Patent Publication Number: US-2006001607-A1

Title: Plasma display apparatus and driving method thereof

Description:
This Nonprovisional application claims priority under 35 U.S.C. § 119(a) on Patent Application No. 2005-0051746, filed in Korea on Jul. 2, 2004 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 apparatus, and more particularly, to a plasma display apparatus and a driving method thereof, which are capable of preventing damage of a driving circuit.  
      2. Description of the Background Art  
      In general, a plasma display apparatus includes a plasma display panel having a front substrate and a rear substrate, and a barrier rib defining one unit cell therebetween. A main discharge gas such as neon (Ne), helium (He) or a combination of neon and helium (Ne+He) and an inert gas containing a small amount of xenon (Xe) are filled into each cell. When the inert gas is discharged due to a high frequency voltage, the inert gas generates vacuum ultraviolet rays and excites phosphor between the barrier ribs, thereby displaying an image. Since such a plasma display panel has a thin and light structure, the plasma display panel has been highlighted as a next generation display apparatus.  
       FIG. 1  is a perspective view illustrating a structure of a general plasma display panel.  
      As shown in  FIG. 1 , the plasma display panel includes a front substrate  100  on a side of which a plurality of a pair of sustain electrodes having a scan electrode  102  and a sustain electrode  103  being in pairs are arranged on a front glass  101  being a display side for displaying an image and a rear substrate  110  on a side of which a plurality of address electrodes  113  are arranged to intersect the pair of sustain electrodes on a rear glass  111  being the rear. The front panel  100  and the rear panel  110  are combined with each other at a predetermined interval therebetween.  
      The front substrate  100  includes a scan electrode  102  and a sustain electrode  103  being in pairs for mutually discharging and sustaining luminescence of a cell in the cell. Each of the scan electrode  102  and the sustain electrode  103  comprises a transparent electrode (a) made of a transparent ITO material and a bus electrode (b) made of a metallic material. One or more upper dielectric layer  104  are coated on the scan electrode  102  and the sustain electrode  103  to limit a discharge current and to insulate the pair of electrodes. Further, a protection layer  105  is formed on a top surface of the upper dielectric layer  104  to ease a discharge condition.  
      On the rear substrate  110 , a plurality of discharge spaces, that is, stripe type (or well type) barrier ribs  112  are parallelly arranged to form a discharge cell. Further, a plurality of address electrodes  113  for performing address discharge are arranged in parallel to the barrier ribs  112 . R, G, B phosphors  114  discharging visible rays are coated on an upper side of the rear substrate  110  to display an image when sustain discharge. A dielctric layer  115  is formed between the address electrodes  113  and the phosphors to protect the address electrodes  113 .  
       FIG. 2  is a view illustrating a method of expressing an image in a conventional plasma display apparatus.  
      As shown in  FIG. 2 , in the plasma display apparatus, one frame is divided into several sub-fields each having a different number of discharge times. Further, light is emitted in a plasma display panel during a sub-field period corresponding to a gray level of an input image signal, thereby expressing an image.  
      Each of the sub-fields is divided into a reset period for uniformly generating discharge, an address period for selecting a discharge cell, and a sustain period for expressing the gray level depending on the number of discharge times. For example, in case that the image is displayed in 256 gray levels, a frame period (16.67 ms) corresponding to 1/60 second is divided into eight sub-fields (SF 1  to SF 8 ) as shown in  FIG. 2 .  
      Further, each of the eight sub-fields is again divided into a reset period, an address period and a sustain period. Here, the sustain period is increased in a ratio of 2 n  (n=0,1,2,3,4,5,6,7) in each sub-field. In this way, since the sustain periods are different in each of the sub-fields, the gray level can be expressed.  
       FIG. 3  is a schematic view illustrating a conventional plasma display apparatus.  
      As shown in  FIG. 3 , the conventional plasma display panel includes a plasma display panel  300 , an image signal processor  310 , a sub-field mapping unit  320 , a data aligner  330 , a data driving unit  340 , a scan driving unit  350 , a sustain driving unit  360  and a controller  370 .  
      In the plasma display panel  300 , there are fromed scan electrodes (Y 1  to Y n ), sustain electrodes (Z) and a plurality of address electrodes (X 1  to X m ) intersecting the scan electrodes (Y 1  to Y n ) and the sustain electrodes (Z).  
