Patent Publication Number: US-7916098-B2

Title: Plasma display apparatus and method of driving the same

Description:
This application claims the benefit of Korean Patent Application No. 10-2006-0068233 filed in Korea on Jul. 20, 2006, which is hereby incorporated by reference. 
     BACKGROUND 
     1. Field 
     This document relates to a plasma display apparatus and a method of driving the same. 
     2. Description of the Related Art 
     A plasma display apparatus includes a plasma display panel displaying an image, and drivers 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 form 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) or a mixture of Ne and He, and a small amount of xenon (Xe). 
     When the plasma display panel is discharged by the application of a high frequency voltage to the unit discharge cell, the inert gas generates vacuum ultraviolet rays, which thereby cause phosphors formed between the barrier ribs to emit light, thus displaying an image. 
     The plasma display panel includes a plurality of electrodes, and the drivers for supplying driving voltages to the plurality of electrodes are connected to the plurality of electrodes. 
     Each driver supplies driving pulses to the plurality of electrodes during a reset period, an address period, and a sustain period, and thus the plasma display panel displays an image. It is important to accurately generate discharges and to optimize the driving conditions when the driving pulses are supplied to the electrodes, respectively. 
     SUMMARY 
     In one aspect, a plasma display apparatus comprises a plasma display panel including a scan electrode, and a scan driver that supplies a setup pulse to the scan electrode, the setup pulse gradually rising to a first voltage level with a first slope, rising from the first voltage level to a second voltage level with a second slope smaller than the first slope, and rising from the second voltage level to a third voltage level with a third slope different from the second slope. 
     In another aspect, a plasma display apparatus comprises a plasma display panel including a scan electrode, and a scan driver that supplies a set-down pulse to the scan electrode, the set-down pulse gradually falling to a fourth voltage level with a fourth slope, falling from the fourth voltage level to a fifth voltage level with a fifth slope smaller than the fourth slope, and falling from the fifth voltage level to a sixth voltage level with a sixth slope different from the fifth slope. 
     In still another aspect, a method of driving a plasma display apparatus including a scan electrode, the method comprises gradually raising a voltage level of the scan electrode to a first voltage level with a first slope, raising the voltage level of the scan electrode from the first voltage level to a second voltage level with a second slope smaller than the first slope, and raising the voltage level of the scan electrode from the second voltage level to a third voltage level with a third slope different from the second slope. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying 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. In the drawings: 
         FIG. 1  illustrates a plasma display apparatus according to an exemplary embodiment; 
         FIG. 2  illustrates a driving waveform of a plasma display apparatus according to an exemplary embodiment; 
         FIG. 3  illustrates a reset pulse of  FIG. 2 ; 
         FIG. 4   a  illustrates a scan driver of a plasma display apparatus according to a first exemplary embodiment; 
         FIG. 4   b  illustrates a driving waveform and switch timing of the scan driver of  FIG. 4   a;    
         FIG. 5   a  illustrates a scan driver of a plasma display apparatus according to a second exemplary embodiment; 
         FIG. 5   b  illustrates a driving waveform and switch timing of the scan driver of  FIG. 5   a;    
         FIG. 6   a  illustrates another driving waveform of the scan driver of  FIG. 5   a ; and 
         FIG. 6   b  illustrates another driving waveform of the scan driver of  FIG. 5   a.    
     
    
    
     DETAILED DESCRIPTION OF EMBODIMENTS 
     A plasma display apparatus comprises a plasma display panel including a scan electrode, and a scan driver that supplies a setup pulse to the scan electrode, the setup pulse gradually rising to a first voltage level with a first slope, rising from the first voltage level to a second voltage level with a second slope smaller than the first slope, and rising from the second voltage level to a third voltage level with a third slope different from the second slope. 
