Patent Publication Number: US-7583242-B2

Title: Plasma display panel, and apparatus and method for driving the same

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application claims priority to and the benefit of Korean Patent Application No. 10-2003-0074235, filed on Oct. 23, 2003, which is hereby incorporated by reference for all purposes as if fully set forth herein. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a plasma display panel (PDP), and more particularly, to an apparatus and a method for driving the PDP. 
     2. Discussion of the Related Art 
     Flat panel displays, such as a liquid crystal displays (LCD), field emission displays (FED), and PDPs, have been developed recently. Generally, as compared to other flat panel displays, the PDP is brighter, has a higher light emitting efficiency and a wider viewing angle. Thus, the PDP is recognized as a substitute for the conventional cathode ray tube (CRT), especially for large displays of greater than forty inches. 
     The PDP displays characters or images with plasma generated by gas discharge, and depending upon its size, it may have hundreds of thousands or millions of pixels arranged in a matrix. A PDP is typically classified as a direct current (DC) or an alternating current (AC) type PDP according to its discharge cell structure and driving voltage waveform shape. 
     The DC PDP has a shortcoming in that current flows in a discharge space when voltage is applied to electrodes in the discharge space, which requires a resistor for restricting the current. To the contrary, the current in the AC DDP is restricted by naturally formed capacitance components, and the electrodes are protected from the impact of ions during discharge because they are covered with a dielectric layer, which results in the AC PDP having a longer lifespan than the DC PDP. 
       FIG. 1  is a partial perspective view of a conventional AC PDP. 
     As shown in  FIG. 1 , pairs of scan electrodes  4  and sustain electrodes  5 , covered by a dielectric layer  2  and a protection layer  3 , are formed parallel on a first substrate  1 . A plurality of address electrodes  8 , covered by an insulation layer  7 , is formed on a second substrate  6 . Barrier ribs  9  are formed in parallel with, and between, the address electrodes  8  on the insulation layer  7 . Further, phosphors  10  are formed on the surface of the insulation layer  7  and both sides of the barrier ribs  9 . The first substrate  1  and the second substrate  6  are sealed together to form a discharge space  11  between them and in such a manner that the scan electrodes  4  and the sustain electrodes  5  are perpendicular to the address electrodes  8 . A portion of the discharge space  11  between a crossing of the address electrode  8  and a pair of the scan electrode  4  and the sustain electrode  5  forms a discharge cell  12 . 
       FIG. 2  shows a tri-electrode plane discharge structure of the PDP. 
     In such a structure, a discharge for forming a wall charge to select a pixel occurs between an address electrode and a scan electrode, and then a discharge for displaying the image occurs repeatedly for a certain period of time between the scan electrode and the sustain electrode. 
     A wall charge means a charge formed on a wall, such as at the dielectric layer of a discharge cell, near the respective electrodes and accumulated on the electrodes. Such a wall charge does not actually contact the electrodes, but rather it is described as being “formed”, “accumulated”, or “piled” on the electrodes. Wall voltage means an electric potential difference formed on the wall of the discharge cell by the wall charge. 
     The barrier ribs form the discharge space and block light generated by a discharge, in order to prevent cross-talk with neighboring pixels. The PDP displays desired colors by making discharges in the pixels, which generate ultra violet rays that excite the phosphors to emit light. 
     A middle gray level should be realized in order for the PDP to adequately function as a color display, and a method for displaying a middle gray level using time-division control has been used. 
       FIG. 3  shows a 6 bit gray level realizing method for an AC PDP, in which one TV field is divided to six subfields SF 1 -SF 6 , and each of the subfields is further divided into an address period A 1 -A 6  and a display discharge sustain period S 1 -S 6 . 
     However, when using the conventional gray level expressing method with N subfields, a color stripe may occur at low and high gray levels due to excessive unit light. 
     SUMMARY OF THE INVENTION 
     The present invention provides a PDP, and an apparatus and method for driving the PDP, with an enhanced ability to express a unit gray level while maintaining linearity of the gray level and the brightness. 