      The image signal processor  310  converts an image signal input from the exterior into an image signal for driving a plasma display apparatus. Such an image signal processor  310  includes an inverse gamma correcting unit (not shown) for inverse gamma correcting an image signal, a gain controller (not shown) for adjusting a gain value of an image signal and a half tone unit (not shown) for enhancing expression of a gray level.  
      The sub-field mapping unit  320  maps an image signal input from the image signal processor  310  by the sub-field unit to a corresponding sub-field.  
      The data aligner  330  realigns by the sub-field an image signal mapped as a sub-field unit by the sub-field mapping unit  320 .  
      The data driving unit  340  applies an address pulse corresponding to the aligned image signal to the address electrodes (X 1  to X m ) formed in the plasma display panel  300 .  
      The scan driving unit  350  drives the scan electrodes (Y 1  to Y n ) formed in the plasma display panel  300 . The scan driving unit  350  applies a setup pulse and a setdown pulse during a reset period, sequentially applies scan pulses during an address period, and applies sustain pulses during a sustain period.  
      The sustain driving unit  360  drives the sustain electrodes (Z) being common electrodes formed in the plasma display panel  300 . The sustain driving unit  360  applies a positive bias pulse during an address period, and alternately applies at least one or more sustain pulses for performing sustain discharge with the scan pulses during a sustain period.  
      The controller  370  controls timing of each driving pulse applied to the data driving unit  340 , the scan driving unit  350  and the sustain driving unit  360  during a reset, an address and a sustain periods. Further, the controller  370  controls image signals realigned by the data aligner  330  depending on an image signal input from the exterior to be sequentially read and then to be supplied by the quantity for a scan line to the data driving unit  340 .  
      Meanwhile, there is a drawback in that each of the driving units  330 ,  340  and  350  is loaded in the conventional plasma display apparatus when a specific pattern is expressed in a picture. Particularly, circuit elements of the scan driving unit  350  and the sustain driving unit  360  are seriously damaged when an alternate pattern is expressed. Here, the alternate pattern means a picture in which a turned-on lines and turned-off lines are alternated. In case that an alternate pattern is sustained for approximately one minute, the sustain driving unit  360  is damaged, and generation of heat is deteriorated in the scan driving unit  350 . The reason caused due to this will be described with reference to  FIGS. 4 and 5 .  
       FIG. 4  is a circuit diagram illustrating a plasma display apparatus in which a conventional alternate pattern is expressed, and  FIG. 5  is a waveform diagram of an address pulse expressing a conventional alternate pattern.  
      Referring to  FIGS. 4 and 5  together, a sustain driving unit  410  includes each switching element for supplying a pulse from a bias voltage source (V zb ) for supplying a bias pulse and a sustain voltage suource (V s ) for supplying a sustain pulse and an energy recovery circuit  413  for recovering or supplying energy when the sustain driving unit  410  is driven. Further, the scan driving unit  420  includes each switching element for supplying a setup pulse, a setdown pulse, a scan pulse and a sustain pulse and an energy recovery circuit (not shown).  
      Here, if an image signal corresponding to an alternate pattern is input to a plasma display apparatus, a high-level address pulse is applied to all the address electrodes when one line is scanned, and a low-level address pulse is applied to all the address electrodes when the next line is scanned.  
      In the sustain driving unit  410 , as an address pulse is applied, a first peak current (I p1 ) and a second peak current (I p2 ) is flown due to a capacitance of a capacitor (C 1 ) formed between an address electrode (X) and a sustain electrode (Z). In other words, the first peak current (I p1 ) is generated when an address pulse applied from a low level to a high level is applied to an address electrode, and the second peak current (I p2 ) is generated when an address pulse applied from a high level to a low level is applied to an address electrode. At this time, there is a drawback in that the sustain driving unit  410  is damaged due to excessive generation of heat while the first peak current (I p1 ) and the second peak current (I p2 ) are flown through a first switch  411  and a scond switch  412  which are turned on during an address period.  
      In the scan driving unit  420 , as an address pulse is applied, a third peak current (I p3 ) and a fourth peak current (I p4 ) is flown due to a capacitance of a capacitor (C 2 ) formed between an address electrode (X) and a sustain electrode (Z). In other words, the first peak current (I p3 ) is generated when an address pulse applied from a low level to a high level is applied to an address electrode, and the second peak current (I p4 ) is generated when an address pulse applied from a high level to a low level is applied to an address electrode. At this time, there is a drawback in that the sustain driving unit  420  is damaged due to excessive generation of heat while the first peak current (I p3 ) and the second peak current (I p4 ) are flown through a third switch  413  and a fourth switch  413  which are turned on during an address period.  
