 7   b , a voltage of the scan electrode Y is supplied to the fluctuation prevention capacitor C 2  through the scan top switch S 9  and the current path diode D 4  during a period ranging from a time when the supplying of the scan reference voltage Vsc to the scan electrode Y is blocked (i.e., a time when the scan top switch S 9  is turned off) to a time when the scan bottom switch S 10  is turned on. Accordingly, the fluctuation prevention capacitor C 2  is charged to the voltage of the scan electrode Y. 
   Since the cathode of the reverse blocking diode D 3  faces toward the scan top switch S 9 , the voltage output the scan electrode Y is not supplied to the scan reference voltage source. 
   As above, since the voltage output from the scan electrode Y is stably charged to the fluctuation prevention capacitor C 2  during the period ranging from the time when the scan top switch S 9  is turned off to the time when the scan bottom switch S 10  is turned on, the scan driver operates stably and the energy efficiency increases. 
   Referring again to  FIG. 6   a , the energy recovery circuit  600  supplies a voltage previously stored in the energy recovery circuit  600  to the scan electrode Y through an energy supply path, and recovers a reactive energy from the scan electrode Y. 
   The energy recovery circuit  600  includes a voltage storing capacitor C 1 , an energy supply control switch S 1 , an energy recovery control switch S 2 , first and second inductors L 1  and L 2 , and first and second reverse blocking diodes D 1  and D 2 . 
   A voltage to be supplied to the scan electrode Y is previously stored in the voltage storing capacitor C 1 . When the energy supply control switch S 1  is turned on, the voltage stored in the voltage storing capacitor C 1  is supplied to the scan electrode Y through an energy supply path passing through the energy supply control switch S 1 , the first reverse blocking diode D 1 , and the first inductor L 1 . 
   When the energy recovery control switch S 2  is turned on, a reactive energy recovered from the scan electrode Y is stored in the voltage storing capacitor C 1  through an energy recovery path passing through the second inductor L 2 , the second reverse blocking diode D 2 , and the energy recovery control switch S 2 . 
   Since the different inductors L 1  and L 2  are disposed on the energy supply path and the energy recovery path, respectively, the amount of heat generated in the energy recovery circuit  600  decreases. 
   More specifically, since the voltage stored in the voltage storing capacitor C 1  is supplied to the scan electrode Y through the first inductor L 1  in the energy supply operation, heat is concentrically generated in the first inductor L 1 . 
   On the other hand, since the reactive energy recovered from the scan electrode Y is stored in the voltage storing capacitor C 1  through the second inductor L 2  in the energy recovery operation, heat is concentrically generated in the second inductor L 2 . 
   As above, the amount of heat generated in a case where the different inductors are used in the energy supply and recovery operations is less than the amount of heat generated in a case where the same inductor is used in the energy supply and recovery operations. Accordingly, a thermal damage to the energy recovery circuit  600  is prevented and the driving stability is improved. 
   The scan and falling signal common supply controller  650  controls the supplying of the negative scan voltage −Vy and the falling signal to the scan drive IC  670 . 
   The scan and falling signal common supply controller  650  includes a scan and falling signal common supply control switch S 8 , and a second variable resistor VR 2  connected to a gate terminal of the scan and falling signal common supply control switch S 8 . 
   A source terminal of the scan and falling signal common supply control switch S 8  is connected to the scan bottom switch S 10  of the scan drive IC  670 , and a drain terminal is connected to a negative scan voltage source. 
   The scan and falling signal common supply controller  650  further includes a voltage stability capacitor C 3 . 
   One terminal of the voltage stability capacitor C 3  is commonly connected to the scan and falling signal common supply control switch S 8  and the negative scan voltage source. The other terminal of the voltage stability capacitor C 3  is commonly connected to the ground level voltage supply controller  620 , the sustain voltage supply controller  610 , the rising signal supply controller  630 , a blocking unit  660 , and the energy recovery unit  600 . 
   The voltage stability capacitor C 3  stores the negative scan voltage −Vy supplied from the negative scan voltage source such that the scan and falling signal common supply controller  650  stably supplies the falling signal or the negative scan voltage −Vy to the scan electrode Y. 
   The scan and falling signal common supply controller  650  needs both a switching control signal for supplying the negative scan voltage −Vy and a switching control signal for supplying the falling signal. 
   A configuration of the scan and falling signal common supply controller  650  considering the switching control signal for supplying the negative scan voltage −Vy and the switching control signal for supplying the falling signal is illustrated in  FIG. 6   b.    