     Additional features of the invention will be set forth in the description which follows, and in part will be apparent from the description, or may be learned by practice of the invention. 
     The present invention discloses an apparatus for driving a plasma display panel, comprising a gamma corrector, a subfield data generator, an average signal level calculator, and an automatic power controller. 
     The gamma corrector receives an image signal and performs a gamma correction according to a gamma correction curve. 
     The subfield data generator generates the image signal output from the gamma corrector as subfield data, according to a subfield generating compression curve, and outputs the subfield data as an address electrode driving signal. 
     The average signal level calculator calculates the average signal level of the image signal output from the gamma corrector and performs a correction according to an average signal level correction inverse curve regarding to a generation of subfields for each gray level. 
     The automatic power controller applies a sustain electrode driving signal and a scan electrode driving signal corresponding to the average signal level. 
     The present invention also discloses an apparatus for driving a plasma display panel, comprising a gamma corrector and a subfield data generator. 
     The gamma corrector receives an image signal and performs a gamma correction according to a gamma correction curve. 
     The subfield data generator generates subfield data from the image signal output from the gamma corrector according to a subfield generating compression curve and outputs the subfield data as an address electrode driving signal. 
     The present invention also discloses a plasma display panel (PDP) comprising a controller, an address electrode driver, a sustain electrode driver, and a scan electrode driver. 
     The PDP includes a plurality of address electrodes, and a plurality of scan electrodes and sustain electrodes arranged in pairs. 
     The controller corrects the image signal input thereto according to a gamma correction, generates subfield data according to a subfield generating compression curve, and outputs the subfield data as an address electrode driving signal. The controller also calculates an average signal level of the gamma-corrected image signal, performs correction according to an average signal level correction inverse curve regarding generation of subfields for each gray level, and outputs a sustain electrode driving signal and a scan electrode driving signal corresponding to the corrected average signal level. 
     The present invention also discloses a method for driving a plasma display panel. 
     In the method, an image signal is gamma corrected according to a gamma correction curve. 
     The gamma-corrected image signal is generated as subfield data according to a subfield generating compression curve, and the subfield data are output as an address electrode driving signal. 
     An average signal level of the gamma-corrected image signal is calculated and a correction is performed according to an average signal level correction inverse curve regarding a generation of subfields for each gray level. 
     It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are intended to provide further explanation of the invention as claimed. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in 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  is a partial perspective view of an AC PDP. 
         FIG. 2  shows a typical tri-electrode plane discharge structure of the AC PDP of  FIG. 1 . 
         FIG. 3  shows a general middle gray level realizing method for the AC PDP of  FIG. 1 . 
         FIG. 4  shows the sustain weight of a 0.5 gray level and a 0.25 gray level at each subfield according to the first exemplary embodiment of the present invention. 
         FIG. 5  shows the results of a comparison of unit light intensity. 
         FIG. 6  shows the comparison results of the ability to express the gray level and frequency of generation of a color stripe with the nonlinear gray level of a 0.5 gray level and a 0.25 gray level. 
         FIG. 7  shows the results of a comparison of subfield generation tables. 
         FIG. 8  is a block diagram of a PDP according to the third exemplary embodiment of the present invention. 
         FIG. 9  shows the controller of  FIG. 8 . 
         FIG. 10  shows a gamma correction curve and a subfield generating compression curve employed in the third exemplary embodiment of the present invention. 
         FIG. 11  shows an average signal level (ASL) correction curve and a subfield generating compression curve employed in the third exemplary embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     In the following detailed description, preferred embodiments of the invention are shown and described, simply by illustrating the best mode contemplated by the inventors of carrying out the invention. The invention can be modified in various obvious respects, all without departing from the invention. Accordingly, the drawings and description are to be regarded as illustrative in nature, and not restrictive. 
     Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings. 
       FIG. 4  shows the sustain weight of a 0.5 gray level and a 0.25 gray level at each subfield according to the first exemplary embodiment of the present invention. 
     Referring to  FIG. 4 , the subfield weight (SF weight) is adjusted in order to reduce the intensity of a unit gray level light. 
