Abstract:
There are provided an organic light emitting diode (OLED) display driving apparatus and a driving method thereof, in which the OLED display panel driving apparatus of a passive matrix type is configured such that its scan driving circuit has 3-state output, and the cathode lines, selected when the scan driving circuit performs a scan operation, maintain grounding, and after data-applied OLED emits light, are switched in a high voltage, and execute a refresh operation to initialize the pixel charges, and with the high impedance state maintained, non-selective common cathode lines turn into a high impedance state so as to remove the parasitic capacitance elements, and reduce the capacitance element functioning as the load of the data driving circuit connected to the OLED anode lines, and without the use of precharge method of maintaining the anode lines above a predetermined voltage quickly by using a voltage source, and applying data by using a current source, the anode lines can be charged within a short time just by necessary current for the lightening of the OLED so as to reduce the power consumption of the data driving circuit, and increase the operation speed.

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to an organic light emitting display device driving apparatus and a driving method thereof, and more particularly to an organic light emitting diode (OLED) display device driving apparatus and a driving method thereof for reducing the power consumption of the driving apparatus and increasing the driving speed by making a scan driving circuit in the passive matrix typed OLED display driving apparatus have 3-state output. (Herein after, it will be referred to as OLED panel driving apparatus.) 
   2. Background of the Related Art 
   A liquid crystal display device is widely used as an image display device of one of TV, a computer, or a portable phone, but it has disadvantages of being thick, heavy, and slow response speed since it requires a back light installed therein. An organic light emitting diode (OLED) display panel is recognized as an image display device which can replace such a display as above (Herein after, it will be referred to as ‘OLED panel’.). The OLED panel includes a very thin organic film being 0.1 μm or being less than 0.1 μm in thickness. When electric current is applied to the organic thin film, electrons and holes are recoupled near the interface of an electron transport layer and a hole transport layer so as to emit light. The light-emitting shows very fast response time less than hundreds of nano seconds. As such, OLED is composed of two polar structure groups, and it is driven by an electric current due to the difference of voltage-current characteristics of a discrete OLED to form a panel. 
     FIG. 1  is a schematic block diagram of a conventional free charge type of an OLED panel driving apparatus. As shown in  FIG. 1 , an OLED panel  10  includes a plurality of common anode lines D 1 , . . . , Dm) and a plurality of common cathode lines S 1 , . . . , Sn, which intersect in a matrix shape, and an OLED  12  is placed at each intersecting point of the matrix, to form a pixel (one pixel being composed of R/G/B.) A data driving circuit  20  is connected to the common anode lines D 1 , . . . , Dm, and a scan driving circuit  30  is connected to the common cathode lines S 1 , . . . , Sn. 
   A scan driving circuit  30  includes a scan output unit  32  which selectively connects the common cathode lines S 1 , . . . , Sn to a high voltage terminal V H  (for example, 15 V) and a grounding earth by a predetermined pattern in accordance with the control of a controlling unit (not shown).  FIG. 2  is a detailed circuit diagram of a scan output unit with respect to one of the common cathode lines of FIG.  1 . As shown in  FIG. 2 , the scan output unit  32  selectively connects one common cathode line S y  to a high voltage terminal V H  or a grounding earth GND in accordance with the logic level of a control signal C SCAN  from an outer controlling unit (not shown). 
     FIG. 3  is a detailed circuit diagram of a data output unit with respect to one common anode line of FIG.  1 . As shown in  FIG. 3 , the data output unit  22  selectively connects each of the common anode lines D 1 , . . . , Dm to a constant current source CC or a grounding earth GND in accordance with the control of a controlling unit (not shown). 
   In the structure described as above, if the scan output unit  32  turns “on” or “off” alternately so as to select any one of the common cathode lines from a first row S 1  to an nth row Sn, the data output unit  22  connects the common anode lines D 1 , . . . , Dm to the constant current source CC for the time width varied by Pulse Width Modulation (PWM) method in accordance with the gray scale of a corresponding pixel, that is, the OLED  12  with synchronized thereto, and a current is applied to the corresponding OLED  12  so as to form one display frame. 
   In the meantime, a parasitic capacitor C exists on the both ends of the anode and the cathode of a diode D since the OLED  12  is composed of an organic thin film, which causes a problem of not-treating of low gray scale in the presence of the parasitic capacitor C. Thus, conventionally, a voltage is applied just as much as to turn “on” the diode D before PWM current is applied on the common anode lines D 1 , . . . , Dm so that the parasitic capacitor C is precharged. Then, for the purpose, a predetermined voltage, for example, precharge voltage terminal V PRE  of about 4˜6 V is further provided on the data output unit  22 . 
     FIG. 4  is a timing chart to illustrate the relations of a scan output timing for one image frame in the conventional precharge-typed OLED panel driving apparatus, and a precharge interval and a data output interval in each scan output interval. As shown in  FIG. 4 , the vertical synchronization signal V sync  is generated every one frame of display, and horizontal synchronization signals H sync  is generated having the same number as that of the common cathode lines n, in the vertical scan period between the vertical synchronization signal V sync , and data is applied to the all common anode lines D 1 , . . . , Dm in the horizontal scan period between the horizontal synchronization signal H sync  at the same time. That is, if the scan output unit  32  connects a first row of common cathode line S 1  to the grounding earth GND in the high voltage terminal V H  in accordance with the outer control signal C SCAN  generated with synchronized to the down edge of each horizontal synchronization signal H sync , the data output unit  22  connects the all common anode lines D 1 , . . . , Dm into a precharge voltage V PRE  in accordance with the control of the outer control signal with synchronized thereto for a predetermined time so as to charge the parasitic capacitor C of the OLED  12 . Then, the data output unit  22  connects each of the common anode lines D 1 , . . . , Dm to the constant current source CC in accordance with the control of the outer control signal PWM, for the PWM time predetermined according to the pixel gray of the OLED  12  connected thereto so that the OLED  12  emits light. Then, if the data output unit  22  again connects the common anode lines D 1 , . . . , Dm to the grounding earth GND in accordance with the control of the outer control signal Reset, the voltage charged in the parasitic capacitor C is discharged. In the same way, the process is executed for up to the nth row of the common cathode line Sn, so as to form a display one frame. 
   However, according to the OLED panel driving apparatus of the conventional precharge typed OLED panel driving apparatus described as above, since the all parasitic capacitors C, connected thereto in parallel, are repeatedly charged and discharged (eventually, because of the conversion of the voltage polarity of the both ends of the OLED), in the process in which the data output unit  22  operates the common anode lines D 1 , . . . , Dm, large amount of current is flowed in the OLED panel  10 , and the power consumption according thereto is as follows by Equation 1.
 
