Patent Publication Number: US-2007097051-A1

Title: Method for driving plasma display panel

Description:
BACKGROUND OF THE INVENTION  
      1. Field of the Invention  
      This invention relates to a plasma display panel, and more particularly to a method of driving a plasma display panel that is adaptive for improving a picture quality.  
      2. Description of the Related Art  
      Generally, a plasma display panel (PDP) excites and radiates a phosphorus material using an ultraviolet ray generated upon discharge of an inactive mixture gas such as He+Xe, Ne+Xe or He+Ne+Xe, to thereby display a picture. Such a PDP is easy to be made into a thin-film and large-dimension type. Moreover, the PDP provides a very improved picture quality owing to a recent technical development.  
       FIG. 1  is a perspective view showing a structure of a conventional alternating current (AC) surface-discharge PDP.  
      Referring to  FIG. 1 , a discharge cell of the conventional three-electrode, AC surface-discharge PDP includes a scan electrode  12 Y and a sustain electrode  12 Z provided on an upper substrate  10 , and an address electrode  20 X provided on a lower substrate  18 .  
      On the upper substrate  10  provided with the scan electrode  12 Y and the sustain electrode  12 Z in parallel, an upper dielectric layer  14  and a protective film  16  are disposed. Wall charges generated upon plasma discharge are accumulated into the upper dielectric layer  14 . The protective film  16  prevents a damage of the upper dielectric layer  14  caused by a sputtering during the plasma discharge and improves the emission efficiency of secondary electrons. This protective film  16  is usually made from magnesium oxide (MgO).  
      A lower dielectric layer  22  and barrier ribs  24  are formed on the lower substrate  18  provided with the address electrode  20 X. The surfaces of the lower dielectric layer  22  and the barrier ribs  24  are coated with a phosphorous material  26 . The address electrode  20 X is formed in a direction crossing the scan electrode  12 Y and the sustain electrode  12 Z. The barrier rib  24  is formed in parallel to the address electrode  20 X to thereby prevent an ultraviolet ray and a visible light generated by a discharge from being leaked to the adjacent discharge cells. The phosphorous material  26  is excited by an ultraviolet ray generated during the plasma discharge to generate any one of red, green and blue visible light rays. An inactive gas for a gas discharge is injected into a discharge space defined between the upper and lower substrate  10  and  18  and the barrier rib  24 .  
      Referring to  FIG. 2 , the conventional AC surface-discharge PDP includes a PDP  30  arranged in a matrix type such that m×n discharge cells are connected to scan electrode lines Y 1  to Ym, sustain electrode lines Z 1  to Zm and address electrode lines X 1  to Xn, a scan driver  32  for driving the scan electrode lines Y 1  to Ym, a sustain driver  34  for driving the sustain electrode lines Z 1  to Zm, and first and second address drivers  36 A and  36 B for making a divisional driving of odd-numbered address electrode lines X 1 , X 3 , . . . , Xn- 3 , Xn- 1  and even-numbered address electrode lines X 2 , X 4 , . . . , Xn- 2 , Xn. The scan driver  32  sequentially applies a scan pulse and a sustain pulse to the scan electrode lines Y 1  to Ym, to thereby sequentially scan discharge cells  1  for each line and sustain a discharge at each of the m×n discharge cells  1 . The sustain driver  34  applies a sustain pulse to all the sustain electrode lines Z 1  to Zm. The first and second address drivers  36 A and  36 M apply image data to the address electrode lines X 1  to Xn in such a manner to be synchronized with a scan pulse. The first address driver  36 A applies image data to the odd-numbered address electrode lines X 1 , X 3 , . . . , Xn- 3 , Xn- 1  while applying image data to the even-numbered address electrode lines X 2 , X 4 , . . . , Xn- 2 , Xn.  