     SUMMARY OF THE INVENTION  
      Accordingly, an object of the present invention is to solve at least the problems and disadvantages of the background art.  
      An object of the present invention is to provide a plasma display apparatus and a driving method thereof, which a data driving unit is controlled when an alternate pattern is expressed so that the number of switching times of address pulses is reduced, thereby preventing damage of a sustain and a scan driving units.  
      To achieve these and other advantages and in accordance with the purpose of the present invention, as embodied and broadly described, there is provided a plasma display apparatus in accordance with a first embodiemt of the present invention including: a pattern recognition unit for recognizing an alternate pattern in which no less than a predetermined number of cells on the Nth line are turned on and no less than a predetermined number of cells on the N+1th line are turned off depending on an image signal input from the exterior; a sub-field mapping unit for mapping the image signal by the sub-field unit to a corresponding sub-field; anda controller for controlling a predetermined number of sub-fields among the whole sub-fields during one frame to be used when the pattern recognition unit recognizes the alternate pattern.  
      In another aspect of a first embodiment of the present invention, there is provided a method of driving a plasma display apparatus including the steps of: recognizing an alternate pattern in which no less than a predetermined number of cells on the Nth line are turned on and no less than a predetermined number of cells on the N+1th line are turned off depending on an image signal input from the exterior; mapping the image signal by the sub-field unit to a corresponding sub-field; and controlling a predetermined number of sub-fields among the whole sub-fields during one frame to be used when the alternate pattern is recognized in the pattern recognition step.  
      In one aspect of a second embodiment of the present invention, there is provide a plasma display apparatus including: a sub-field mapping unit for mapping an image signal input from the exterior by the sub-field unit to a corresponding sub-field; a pattern recognition unit for recognizing an alternate pattern in which no less than a predetermined number of cells on the Nth line are turned on and no less than a predetermined number of cells on the N+1th line are turned off by comparing a mapping code of the mapped image signal; and a controller for controlling a predetermined number of sub-fields among the whole sub-fields during one frame to be used when the pattern recognition unit recognizes the alternate pattern.  
      In another aspect of a second embodiment of the present invention, there is provided a method of driving a plasma display apparatus including the steps of: mapping an image signal input from the exterior by the sub-field unit to a corresponding sub-field; recognizing an alternate pattern in which no less than a predetermined number of cells on the Nth line are turned on and no less than a predetermined number of cells on the N+1th line are turned off by comparing a mapping code of the mapped image signal; and controlling a predetermined number of sub-fields among the whole sub-fields during one frame to be used when the alternate pattern is recognized in the pattern recognition step.  
      In a plasma display apparatus and a driving method thereof according to the present invention, a predetermined number of sub-fields among the whole sub-fields are controlled to be used during one frame when an alternate pattern is recognized so that a generated peak current is reduced, thereby preventing damage of a sustain and a scan driving units.  
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
      The invention will be described in detail with reference to the following drawings in which like numerals refer to like elements.  
       FIG. 1  is a perspective view illustrating a structure of a general plasma display panel;  
       FIG. 2  is a view illustrating a method of expressing an image in a conventional plasma display panel;  
       FIG. 3  is a schematic view illustrating a conventional plasma display apparatus;  
       FIG. 4  is a circuit diagram illustrating a plasma display apparatus in which a conventional alternate pattern is expressed;  
       FIG. 5  is a waveform diagram of an address pulse expressing a conventional alternate pattern;  
       FIG. 6  is a schematic view illustrating a plasma display apparatus according to a first embodiment of the present invention;  
       FIG. 7  is a schematic block diagram illustrating a pattern recognition unit according to a first embodiment of the presnent invention;  
       FIG. 8  is a view illustrating an operating characteristic of a pattern recognition unit according to a first embodiment of the present invention;  
       FIG. 9  is a truth table illustrating a control operation of a contriler in a plasma display apparatus according to a first embodiment of the present invention;  
       FIG. 10  is a schematic view illustrating a plasma display apparatus according to a second embodiment of the present invention;  
       FIG. 11  is a schematic block diagram illustrating a pattern recognition unit according to a second embodiment of the present invention; and  
       FIG. 12  is a view illustrating an operation characteristic of a pattern recognition unit according to a second embodiment of the present invention. 