     In the first exemplary embodiment, among N members of SFs, one SF with half the number of sustain pulses of a least significant bit (LSB) is made and added so as to express a 0.5 gray level (0.5 LSB). 
     In order to further reduce the intensity of a unit gray level light, one SF with half the number of sustain pulses a 0.5 LSB is made to express a 0.25 gray level (0.25 LSB). 
     According to the first exemplary embodiment having the sustain weight of 0.5 LSB/0.25 LSB as shown in  FIG. 4 , the ability to express the low gray level may be enhanced as the intensity of a unit gray level light decreases, but nonlinearity of gray level occurs. 
       FIG. 5  shows the result of comparison of unit light intensity between the prior art (1 LSB) and the first exemplary embodiment, in which the 0.25 LSB provides for an irregular increase of the gray level, thereby resulting in an irregular increase in luminance. 
       FIG. 6  shows the comparison result of the ability to express the gray level and frequency of generation of color stripes between the linear gray level of 1 LSB and the nonlinear gray level of 0.5 LSB/0.25 LSB. 
     Referring to  FIG. 6 , the gray level expression is improper at low and high loads because the gray level is nonlinear in the first exemplary embodiment. 
     In order to amend this nonlinearity, the second exemplary embodiment performs Compressed Subfield Generation Table (SF-Gen Table) mapping, i.e. nonlinear data mapping. 
     Since the number of gray levels that may be assigned for SF-Gen Table mapping is restricted, there may be many assigned low gray levels and few assigned high gray levels in the second exemplary embodiment. 
     A nonlinear SF-Gen Table in which 512 outputs are compressed to 256 outputs is applied to the 0.5 LSB, and a nonlinear SF-Gen Table in which 1024 outputs are compressed to 256 outputs is applied to the 0.25 LSB. 
       FIG. 7  shows the results of comparison of the SF-Gen Table between 1 LSB and 0.25 LSB (or 0.5 LSB) of the second exemplary embodiment of the present invention. 
     When applying the SF-Gen Table of  FIG. 7 , the luminance with respect to the input gray level is generated in accordance with SF-Gen Table with gamma off. 
     However, luminance nonlinearity may still occur when applying the Compressed SF-Gen Table according to the second exemplary embodiment. 
     Accordingly, in the third exemplary embodiment, the linear luminance characteristic may be achieved by amending the nonlinear luminance characteristic of the SF-Gen Table with a gamma correction curve at the gamma block. 
       FIG. 8  is a block diagram of the PDP according to the third exemplary embodiment of the present invention. 
     Referring to  FIG. 8 , the PDP includes a plasma panel  100 , a controller  200 , an address electrode driver  300 , a scan (“Y”) electrode driver  400 , and a sustain (“X”) electrode driver  500 . 
     The plasma panel  100  includes a plurality of address electrodes A 1 -A m , arranged in a column direction, and a plurality of X electrodes X 1 -X n  and a plurality of Y electrodes Y 1 -Y n , arranged in a zigzag fashion in a row direction. The X electrodes X 1 -X n  correspond to the respective Y electrodes Y 1 -Y n . Further, the plasma panel  100  is comprised of a first glass substrate (not shown) on which the X and Y electrodes X 1 -X n  and Y 1 -Y n  are arranged, and a second glass substrate (not shown) on which the address electrodes A 1 -A m  are arranged. The two glass substrates are sealed together, with a discharge space between them, so that the X electrodes X 1 -X n  and the Y electrodes Y 1 -Y n  are perpendicular to the address electrodes A 1 -A m . Discharge spaces at the intersections between the address electrodes A 1 -A m  and the X and Y electrodes X 1 -X n  and Y 1 -Y n  form discharge cells. 
     The controller  200  gamma corrects the input image signal according to its stored gamma correction curve, generates subfield data according to the compressed subfield generation table, and outputs the subfield data as the address electrode driving signal. The controller  200  also calculates the average signal level (ASL) of the gamma-corrected image signal, performs a correction according to the ASL correction inverse curve regarding the generation of the subfields for each gray level, and outputs a sustain electrode driving signal and a scan electrode driving signal corresponding to the corrected ASL. 