   Referring to  FIG. 6   b , a control signal input terminal ({circle around ( 1 )}) for falling signal supply and a control signal input terminal ({circle around ( 2 )}) for negative scan voltage supply are connected to the gate terminal of the scan and falling signal common supply control switch S 8 . 
   The second variable resistor VR 2  is disposed in the control signal input terminal ({circle around ( 1 )}) for falling signal supply. The second variable resistor VR 2  is not disposed in the control signal input terminal ({circle around ( 2 )}) for negative scan voltage supply. 
   A control signal for falling signal supply is input to the control signal input terminal ({circle around ( 1 )}) for falling signal supply when supplying the falling signal. Accordingly, the falling signal with a gradually falling voltage is supplied to the scan electrode Y using the second variable resistor VR 2 . 
   More specifically, when the scan and falling signal common supply control switch S 8  is turned on and the control signal for falling signal supply is input to the control signal input terminal ({circle around ( 1 )}) for falling signal supply, a channel width of the scan and falling signal common supply control switch S 8  is controlled by the second variable resistor VR 2 . Accordingly, the falling signal with the gradually falling voltage is generated and the falling signal is supplied to the scan electrode Y. 
   When supplying the negative scan voltage −Vy, a control signal for negative scan voltage supply is input to the control signal input terminal ({circle around ( 2 )}) for negative scan voltage supply. Accordingly, the negative scan voltage −Vy is supplied to the scan electrode Y. 
   The sustain voltage supply controller  610  of  FIG. 6   a  includes a sustain voltage supply control switch S 3 . The sustain voltage supply controller  610  controls the supplying of the sustain voltage Vs to the scan electrode Y using the sustain voltage supply control switch S 3 . 
   The ground level voltage supply controller  620  includes a ground level voltage supply control switch S 4 . The ground level voltage supply controller  620  controls the supplying of the ground level voltage GND to the scan electrode Y using the ground level voltage supply control switch S 4 . 
   The rising signal supply controller  630  includes a rising signal supply control switch S 5 , and a first variable resistor VR 1  connected to a gate terminal of the rising signal supply control switch S 5 . The rising signal supply controller  630  controls the supplying of the rising signal to the scan electrode Y using the rising signal supply control switch S 5  and the first variable resistor VR 1 . 
   The blocking unit  660  is disposed between the ground level voltage supply controller  620  and the scan and falling signal common supply controller  650 . 
   The blocking unit  660  includes a blocking switch S 7 . The blocking switch S 7  prevents an inverse current flowing from the scan and falling signal common supply controller  650  into the ground through the ground level voltage supply controller  620 . 
   One terminal of the sustain voltage supply controller  610  is commonly connected to a sustain voltage source and one terminal of the rising signal supply controller  630 . The other terminal of the sustain voltage supply controller  610  is commonly connected to the other terminal of the rising signal supply controller  630 , one terminal of the ground level voltage supply controller  620  and one terminal of the energy recovery circuit  600 . The other terminal of the energy recovery circuit  600  and the other terminal of the ground level voltage supply controller  620  are grounded. 
   Although a case where the switches used in the driver function as a field effect transistor (FET) has been illustrated and described above, various transistor such as an insulated gate bipolar transistor (IGBT) is applicable. 
     FIG. 8  illustrates one example of an operation of a driver of the plasma display apparatus according to one embodiment. 
   Referring to  FIG. 8 , the ground level voltage supply control switch S 4 , the blocking switch S 7 , and the scan bottom switch S 10  are turned on such that the ground level voltage GND is supplied to the scan electrode Y. Accordingly, the voltage of the scan electrode Y is equal to the ground level voltage GND prior to a period d 1 . 
   During the period d 1 , when the rising signal supply control switch S 5  is turned on in a turn-on state of the blocking switch S 7 , a channel width of the rising signal supply control switch S 5  is controlled by the first variable resistor VR 1 . Accordingly, the rising signal with a gradually rising voltage is generated and the rising signal is supplied to the scan electrode Y. During the period d 1 , the voltage of the scan electrode Y gradually rises from the first voltage V 1  to the second voltage V 2  with the first slope. 
   The highest voltage during the period d 1  is equal to the sustain voltage Vs, and the second voltage V 2  is equal to the sustain voltage Vs. 
   During a period d 2 , the rising signal supply control switch S 5  is turned off and the energy recovery control switch S 2  is then turned on in turn-on states of the blocking switch S 7  and the scan bottom switch S 10 . As a result, a reactive voltage recovered from the scan electrode Y is stored in the voltage storing capacitor C 1  through the scan bottom switch S 10 , the blocking switch S 7 , the second inductor L 2 , the second diode D 2 , and the energy recovery control switch S 2 . During the period d 2 , the voltage of the scan electrode Y falls from the second voltage V 2  to the third voltage V 3  with the second slope. 