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS  
      Preferred embodiments of the present invention will be described in a more detailed manner with reference to the drawings.  
      A plasma display apparatus according to a first embodiment of the present invention includes: a pattern recognition unit for recognizing an alternate pattern in which no less than a predetermined number of cells on the Nth line are turned on and no less than a predetermined number of cells on the N+1th line are turned off depending on an image signal input from the exterior; a sub-field mapping unit for mapping the image signal by the sub-field unit to a corresponding sub-field; and a controller for controlling a predetermined number of sub-fields among the whole sub-fields during one frame to be used when the pattern recognition unit recognizes the alternate pattern.  
      Preferably, the pattern recognition unit includes: a center cell setting unit for setting at least no less than two cells as center cells during one frame; a first threshold comparator for comparing a difference between a gray level value of the center cell and a gray level value of a cell adjacent thereto in a horizontal direction with a first threshold value; a second threshold comparator for comparing a difference between a gray level value of the center cell and a gray level value of a cell adjacent thereto in a vertical direction with a second threshold value; a third threshold comparator for evaluating the number of center cells which are less than the first threshold value and more than the second threshold value and comparing the number thereof with a third threshold value; and a pattern recognition information generator for determining an image signal of the frame as an alternate pattern and generating alternate pattern recognition information when the number of the center cells is more than the third threshold value.  
      Preferably, the first threshold value comparator compares gray level values of at least no less than two cells adjacent to the center cell as a cneter.  
      A plasma display apparatus according to a second embodiment of the present invention includes: a sub-field mapping unit for mapping an image signal input from the exterior by the sub-field unit to a corresponding sub-field; a pattern recognition unit for recognizing an alternate pattern in which no less than a predetermined number of cells on the Nth line are turned on and no less than a predetermined number of cells on the N+1th line are turned off by comparing a mapping code of the mapped image signal; and a controller for controlling a predetermined number of sub-fields among the whole sub-fields during one frame to be used when the alternate pattern is recognized in the pattern recognition step.  
      Preferably, the pattern recognition unit includes: a center cell setting unit for setting at least no less than two cells as center cells during one sub-field period; a first threshold comparator for comparing the number of cells having the same mapping codes as that of the center cell on the same line as that of the center cell with a first threshold value during the sub-field period; a second threshold comparator for comparing the number of cells having mapping codes different from that of the center cell on the next line of the center cell with a second threshold value during the sub-field period; a third threshold comparator for evaluating the number of center cells which are more than the first threshold value and the second threshold value and comparing the number thereof with a third threshold value; and a pattern recognition information generator for determining an image signal of the frame as an alternate pattern during one frame and generating alternate pattern recognition information when the number of the center cells is more than the third threshold value.  
      Preferably, the apparatus of the present invention further includes: a data aligner for realigning by the sub-field an image signal mapped to the sub-field; and a data driving unit for applying an address pulse corresponding to the aligned image signal to an address electrode under control of the controller.  
      Preferably, the controller controls sub-fields cut off when the alternate pattern is recognized to be selected, and controls a cutoff signal for turning off a switching element of the data driving unit during an address period of the selected sub-field to be applied to the data driving unit.  
      Preferably, the controller controls the sub-fields cut off not to be consecutive to each other.  
      Preferably, the controller controls the number of sustain pulses applied depending on sub-fields used during one frame.  
      A method of driving a plasma display apparatus according to a first embodiment of the present invention includes the steps of: recognizing an alternate pattern in which no less than a predetermined number of cells on the Nth line are turned on and no less than a predetermined number of cells on the N+1th line are turned off depending on an image signal input from the exterior; mapping the image signal by the sub-field unit to a corresponding sub-field; and controlling a predetermined number of sub-fields among the whole sub-fields during one frame to be used when the alternate pattern is recognized in the pattern recognition step.  
      Preferably, the pattern recognition step includes the steps of: setting at least no less than two cells as center cells during one frame; comparing a difference between a gray level value of the center cell and a gray level value of a cell adjacent thereto in a horizontal direction with a first threshold value; comparing a difference between a gray level value of the center cell and a gray level value of a cell adjacent thereto in a vertical direction with a second threshold value; evaluating the number of center cells which are less than the first threshold value and more than the second threshold value and comparing the number thereof with a third threshold value; and determining an image signal of the frame as an alternate pattern and generating alternate pattern recognition information when the number of the center cells is more than the third threshold value.  