 P   d   =n*m*C*V   H   2   *f   clk   [Equation 1]
 
   In the Equation 1, the number from 1 to n presents the number of the common cathode lines, m presents the number of the common anode lines, C presents a parasitic capacitance, V H  presents high voltage applied to the anode, and fclk presents the operation frequency of the scan driving circuit  30 . As shown in Equation 1, since the conventional OLED panel driving apparatus requires a large amount of current during charge-discharge, the power consumption is increased, and the operation speed of the data driving circuit is decreased. 
   SUMMARY OF THE INVENTION 
   An object of the invention is to solve at least the above problems and/or disadvantages and to provide at least the advantages described hereinafter. 
   Accordingly, one object of the present invention is to solve the foregoing problems by providing an OLED panel driving apparatus and a driving method thereof, in which the passive matrix typed OLED panel driving apparatus is configured such that its scan driving circuit has 2-state outputs of at least a scan state and a high impedance state, and its power consumption is reduced and the operation speed is increased by removing parasitic capacitance with a non-selective common cathode line in a high impedance state. 
   Another object of the present invention to provide an OLED panel driving apparatus and a driving method thereof for preventing the degradation caused from the maintenance of the same polarity in the both ends of the OLED, by making its scan driving circuit have 3-state outputs of high voltage state, scan state and high impedance state, and by making the non-selective common cathode line in high voltage state before turning into high impedance state so as to invert the polarity of its parasitic capacitance. 
   The foregoing and other objects and advantages are realized by providing an OLED panel driving apparatus having an OLED in each intersecting point of a plurality of common anode lines and a plurality of common cathode lines, which are aligned in a matrix configuration, to form a pixel, in which the OLED panel driving apparatus may include a data driving circuit connected to a plurality of common anode lines, and having a plurality of data output unit selectively connecting each of the common anode lines to a constant current source or a high impedance terminal HIZ; and a scan driving circuit connected to the plurality of common cathode lines, and having a plurality of scan output units selectively connecting each of the common cathode lines at least to a high impedance terminal HIZ or a grounding earth. Preferably, the scan output unit may further include a high voltage terminal to selectively connect each of the common cathode lines to the high voltage terminal, the high impedance terminal HIZ or the grounding earth. The scan output unit may preferably further include a high voltage terminal to selectively connect each of the common cathode lines to the high voltage terminal, the high impedance terminal HIZ or the grounding earth. 
   Further, a data driving circuit having a plurality of data output units selectively connected to the grounding earth is further provided. There is also provided an OLED control circuit for generating various signals including a horizontal synchronization signal, a vertical synchronization signal and a display data signal. 
   Further, the scan driving circuit may include a scan output unit; a shift register unit for generating a scan control signal C SCAN  with respect to the common cathode line; and a control logic unit for executing the logic processing of the scan control signal C SCAN  supplied from the shift register unit in order to generate a high impedance control signal C HIZ , and to supply to the scan output unit. 
   Further, the scan output unit may include an inverter gate, its input end being connected to the high impedance control signal end C HIZ ; a NOR gate, its one input end being connected to the scan control signal end C SCAN , and its the other input end being connected to the high impedance control signal end C HIZ ; a NAND gate, its one input end being connected to the scan control signal end C SCAN , and its the other input end being connected to the output end of the inverter gate; a first level shifter being connected to the output end of the NAND gate and converting logic level into the high voltage level; a second level shifter being connected to the output end of the NOR gate and converting logic level into the high voltage level; a first PMOSFET having a gate connected to the first level shift and a source connected to the high voltage terminal; and a first NMOSFET having a gate connected to the second level shift, a drain connected to the drain of the first PMOSFET, and a source being grounded, and the common cathode lines are connected to the first PMOSFET and the drain of the first NMOSFET. 
