Abstract:
A method and apparatus for adjusting a gain for each position of a plasma display panel for improving a brightness uniformity of a picture field is disclosed. In the method and apparatus, a gain of data to be displayed at a first position of a field of the plasma display panel is controlled into a first gain value. A gain of data to be displayed at a second position of said field is controlled into a second gain value.

Description:
This application claims the benefit of Korean Patent Application No. P2003-40121 filed in Korea Jun. 20, 2003, which is hereby incorporated by reference. 
   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   This invention relates to a plasma display panel, and more particularly to a method and apparatus for adjusting a gain for each position of a plasma display panel that is adaptive for improving a brightness uniformity of a picture field. 
   2. Description of the Related Art 
   Generally, a plasma display panel (PDP) displays a picture by utilizing a visible light emitted from a phosphorus material when an ultraviolet ray generated by a gas discharge excites the phosphorus material. The PDP has advantages in that it has a thinner thickness and a lighter weight in comparison to the existent cathode ray tube (CRT) and is capable of realizing a high resolution and a large-scale screen. 
   Referring to  FIG. 1  and  FIG. 2 , a conventional three-electrode, AC surface-discharge PDP includes scan electrodes Y 1  to Yn and sustain electrodes Z provided on an upper substrate  10 , and address electrodes X 1  to Xm provided on a lower substrate  18 . Discharge cells  1  of the PDP are provided at intersections among the scan electrodes Y 1  to Yn, the sustain electrodes Z and the address electrodes X 1  to Xm. 
   Each of the scan electrodes Y 1  to Yn and the sustain electrodes Z includes a transparent electrode  12 , and a metal bus electrode  11  having a smaller line width than the transparent electrode  12  and provided at one edge of the transparent electrode  12 . The transparent electrode  12  is usually formed from indium-tin-oxide (ITO) on the upper substrate  10 . The metal bus electrode  11  is usually formed from a metal on the transparent electrode  12  to thereby reduce a voltage drop caused by the transparent electrode  12  having a high resistance. On the upper substrate  10  provided with the scan electrodes Y 1  to Yn and the sustain electrodes Z, an upper dielectric layer  13  and a protective film  14  are disposed. Wall charges generated upon plasma discharge are accumulated onto the upper dielectric layer  13 . The protective film  14  protects the electrodes Y 1  to Yn and Z from a sputtering generated upon plasma discharge, and enhances an emission efficiency of secondary electrons. This protective film  14  is usually made from magnesium oxide (MgO). 
   The address electrodes X 1  to Xm are formed on a lower substrate  18  in a direction crossing the scan electrodes Y 1  to Yn and the sustain electrodes. A lower dielectric layer  17  and barrier ribs  15  are formed on the lower substrate  18 . A phosphorous material layer  16  is formed on the surfaces of the lower dielectric layer  17  and the barrier ribs  15 . The barrier ribs  15  are formed in parallel to the address electrodes X 1  to Xm to physically divide the discharge cells  1 , thereby shutting off electrical and optical interferences between the adjacent discharge cells  1 . The phosphorous material layer  16  is excited and radiated by an ultraviolet ray generated during the plasma discharge to generate any one of red, green and blue visible light rays. 
   An inactive mixture gas, such as He+Xe, Ne+Xe or He+Ne+Xe, for a discharge is injected into a discharge space defined between the upper/lower substrates  10  and  18  and the barrier ribs  15 . 
   Such a PDP makes a time-divisional driving of one frame, which is divided into various sub-fields having a different light-emission frequency, so as to express gray levels of a picture. Each sub-field is again divided into a reset period for uniformly causing a discharge, an address period for selecting a discharge cell and a sustain period for realizing the gray levels depending on the discharge frequency. For instance, when it is intended to display a picture of 256 gray levels, a frame interval equal to 1/60 second (i.e. 16.67 msec) is divided into 8 sub-fields. Each of the 8 sub-fields is again divided into an address period and a sustain period. Herein, the reset period and the address period of each sub-field are equal every sub-field, whereas the sustain period and the discharge frequency are increased at a ration of 2 n  (wherein n=0, 1, 2, 3, 4, 5, 6 and 7) at each sub-field in proportion to the number of sustaining pulses. As the sustain period is differentiated at each sub-field as mentioned above, gray levels of a picture can be implemented. 