      The AC surface-discharge PDP driven as mentioned above requires a high voltage more than hundreds of volts for an address discharge and a sustain discharge. Accordingly, in order to minimize a driving power required for the address discharge and the sustain discharge, the scan driver  32  and the sustain driver is additionally provided with an energy recovering apparatus  38  as shown in  FIG. 3 . The energy recovering apparatus  38  recovers a voltage charged in the scan electrode line Y and the sustain electrode line Z and re-uses the recovered voltage as a driving voltage for the next discharge.  
      Such a conventional driving apparatus  38  includes an inductor L connected between a panel capacitor Cp and a source capacitor Cs, and first and third switches S 1  and S 3  connected, in parallel, between the source capacitor Cs and the inductor L. A scan/sustain driver  32  is comprised of second and fourth switches S 2  and S 4  connected, in parallel, between the panel capacitor Cp and the inductor L. The panel capacitor Cp is an equivalent expression of a capacitance formed between the scan electrode line Y and the sustain electrode line Z. The second switch S 2  is connected to a sustain voltage source Vsus while the fourth switch S 4  is connected to a ground voltage source GND. The source capacitor Cs recovers and charges a voltage charged in the panel capacitor Cp upon sustain discharge and re-supply the charged voltage to the panel capacitor Cp. The source capacitor Cs has a large capacitance value such that it can charge a voltage Vsus/2 equal to a half value of the sustain voltage Vsus. The first to fourth switches S 1  to S 4  controls a flow of current. The energy recovering apparatus  38  provided at the sustain driver  34  are formed around the panel capacitor Cp symmetrically with the scan driver  32 .  
       FIG. 4  is a timing diagram and a waveform diagram representing on/off timings of the switches shown in  FIG. 3  and an output waveform of the panel capacitor.  
      An operation procedure of the energy recovering apparatus  38  shown in  FIG. 3  will be described in conjunction with  FIG. 4 .  
      First, it is assumed that a voltage charged between the scan electrode line Y and the sustain electrode line Z, that is, a voltage charged in the panel capacitor Cp prior to the T 1  period should be 0 volt, and a voltage Vsus/2 has been charged in the source capacitor Cs.  
      In the T 1  period, the first switch S 1  is turned on, to thereby form a current path extending from the source capacitor Cs, via the first switch S 1  and the inductor L, into the panel capacitor Cp. At this time, the inductor L and the panel capacitor L forms a serial resonance circuit. Since a voltage Vsus/2 has been charged in the source capacitor Cs, a voltage of the panel capacitor Cp rises into a sustain voltage Vsus equal to twice the voltage of the source capacitor Cs with the aid of a current charge/discharge of the inductor L in the serial resonance circuit.  
      In the T 2  period, the second switch S 2  is turned on to thereby apply the sustain voltage Vsus to the scan electrode line Y. The sustain voltage Vsus applied to the scan electrode line Y prevents a voltage of the panel capacitor Cp from falling into less than the sustain voltage Vsus to thereby cause a normal sustain discharge. Since a voltage of the panel capacitor Cp has risen into the sustain voltage Vsus in the T 1  period, a driving power supplied from the exterior for the purposing of causing the sustain discharge is minimized.  
      In the T 3  period, the first switch S 1  is turned off and the panel capacitor Cp keeps the sustain voltage Vsus. In the T 4  period, the second switch S 2  is turned off while the third switch S 3  is turned on. If the third switch S 3  is turned on, then a current path extending from the panel capacitor Cp, via the inductor L and the third switch S 3 , into the source capacitor Cs is formed to thereby recover a voltage charged in the panel capacitor Cp into the source capacitor Cs. While the panel capacitor Cp is discharged, a voltage of the panel capacitor Cp falls. At the same time, a voltage Vsus/2 is charged in the source capacitor Cs. After a voltage Vsus/2 was charged in the source capacitor Cs, the third switch S 3  is turned off while the fourth switch S 4  is turned on. In the fifth period when the fourth switch S 4  is turned on, a current path extending from the panel capacitor Cp into the ground voltage source GND, thereby allowing a voltage of the panel capacitor Cp to falls into 0 volt. In the T 6  period, a state in the T 5  period is kept for a certain time as it is. An AC driving pulse applied to the scan electrode line Y and the sustain electrode line Z is obtained by periodically repeating an operation procedure in the T 1  to T 6  periods.  