   Further, the shift register unit may be configured to have shift registers as many as the number of the common cathode lines; the vertical synchronization signal is applied to data input end of a first row of a shift register in the shift registers; the horizontal synchronization signal is applied to the all clock ends of the shift register; and the output of one row of the shift registers is connected to a corresponding row of a scan control signal end C SCAN  in the scan output unit, and to a data input end of a next row of the shift register. 
   Further, the control logic unit may be configured to have 2-input XNOR gates as many as the number of the common cathode lines; one input end of each of the XNOR gates is connected to the output end of its corresponding row of the shift register; the other input end of each of the XNOR gates is connected to the output end of a next row of the shift register; and the output end is connected to the high impedance control signal end C HIZ  of its corresponding row of the scan output unit. 
   Further, wherein the data driving circuit may include a data output unit; a shift register/latch unit for sequentially shifting and storing the data applied to the common anode line in accordance with the control signal from the OLED control circuit; and a PWM generating unit for converting the data supplied from the shift register/latch unit into a control signal PWM having various time width in accordance with gray level of the data, and supplying to the data output unit. 
   Further, the data output unit may include a second PMOSFET and a third PMOSFET to form current mirror circuits; a third level shifter for converting the logic level of the control signal PWM supplied from the PWM generating unit into the high voltage level; and a fourth PMOSFET for selectively connecting the common anode line to the constant current source and the high impedance terminal HIZ with “on”/“off” by the third level shifter. 
   Further, a second NMOSFET is provided for grounding the common anode line with “on” by an outer control signal Reset in the “off” state of the fourth PMOSFET. 
   In another aspect of the present invention, a method of driving an OLED panel of the present invention is provided, in which the OLED panel has an OLED in each intersecting point of a plurality of common anode lines and a plurality of common cathode lines, which are aligned in a matrix configuration, to form a pixel, and the method may include the step of maintaining, in a high impedance state, the common cathode lines in the rest of the rows except one row of the currently scanned common cathode line while being sequentially scanned after converted into grounding level GND in the process of applying constant current to the common anode lines by a control signal PWM having various time width in accordance with gray level of displayed pixel data. 
   Further, the driving method of the present invention is characterized in that the row of the common cathode line right prior to the row of the currently scanned common cathode line is connected to a high voltage terminal so as to invert the polarity of the parasitic capacitance and prevent the degradation of the OLED. 
   Additional advantages, objects, and features of the invention will be set forth in part in the description which follows and in part will become apparent to those having ordinary skill in the art upon examination of the following or may be learned from practice of the invention. The objects and advantages of the invention may be realized and attained as particularly pointed out in the appended claims. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention will be described in detail with reference to the following drawings in which like reference numerals refer to like elements wherein: 
       FIG. 1  is a schematic block diagram of a conventional precharge-typed OLED panel driving apparatus; 
       FIG. 2  is a detailed circuit diagram of  FIG. 1  to illustrate a scan output unit relative to one common cathode line; 
       FIG. 3  is a detailed circuit diagram of  FIG. 1  to illustrate a data output unit relative to one common anode line; 
       FIG. 4  is a timing chart to illustrate the relations of a scan output timing for one image frame in the conventional precharge-typed OLED panel driving apparatus, and a precharge interval and a data output interval in each scan output interval; 
       FIG. 5  is a block diagram of an OLED panel driving apparatus of the present invention; 
       FIG. 6  is a block diagram of a scan output unit relative to one common cathode line of  FIG. 5 ; 
       FIG. 7  is a detailed circuit diagram of  FIG. 6 ; 
       FIG. 8  is a block diagram of a data output unit relative to one common anode line of  FIG. 5 ; 
       FIG. 9  is a block diagram of an OLED panel driving apparatus of the present invention; 
       FIG. 10  is a detailed circuit diagram of a scan driving circuit of  FIG. 9 ; and 
       FIG. 11  is an operation timing diagram of a scan driving circuit and a data driving circuit to illustrate a method of driving an OLED panel of the present invention. 
   

   DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
   The following detailed description will present a driving apparatus of an OLED panel, and a driving method thereof according to a preferred embodiment of the invention in reference to the accompanying drawings. 
     FIG. 5  is a block diagram of an OLED panel driving apparatus of the present invention. As shown in  FIG. 5 , the OLED panel  10  is composed of a plurality of common anode lines D 1 , . . . , Dm and a plurality of common cathode lines S 1 , . . . , Sn, which are aligned in a matrix shape, and an OLED  12  is located in each of the intersecting points so as to form a pixel. A data driving circuit  20 ′ is connected to the common anode lines D 1 , . . . , Dm, and a scan driving circuit  30 ′ is connected to the common cathode lines S 1 , . . . , Sn. 
   The scan driving circuit  30 ′ includes a scan output unit  32 ′, which selectively connects the common cathode lines S 1 , . . . , Sn to a high voltage terminal. (for example, 15V) V H , a high impedance terminal HIZ, and a grounding earth GND in predetermined patterns in accordance with the control of a control unit (not shown). The high voltage terminal V H  is provided to prevent the OLED  12  from being degraded, which is caused from that the both ends of the OLED  12  is continuously maintained in the same polarity, by inverting the polarity of a parasitic capacitor, that is, the voltage polarity of the both ends of the OLED  12 . Its operation will be described herein after. 
     FIG. 6  is a block diagram of a scan output unit relative to one common cathode line of FIG.  5 . As shown in  FIG. 6 , each scan output unit  32 ′ includes an inverter gate INV, its input end being connected to a high impedance control signal end C HIZ , a NOR gate, its input end being connected to a scan control signal end C SCAN , and its the other input end being connected to a high impedance control signal end C HIZ , NAND gate, its one input end being connected to a scan control signal end C SCAN , and its the other end being connected to the output end of an inverter gate INV, a first level shift LS 1  being connected to the output end of the NAND gate NAND to convert its logic level Vcc to a high voltage level V H , a second level shift LS 2  being connected to the output end of the NOR gate NOR to convert its logic level Vcc to a high voltage level V H , PMOSFET PMT 1 , a gate being connected to the first level shift LS 1 , and a source being connected to the high voltage terminal V H , and NMOSFET NMT 1 , a gate connected to the second level shift LS 2 , and a drain being connected to the drain of the PMOSFET PMT 1 , and a source grounded, and the common cathode line S y  is connected to the drains of PMOSFET PMT 1  and NMOSFET NMT 1 . 
   In the structure described as above, if a logic signal “0” is output from an outer control unit (not shown) to the scan control signal end C SCAN  and the high impedance control signal end C HIZ  respectively, a logic signal “1” is output from the NAND gate NAND and NOR gate NOR respectively, and the logic signal “1” is converted into a high voltage level V H  in the first level shift LS 1 , and the second level shift LS 2 , and so, the common cathode line S y  is connected to a grounding earth GND with the PMOSFET PMT 1  being “off”, but the NMOSFET NMT 1  being “on”. 
   If a logic signal “1” is output to the scan control signal end C SCAN , and a logic signal “0” is output to the high impedance control signal end C HIZ  respectively, a logic signal “0” is output from the NAND gate NAND and NOR gate NOR respectively, and the logic signal “0” is converted into a low voltage level in the first level shift LS 1  and the second level shift LS 2 , and so, the common cathode line S y  is connected to a high voltage terminal V H  with the PMOSFET PMT 1  being “on”, but the NMOSFET NMT 1  being “off”. 
   In the meantime, if a logic signal “1” is output to the high impedance control signal end C HIZ , a logic signal “1” is output from the NAND gate NAND regardless the level of the logic signal input to the scan control signal end C SCAN , and a logic signal “0” is output from the NOR gate NOR. Accordingly, the PMOSFET PMT 1  and the NMOSFET NMT 1  are all “off”, and the common cathode line S y  gets into a state of being connected to the high impedance terminal HIZ functionally, that is, in a floating state. Table 1 is a truth table to show the above operation. 
   