   The operation performed during the period d 2  is substantially equal to the operation for supplying the sustain signal to the scan electrode and/or the sustain electrode during the sustain period. More specifically, the operation performed during the period d 2  is substantially equal to the operation performed during the voltage recovery period (d 2 ) of the sustain signal in  FIG. 5   b.    
   Accordingly, the second slope of the first signal is substantially equal to the slope of the sustain signal in the voltage recovery period (d 2 ) in  FIG. 5   b.    
   During the periods d 1  and d 2 , the first signal is supplied to the scan electrode Y. 
   During a period d 3 , the ground level voltage supply controller  620  is turned on such that the ground level voltage GND is supplied to the scan electrode Y. 
   During a period d 4 , the blocking switch S 7 , the scan bottom switch S 10 , the energy recovery control switch S 2 , and the ground level voltage supply control switch S 4  are turned off. The scan top switch S 9  is turned on. 
   The scan reference voltage Vsc is supplied to the scan electrode Y through the scan reference voltage supply controller  640 . Accordingly, the voltage of the scan electrode Y sharply rises to the scan reference voltage Vsc. Therefore, the fourth voltage V 4  of the second signal is equal to the scan reference voltage Vsc. 
   The blocking switch S 7 , the rising signal supply control switch S 5 , and the scan bottom switch S 10  are turned on such that the channel width of the rising signal supply control switch S 5  is controlled by the first variable resistor VR 1 . Accordingly, the rising signal with a gradually rising voltage is generated and the rising signal is supplied to the scan electrode Y. During the period d 4 , the voltage of the scan electrode Y gradually rises from the fourth voltage V 4  to the fifth voltage V 5  with the third slope. 
   The highest voltage during the period d 4  is equal to a sum of the sustain voltage Vs and the scan reference voltage Vsc. 
   During a period d 5 , the scan top switch S 9 , the blocking switch S 7 , and the rising signal supply control switch S 5  are turned off, and the scan bottom switch S 10  and the scan and falling signal common supply control switch S 8  are turned on. Accordingly, the voltage of the scan electrode Y gradually falls. 
   During the period d 5 , as illustrated in  FIG. 6   b , the control signal for falling signal supply is input to the control signal input terminal ({circle around ( 1 )}) for falling signal supply which is connected to the gate terminal of the scan and falling signal common supply control switch S 8 . 
   During the period d 5 , the voltage of the scan electrode Y may fall to the negative scan voltage −Vy. 
   As above, the first signal and the second signal are supplied to the scan electrode Y. 
   The first signal and the second signal may be supplied to the scan electrode Y during reset periods of all subfields of a frame. Alternatively, the first signal and the second signal may be supplied to the scan electrode Y during a reset period of a predetermined subfield of a plurality of subfields of a frame. 
     FIGS. 9   a  and  9   b  illustrate one example of a method of using a first signal and a second signal during a predetermined subfield of a plurality of subfields of a frame. 
   Referring to  FIG. 9   a , in a case where one frame includes a total of 12 subfields, the first signal and the second signal are supplied to the scan electrode Y during reset periods of first to ninth subfields SF 1 -SF 9 . The second signal is supplied to the scan electrode Y during reset periods of tenth to twelfth subfields SF 10 -SF 12 . The second signal supplied during the tenth to twelfth subfields SF 10 -SF 12  is substantially equal to the second signal supplied during the first to ninth subfields SF 1 -SF 9 . 
   The  12  subfields SF 1 -SF 12  are arranged in increasing order of gray level weight. 
   Since the number of sustain signals supplied during sustain periods of the low gray weight subfields is less than the number of sustain signals supplied during sustain periods of the high gray weight subfields, an unstable discharge may occur in the low gray weight subfields. Therefore, the first signal and the second signal are supplied in the low gray weight subfields. 
   Referring to  FIG. 9   b , in a case where one frame includes a total of 12 subfields, the first signal and the second signal are supplied to the scan electrode Y during reset periods of first to eighth subfields SF 1 -SF 8 . The second signal is supplied to the scan electrode Y during reset periods of ninth to twelfth subfields SF 9 -SF 12 . 
   The highest voltage level of the second signal is the largest in the low gray level subfields, and is the smallest in the high gray level subfields. 