     The scan driver may include a voltage unit supplying a sustain voltage to the scan electrode, a first voltage supply unit supplying the first voltage level to the scan electrode, and a setup slope controller that receives the first voltage level and the sustain voltage and supplies the setup pulse having the first, second, and third slopes to the scan electrode. 
     The setup slope controller may include first and second switches connected in parallel to each other, a first variable resistor connected to the first switch, a second variable resistor connected to the second switch, and a capacitor whose both terminals are connected to the first voltage supply unit and the voltage unit, respectively, wherein a magnitude of the first variable resistor may be different from a magnitude of the second variable resistor. 
     The first and second switches may be turned on, and thus, the first slope may be formed. The first switch may remain in a turn-on state and the second switch may be turned off, and thus, the second slope may be formed. The first switch may be turned off and the second switch may be turned on, and thus, the third slope may be formed. 
     The setup slope controller may include a first switch connected to the voltage unit, a first variable resistor connected to the first switch, a second switch receiving the first voltage level, a second variable resistor connected to the second switch, and a capacitor whose both terminals are connected to one terminal of the second switch and the voltage unit, respectively, wherein a magnitude of the first variable resistor may be different from a magnitude of the second variable resistor. 
     The first and second switches may be turned on, and thus, the first slope may be formed. The first switch may remain in a turn-on state and the second switch may be turned off, and thus, the second slope may be formed. The first switch may be turned off and the second switch may be turned on, and thus, the third slope may be formed. 
     The scan driver may supply a set-down pulse having a plurality of slopes to the scan electrode after the supply of the setup pulse. 
     A plasma display apparatus comprises a plasma display panel including a scan electrode, and a scan driver that supplies a set-down pulse to the scan electrode, the set-down pulse gradually falling to a fourth voltage level with a fourth slope, falling from the fourth voltage level to a fifth voltage level with a fifth slope smaller than the fourth slope, and falling from the fifth voltage level to a sixth voltage level with a sixth slope different from the fifth slope. 
     The scan driver may include a second voltage supply unit supplying a scan voltage to the scan electrode, and a set-down slope controller that receives the scan voltage from the second voltage supply unit and supplies the set-down pulse having the fourth, fifth, and sixth slopes to the scan electrode. 
     The set-down slope controller may include third and fourth switches connected to the second voltage supply unit, a third variable resistor connected to the third switch, and a fourth variable resistor connected to the fourth switch, wherein a magnitude of the third variable resistor may be different from a magnitude of the fourth variable resistor. 
     The third and fourth switches may be turned on, and thus, the fourth slope may be formed. The third switch may remain in a turn-on state and the fourth switch may be turned off, and thus, the fifth slope may be formed. The third switch may be turned off and the fourth switch may be turned on, and thus, the sixth slope may be formed. 
     The set-down slope controller may include a third switch connected to a ground level voltage supply unit, a third variable resistor connected to the third switch, a fourth switch connected to the second voltage supply unit, and a fourth variable resistor connected to the fourth switch, wherein a magnitude of the third variable resistor may be different from a magnitude of the fourth variable resistor. 
     The third and fourth switches may be turned on, and thus, the fourth slope may be formed. The third switch may remain in a turn-on state and the fourth switch may be turned off, and thus, the fifth slope may be formed. The third switch may be turned off and the fourth switch may be turned on, and thus, the sixth slope may be formed. 
     The plasma display panel may further include a sustain electrode, the scan driver may supply a set-down pulse that is maintained at the fourth voltage level and then fall with the sixth slope, and a sustain driver may supply a positive bias voltage level to the sustain electrode during a period of time during which the set-down pulse is maintained at the fourth voltage level. 
     A magnitude of the sixth slope may be smaller than a magnitude of the fourth slope. 
     The positive bias voltage level may be substantially equal to a sustain voltage level. 
     The positive bias voltage level may be lower than a sustain voltage level. 