     
       
             
             
             
             
             
             
             
           
         
             
               TABLE 1 
             
             
                 
             
             
               C SCAN   
               C HIZ   
               VNAND 
               VNOR 
               PMOSFET 
               NMOSFEt 
               S y   
             
             
                 
             
           
           
             
               0 
               0 
               1 
               1 
               Off 
               On 
               GND 
             
             
               1 
               0 
               0 
               0 
               On 
               Off 
               V H   
             
             
               0 
               1 
               1 
               0 
               Off 
               Off 
               HIZ 
             
             
               1 
               1 
               1 
               0 
               Off 
               Off 
               HIZ 
             
             
                 
             
           
        
       
     
   
     FIG. 7  is a detailed circuit diagram of the scan output unit in FIG.  6 . 
   In the meantime, a data output unit  22 ′ selectively connects each of the common anode lines D 1 , . . . , Dm to a constant current source CC and a high impedance terminal HIZ in accordance with the control of a control unit (not shown).  FIG. 8  is a block diagram of a data output unit relative to one common cathode line of FIG.  5 . As shown in  FIG. 8 , the data output unit  22 ′ includes two PMOSFETs forming current mirror circuits PMT 2 , PMT 3 , a constant current source CC being connected to the current mirror circuits, a third level shift LS 3  converting the logic level of an outer control signal PWM into a high voltage level V H , and a PMOSFET PMT 4  for applying a constant current to the common anode line D x  with the “on”/“off” by the third level shift LS 3 . In the drawing, a reference number NMT 2  presents NMOSFET for grounding the common anode line D x  turning “on” by an outer control signal Reset in the “off” state of the PMOSFET PMT 4 . 
     FIG. 9  is a block diagram of an OLED panel driving apparatus of the present invention. As shown in  FIG. 9 , the OLED panel driving apparatus of the present invention mainly includes a scan driving circuit  20 ′, a data driving circuit  30 ′, and an OLED control circuit  40  for outputting various clock signals PWM CLK, Data CLK, etc. and Display data and control signal V sync , H sync , etc. to the scan driving circuit  20 ′ and the data driving circuit  30 ′. 
   In the aforementioned structure, the data driving circuit  20 ′ includes an aforementioned data output unit  22 ′ (it is referred to as “current output unit” in the drawing after a typical term in the related art), a shift register/latch unit  28  for sequentially shifting and storing R,G,B display data applied from the OLED control circuit  40  with synchronized by a data clock signal CLK, that is, the data finally applied to the common anode lines D 1 , . . . , Dm, and a PWM generating unit  26  for converting the data supplied from the shift register/latch  28  into signal having different time width in accordance with the gray level, and supplying to the data output unit  22 ′. The OLED control circuit  40  supplies PWM clock signal PWM CLK to the PWM generating unit  26 . 
   Further, the scan driving circuit  30 ′ includes an aforementioned scan output unit  32 ′ (it is referred to as “high voltage output buffer unit” in the drawing after a typical term in the related art), a shift register unit  38  for generating a scan control signal C SCAN  with respect to the common cathode lines S 1 , . . . ,Sn selected in accordance with a horizontal synchronization signal H sync  supplied from the OLED control circuit  40 , and a control logic unit  36  executing logic-processing for the scan control signal C SCAN  supplied from the shift register unit  38 , and generating a scan control signal C SCAN  and a high impedance control signal C HIZ , and supplying to the scan output unit  22 ′. 