   More specifically, the highest voltage level Vpeak 1  of the second signal supplied during the reset periods of the first to third subfields SF 1 -SF 3  is more than the highest voltage level Vpeak 2  of the second signal supplied during the reset periods of the fourth to eighth subfields SF 4 -SF 8 . Further, the highest voltage level Vpeak 2  is more than the highest voltage level Vpeak 3  of the second signal supplied during the reset periods of the ninth to twelfth subfields SF 9 -SF 12 . 
   Although  FIG. 9   b  has illustrated and described a case where the highest voltages Vpeak 1  of the second signals supplied during the reset periods of the first to third subfields SF 1 -SF 3  are equal to one another, the present embodiment is not limited thereto. 
   For example the highest voltage level of the second signal supplied during the reset period of the first subfield SF 1  may be set to be more than the highest voltage level of the second signal supplied during the reset period of the second subfield SF 2 . 
   As above, as the gray level weight increases, the highest voltage level of the second signal is reduced. Accordingly, contrast is improved. 
   Widths W 1  and W 2  of the second signal supplied to the scan electrode Y during the reset periods of the first to eighth subfields SF 1 -SF 8  may be set to be less than a width W 3  of the second signal supplied to the scan electrode Y during the reset periods of the ninth to twelfth subfields SF 9 -SF 12 . 
   In other words, a width of the second signal in a subfield where one reset signal (i.e., the second signal) is supplied may be set to be more than a width of the second signal in a subfield where two reset signals (i.e., the first and second signals) are supplied 
   Since one reset signal is supplied in the high gray level subfields, a duration of the reset period is secured such that a sufficient amount of wall charges are accumulated. 
   Further, the width W 1  of the second signal in the relatively low gray level subfields SF 1 -SF 3  among the subfields SF 1 -SF 9  where two reset signals are supplied may set to be more than the width W 2  of the second signal in the relatively high gray level subfields SF 4 -SF 9 . 
   For example, the width W 1  of the second signal supplied during the reset periods of the first to third subfields may be set to more than the width W 2  of the second signal supplied during the reset periods of the fourth to eighth subfields. 
   Accordingly, contrast is improved and a margin of the reset period is secured. 
   Although  FIG. 9   b  has illustrated and described a case where the widths W 1  of the second signals supplied during the reset periods of the first to third subfields SF 1 -SF 3  are equal to one another, the present embodiment is not limited thereto. 
   For example, a width of the second signal supplied during the reset period of the first subfield SF 1  may be set to be more than a width of the second signal supplied during the reset period of the second subfield SF 2 . 
   As above, as the gray level weight increases, the width of the second signal is reduced. 
   Before supplying the first signal, a falling signal with a gradually falling voltage is supplied to the scan electrode during at least one subfield where the first signal and the second signal are supplied to the scan electrode Y. 
   The following is a detailed description of the falling signal with reference to  FIG. 10 . 
   As illustrated in an area B of  FIG. 10 , before supplying the first signal, a falling signal with a gradually falling voltage is supplied to the scan electrode during at least one subfield where the first signal and the second signal are supplied to the scan electrode Y. 
   During the supplying of the falling signal, a third sustain bias voltage Vz 3  is supplied to the sustain electrode Z. The third sustain bias voltage Vz 3  is higher than the second sustain bias voltage Vz 2  supplied to the sustain electrode Z during the address period. 
   Accordingly, wall charges of a positive polarity are accumulated on the scan electrode Y inside the discharge cell, and wall charges of a negative polarity are accumulated on the sustain electrode Z. 
   The first signal and the second signal are supplied to the scan electrode Y in the above state of the wall charges distributed inside the discharge cell, thereby easily generating the reset discharge. Accordingly, an initialization operation by the reset discharge is performed more efficiently. 
   Further, although the voltages of the first signal and the second signal are reduced in the above state of the wall charges distributed inside the discharge cell, a reset discharge occurs and an initialization operation by the reset discharge is performed. 
   The third sustain bias voltage Vz 3  may be substantially equal to the sustain voltage Vs supplied during the sustain period. 
   As above, although an image having the same pattern is displayed on the screen for a predetermined period of time in the plasma display apparatus according to one embodiment, the generation of image retention is prevented. 
   The foregoing embodiments and advantages are merely exemplary and are not to be construed as limiting the present invention. The present teaching can be readily applied to other types of apparatuses. The description of the foregoing embodiments is intended to be illustrative, and not to limit the scope of the claims. Many alternatives, modifications, and variations will be apparent to those skilled in the art. In the claims, means-plus-function clauses are intended to cover the structures described herein as performing the recited function and not only structural equivalents but also equivalent structures. Moreover, unless the term “means” is explicitly recited in a limitation of the claims, such limitation is not intended to be interpreted under 35 USC 112(6).