Patent Publication Number: US-7714805-B2

Title: Method of driving plasma display panel

Description:
This Nonprovisional application claims priority under 35 U.S.C. §119(a) on Patent Application No. 10-2003-0102174 filed in Korea on Dec. 31, 2003, the entire contents of which are hereby incorporated by reference. 
   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to a plasma display panel, and more particularly to a method of driving a plasma display panel, which can improve display quality. 
   2. Description of the Background Art 
   In the recent information society, the importance of a display device as a visual information transmission medium has been stressed than ever. A cathode-ray tube or a Braun tube which is being widely used is heavy and bulky. Hence, various types of flat panel display devices which are capable of overcoming the disadvantages of the cathode-ray tube are being developed. 
   These flat panel display devices include a plasma display panel (PDP), a field emission display, an electro-luminescence, etc. 
   The PDP out of these devices displays images and moving pictures, including characters or graphics, by irradiating phosphors by ultraviolet rays of 147 nm generated during a discharge of a mixed gas of He+Xe, Ne+Xe or He+Xe+Ne. The PDP is not only easy to make its thickness thin and its size large but also feasible to greatly improve picture quality thanks to the recent development of technology. 
   Especially, a tri-electrode AC (Alternative Current) surface-discharge PDP lowers a voltage necessary for a discharge by accumulating barrier charges using a dielectric layer, and has the advantages of a low-voltage driving operation and long life. 
     FIG. 1  is a perspective view illustrating a discharge cell of a general tri-electrode AC surface-discharge PDP. 
   Referring to  FIG. 1 , a discharge cell of the PDP includes a scan electrode Y and a sustain electrode Z formed both on an upper substrate  10 , and an address electrode X formed on a lower substrate  18 . The scan and sustain electrodes Y and Z include transparent electrodes  12 Y and  12 Z, respectively, and includes metal bus electrodes  13 Y and  13 Z, respectively, which are narrower in line width than the transparent electrodes  12 Y and  12 Z and formed at the edges of the transparent electrodes  12 Y and  12 Z. 
   The transparent electrodes  12 Y and  12 Z formed on the upper substrate  10  are made of Indium-Tin-Oxide (ITO). The metal bus electrodes  13 Y and  13 Z formed on the transparent electrodes  12 Y and  12 Z are made of metal, such as chrome (Cr), serving to reduce a drop in a voltage caused by the transparent electrodes  12 Y and  12 Z having high resistance. An upper dielectric layer  14  and a protective layer  16  are formed on the upper substrate  10  on which the scan and sustain electrodes are formed in parallel. Barrier charges generated during a plasma discharge are formed on the upper dielectric layer  14 . The protective layer  16  protects the upper dielectric layer  14  from damaging by a sputtering generated during the plasma discharge and also increases the efficiency of secondary electron emission. A magnesium oxide (MgO) is usually used as the protective layer  16 . 
   A lower dielectric layer  22  and a barrier rib  24  are formed on the lower substrate  18  on which the address electrode X is formed. A phosphor layer  26  is coated over the surfaces of the lower dielectric layer  22  and the barrier rib  24 . The address electrode X is perpendicular to the scan and sustain electrodes Y and Z. The barrier rib  24  is formed in parallel to the address electrode X and prevents ultraviolet rays and visual rays generated by a discharge from leaking to an adjacent cell. The phosphor layer  26  is excited by ultraviolet rays generated during a plasma discharge and generates any one visual ray among red, green and blue. An inert mixed gas is injected into a discharge space provided between the upper and lower substrates  10  and  18  and the barrier rib  24 . 
   In order to achieve a gray scale of an image, the PDP is driven on a time-division basis by dividing one frame into subfields each having the different number of irradiations. Each subfield has a reset period for resetting the entire screen, an address period for selecting a scan line and selecting a cell in the selected scan line, and a sustain period for achieving a gray scale according to the number of discharges. 
   The reset period is further divided into a set-up period for supplying a ramp-up waveform and a set-down period for supplying a ramp-down waveform. For example, if it is desired to display an image by 256 gradations, one frame period corresponding to 1/60 seconds (16.67 ms) is divided into 8 subfields SF 1  to SF 9 , as shown in  FIG. 2 . Each of the 8 subframes SF 1  to SF 8  is further divided into the reset period, the address period and the sustain period as described above. The reset and address periods in each subfield are identical with respect to the respective subfields, while the sustain period increases at the rate of 2n (where n is 0, 1, 2, 3, 4, 5, 6 and 7). 
     FIG. 3  is a waveform diagram illustrating a driving method of the PDP. 
   Referring to  FIG. 3 , the PDP is separately driven according to a reset period for resetting the entire screen, an address period for selecting a cell, and a sustain period for sustaining a discharge of the selected cell. 