      Preferably, gray level values of at least no less than two cells adjacent to the center cell as a cneter are compared in the first threshold value comparing step.  
      A method of driving a plasma display apparatus according to a second embodiment of the present invention includes the steps of: mapping an image signal input from the exterior by the sub-field unit to a corresponding sub-field; recognizing an alternate pattern in which no less than a predetermined number of cells on the Nth line are turned on and no less than a predetermined number of cells on the N+1th line are turned off by comparing a mapping code of the mapped image signal; and controlling a predetermined number of sub-fields among the whole sub-fields during one frame to be used when the pattern recognition unit recognizes the alternate pattern.  
      Preferably, the pattern recognition step includes the steps of: setting at least no less than two cells as center cells during one sub-field period; comparing the number of cells having the same mapping codes as that of the center cell on the same line as that of the center cell with a first threshold value during the sub-field period; comparing the number of cells having mapping codes different from that of the center cell on the next line of the center cell with a second threshold value during the sub-field period; evaluating the number of center cells which are more than the first threshold value and the second threshold value and comparing the number thereof with a third threshold value; and determining an image signal of the frame as an alternate pattern during one frame and generating alternate pattern recognition information when the number of the center cells is more than the third threshold value.  
      Preferably, the method of the present invention further includes the steps of: realigning by the sub-field an image signal mapped to the sub-field; and applying an address pulse corresponding to the aligned image signal to an address electrode under control of the controller.  
      Preferably, sub-fields cut off are selected when the alternate pattern is recognized, and a cutoff signal for turning off a switching element of the data driving unit during an address period of the selected sub-field is applied to the data driving step in the control step.  
      Preferably, the sub-fields cut off are not consecutive to each other in the control step.  
      Preferably, the number of sustain pulses applied depending on sub-fields used during one frame is controlled in the control step.  
      Hereinafter, preferred embodiments of the present invention will be described in a more detailed manner with reference to the drawings.  
     FIRST EMBODIMENT  
       FIG. 6  is a schematic view illustrating a plasma display apparatus according to a first embodiment of the present invention.  
      As shown in  FIG. 6 , the plasma display apparatus according to the first embodiment of the present invention includes a plasma display panel  600 , a pattern recognition unit  610 , an image signal processor  620 , a sub-field mapping unit  630 , a data aligner  640 , a controller  650 , a data driving unit  660 , a scan driving unit  670  and a sustain driving unit  680 .  
      In the plasma display panel  600 , there are fromed scan electrodes (Y 1  to Y n ), sustain electrodes (Z) and a plurality of address electrodes (X 1  to X m ) intersecting the scan electrodes (Y 1  to Y n ) and the sustain electrodes (Z).  
      The pattern recognition unit  610  recognizes an alternate pattern in which no less than a predetermined number of cells on the Nth line are turned on, and no less than a predetermined number of cells on the N+1th line are turned off depending on an image signal input from the exterior. In other words, the pattern recognition unit  610  according to a first embedment of the present invention judges an image signal displayed as an alternate pattern by comparing gray level values of image signals assigned to each cell. To this end, the pattern recognition unit  610  sets a center cell and detects an alternate pattern by comparing a difference of the gray level values with a predetermined threshold value. This will be described in a more detailed manner with reference to  FIGS. 7 and 8  hereafter.  
      The image signal processor  620  converts an exernal image signal input from the pattern recognition unit  610  into an image signal for driving a plasma display apparatus. Such an image signal processor  620  includes an inverse gamma correcting unit (not shown) for inverse gamma correcting an image signal, a gain controller (not shown) for adjusting a gain value of an image signal and a half tone unit (not shown) for enhancing expression of a gray level.  
      The sub-field mapping unit  630  maps an image signal input from the image signal processor  620  by the sub-field unit to a corresponding sub-field.  
      The data aligner  640  realigns by the sub-field an image signal mapped as a sub-field unit by the sub-field mapping unit  630 .  
      The controller  650  controls timing of each driving pulse applied to the data driving unit  660 , the scan driving unit  670  and the sustain driving unit  680  during a reset, an address and a sustain periods. Further, the controller  650  controls image signals realigned by the data aligner  640  depending on an image signal input from the exterior to be sequentially read and then to be supplied by the quantity for a scan line to the data driving unit  660 .  