      The scan electrode lines Y of the PDP driven in this manner are supplied with a sustain pulse in the sustain period, and are additionally supplied with a reset pulse and a scan pulse in the initialization period and the address period, respectively. Accordingly, the scan driver  32  is provided with a plurality of scan drive integrated circuits and a plurality of high-voltage switches. On the other hand, since the sustain pulse only is supplied, the sustain electrode line Z is directly connected to the sustain driver  34 . As a result, a resistance of the current path at the scan driver  32  and the scan electrode line Y becomes larger than that of the current path at the sustain driver  34  and the sustain electrode line Z. Further, the scan driver  32  has a smaller current supply capability than the sustain driver  34 .  
      In spite of such a resistance different of the current path and such a difference in the current supply capability, pulse widths TP 1  and TP 2  of a first sustain pulse SUS 1  and a second sustain pulse SUS 2  applied to the scan electrode line Y and the sustain electrode line Z during the sustain period, respectively are equal to each other as shown in  FIG. 5 . In other words, a rising edge Tr 1  of the first sustain pulse SUS 1  is identical to a rising edge Tr 2  of the second sustain pulse SUS 2 , and a falling edge Tf 1  of the first sustain pulse SUS 1  is identical to a falling edge of Tf 2  of the second sustain pulse SUS 2 . Herein, the rising edges Tr 1  and Tr 2  of the first and second sustain pulses are time intervals going from an operation time of the energy recovering apparatus  38  shown in  FIG. 3  until a turning-on time of the second switch S 2  while the falling edges Tf 1  and Tf 2  thereof are time intervals going from an operation time of the energy recovering apparatus  38  into the fourth switch S 4 .  
      Accordingly, intensities of sustain discharges caused by the first and second sustain pulses SUS 1  and SUS 2  applied to the scan electrode line Y and the sustain electrode line Z, respectively are differentiated to raises problems of an irregular discharge and hence a deterioration of picture quality. Particularly, such problems become more serious when a width of each of the first and second sustain pulses SUS 1  and SUS 2  is approximately 2 μs as a resolution is larger.  
     SUMMARY OF THE INVENTION  
      Accordingly, it is an object of the present invention to provide a method of driving a plasma display panel that is adaptive for improving a picture quality.  
      In order to achieve these and other objects of the invention, a method of driving a plasma display panel according to an embodiment of the present invention, having first and second row electrodes and a heat electrode and including a sustain period for implementing a gray scale depending upon a discharge frequency, includes the step of alternately applying first and second sustain pulses having a different width during the sustain period to the first and second row electrodes.  
      In the method, a resistance going from a first driver generating the first sustain pulse into the first row electrode is different from a resistance going from a second driver generating the second sustain pulse into the second row electrode.  
      Herein, said resistance going the first driver into the first row electrode is larger than a resistance going the second driver into the second row electrode.  
      A width of the first sustain pulse is longer than that of the second sustain pulse.  
      A sustain period of the first sustain pulse is longer than that of the second sustain pulse.  
      A rising edge caused by an energy recovering circuit of the first sustain pulse is shorter than a rising edge caused by the energy recovering circuit of the second sustain pulse.  
      Alternatively, a resistance going from the second driver into the second row electrode is larger than a resistance going from the first driver into the first row electrode.  
      A width of the second sustain pulse is longer than that of the first sustain pulse.  
      A sustain period of the second sustain pulse is longer than that of the first sustain pulse.  