     FIG. 3  schematically shows a driving circuit for the PDP. 
   Referring to  FIG. 3 , the driving circuit for the PDP includes a gain adjuster  32 , an error diffuser  33  and a sub-field mapping unit  34  connected between a first inverse gamma adjuster  31 A and a data aligner  35 , and an average picture level (APL) calculator  36  connected between a second inverse gamma adjuster  31 B and a waveform generator  37 . 
   Each of the first and second inverse gamma adjusters  31 A and  31 B makes an inverse gamma correction of digital video data RGB from an input line  30  to thereby linearly convert brightness according to gray level values of image signals. 
   The gain adjuster  32  adjusts an effective gain for each of red, green and blue data to thereby compensate for a color temperature. 
   The error diffuser  33  diffuses a quantized error of the digital video data RGB inputted from the gain adjuster  32  into the adjacent cells to thereby make a fine control of a brightness value. To this end, the error diffuser  33  divides the data into a positive number part and a decimal fraction part and then multiplies the decimal fraction part by a Floyd-Steinberg coefficient. 
   The sub-field mapping unit  34  maps a data from the error diffuser  33  onto a sub-field pattern stored in advance for each bit and applies the mapped data to the data aligner  35 . 
   The data aligner  35  applies digital video data inputted from the sub-field mapping unit  34  to a data driving circuit of the PDP  38 . The data driving circuit is connected to the data electrodes of the PDP  38  to latch a data from the data aligner  35  for each one horizontal line and then apply the latched data to the data electrodes of the PDP  38  for each one horizontal period. 
   The APL calculator  36  detects an average brightness per frame of digital video data RGB inputted from the second inverse gamma adjuster  31 B, that is, an average picture level (APL), and outputs information about the number of sustaining pulses corresponding to the detected APL. 
   The waveform generator  37  generates a timing control signal in response to the information about the number of sustaining pulses from the APL calculator  36 , and applies the timing control signal to a scan driving circuit and a sustain driving circuit (not shown). The scan driving circuit and the sustain driving circuit apply a sustaining pulse to the scan electrodes and the sustain electrodes of the PDP  38  during the sustain period in response to the timing control signal from the waveform generator  38 . 
   Such a PDP has a larger size, such as 40″, 50″, 60″ or the like, than other flat panel displays (FPDs). Thus, since a length of each electrode X, Y and Z of the PDP is large, a voltage drop caused by the large electrode length emerges on the center field and the peripheral field of the PDP at a relatively large difference. Furthermore, since a discharge gas is injected into the interior of the PDP at a lower pressure than the atmospheric pressure, a force applied to the substrates  10  and  18  at the center field where the upper substrate  10  and the lower substrate  18  are supported only by the barrier ribs  15  becomes different from a force applied to the substrates  10  and  18  at the peripheral field where the upper substrate  10  is joined with the lower substrate  18  by a sealant (not shown). This causes the PDP to have a different size of cell  1  at the center field and the peripheral field although having a difference depending upon of a model and a dimension of the PDP. As a result, although the conventional PDP has somewhat difference depending upon a panel size, brightness at the center field of the PDP becomes approximately 20% lower than brightness at the peripheral field thereof in each of the horizontal direction (or x direction) and the vertical direction (or y direction) as shown in  FIG. 4 . 
   Such brightness non-uniformity at the center field and the peripheral field can not be substantially overcome by the circuit shown in  FIG. 3 . For instance, the driving circuit as shown in  FIG. 3  can control red, green and blue data differently for each data, but can not control the data differently for each center field and each peripheral field of the PDP. Therefore, the conventional PDP raises another problem in that, as brightness at the center field is heightened, brightness at the peripheral field also becomes higher, thereby still presenting a brightness difference between the center field and the peripheral field and hence causing higher power consumption. 