      The controller  650  according to the first embodiment of the present invention controls a predetermined number of sub-fields among the whole sub-fields to be used during one frame when the pattern recognition unit  610  recognizes an alternate pattern. First, an alternate pattern recognition information is transmitted from the pattern recognition unit  610  to the controller  650 . Thereafter, the controller  650  selects sub-fields cut off among data of an image signal supplied by the quantity for a scan line to the data driving unit  660 , and then applies a cutoff signal turning off an switching element of the data driving unit  660  to the data driving unit  660  druing an address period of the selected sub-fields. At this time, an address pulse is not applied to the whole picture due to the cutoff signal in the corresponding sub-field period. Accordingly, the numbers of switching times of a switching element is reduced, thereby decreasing a peak current.  
      Meanwhile, since an address pulse of the corresponding sub-fields is cut off, there is generated a pause period in which an image of the whole picture is not displayed in the sub-field period. If an address pulse is applied so that a picture is instantaneously displayed after such a pause period is sustained for no less than a predetermined period, there is generated a flicker. In consideration of this, the controller  650  controls sub-fields cut off to be consecutive to each other. In other words, the controller  650  controls a pause period to be sustained.  
      Further, the controller  650  according to an first embodiment of the present invention controls the number of sustain pulses applied depending on a combination of the rest of the sub-fields used during a frame to prevent an image displayed from being distorted due to sub-fields cut off. Thus, it is possible to prevent an image from being distorted when an alternate pattern is expressed.  
      The data driving unit  660  applies an address pulse corresponding to an image signal aligned by the data aligner  640  to address electrodes (X 1  to X m ) formed in the plasma display panel  600 . At this time, predetermined sub-fields are cut off depnding on a cutoff signal of the foregoing controller  650  when an alternate pattern is expressed so that the number of switching times is reduced.  
      The scan driving unit  670  drives scan electrodes (Y 1  to Y n ) formed in the plasma display panel  600 . The scan driving unit  670  applies a setup pulse and a setdown pulse during a reset period, sequentially applies scan pulses during an address period, and applies sustain pulses during a sustain period. In the scan driving unit  670  according to a first embodiment of the present invention, a peak current generated during an address period is reduced as the number of switching times of the data driving unit  660  is decreased when an alternate pattern is expressed. Further, the scan driving unit  670  applies the number of sustain pulses controlled by the controller  650  during a sustain period of the used sub-fields.  
      The sustain driving unit  680  drives sustain electrodes (Z) being common electrodes formed in the plasma display panel  600 . The sustain driving unit  680  applies a positive bias pulse during an address period, and applies a positive bias pulse during an address period, and alternately applies at least one or more sustain pulses for performing sustain discharge with the scan pulses during a sustain period. In the sustain driving unit  680  according to a first embodiment of the present invention, a peak current generated during an address period is reduced as the number of switching times of the data driving unit  660  is decreased when an alternate pattern is expressed. Further, the sustain driving unit  680  applies the number of sustain pulses controlled by the controller  650  during a sustain period of the used sub-fields. In such a plasma display apparatus according to a first embodiment of the present invention, a pattern recognition unit for recognizing an alterate pattern will be described in a more detailed manner with reference to  FIGS. 7 and 8 .  
       FIG. 7  is a schematic block diagram illustrating a pattern recognition unit according to a first embodiment of the presnent invention, and  FIG. 8  is a view illustrating an operating characteristic of a pattern recognition unit according to a first embodiment of the present invention.  
      Referring to  FIG. 7 , The pattern recognition unit according to the first embodiment of the present invention includes a center cell setting unit  710 , a first threshold value comparator  720 , a second threshold value comparator  730 , a third threshold value comparator  740  and a pattern recognition information generator  750 . Referring to  FIGS. 7 and 8  together, an operation of the pattern recognition unit will be described.  
      The center cell setting unit  710  sets at least no less than two cells as center cells during a frame. Arbitrary cells are set as center cells for the whole picture to detect an alternate pattern. In other words, a cell (X N ) on the Nth line is set as a center cell.  
      The first threshold value comparator  720  compares a difference between a gray level value of the set center cell and a gray level value of a cell that is adjacent thereto in a horizontal diriction with a first threshold value. At this time, it is preferred that the first threshold value comparator  720  compares a gray level value of the center cell (X N ) as a reference with gray level values of at least no less than two cells that are adjacent thereto in the horizontal direction to have a better reliability when an alternate pattern is detected. In other words, after the first threshold value comparator  720  evaluates differences between a gray level value of the center cell (X N ) on the Nth line and each gray level values of cells (X N− 1, X N+ 1) that are adjacent thereto in the horizontal direction, the first threshold value comparator  720  compares a mean value of the difference values with the first threshold value. Here, if a difference of gray level values is less than the first threshold value, there is a little or no difference of gray values between cells adjacent in the horizontal direction. Thus, a data driving unit performs identical or similar switching operations for the cells.  