      A rising edge caused by an energy recovering circuit of the second sustain pulse is shorter than a rising edge caused by the energy recovering circuit of the first sustain pulse. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
      These and other objects of the invention will be apparent from the following detailed description of the embodiments of the present invention with reference to the accompanying drawings, in which:  
       FIG. 1  is a perspective view representing a structure of a conventional AC surface-discharge plasma display panel;  
       FIG. 2  is a plan view showing an arrangement structure of overall electrode lines and discharge cells of the plasma display panel in  FIG. 1 ;  
       FIG. 3  is a circuit diagram of a conventional energy recovering apparatus provided at the pre-stage of the sustain driver in  FIG. 2 ;  
       FIG. 4  is a timing diagram and a waveform diagram representing an ON/OFF timing of each switch shown in  FIG. 2  and an output waveform of the panel capacitor;  
       FIG. 5  is a detailed waveform diagram of a sustain pulse applied to the sustain electrode pair shown in  FIG. 2 ;  
       FIG. 6  is a waveform diagram for explaining a method of driving a plasma display panel according to an embodiment of the present invention;  
       FIG. 7A  and  FIG. 7B  are detailed waveform diagrams of the first and second sustain pulses in the sustain period shown in  FIG. 6 ; and  
       FIG. 8A  and  FIG. 8B  are detailed waveform diagrams showing another shapes of the first and second sustain pulses in the sustain period shown in  FIG. 6 . 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       FIG. 6  shows a method of driving a plasma display panel according to an embodiment of the present invention.  
      Referring to  FIG. 6 , each sub-field is divided into an initialization period for initializing cells of the entire field, and a sustain period for implementing a gray scale depending upon an address period for selecting a discharge cell and a discharge frequency.  
      In the initialization period, a rising ramp waveform Ramp-up generated at the scan driver is simultaneously applied to all the scan electrodes. The rising ramp waveform Ramp-up causes a weak discharge within cells of the entire field to thereby generate wall charges within the cells. After the rising ramp waveform Ramp-up was applied, a falling ramp waveform Ramp-down is simultaneously applied to the scan electrodes Y. The falling ramp waveform Ramp-down causes a weak erasure discharge with the cells, to thereby uniformly left wall charges required for the address discharge within the cells of the entire field.  
      In the address period, a negative scan pulse Scan is sequentially applied to the scan electrodes Y and, at the same time, a positive data pulse data is applied to the address electrodes X. An address discharge is generated within the cells to which the scan pulse Scan and the data pulse data are applied. Wall charges are generated within the cells selected by the address discharge. A positive direct current (DC) voltage zdc is applied to the sustain electrodes Z in the set-down period and the address period.  
      In the sustain period, the first and second sustain pulses SUS 1  and SUS 2  are alternately applied to the scan electrodes Y and the sustain electrodes Z. The cell selected by the address discharge causes a sustain discharge taking a surface-discharge type between the scan electrode Y and the sustain electrode Z whenever each of the sustain pulses SUS 1  and SUS 2  is applied while the wall charges within the cell being added to the sustain pulses SUS 1  and SUS 2 .  
      Widths of the first and second sustain pulses SUS 1  and SUS 2  applied to the scan electrode Y and the sustain electrode Z, respectively are differentiated. This will be described in detail with reference to  FIG. 7A  to  FIG. 8B .  
       FIG. 7A  and  FIG. 7B  show a sustain pulse applied when a resistance of the current path extending from the scan driver into the scan electrode line Y is smaller than that of the current path extending from the sustain driver into the sustain electrode line Z.  
      Referring to  FIG. 8A  and  FIG. 8B , a width TP 1  of the first sustain pulse SUS 1  applied to the scan/sustain electrode line Y is smaller than a width TP 2  of the second sustain pulse SUS 2  applied to the sustain electrode line Z.  
      As shown in  FIG. 8A , a rising edge Tr 1  of the first sustain pulse SUS 1  is identical to a rising edge Tr 2  of the second sustain pulse SUS 2 ; a sustain interval Ts 1  of the first sustain pulse SUS 1  is shorter than a sustain interval Ts 2  of the second sustain pulse SUS 2 ; and a falling edge Tf 1  of the first sustain pulse SUS 1  is identical to a falling edge Tf 2  of the second sustain pulse SUS 2 .  