     A method of driving a plasma display apparatus including a scan electrode, the method comprises gradually raising a voltage level of the scan electrode to a first voltage level with a first slope, raising the voltage level of the scan electrode from the first voltage level to a second voltage level with a second slope smaller than the first slope, and raising the voltage level of the scan electrode from the second voltage level to a third voltage level with a third slope different from the second slope. 
     The method may further comprise gradually lowering the voltage level of the scan electrode to a fourth voltage level with a fourth slope, lowering the voltage level of the scan electrode from the fourth voltage level to a fifth voltage level with a fifth slope smaller than the fourth slope, and lowering the voltage level of the scan electrode from the fifth voltage level to a sixth voltage level with a sixth slope different from the fifth slope. 
     The plasma display apparatus may further include a sustain electrode, the voltage level of the scan electrode may be maintained at the fourth voltage level and then fall with the sixth slope, and a positive bias voltage level may be supplied to the sustain electrode during a period of time during which the voltage level of the scan electrode is maintained at the fourth voltage level. 
     Embodiments will be described in a more detailed manner with reference to the drawings. 
       FIG. 1  illustrates a plasma display apparatus according to an exemplary embodiment. As illustrated in  FIG. 1 , a plasma display apparatus according to an exemplary embodiment includes a plasma display panel  100 , a scan driver  121 , a data driver  122 , a sustain driver  123 , a controller  124 , and a driving voltage generator  125 . 
     The plasma display panel  100  includes a front substrate (not shown) and a rear substrate (not shown), which are coalesced with each other at a given distance therebetween. On the front substrate, scan electrodes Y 1  to Yn and sustain electrodes Z are formed. On the rear substrate, data electrodes X 1  to Xm are formed to intersect the scan electrodes Y 1  to Yn and the sustain electrodes Z. 
     Under the control of the controller  124 , the scan driver  121  supplies a reset pulse for initializing a state of wall charges distributed in discharge cells to the scan electrodes Y 1  to Yn during a reset period. The reset pulse includes a setup pulse and a set-down pulse. The scan driver  121  optimizes a discharge by controlling slopes of the setup pulse and the set-down pulse. 
     Under the control of the controller  124 , the scan driver  121  sequentially supplies scan pulses each having the lowest voltage level corresponding to a scan voltage −Vy to the scan electrodes Y 1  to Yn during an address period. The scan driver  121  supplies a scan reference voltage Vsc to the scan electrodes Y 1  to Yn to which the scan pulses are not supplied. 
     Under the control of the controller  124 , the scan driver  121  supplies a sustain pulse to the scan electrodes Y 1 - to Yn during a sustain period to generate a sustain discharge inside discharge cells selected during the address period. 
     The data driver  122  supplies data pulses to the data electrodes X 1  to Xm during the address period to select discharges cells in which a sustain discharge will be generated. 
     Under the control of the controller  124 , the sustain driver  123  supplies a sustain bias voltage Vz to the sustain electrodes Z during the address period. The sustain driver  123  can control supply timing of the sustain bias voltage Vz. The supply timing of the sustain bias voltage Vz will be described in detail with reference to  FIGS. 6   a  and  6   b.    
     The sustain driver  123  supplies a sustain pulse to the sustain electrodes Z during the sustain period. The scan driver  121  and the sustain driver  123  alternately supply the sustain pulses. 
     The controller  124  receives a vertical/horizontal synchronization signal and a clock signal, and generates timing control signals CTRX, CTRY and CTRZ for controlling operation timing and synchronization of each driver  121 ,  122  and  123  during the reset, address, and sustain periods. The controller  124  supplies the timing control signals CTRX, CTRY and CTRZ to the corresponding drivers  121 ,  122  and  123 . 
     The driving voltage generator  125  generates a setup voltage for forming the setup pulse, the scan reference voltage Vsc, the scan voltage −Vy, a sustain voltage Vs corresponding to the highest voltage level of the sustain pulse, and a data voltage Va corresponding to the highest voltage level of the data pulse. 