      The second threshold value comparator  730  compares a difference between a gray level value of the center cell (X N ) that is less than the first threshold value judged by the first threshold value comparator  720  and a gray level value of a cell that is adjacent thereto in a vertical direction with a second threshold value. In other words, after the second threshold value comparator  730  evaluates a difference between a gray level value of the center cell (X N ) on the Nth line and a gray level value of a cell (X N+1 ) that is adjacent thereto in the vertical direction, the first threshold value comparator  720  compares the difference value with the second threshold value. Here, if a difference of gray level values is more than the second threshold value, there is a large difference of gray values between cells adjacent in the vertical direction. Thus, a data driving unit performs different switching operations for each of the cells.  
      For example, if a gray level value of the center cell (X N ) on the Nth line is small and a gray level value of the cell on the N+1th line is big, the center cell (X N ) is mainly turned on in a sub-field being in charge of a low gray level and the cell (X N+1 ) on the N+1th line is mainly turned on in a sub-field being in charge of a gray level that is not the low gray level. In other words, the center cell (X N ) on the Nth line is turned on and the cell (X N+1 ) on the N+1th line is turned off in a sub-field being in charge of a low gray level, and the cells are conversely switched in a sub-field being in charge of a high gray level.  
      The third threshold value comparator  740  compares the number of the center cells with a third threshold value by evaluating the number of center cells that are less than the first threshold value and more than the second threshold value depending on a result judged by the first threshold value comparator  720  and a result judged by the second threshold value comparator  730 . Therefore, if the number of center cells is more than the third threshold value in the wole picture during a frame, the corresponding frame is determined as an alternate pattern.  
      The pattern recognition information generator  750  determines an image signal of a frame as an alternate pattern when the number of center cells is more than the third threshold value. Thereafter, the pattern recognition information generator  750  generates alternate pattern recognition information and then transmits it to the controller  650 .  
       FIG. 9  is a truth table illustrating a control operation of a contrller in a plasma display apparatus according to a first embodiment of the present invention.  
      Referring to  FIG. 9 , a data driver IC (Integrated Circuit; not shown) of a data driving unit is controlled during an address period in accordance with the truth table shown in  FIG. 9 . Particularly, a drive output state  920  is determined depending on a truth value of LBLK  910  controlled by a controller in a first embodiment of the present invention.  
      In other words, the controller controls a truth value of LBLK  910  to be “LOW” in an address period of a sub-field required to be cut off. Thus, since an output value of a data driver IC is “LOW”, an address pulse is not applied to an address electrode.  
      Further, a truth value is applied as “HIGH” in an address period used during a frame so that an address pulse is applied to an address electrode.  
      As described above, an alternate pattern is recognized by comparing gray level values of an input signal, and sub-fields used in accordance with this are reduced in a first embodiment of the present invention. Therefore, the number of switching times of an address driving unit is reduced, and damage of a sustain and a scan driving units can be prevented.  
     SECOND EMBODIMENT  
       FIG. 10  is a schematic view illustrating a plasma display apparatus according to a second embodiment of the present invention.  
      As show in  FIG. 10 , the plasma display apparatus according to the second embodiment of the present invention includes a plasma display panel  1000 , an image signal processor  1010 , a sub-field mapping unit  1020 , a pattern recognition unit  1030 , a data aligner  1040 , a controller  1050 , a data driving unit  1060 , a scan driving unit  1070  and a sustain driving unit  1080 . Here, description of the plasma display panel  1000 , the image signal processor  1010 , the sub-field mapping unit  1020 , the data aligner  1040 , the controller  1050 , the data driving unit  1060 , the scan driving unit  1070  and the sustain driving unit  1080  will be omitted, since each of them has the same operation characteristics as each funtion unit of a plasma display apparatus shown in  FIG. 6  according to the first embodiment of the present invention.  