   SUMMARY OF THE INVENTION 
   Accordingly, it is an object of the present invention to provide a method and apparatus for adjusting a gain for each position of a plasma display panel that is adaptive for improving a brightness uniformity of a picture field. 
   In order to achieve these and other objects of the invention, a gain adjusting method for each position of a plasma display panel according to an aspect or the present invention includes the steps of setting a gain value differently depending upon a position of a field of the plasma display panel; controlling a gain of data to be displayed at a first position of said field into a first gain value; and controlling a gain of data to be displayed at a second position of said field into a second gain value. 
   In the gain adjusting method, the first position of said field is within a certain size of center area positioned at the center of said field and at a portion adjacent to the center thereof. 
   The second position of said field is within the peripheral area of said field other than the center area. 
   Herein, the first gain value is larger than the second gain value. 
   A gain adjusting method for each position of a plasma display panel according to another aspect of the present invention includes the steps of assigning a gain value to each of at least two blocks divided from a field of the plasma display panel; and differently controlling a gain of data to be displayed on different blocks, of said blocks, into a gain value assigned for each block. 
   In the gain adjusting method, said field is divided into M×N blocks (wherein M and N are integers) each of which includes a plurality of pixels. 
   Said field is divided into a certain size of center block positioned at the center of said field and at a portion adjacent to the center thereof and a peripheral block of said field other than said center area. 
   Said field is divided into a plurality of pixel rows arranged in a x-axis direction of said field and a plurality of pixel columns arranged in a y-axis direction of said field. 
   A gain adjusting apparatus for each position of a plasma display panel according to still another aspect of the present invention includes a first gain adjuster for controlling a gain of data to be displayed at a first position of a field of the plasma display panel into a first gain value; and a second gain adjuster for controlling a gain of data to be displayed at a second position of said field into a second gain value. 
   In the gain adjusting apparatus, the first position of said field is within a certain size of center area positioned at the center of said field and at a portion adjacent to the center thereof. 
   The second position of said field is within the peripheral area of said field other than the center area. 
   Herein, the first gain value is larger than the second gain value. 
   A gain adjusting apparatus for each position of a plasma display panel according to still another aspect of the present invention includes a gain adjuster for differently controlling a gain of data to be displayed on different blocks of a field of the plasma display panel into a gain value assigned for each of at least two blocks divided from said field. 
   In the gain adjusting apparatus, said field is divided into M×N blocks (wherein M and N are integers) each of which includes a plurality of pixels. 
   Said field is divided into a certain size of center block positioned at the center of said field and at a portion adjacent to the center thereof and a peripheral block of said field other than said center area. 
   Said field is divided into a plurality of pixel rows arranged in a x-axis direction of said field and a plurality of pixel columns arranged in a y-axis direction of said field. 

   
     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 schematic plan view showing a configuration of a conventional plasma display panel; 
       FIG. 2  is a detailed perspective view showing a structure of the cell shown in  FIG. 1 ; 
       FIG. 3  is a block diagram showing a configuration of a driving circuit for the conventional plasma display panel; 
       FIG. 4  depicts brightness for each position of the plasma display panel; 
       FIG. 5  is a block diagram showing a configuration of a driving circuit for a plasma display panel according to an embodiment of the present invention; 
       FIG. 6  is a block diagram of a gain adjusting apparatus for each position of a plasma display panel according to a first embodiment of the present invention; 
       FIG. 7  is a block diagram of a gain adjusting apparatus for each position of a plasma display panel according to a second embodiment of the present invention; 
       FIG. 8  depicts the center field and the peripheral field of the plasma display panel; 
       FIG. 9  is a block diagram of a gain adjusting apparatus for each position of a plasma display panel according to a third embodiment of the present invention; 
       FIG. 10  illustrates a plurality of data rows applied to the plasma display panel; and 
       FIG. 11  illustrates a plurality of data columns applied to the plasma display panel. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
   Referring to  FIG. 5 , a PDP driving apparatus according to an embodiment of the present invention includes a first gain adjuster  51 , first and second inverse gamma adjusters  52 A and  52 B connected to the first gain adjuster  51 , a second gain adjuster  53 , an error diffuser  54  and a sub-field mapping unit  55  that are connected between the first inverse gamma gain adjuster  52 A and a data aligner  56 , and an average picture level (APL) calculator  57  connected between the second inverse gamma adjuster  52 B and a waveform generator  58 . 