       FIG. 2  illustrates a driving waveform of a plasma display apparatus according to an exemplary embodiment. 
     The scan driver  121  supplies a setup pulse PR to the scan electrode Y during a setup period SU of a reset period RP to generate a weak discharge within discharge cells of the whole screen. Hence, wall charges are produced within the discharge cells. 
     The setup pulse PR rises to a first voltage level Vst with a first slope, rises from the first voltage level Vst to a second voltage level Vset 1  with a second slope smaller than the first slope, and rises from the second voltage level Vset 1  to a third voltage level Vset 2  with a third slope different from the second slope. 
     The scan driver  121  supplies a set-down pulse NR to the scan electrode Y during a set-down period SD of the reset period RP. The set-down pulse NR generates a weak erase discharge within the discharge cells to make the remaining wall charges within the discharge cells uniform. 
     The set-down pulse NR falls to a fourth voltage level with a fourth slope, falls from the fourth voltage level to a fifth voltage level with a fifth slope smaller than the fourth slope, and falls from the fifth voltage level to a sixth voltage level with a sixth slope different from the fifth slope. The set-down pulse NR will be described in detail with reference to  FIGS. 4   a  and  4   b.    
     During an address period AP, the scan driver  121  supplies a scan pulse SCNP to the scan electrode Y, and the data driver  122  supplies a data pulse DP to the data electrode X. As the voltage difference between the scan pulse SCNP and the data pulse DP is added to the wall voltage generated during the reset period RP, an address discharge is generated within the discharge cells to which the data pulse DP is supplied. 
     The sustain driver  123  supplies a positive bias voltage Vzb to the sustain electrode Z during the set-down period SD and the address period AP so that an erroneous discharge does not occur between the sustain electrode Z and the scan electrode Y. 
     During a sustain period SP, the scan driver  121  and the sustain driver  123  alternately supply a sustain pulse SUSP to the scan electrode Y and the sustain electrode Z to generate a sustain discharge. 
       FIG. 3  illustrates a reset pulse of  FIG. 2 . As illustrated in  FIG. 3 , the scan driver  121  supplies the setup pulse PR having the first, second and third slopes to the scan electrode Y. 
     With the supply of the setup pulse PR, a voltage level of the scan electrode Y rises to the first voltage level Vst with the first slope, rises from the first voltage level Vst to the second voltage level Vset 1  with the second slope smaller than the first slope, and rises from the second voltage level Vset 1  to the third voltage level Vset 2  with the third slope smaller than the second slope. The first voltage level Vst may be substantially equal to the highest voltage level of the sustain pulse SUSP of  FIG. 2 . 
     The setup pulse PR having the first, second and third slopes can optimize the discharge conditions. For example, the setup pulse PR having the first slope gradually changes a voltage level of the scan electrode Y during a period t 1 , thereby preventing the occurrence of a peaking current and generating an effective discharge. 
     Further, it is easy to remove wall charges using the setup pulse PR having the first, second and third slopes. Hence, an erroneous discharge can be prevented. The setup pulse PR suitable for various driving conditions can be supplied by controlling the slope of the setup pulse PR. 
       FIG. 4   a  illustrates a scan driver of a plasma display apparatus according to a first exemplary embodiment.  FIG. 4   b  illustrates a driving waveform and switch timing of the scan driver of  FIG. 4   a.    
     The scan driver  121  of  FIG. 4   a  includes a voltage unit  410 , a first voltage supply unit Vst, a setup slope controller  420 , a second voltage supply unit −Vy, a set-down slope controller  430 , and a scan driving unit  440 . 
     The voltage unit  410  supplies a ground level voltage GND or a sustain voltage Vs. Although the voltage unit  410  supplies the sustain voltage Vs in the first exemplary embodiment, the voltage unit  410  can supply another voltage level other than the sustain voltage Vs. 
     The first voltage supply unit Vst supplies the first voltage level. 