     FIG. 10  is a detailed circuit diagram of a scan driving circuit of FIG.  9 . As shown in  FIG. 10 , the shift register unit  38  is configured such that unit shift registers SR 1 , . . . , SRn having the same number as that of the common cathode lines, n, are aligned in series, and horizontal synchronization signals H sync  are supplied to the clock ends of the all shift registers SR 1 , . . . , SRn. Then, to the data input end of the first row of the shift register SR 1 , a vertical synchronization signal, being output from the OLED control circuit  40 , is supplied, and in the rest of the shift registers SR 1 , . . . , SRn, the output of any row of the shift register SRy is directly connected to a corresponding scan control signal end C SCAN  of the scan output unit  32 ′, and at the same time, is connected to the data input end of the next row of the shift register SRy+1. The shift registers SR 1 , . . . , SRn are composed of negative-truth logic circuits, and structured to operate at the down-edges of the data signal and clock signal. 
   A control logic unit  36  has 2-inputs, and is also composed of unit XNOR gates XNOR 1 , . . . , XNORn as many as the number of the common cathode lines, n, and one input end of each row of the XNOR gate XNORy is connected to the output end of its corresponding row of the shift register SR y , and the other input end is connected to the output end of next row of the shift register SR y+1 , and the output end is connected to the corresponding high impedance control signal end C HIZ  of the scan output unit  32 ′. 
   Now herein after, the operation of the OLED panel driving apparatus of the present invention and its method will be explained in detail. 
     FIG. 11  is an operation timing diagram of a scan driving circuit and a data driving circuit to illustrate a method of driving an OLED panel of the present invention. As shown in  FIG. 11 , a vertical synchronization signal V sync  is generated every frame of display, and horizontal synchronization signals H sync , being as many as the number of the common cathode lines n, are generated in the vertical scan period between the vertical synchronization signals, and data is applied to the all common anode lines D 1 , . . . , Dm in the horizontal scan period between the horizontal synchronization signals H sync  at the same time. Describing this in more detail, the vertical synchronization signal V sync  generated from the OLED control circuit  40  is supplied into the data input end of a first row of the shift register SR 1  of the scan driving circuit  30 ′, and at the same time, if the horizontal synchronization signal H sync  is supplied to the clock end, the first row of the shift register SR 1  operates at the down edge of the vertical synchronization signal V sync  and the horizontal synchronization signal H sync , and logic signal “0” is output to its output end, that is, a scan control signal end C SCAN . 
   Then, the signals output as above are supplied to a first row of the scan control signal end C SCAN  of the scan output unit  32 ′ and to one input end of a first row of XNOR gate XNOR 1 , and since the other input end of the first row of XNOR gate XNOR 1  is connected to the output end of a second row of the shift register SR 2 , logic signal “0” is output to the output end of the first row of the XNOR gate XNOR 1 , that is, high impedance control signal end C HIZ . Then, logic signal “1” is output into the output ends of the shift registers SR 2 , . . . , SRn and XNOR gates XNOR 2 , . . . , XNORn under a second row. 
   In accordance with the states of the scan control signal C SCAN  and the high impedance control signal C HIZ , the scan output unit  32 ′ operates as shown in the truth table of the Table 1 so as to connect the first row of the common cathode line S 1  to the grounding earth GND in a high impedance state HIZ, that is, in a floating state. Then, in accordance with the control of the outer control signal PWM generated from the PWM generating unit  26  with synchronized by the horizontal synchronization signal H 1  in a horizontal scanning period with respect to the first row, with the PMOSFET PMT 4  of the data output unit  22 ′ “on”, each of the common anode lines D 1 , . . . Dm is connected to the constant current source CC for a predetermined PWM time in accordance with the pixel gray of the OLED  12  connected thereto so that the OLED  12  emits light, and then, with the PMOSFET PMT 4  “off”, the common anode lines D 1 , . . . , Dm maintain a high impedance state HIZ. 
   In the meantime, while the first row of the common cathode line S 1  is selected, the common cathode lines S 2 , . . . , Sn of the row under the second row are maintained in a high impedance state HIZ, and it can be illustrated as a truth table in Table 2. Further, the letter and numbers presented as italic in the Table 2 and the Tables 3 and 4 mentioned later present the row selected at present. 
   