   The first gain adjuster  51  controls a gain of digital video data RGB to be supplied to the peripheral field of the PDP and a gain of digital video data RGB to be supplied to the center field thereof differently depending upon a brightness difference between the peripheral field and the center field of the PDP, thereby compensating for a brightness difference between the peripheral field and the center field of the PDP. 
   Each of the first and second inverse gamma adjusters  52 A and  52 B makes an inverse gamma correction of digital video data RGB from the first gain adjuster  51  to thereby linearly convert brightness according to gray level values of image signals. 
   The second gain adjuster  53  adjusts an effective gain for each of red, green and blue data to thereby compensate for a color temperature. 
   The error diffuser  54  diffuses a quantized error of the digital video data RGB inputted from the second gain adjuster  53  into the adjacent cells to thereby make a fine control of a brightness value. To this end, the error diffuser  54  divides the data into a positive number part and a decimal fraction part and then multiplies the decimal fraction part by a Floyd-Steinberg coefficient. 
   The sub-field mapping unit  55  maps a data from the error diffuser  54  onto a sub-field pattern stored in advance for each bit, and applies the mapped data to the data aligner  56 . 
   The data aligner  56  applies digital video data inputted from the sub-field mapping unit  55  to a data driving circuit of the PDP  59 . The data driving circuit is connected to the data electrodes of the PDP  59  to latch a data from the data aligner  35  for each one horizontal line and then apply the latched data to the data electrodes of the PDP  59  for each one horizontal period. 
   The APL calculator  57  detects an average brightness per frame of digital video data RGB inputted from the second inverse gamma adjuster  52 B, that is, an average picture level (APL), and outputs information about the number of sustaining pulses corresponding to the detected APL. 
   The waveform generator  58  generates a timing control signal in response to the information about the number of sustaining pulses from the APL calculator  57 , and applies the timing control signal to a scan driving circuit and a sustain driving circuit (not shown). The scan driving circuit and the sustain driving circuit apply a sustaining pulse to the scan electrodes and the sustain electrodes of the PDP  59  during the sustain period in response to the timing control signal from the waveform generator  58 . 
   The gain adjusting apparatus for each position of the PDP according to the embodiment of the present invention uniforms a brightness different at the entire field of the PDP with the aid of the first gain adjuster  51 . 
     FIG. 6  shows a first embodiment of the first gain adjuster  51 . 
   Referring to  FIG. 6 , the first gain adjuster  51  according to the first embodiment of the present invention includes a data re-aligner  61  for re-aligning digital video data RGB into predetermined M×N picture blocks, and M×N gain adjusters GC 11  to GCMN for adjusting each gain of data MSK(RGB) divided into the M×N picture blocks. 
   The M×N picture blocks set at the data re-aligner  61  are identical to M×N picture blocks divided from the effective field of the PDP. Each of the picture blocks divided from the effective field of the PDP includes a plurality of pixels. The data re-aligner  61  has a frame memory for storing data, and a multiplexer for dividing the data from the frame memory to each picture block. 
   The gain adjusters GC 11  to GC 1 N, GC 21  to GCM 1 , GCM 2  to GCMN and GCMN at the peripheral picture blocks multiplies data to be supplied to the peripheral field of the PDP by a gain value less than a predetermined reference gain value, thereby relatively lowering a gain of the peripheral field data of the PDP in comparison with the center field data thereof. On the other hand, the gain adjusters 
           (     GC   ⁢     M   2     ⁢     N   2       )         
multiplies data to be supplied to the center field of the PDP by a gain value more than the predetermined reference gain value, thereby relatively heightening a gain of the peripheral field data of the PDP in comparison with the center field data.
 
     FIG. 7  shows a second embodiment of the first gain adjuster  51 . 