      The pattern recognition unit  1030  according to the secod embodiment of the present invention is located at the back end of the sub-field mapping unit  1020 . The pattern recognition unit  1030  recognizes an alternate pattern in which no less than a predetermined number of cells on the Nth line are turned on by comparing mapping codes of an image signal mapped in the sub-field mapping unit  1020  and no less than a predetermined number of cells on the N+1th line are turned off. In other words, the pattern recognition unit  1030  according to a second embodiment of the present invention judges an image signal displayed as an alternate pattern by comparing mapping codes of an image signal assigned to the whole cells in each sub-field. To this end, the pattern recognition unit  1030  sets a center cell and detects an alternate pattern by comparing the number of cells with a predetermined threshold value. This will be described in a more detailed manner with reference to  FIGS. 11 and 12  hereafter.  
      The controller  1050  according to a second embodiment of the present invention contras sub-fields cut off not to be consecutive to each other and controls the number of sustain pulses applied in sub-fields using a predetermined number of sub-fields when an alternate pattern is expressed as described in the first embodiment of the present invention.  
       FIG. 11  is a schematic block diagram illustrating a pattern recognition unit according to a second embodiment of the present invention, and  FIG. 12  is a view illustrating an operation characteristic of a pattern recognition unit according to a second embodiment of the present invention.  
      As shown in  FIG. 11 , the pattern recognition unit according to the second embodiment of the present invention includes a center cell setting unit  1110 , a first threshold value comparator  1120 , a second threshold value comparator  1130 , a third threshold value comparator  1140  and a pattern recognition information generator  1150 . An operation of the pattern recognition unit will be described with reference to  FIGS. 11 and 12  together.  
      The center cell setting unit  1110  sets at least no less than two cells as center cells in one sub-field period. Contrary to the first embodiment of the present invention, the center cell setting unit  1110  sets arbitrary cells as a center cell for detecting an alternate pattern for the whole picture by the sub- field period unit in a second embodiment of the present invention. In other words, a cell (X N ) on the Nth line is set as a center cell.  
      The first threshold value comparator  1120  compares the number of cells having the same mapping codes as that of the center cell on the same line as that of the center cell with a first threshold value during the sub-field period. In other words, the first threshold value comparator  1120  evaluates the number of cells having the same mapping codes as that of the center cell (X N ) among cells ( . . . , XN−1, XN+1, . . . ) on the same line as that of the center cell (X N ) for the center cell (X N ) on the Nth line, and compares the number thereof with the first threshold value. Here, if the number of cells having the same mapping codes is more than the first threshold value during a corresponding sub-field period, switching elements of a data driving unit on the Nth line are approximately identically switched. At this time, the mapping code is a code having a value of “0” or “1” mapped by the sub-field unit to apply an address pulse.  
      The second threshold value comparator  1130  compares the number of cells having mapping codes different from that of the center cell on the next line of the center cell that is more than the first threshold value judged by the first threshold value comparator  1120  with a second threshold during the sub-field period. In other words, the first threshold value comparator  1120  evaluates the number of cells having mapping codes different from that of the center cell (X N ) among cells ( . . . , X N+1 −1, X N+1 +1, . . . ) on the N+1th line for the center cell (X N ) on the Nth line, and compares the number thereof with the second threshold value. Here, if the number of cells having mapping codes different from each other is more than the second threshold value during a corresponding sub-field period, switching elements of a data driving unit on the N+1th line and on the Nth line are approximately conversely switched to each other.  
      The third threshold value comparator  1140  evaluates the number of center cells that are more than the first and the second threshold values depending on a result judged by the first threshold value comparator  1120  and a result judged by the second threshold value comparator  1130 , and compares the number thereof with a third threshold value. Therefore, if the number of center cells is more than the third threshold value in the wole picture during a frame, the corresponding sub-field is determined as an alternate pattern during a frame.  
      The pattern recognition information generator  1150  determines an image signal of the sub-field as an alternate pattern during a fram when the number of center cells is more than the third threshold value. Thereafter, the pattern recognition information generator  1150  generates alternate pattern recognition information and then transmits it to the controller  650 .  
      As described above, a pattern recognition unit is located at the back end of a sub-field mapping unit and detects an alternate pattern by the sub-field unit in a second embodiment of the present invention, thereby detecting switching operations of a data driving unit more reliably than in the first embodiment of the present invention. Further, it is possible to effectively detect sub-fields used during one frame.  
      The invention being thus described, it will be obvious that the same may be varied in many ways. Such variations are not to be regarded as a departure from the spirit and scope of the invention, and all such modifications as would be obvious to one skilled in the art are intended to be included within the scope of the following claims.