     The setup slope controller  420  includes first and second switches Qsu 1  and Qsu 2 , first and second variable resistors VR 1  and VR 2 , and a capacitor Cp. The setup slope controller  420  receives the first voltage level Vst and the sustain voltage Vs, and supplies the setup pulse PR having the first, second, and third slopes to the scan electrode Y. 
     In the setup slope controller  420 , the first and second switches Qsu 1  and Qsu 2  are connected in parallel to each other. The first variable resistor VR 1  is connected to the first switch Qsu 1 , and the second variable resistor VR 2  is connected to the second switch Qsu 2 . The capacitor Cp includes one terminal ter 1  connected to the voltage unit  410 , and the other terminal ter 2  connected to a common terminal of the first and second switches Qsu 1  and Qsu 2 . 
     As illustrated in  FIG. 4   b , during a period t 1  of a reset period, the voltage unit  410  supplies a ground level voltage GND, and a switch Q 1  is turned off. Further, the first and second switches Qsu 1  and Qsu 2  of the setup slope controller  420  are turned on, and a switch Q 2  and a switch Qb of the scan driving unit  440  are turned on. 
     As a result, the capacitor Cp connected to the first voltage supply unit Vst and the voltage unit  410  is charged to the first voltage level Vst, and the first voltage level Vst is supplied to the scan electrode Y due to the turned-on first and second switches Qsu 1  and Qsu 2 . Since the first and second switches Qsu 1  and Qsu 2  operate in an active area, a voltage level of the scan electrode Y gradually rises to the first voltage level Vst with the first slope. A magnitude of the first slope is controlled by the first and second variable resistors VR 1  and VR 2  connected to the first and second switches Qsu 1  and Qsu 2 . 
     When the first and second switches Qsu 1  and Qsu 2  are simultaneously turned on, a line resistance decreases due to an increase in a current path. Therefore, a voltage level of the scan electrode Y rapidly rises to the first voltage level Vst. 
     During a period t 2  of the reset period, the voltage unit  410  supplies the sustain voltage Vs, and the switch Q 1  remains in a turn-off state. In the setup slope controller  420 , the first switch Qsu 1  remains in a turn-on state, and the second switch Qsu 2  is turned off. The switch Q 2  and the switch Qb of the scan driving unit  440  remain in a turn-on state. 
     Since the capacitor Cp is charged to the first voltage level Vst during the period t 1 , the voltage unit  410  supplies the sustain voltage Vs to one terminal ter 1  of the capacitor Cp during the period t 2  and a voltage of the other terminal ter 2  of the capacitor Cp is equal to a sum of the first voltage level Vst and the sustain voltage Vs. 
     The voltage of the other terminal ter 2  of the capacitor Cp is supplied to the scan electrode Y through the first switch Qsu 1 , the switch Q 2 , and the switch Qb. Hence, a voltage level of the scan electrode Y gradually rises from the first voltage level Vst to the second voltage level Vset 1  with the second slope. A magnitude of the second slope is smaller than a magnitude of the first slope. As above, since the first and second switches Qsu 1  and Qsu 2  are turned on during the period t 1  and only the first switch Qsu 1  is turned on during the period t 2 , the magnitude of the first slope formed during the period t 1  of a small line resistance is larger than the magnitude of the second slope. 
     The second slope is controlled depending on the first variable resistor VR 1  connected to the first switch Qsu 1 . 
     During a period t 3  of the reset period, the voltage unit  410  supplies the sustain voltage Vs, and the switch Q 1  remains in a turn-off state. In the setup slope controller  420 , the first switch Qsu 1  is turned off, and the second switch Qsu 2  is turned on. The switch Q 2  and the switch Qb of the scan driving unit  440  remain in a turn-on state. 
     Since a voltage of the other terminal ter 2  of the capacitor Cp is equal to a sum of the first voltage level Vst and the sustain voltage Vs, a voltage level of the scan electrode Y gradually rises from the second voltage level Vset 1  to the third voltage level Vset 2  with the third slope. The third slope is controlled depending on the second variable resistor VR 2  connected to the second switch Qsu 2 . 