     
       
             
             
             
             
             
             
           
             
             
             
             
             
             
           
         
             
                 
               TABLE 2 
             
             
                 
                 
             
             
                 
                 
                 
                 
               XNOR 
                 
             
             
                 
               SR output 
               XNOR 
               XNOR 
               output 
                 
             
             
                 
               (C SCAN ) 
               Input 1 
               Input 2 
               (C HIZ ) 
               S y   
             
             
                 
                 
             
           
           
             
                 
             
           
        
         
             
               
                 first row 
               
               
                 0 
               
               
                 0 
               
               
                 1 
               
               
                 0 
               
               
                 GND 
               
             
             
               Under a second row 
               1 
               1 
               1 
               1 
               HIZ 
             
             
                 
             
           
        
       
     
   
   Then, in the aforementhioned method, when a second row of the common cathode line S 2  is connected to the grounding earth GND in a high impedance state HIZ, that is, in a floating state, the OLED  12  connected thereto emits light, and during the period, when the scan output unit  32 ′ connects the first row of the common cathode line S 1  to the high voltage terminal V H  in accordance with the high impedance control signal C HIZ  and the scan control signal C SCAN , the polarity of the parasitic capacitor C of the OLED  12  connected thereto is inverted, and the degradation of the OLED  12  can be prevented (refresh). The operation can be shown in Table 4 as a truth table. 
   
     
       
             
             
             
             
             
             
           
             
             
             
             
             
             
           
         
             
                 
               TABLE 3 
             
             
                 
                 
             
             
                 
                 
                 
                 
               XNOR 
                 
             
             
                 
               SR output 
               XNOR 
               XNOR 
               output 
                 
             
             
                 
               (C SCAN ) 
               input 1 
               input 2 
               (C HIZ ) 
               S y   
             
             
                 
                 
             
           
           
             
                 
             
           
        
         
             
               First row 
               1 
               1 
               0 
               0 
               V H   
             
             
               
                 Second row 
               
               
                 0 
               
               
                 0 
               
               
                 1 
               
               
                 1 
               
               
                 GND 
               
             
             
               Under third row 
               1 
               1 
               1 
               1 
               HIZ 
             
             
                 
             
           
        
       
     
   
   Then, a three row of the common cathode line S 3  is connected to a grounding earth GND, and while the OLED  12  connected thereto emits light, the second row of the common cathode line S 2  is connected to a high voltage terminal V H , and the parasitic capacitor C of the OLED  12  connected thereto is discharged. Then, sequentially while the OLED  12  connected to the last row of the common cathode line Sn emits light, the OLED  12  connected to the first row of the common cathode line S 1  maintains a high impedance state by an outer control signal C HIZ . The operation can be shown in Table 4 as a truth table. 
   