   During the reset period, a ramp-up waveform is simultaneously applied to all the scan electrodes Y during a set-up period. In this case, the scan electrodes Y are raised up to a voltage Vp for discharging cells. By this ramp-up waveform, a weak discharge occurs within the cells of the entire screen and wall charges are created within the cells. During a set-down period after the ramp-up waveform is supplied, a ramp-down waveform falling from a positive-polarity voltage lower than the peak voltage of the ramp-up waveform is simultaneously applied to all the scan electrodes Y. The ramp-down waveform creates a weak erase discharge within the cells, erasing unnecessary charges out of the wall charges and space charges generated by the set-up discharge and uniformly sustaining the wall charges necessary for an address discharge within the cells of the entire screen. 
   During the address period, a negative-polarity scan pulse Scan is sequentially applied to the scan electrodes Y and at the same time a positive-polarity data pulse is applied to the address electrodes. A difference between a voltage Vy of the scan pulse and a voltage Va of the data pulse is added to a wall voltage generated during the reset period to create the address discharge within the cells. The wall charges are generated within the selected cells by the address discharge. 
   Meanwhile, during the set-down period and the address period, a positive-polarity direct current (DC) voltage of a sustain voltage level Vs is supplied to the sustain electrodes Z. 
   During the sustain period, a sustain pulse Sus of the sustain voltage level Vs is alternatively applied to the scan electrodes Y and the sustain electrodes Z. Then the wall voltage within the cell is added to the sustain pulse Sus by the address discharge, and a sustain discharge is created between the scan and sustain electrodes Y and Z as a form of a surface discharge whenever each sustain pulse Sus is applied. Finally, after the sustain discharge is completed, an erase ramp waveform having a narrow pulse width is supplied to the sustain electrodes Z, erasing the wall charges within the cell. 
   In the above-described PDP, a preliminary waveform is supplied during a preliminary period as shown in  FIG. 4  in order to ensure time to raise a plurality of voltage sources Vp, Vs, Vy and Va to desired voltages when a power source is turned on. 
   In this case, the data pulse is not supplied during the address period so as not to create a discharge during the preliminary period. During the reset and sustain periods, the same waveforms as  FIG. 3  are applied and thus a detailed description thereof will not be given. 
   During the preliminary period, however, an undesired sustain discharge occurs, and an afterimage is displayed on the panel. In more detail, the power source of the PDP is randomly turned off by a user at any time, the wall charges remain within the discharge cells. Especially, such wall charges remain largely within the discharge cells displaying bright luminescence before the power source of the PDP is turned off and the undesired sustain discharge occurs during the sustain period of the preliminary period by these remaining charges. Consequently, the afterimage is displayed in a part of the discharge cells which have displayed a bright screen when the power source of the PDP is turned off. 
   SUMMARY OF THE INVENTION 
   Accordingly, an object of the present invention is to solve at least the problems and disadvantages of the background art. 
   According to an aspect of the present invention, there is provided a method for driving a PDP separately during a data driving period for supplying a driving waveform and a preliminary period for raising voltages for supplying the driving waveform up to a desired voltage, in order to display an image in each discharge cell, wherein a waveform supplied to electrodes during a sustain period of the data driving period is different from a waveform supplied to the electrodes during a sustain period of the preliminary period. 
   According to the present invention, brightness, efficiency and the contrast ratio are improved and high-speed driving is accomplished. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The above and other objects, features and advantages of the present invention will be apparent from the following detailed description of the preferred embodiments of the invention in conjunction with the accompanying drawings, in which: 
       FIG.1  is a perspective view illustrating a discharge cell of a general tri-electrode AC surface-discharge PDP; 
       FIG. 2  is a diagram illustrating one frame of the PDP; 
       FIG. 3  is a waveform diagram illustrating a driving method of the PDP; 
       FIG. 4  illustrates a preliminary discharge waveform of the PDP according to a prior art; 
       FIG. 5  illustrates a preliminary discharge waveform of the PDP according to a first embodiment of the present invention; 
       FIG. 6  illustrates a preliminary discharge waveform of the PDP according to a second embodiment of the present invention; 
       FIG. 7  illustrates a preliminary discharge waveform of the PDP according to a third embodiment of the present invention; 
       FIG. 8  illustrates a preliminary discharge waveform of the PDP according to a fourth embodiment of the present invention; and 
       FIG. 9  illustrates a preliminary discharge waveform of the PDP according to a fifth embodiment of the present invention. 
       FIG. 10  illustrates both a preliminary discharge waveform and a waveform diagram illustrating a driving method in a single figure. 
   

   DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
   Reference will now be made in detail to the present preferred embodiments of the invention, examples of which are illustrated in the accompanying drawings. 