     A magnitude of the first variable resistor VR 1  may be different from a magnitude of the second variable resistor VR 2 . Hence, the magnitudes of the first, second and third slopes can variously change. 
     Although  FIGS. 2 and 3  illustrate the set-down pulse having one slope, a set-down pulse having a plurality of slopes will be described in detail with reference to  FIGS. 4   a  and  4   b.    
     The second voltage supply unit −Vy supplies a scan voltage. 
     The set-down slope controller  430  supplies a set-down pulse PD to the scan electrode Y. The set-down pulse PD falls to a fourth voltage level with a fourth slope, falls from the fourth voltage level to a fifth voltage level Vsd 5  with a fifth slope smaller than the fourth slope, and falls from the fifth voltage level Vsd 5  to a sixth voltage level Vsd 6  with a sixth slope different from the fifth slope. The set-down slope controller  430  receives the scan voltage from the second voltage supply unit −Vy, and supplies the set-down pulse PD having the fourth, fifth and sixth slopes to the scan electrode Y. 
     The set-down slope controller  430  includes a third switch Qsd 3 , a fourth switch Qsd 4 , a third variable resistor VR 3 , and a fourth variable resistor VR 4 . One terminal of each of the third switch Qsd 3  and the fourth switch Qsd 4  is connected to the second voltage supply unit −Vy. The third variable resistor VR 3  is connected to the third switch Qsd 3 , and the fourth variable resistor VR 4  is connected to the fourth switch Qsd 4 . 
     After the supply of the setup pulse PR, as illustrated in  FIG. 4   b , the set-down pulse PD perpendicularly falls from the third voltage level Vset 2  to the sustain voltage Vs, and then falls to the fourth voltage level with the fourth slope during a period t 4 . The fourth voltage level may be equal to a ground level voltage GND. 
     During the period t 4  of a set-down period of the reset period, the third and fourth switches Qsd 3  and Qsd 4  are turned on, and the switch Qb is turned on. Since the third and fourth switches Qsd 3  and Qsd 4  operate in an active area, a voltage level of the scan electrode Y falls to the fourth voltage level with the fourth slope. A magnitude of the fourth slope is controlled by the third and fourth variable resistors VR 3  and VR 4  connected to the third and fourth switches Qsd 3  and Qsd 4 . 
     During a period t 5  of the set-down period, the third switch Qsd 3  remains in a turn-on state, the fourth switch Qsd 4  is turned off, and the switch Qb is turned on. Hence, a voltage level of the scan electrode Y falls from the fourth voltage level to the fifth voltage level Vsd 5  with the fifth slope. A magnitude of the fifth slope is smaller than a magnitude of the fourth slope. This reason is to increase a current path when the third and fourth switches Qsd 3  and Qsd 4  are turned on during the period t 4  and to reduce a current path when only the third switch Qsd 3  is turned on during the period t 5 . The fifth slope can be controlled depending on the third variable resistor VR 3  connected to the third switch Qsd 3 . 
     During a period t 6  of the set-down period, the third switch Qsd 3  is turned off, the fourth switch Qsd 4  is turned on, and the switch Qb remains a turn-on state. Hence, a voltage level of the scan electrode Y falls from the fifth voltage level Vsd 5  to the sixth voltage level Vsd 6  with the sixth slope. The sixth slope can be controlled depending on the fourth variable resistor VR 4  connected to the fourth switch Qsd 4 . The sixth voltage level Vsd 6  may be equal to the scan voltage −Vy. 
     Since the set-down pulse PD has a plurality of slopes, the discharge conditions of the plasma display panel can be optimized. 