   Referring to  FIG. 7 , the first gain adjuster  51  according to the second embodiment of the present invention includes a data re-aligner  71  for re-aligning digital video data RGB into a predetermined center picture block and a predetermined peripheral picture block, a center gain adjuster  72  for adjusting a gain of center picture block data C(RGB), and a peripheral gain adjuster  73  for adjusting a gain of peripheral picture block data P(RGB). 
   The center picture block and the peripheral picture block set at the data re-aligner  71  are identical to a center picture block C and a peripheral picture block P divided from the effective field of the PDP as shown in  FIG. 8 . Each of the center picture block C and the peripheral picture block P divided from the effective field of the PDP includes a plurality of pixels, The data re-aligner  71  has a frame memory for storing data, and a multiplexer for dividing the data from the frame memory to the center picture block and the peripheral picture block. 
   The center gain adjuster  72  multiplies data to be supplied to the center picture block C of the PDP by a gain value more than a predetermined reference gain value, thereby relatively heightening a gain of the center field data of the PDP in comparison with the peripheral field data thereof. 
   The peripheral gain adjuster  73  multiplies data to be supplied to the peripheral picture block P of the PDP by a gain value less than a predetermined reference gain value, thereby relatively lowering a gain of the peripheral field data of the PDP in comparison with the center field data thereof. 
     FIG. 9  shows a third embodiment of the first gain adjuster  51 . 
   Referring to  FIG. 9 , the first gain adjuster  51  according to the third embodiment of the present invention includes a data re-aligner  81  for separating digital video data RGB into predetermined x-axis data x(RGB) and predetermined y-axis data y(RGB), a X-axis gain adjuster  82  for adjusting a gain of x-axis data X(RGB), and a y-axis gain adjuster  83  for adjusting a gain of y-axis data y(RGB). 
   The data re-aligner  81  applies each row data RD 1  to RDn, as shown in  FIG. 10 , arranged in parallel along the x-axis, of nm pixels of the PDP arranged in a matrix type, to the x-axis gain adjuster  82  while applying each column data CD 1  to CD 3   m , as shown in  FIG. 11 , arranged in parallel along the y-axis to the y-axis gain adjuster  83 . The data re-aligner  81  has a frame memory for storing data, and a line memory and a switching device for separating the data from the frame memory into x-axis data x(RGB) and y-axis data y(RGB) to divisionally apply them to the x-axis gain adjuster  82  and the y-axis gain adjuster  83 , respectively. 
   The x-axis gain adjuster  82  multiplies data arranged at the center, of each row data RD 1  to RDn as shown in  FIG. 10 , for example, the first-row center data 
           (       …   ⁢           ⁢   R   ⁢     n   2       ,     G   ⁢     n   2       ,     B   ⁢     n   2     ⁢           ⁢   …       )         
by a gain value more than a predetermined reference gain value, thereby relatively heightening a gain of each row center data in comparison with each row peripheral data, for example, the first-row peripheral data R 1 , G 1 , B 1 , Rm, Gm and Bm.
 
   The y-axis gain adjuster  83  multiplies data arranged at the center, of each column data CD 1  to CD 3   m  as shown in  FIG. 11 , for example, the 3 mth-column center data 
           (         …   ⁢           ⁢   B   ⁢     1   2     ⁢   n   ⁢           ⁢   m     -   1     ,     B   ⁢     1   2     ⁢   n   ⁢           ⁢   m     ,       B   ⁢     1   2     ⁢   n   ⁢           ⁢   m     +     1   ⁢           ⁢   …         )         
by a gain value more than a predetermined reference gain value, thereby relatively heightening a gain of each column center data in comparison with each column peripheral data, for example, the 3 mth-column peripheral data Bm, B 2   m , B 3   m  and Bnm.
 
   As described above, according to the present invention, an effective field of the PDP is divided into M×N block to control a gain of data independently for each block data. Alternatively, according to the present invention, an effective field of the PDP is divided into the center field and the peripheral field to control a gain of data independently for each block data or to control a gain of data independently for each x-axis data and each y-axis data. Accordingly, a gain of data to be supplied to the center field of the PDP is relatively heightened in comparison with that of data to be supplied to the peripheral field thereof, thereby realizing a brightness uniformity of a picture field. 
   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.