   In order to display an image in each discharge cell, in a method for driving a PDP according to the present invention, the PDP is driven separately during a data driving period for supplying a driving waveform and during a preliminary period for raising voltages for supplying the driving waveform up to a desired voltage, in which case a waveform supplied to electrodes during a sustain period of the data driving period is different from a waveform supplied to the electrodes during a sustain period of the preliminary period. 
   In the method, a ground voltage is supplied to a scan electrode and a sustain electrode contained in the discharge cell during a sustain period of a subfield contained in the preliminary period. 
   The method includes the steps of supplying a first sustain pulse to a scan electrode contained in the discharge cell during a sustain period of a subfield contained in the preliminary period, and supplying a second sustain pulse synchronized with the first sustain pulse to a sustain electrode contained in the discharge cell. 
   In the method, either the scan electrode or the sustain electrode contained in the discharge cell is floated during the sustain period of the subfield contained in the preliminary period. 
   In the method, a sustain pulse is supplied to the other electrode which is not floated. 
   In the method, a scan electrode and a sustain electrode contained in the discharge cell are floated during a sustain period of a subfield contained in the preliminary period. 
   In the method, a ground voltage is supplied to electrodes contained in the discharge cell during a sustain period of a subfield contained in the preliminary period. 
   In the method, the ground voltage is applied to the electrodes contained in the discharge cell for 1 to 3 seconds, preferably 2 seconds, during the sustain period of the subfield contained in the preliminary period. 
   Preferred embodiments of the present invention will be described in more detail with reference to  FIGS. 5 to 9 . 
     FIG. 5  illustrates a preliminary discharge waveform of the PDP according to a first embodiment of the present invention. 
   Referring to  FIG. 5 , the preliminary discharge waveform is separately driven according to a reset period for resetting discharge cells, an address period for selecting the discharge cells, and a sustain period for sustaining a discharge of the cells. The preliminary waveform is supplied prior to the data driving waveform shown in  FIG. 3 . 
   During the reset period, a ramp-up waveform is simultaneously applied to all the scan electrodes Y during a set-up period. By this ramp-up waveform, a weak discharge occurs within the cells of the entire screen, creating wall charges within the cells. A reset discharge does not occur within the discharge cells because the voltage of the ramp-up waveform is not raised to a desired voltage Vp. During a set-down period after the ramp-up waveform is supplied, a ramp-down waveform falling from a positive-polarity voltage lower than the peak voltage of the ramp-up waveform is simultaneously supplied to the scan electrodes Y. 
   During the address period, a negative-polarity scan pulse Scan is sequentially applied to the scan electrodes Y and a ground voltage is applied to the address electrodes X. Since there is no a voltage difference enough to create an address discharge between the scan electrodes Y and the address electrodes X, that is, since a data pulse is not supplied, the address discharge does not occur. 
   Meanwhile, a positive-polarity DC voltage of a sustain voltage level Vs is supplied to the sustain electrodes Z during the set-down and address periods. 
   During the sustain period, the ground voltage is applied to the scan electrodes Y and the sustain electrodes Z. Thus if the ground voltage is applied to the scan electrodes Y and the sustain electrodes Z, a sustain discharge does not occur during the sustain period of a subfield contained in a preliminary period. That is, since a discharge does not occur between the scan electrodes Y and the sustain electrodes Z, it is possible to prevent an afterimage from being displayed during the preliminary period. 
   Actually, a plurality of subfields shown in  FIG. 5  is applied during the preliminary period so as to raise the voltages of the electrodes Y, Z and X up to a desired voltage, for example, Vp, Vy, Vs or Va. Thereafter, the data driving waveform shown in  FIG. 3  is applied to the scan, sustain and address electrodes to achieve the image of the PDP. As illustrated in  FIGS. 3 and 5 , the preliminary discharge waveform and the data driving waveform differ from each other. 
     FIG. 6  illustrates a preliminary discharge waveform of the PDP according to a second embodiment of the present invention. 
   Referring to  FIG. 6 , the preliminary discharge waveform is separately driven according to a reset period for resetting discharge cells, an address period for selecting the discharge cells, and a sustain period for sustaining a discharge of the cells. 
   The reset period and the address period have the same waveform as the first embodiment of the present invention and thus a detailed description thereof is omitted. 
   During the sustain period, the sustain pulse Sus which is synchronized, that is the sustain pulse Sus of the same magnitude and the same time period is applied to the scan electrodes Y and the sustain electrodes Z. Thus if the synchronized sustain pulse Sus is applied to the scan electrodes Y and the sustain electrodes Z, since there is no voltage difference between the scan electrodes Y and the sustain electrodes Z, a sustain discharge does not occur between the scan electrodes Y and the sustain electrodes Z. Therefore, it is possible to prevent an afterimage from being displayed during the preliminary period. 