      As shown in  FIG. 8B , a rising edge Tr 1  of the first sustain pulse SUS 1  is longer than to a rising edge Tr 2  of the second sustain pulse SUS 2 ; a sustain interval Ts 1  of the first sustain pulse SUS 1  is shorter than a sustain interval Ts 2  of the second sustain pulse SUS 2 ; and a falling edge Tf 1  of the first sustain pulse SUS 1  is identical to a falling edge Tf 2  of the second sustain pulse SUS 2 . As a rising edge of the sustain pulse is smaller, a discharge intensity becomes relatively larger. The rising edge Tr 2  of the second sustain pulse SUS 2  shorter than the rising edge Tr 1  of the first sustain pulse SUS 1  cause relatively larger discharge intensity. Herein, the rising edges Tr 1  and Tr 2  mean time intervals going from an operation time of the energy recovering circuit shown in  FIG. 3  until an turning-on time of the second switch S 2 .  
      Accordingly, the second sustain pulse SUS 2  having a larger pulse width than the first sustain pulse SUS 1  compensates for a resistance of the current path extending from the sustain driver into the sustain electrode line Z. Thus, a sustain discharge intensity between the scan electrode line Y and the sustain electrode line Z becomes equal. If the discharge intensity is equal, then a discharge becomes uniform to thereby improve a picture quality.  
      Referring to  FIG. 7A  and  FIG. 7B , a width TP 1  of the first sustain pulse SUS 1  applied to the scan/sustain electrode line Y is larger than a width TP 2  of the second sustain pulse SUS 2  applied to the sustain electrode line Z.  
      As shown in  FIG. 7A , a rising edge Tr 1  of the first sustain pulse SUS 1  is identical to a rising edge Tr 2  of the second sustain pulse SUS 2 ; a sustain interval Ts 1  of the first sustain pulse SUS 1  is longer than a sustain interval Ts 2  of the second sustain pulse SUS 2 ; and a falling edge Tf 1  of the first sustain pulse SUS 1  is identical to a falling edge Tf 2  of the second sustain pulse SUS 2 .  
      As shown in  FIG. 7B , a rising edge Tr 1  of the first sustain pulse SUS 1  is shorter than to a rising edge Tr 2  of the second sustain pulse SUS 2 ; a sustain interval Ts 1  of the first sustain pulse SUS 1  is longer than a sustain interval Ts 2  of the second sustain pulse SUS 2 ; and a falling edge Tf 1  of the first sustain pulse SUS 1  is identical to a falling edge Tf 2  of the second sustain pulse SUS 2 . As a rising edge of the sustain pulse is smaller, a discharge intensity becomes relatively larger. The rising edge Tr 1  of the first sustain pulse SUS 1  shorter than the rising edge Tr 2  of the second sustain pulse SUS 2  cause relatively larger discharge intensity.  
      Accordingly, the first sustain pulse SUS 1  having a larger pulse width than the second sustain pulse SUS 2  compensates for a resistance of the current path extending from the scan driver into the scan electrode line Y. Thus, a sustain discharge intensity between the scan electrode line Y and the sustain electrode line Z becomes equal. If the discharge intensity is equal, then a discharge becomes uniform to thereby improve a picture quality.  
      As described above, the method of driving the plasma display panel according to the present invention differentiates rising edges and sustain intervals of the first and second sustain pulses, thereby allowing the widths of the first and second sustain pulses to be different from each other. In other words, a sustain pulse having a relatively larger pulse width is applied to the electrode line having a relatively larger resistance of the current path extending from the electrode line into the driver. Accordingly, the sustain discharge intensity between the scan electrode and the su stain electrode is equal, so that it becomes possible to prevent an excessive discharge and hence improve a driving voltage margin.  
      Although the present invention has been explained by the embodiments shown in the drawings described above, it should be understood to the ordinary skilled person in the art that the invention is not limited to the embodiments, but rather that various changes or modifications thereof are possible without departing from the spirit of the invention. Accordingly, the scope of the invention shall be determined only by the appended claims and their equivalents.