     A switch Q 5  supplies a scan reference voltage Vsc of  FIG. 2  to the scan electrode Y during an address period. A switch Q 6  supplies a scan pulse SCNP of  FIG. 2  to the scan electrode Y during the address period. The switch Q 2  is turned off during the periods t 4  to t 6 . 
     Since a magnitude of the fourth slope is larger than a magnitude of the fifth slope in the set-down pulse PD, a duration of the set-down period can be reduced. In other words, since the set-down pulse PD generates a weak discharge in the second half of the set-down period, a duration of the set-down period can be reduced when the magnitude of the fourth slope is larger than the magnitude of the fifth slope. 
     Further, if the slope of the set-down pulse PD supplied to the scan electrode in the first half of the set-down period is large, an erroneous discharge may be easily generated. Therefore, an erroneous discharge can be prevented by controlling a supply time point of a positive bias voltage level supplied to the sustain electrode. For instance, an erroneous discharge caused by a voltage difference between the scan electrode and the sustain electrode can be prevented by supplying a positive bias voltage level at any falling time point of the set-down pulse, for instance, during a period of time during which the set-down pulse is maintained at the first voltage level Vst. 
       FIG. 5   a  illustrates a scan driver of a plasma display apparatus according to a second exemplary embodiment.  FIG. 5   b  illustrates a driving waveform and switch timing of the scan driver of  FIG. 5   a.    
     A setup slope controller  420 ′ includes a first switch Qsu 1  connected to a voltage unit  410 , a first variable resistor VR 1  connected to the first switch Qsu 1 , a second switch Qsu 2  receiving a fist voltage level, a second variable resistor VR 2  connected to the second switch Qsu 2 , and a capacitor Cp whose both terminals are connected to one terminal of the second switch Qsu 2  and the voltage unit  410 , respectively. 
     As illustrated in  FIG. 5   b , during a period t 1  of a reset period, the voltage unit  410  enters into a floating state, and switches Q 1  and Q 2  are turned on. Further, the first and second switches Qsu 1  and Qsu 2  of the setup slope controller  420 ′ are turned on, and the switch Q 2  and a switch Qb of a scan driving unit  440  are turned on. 
     A first voltage level Vset 1 ′ is supplied to the scan electrode Y due to the turned-on first and second switches Qsu 1  and Qsu 2 . Since the first and second switches Qsu 1  and Qsu 2  operate in an active area, a voltage level of the scan electrode Y gradually rises to the first voltage level Vset 1 ′ with a first slope. A magnitude of the first slope is controlled by the first and second variable resistors VR 1  and VR 2  connected to the first and second switches Qsu 1  and Qsu 2 . 
     When the first and second switches Qsu 1  and Qsu 2  are simultaneously turned on, a voltage level of the scan electrode Y rapidly rises to the first voltage level Vset 1 ′ due to an increase in a current path. 
     During a period t 2 , the voltage unit  410  remains in a floating state, and the switches Q 1 , Q 2  and Qb remain in a turn-on state. Further, the first switch Qsu 1  remains in a turn-on state, and the second switch Qsu 2  is turned off. Hence, a voltage level of the scan electrode Y rises from the first voltage level Vset 1 ′ to a second voltage level with a second slope. The second voltage level is equal to a sustain voltage Vs. A magnitude of the second slope is smaller than a magnitude of the first slope due to a reduction in a current path during the period t 2 . 
     During a period t 3 , the voltage unit  410  supplies the sustain voltage Vs, and the switches Q 1 , Q 2  and Qb remain in a turn-on state. Further, the first switch Qsu 1  is turned off, and the second switch Qsu 2  is turned on. Hence, one terminal ter 1  of the capacitor Cp is charged to the sustain voltage Vs, and a voltage of the other terminal ter 2  of the capacitor Cp is equal to a sum of a first voltage level Vst supplied by a first voltage supply unit Vst and the sustain voltage Vs. Accordingly, a voltage level of the scan electrode Y rises from the second voltage level Vs to a third voltage level (Vst+Vs) with a third slope. 