   Actually, a plurality of subfields shown in  FIG. 6  is applied during the preliminary period so as to raise the voltages of the electrodes Y, Z and X up to a desired voltage, for example, Vp, Vy, Vs or Va. Thereafter, the data driving waveform shown in  FIG. 3  is applied to the scan, sustain and address electrodes to achieve the image of the PDP. As illustrated in  FIGS. 3 and 6 , the preliminary discharge waveform and the data driving waveform differ from each other. 
     FIG. 7  illustrates a preliminary discharge waveform of the PDP according to a third embodiment of the present invention. 
   Referring to  FIG. 7 , the preliminary discharge waveform is separately driven according to a reset period for resetting discharge cells, an address period for selecting the discharge cells, and a sustain period for sustaining a discharge of the cells. 
   The reset period and the address period have the same waveform as the first embodiment of the present invention and thus a detailed description thereof is omitted. 
   During the sustain period, the sustain pulse Sus is applied to at least one of the scan electrodes Y and the sustain electrodes Z. Half the sustain pulse Sus is induced to the other electrodes Y or Z. In this case, half of the sustain pulse Sus is induced as a floating state. Thus, a sustain discharge does not occur between the scan electrodes Y and the sustain electrodes Z. Therefore, it is possible to prevent an afterimage from being displayed during the preliminary period. 
   Actually, a plurality of subfields shown in  FIG. 7  is applied during the preliminary period so as to raise the voltages of the electrodes Y, Z and X up to a desired voltage, for example, Vp, Vy, Vs or Va. Thereafter, the data driving waveform shown in  FIG. 3  is applied to the scan, sustain and address electrodes to achieve the image of the PDP. As illustrated in  FIGS. 3 and 7 , the preliminary discharge waveform and the data driving waveform differ from each other. 
     FIG. 8  illustrates a preliminary discharge waveform of the PDP according to a fourth embodiment of the present invention. 
   Referring to  FIG. 8 , the preliminary discharge waveform is separately driven according to a reset period for resetting discharge cells, an address period for selecting the discharge cells, and a sustain period for sustaining a discharge of the cells. 
   The reset period and the address period have the same waveform as the first embodiment of the present invention and thus a detailed description thereof is omitted. 
   During the sustain period, the sustain pulse Sus of a floated state is applied to the scan electrodes Y and the sustain electrodes Z. Thus, a sustain discharge does not occur between the scan electrodes Y and the sustain electrodes Z. Therefore, it is possible to prevent an afterimage from being displayed during the preliminary period. 
   Actually, a plurality of subfields shown in  FIG. 8  is applied during the preliminary period so as to raise the voltages of the electrodes Y, Z and X up to a desired voltage, for example, Vp, Vy, Vs or Va. Thereafter, the data driving waveform shown in  FIG. 3  is applied to the scan, sustain and address electrodes to achieve the image of the PDP. As illustrated in  FIGS. 3 and 8 , the preliminary discharge waveform and the data driving waveform differ from each other. 
     FIG. 9  illustrates a preliminary discharge waveform of the PDP according to a fifth embodiment of the present invention. 
   Referring to  FIG. 9 , a ground voltage is applied to the electrodes Y, Z and X during the preliminary period prior to the data driving period for supplying a driving waveform in order to display an image in each discharge cell. The preliminary period is set to 1 to 3 seconds, preferably, 2 seconds so as to raise the voltages of the driving waveform up to a desired voltage, for example, Vp, Va, -Vy or Vs. In other words, as shown in the preliminary discharge waveform of the PDP of  FIG. 5 , the ground voltage is supplied to the scan electrodes Y, the sustain electrodes Z and the address electrodes X for 1 to 3 seconds, preferably 2 seconds. In this case, during the preliminary discharge period, charges existing within the discharge cells during a previous driving state of the PDP that is, during a turn-off operation of the PDP are eliminated. Therefore, an afterimage caused by the previous driving state doesn&#39;t occur and the display quality of the PDP can be improved. Thereafter, during the data driving period, desired voltages are supplied to the scan electrodes Y, the sustain electrodes Z and the address electrodes X, and the PDP displays an image stably. 
   A method for driving a PDP according to the present invention does not create a sustain discharge during a sustain period and prevents an afterimage caused by a previous state when the PDP is turned on from being displayed, improving display quality. Moreover, the method eliminates charges within a discharge cell by supplying a ground voltage to electrodes for 1 to 3 seconds, preferably 2 seconds, before a data driving waveform is supplied, preventing an afterimage from being displayed and improving display quality. 
   According to the present invention, brightness, efficiency and the contrast ratio are improved and high-speed driving is accomplished. 
   While the present invention has been described with reference to the particular illustrative embodiments, it is not to be restricted by the embodiments but only by the appended claims. It is to be appreciated that those skilled in the art can change or modify the embodiments without departing from the scope and spirit of the present invention.