     
       
             
             
             
             
             
             
           
             
             
             
             
             
             
           
         
             
                 
               TABLE 4 
             
             
                 
                 
             
             
                 
                 
                 
                 
               XNOR 
                 
             
             
                 
               SR output 
               XNOR 
               XNOR 
               output 
                 
             
             
                 
               (C SCAN ) 
               input 1 
               input 2 
               (C HIZ ) 
               S y   
             
             
                 
                 
             
           
           
             
                 
             
           
        
         
             
               First row 
               1 
               1 
               1 
               1 
               HIZ 
             
             
               Second row 
               1 
               1 
               0 
               0 
               V H   
             
             
               
                 third row 
               
               
                 0 
               
               
                 0 
               
               
                 1 
               
               
                 0 
               
               
                 GND 
               
             
             
               Under fourth row 
               1 
               1 
               1 
               1 
               HIZ 
             
             
                 
             
           
        
       
     
   
   As described above, in the OLED panel driving method of the present invention, any one row of the common cathode line S y  is sequentially scanned to the grounding level GND in a high impedance state HIZ, and while next row of the common cathode line S y+1  is selected (scanned), the row of the common cathode line S y  is connected to a high voltage terminal V H  to invert the polarity of the parasitic capacitor C of the OLED  12  connected thereto, and then, from the point when the next row after the above next row of the common cathode line S y+2  is selected (scanned), the row of the common cathode line S y  is maintained in a high impedance state HIZ. As a result, according to the OLED panel driving method of the present invention, the period, in which a parasitic capacitor C is formed between the anode and the cathode of the OLED  12 , is only the state in which the common cathode line S y  is connected to a high voltage terminal V H  or the grounding earth GND, and a parasitic capacitance does not exists in the state that it is connected to the high impedance terminal HIZ. 
   Therefore, in the OLED driving method of the present invention, since the parasitic capacitance exist only in the OLED connected to one common cathode line connected to the grounding earth GND, and the OLED connected to one common cathode line connected to the high voltage terminal V H , desired gray can be expressed without the use of the precharge as in the conventional case, and further, its power consumption can be reduced down to 2/n compared with that of the conventional case. This can be presented as Equation 2 as follows.
 
 P   d =2 *m*C*V   H   2   *f   clk   [Equation 2]
 
   In the Equation 2, C presents parasitic capacitor existing in the OLED  12 , m presents the number of the common anode lines, V H  presents the high voltage applied to the anode, and fclk presents the operation frequency of the scan driving circuit  30 ′. For example, in the case of an OLED panel driving apparatus having a resolution of 128×160, since the number n of the cathode lines of the OLED is 160, the power consumption can be reduced down to {fraction (1/80)}. 
   The OLED panel driving apparatus and the driving method thereof of the present invention are not limited to the exemplary embodiments described as above, and it will be understood that various modifications and applications are possible within the sprit and scope of the present invention. 
   As described above, according to the OLED panel driving apparatus and the driving method thereof of the present invention, low gray processing is possible just by the PWM data current without the use of the precharge method, so as to reduce the power consumption generated due to the precharge, and allow speedy operation. 
   While the invention has been shown and described with reference to certain preferred embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the appended claims. For example, while the invention has been described in the specific content of an OLED panel driving apparatus and a driving method thereof, those skilled in the art will appreciate that various applications are possible for the apparatus and method. 
   The foregoing embodiments and advantages are merely exemplary and are not to be construed as limiting the present invention. The present teaching can be readily applied to other types of apparatuses. The description of the present invention is intended to be illustrative, and not to limit the scope of the claims. Many alternatives, modifications, and variations will be apparent to those skilled in the art. In the claims, means-plus-function clauses are intended to cover the structures described herein as performing the recited function and not only structural equivalents but also equivalent structures.