     The address electrode driver  300  receives the address electrode driving signal from the controller  200  and applies a display data signal to the respective address electrodes A 1 -A m , thereby selecting the discharge cells to be displayed. 
     The X electrode driver  500  receives the X electrode driving signal from the controller  200 , and applies a driving voltage to the X electrodes X 1 -X n . 
     The Y electrode driver  400  receives the Y electrode driving signal from the controller  200 , and applies a driving voltage to the Y electrodes Y 1 -Y n . 
       FIG. 9  is a detailed view of the controller  200 . 
     Referring to  FIG. 9 , the controller  200  is comprised of a gamma corrector  210  for receiving the image signal and gamma correcting it according to the gamma correction curve stored therein; a subfield data generator  220  for generating the subfield data according to the compressed subfield generation table and outputting the subfield data as the address electrode driving signal; an ASL calculator  230  for calculating the ASL of the image signal output from the gamma corrector and performing the correction according to the ASL correction inverse curve regarding the generation of the subfields for each gray level; and an automatic power controller (APC)  250  for applying a sustain electrode driving signal and a scan electrode driving signal corresponding to the ASL. 
     The operation of the PDP according to the third exemplary embodiment of the present invention will now be described in detail. 
     The gamma corrector  210  receives the input image signal, performs the gamma correction according to the gamma correction curve stored therein, as shown in  FIG. 10 , and outputs the correction result. 
     The subfield data generator  220  receives the image signal output from the gamma corrector  210 , generates the subfield data according to the compressed SF-Gen Table stored therein, as shown in  FIG. 10 , and outputs the subfield data as the address electrode driving signal. 
     As shown in  FIG. 10 , the PDP has a final linear luminance characteristic because the gamma correction curve of the gamma corrector  210  corrects the nonlinear characteristic of the compressed SF-Gen Table. 
     Additionally, the ASL calculator  230  calculates the ASL of the image signal and performs a correction according to the ASL correction inverse curve stored therein, as shown in  FIG. 11 . 
     The APC controller  250  then applies the sustain electrode driving signal and the scan electrode driving signal corresponding to the ASL. 
     In that situation, linear gray mapping is generally employed when the load ratio ASL of the image is calculated with the sum of the output data of the gamma corrector  210 . But the SF-Gen Table, employed for the image data displayed on the screen, may cause a nonlinear relation between power consumption and the ASL. Accordingly, in order to maintain the linear relation between the ASL and the power consumption, the ASL correction inverse curve regarding the generation of the subfields at each gray level may be applied. 
     The address electrode driver  300  receives the address electrode driving signal from the subfield data generator  220 , and applies the display data signal to the respective address electrodes A 1 -A m  to select the discharge cells to be displayed. 
     The X electrode driver  500  receives the X electrode driving signal from the APC controller  250  and applies the driving voltage to the X electrodes X 1 -X n , and the Y electrode driver  400  receives the Y electrode driving signal from the APC controller  250  and applies the driving voltage to the Y electrodes Y 1 -Y n . 
     Then, the image data is displayed on the plasma panel  100 . 
     In the third exemplary embodiment of the present invention, the gamma corrector  210  corrects the nonlinearity of the subfield compression curve by performing the correction with the gamma correction curve, and the ASL calculator  230  maintains the linear relation of the power consumption to the ASL with the ASL correction inverse curve. 
     The gamma correction curve and the ASL correction inverse curve may be employed individually. 
     According to exemplary embodiments of the present invention, a PDP and an apparatus and method for driving the PDP are provided, in which dot noise may be reduced by reducing the unit gray level light, and the ability to express a low gray level may be enhanced by the reduction of light intensity per unit step. 
     It will be apparent to those skilled in the art that various modifications and variation can be made in the present invention without departing from the spirit or scope of the invention. Thus, it is intended that the present invention cover the modifications and variations of this invention provided they come within the scope of the appended claims and their equivalents.