     When a magnitude of the second variable resistor VR 2  is different from a magnitude of a third variable resistor VR 3 , the second slope may be different from the third slope. 
     A set-down slope controller  430 ′ includes a third switch Qsd 3 , a fourth switch Qsd 4 , a third variable resistor VR 3 , and a fourth variable resistor VR 4 . One terminal of the third switch Qsd 3  is connected to a ground level voltage supply unit GND, and one terminal of the fourth switch Qsd 4  is connected to the second voltage supply unit −Vy. The third variable resistor VR 3  is connected to the third switch Qsd 3 , and the fourth variable resistor VR 4  is connected to the fourth switch Qsd 4 . 
     During a period t 4 , the third and fourth switches Qsd 3  and Qsd 4  are turned on, and the switches Q 2  and Qb are turned on. Hence, a voltage level of the scan electrode Y gradually falls to a fourth voltage level Vsd 4  with a fourth slope. 
     During a period t 5 , the third switch Qsd 3  remains in a turn-on state, the fourth switch Qsd 4  is turned off, and the switches Q 2  and Qb remain in a turn-on state. Hence, a voltage level of the scan electrode Y gradually falls from the fourth voltage level Vsd 4  to a fifth voltage level Vsd 5  with a fifth slope. The fifth voltage level Vsd 5  is substantially equal to a ground level voltage GND. A magnitude of the fifth slope is smaller than a magnitude of the fourth slope due to a reduction in a current path during the period t 5 . 
     During a period t 6 , the third switch Qsd 3  is turned off, the fourth switch Qsd 4  is turned on, the switch Q 2  is turned off, and the switch Qb remains in a turn-on state. Hence, a voltage level of the scan electrode Y gradually falls from the fifth voltage level Vsd 5  to a sixth voltage level Vsd 6  with a sixth slope. The sixth voltage level Vsd 6  is substantially equal to the scan voltage −Vy. When a magnitude of the third variable resistor VR 3  is different from a magnitude of a fourth variable resistor VR 4 , the fifth slope may be different from the sixth slope. 
       FIG. 6   a  illustrates another driving waveform of the scan driver of  FIG. 5   a.    
     During a period t 4 , the third switch Qsd 3  and the fourth switch Qsd 4  are simultaneously turned on. When a voltage level of the scan electrode Y is equal to a ground level voltage GND, the third switch Qsd 3  remains in a turn-on state and the fourth switch Qsd 4  is turned off during a period t 5 . During a period t 6 , the third switch Qsd 3  is turned off, and the fourth switch Qsd 4  is turned on. A magnitude of a sixth slope of the period t 6  is smaller than a magnitude of a fourth slope of the period t 4 . 
     The sustain driver  123  of  FIG. 1  supplies a positive bias voltage Vzb to the sustain electrode Z during the period t 5 . The positive bias voltage Vzb is substantially equal to the sustain voltage Vs. 
     If the magnitude of the fourth slope is larger than a magnitude of a fifth slope in a set-down pulse PD, an erroneous discharge may be easily generated. Therefore, an erroneous discharge can be prevented by controlling a supply time point of the positive bias voltage Vzb supplied to the sustain electrode Z. For instance, when a voltage level of the scan electrode Y is maintained at a ground level voltage GND during the period t 5 , an erroneous discharge caused by a voltage difference between the scan electrode and the sustain electrode can be prevented due to the supply of the positive bias voltage Vzb. 
       FIG. 6   b  illustrates another driving waveform of the scan driver of  FIG. 5   a . As illustrated in  FIG. 6   b , the sustain driver  123  of  FIG. 1  can supply a positive bias voltage Vzb having a predetermined voltage level Vz to the sustain electrode Z during a period t 5 . The predetermined voltage level Vz may be lower than the sustain voltage Vs. 
     The sustain driver  123  controls the positive bias voltage Vzb to optimize the discharge conditions. 
     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.