Abstract:
Provided is a flat panel display and a method for driving the same. The flat panel display comprises a substrate, a pixel part having a plurality of sub-pixels formed on the substrate; and a data driver supplying to the pixel part data signals and charge signals containing charge values that correspond to the data signals. Each charge signal comprises a first charge signal and a second charge signal, and the first charge signal is a voltage signal selected from a plurality of preset voltage levels. The second charge signal is a current signal corresponding to the difference between the voltage value corresponding to the first charge signal and the charge value that corresponds to the data signal.

Description:
CROSS-REFERENCE 
       [0001]    This application claims priority to and the benefit of Korea Patent Application No. 10-2006-0063653, filed on Jul. 6, 2006, the entire content of which is incorporated herein by reference. 
       BACKGROUND 
       [0002]    1. Field 
         [0003]    The present invention relates to a flat panel display and a method for driving the same. 
         [0004]    2. Related Art 
         [0005]    Among various flat panel display devices, a light emitting display device is generally advantageous of a fast response rate and low power consumption. Since a light emitting display device does not need a backlight, it can be manufactured lightweight. 
         [0006]    In particular, an organic light emitting display device comprises an organic emission layer formed between an anode and a cathode. Thus, holes supplied from an anode and electrons supplied from a cathode are connected together within the organic emission layer to produce excitons, which are electron-hole pairs. When these excitons transit to a ground state, a certain level of energy is produced, and this energy causes the organic light emitting display device to emit light. 
         [0007]    A flat panel display represents an image by applying data signals within a duration that scan signals are applied. However, since each sub-pixel has a parasitic capacitance, it is hard to represent gray scales exactly when the data signals are inputted. For this reason, a pre-charge signal is supplied to preliminarily charge sub-pixels and, after data signals are applied, a discharge signal is supplied to a pixel part to discharge the sub-pixels. 
         [0008]    According to conventional technology, however, pre-charge signals are applied indiscriminately. Thus, an actually needed pre-charge signal is not applied to the pixel part. Also, since a discharge signal is applied with no regard to the data signals to be applied in the next frame, the pixel part is indiscriminately discharged by the discharge signal to a predetermined level. This results in wasteful consumption of power by the unnecessary supply of a pre-charge or discharge signal. 
       SUMMARY 
       [0009]    An embodiment of the present invention provides a flat panel display that can exactly represent a desired image with reduced power consumption, and a driving method thereof. 
         [0010]    According to an aspect of the present invention, provided is a flat panel display comprising a substrate, a pixel part having a plurality of sub-pixels formed on the substrate, and a data driver supplying to the pixel part data signals and charge signals containing charge values that correspond to the data signals. Each charge signal includes a first charge signal and a second charge signal, and the first charge signal is a voltage signal selected from a plurality of preset voltage levels. Herein, the second charge signal is a current signal corresponding to the difference between the voltage value corresponding to the first charge signal and the charge value that corresponds to the data signal. 
         [0011]    According to another aspect of the present invention, provided is a method for driving the flat panel comprising supplying a scan signals to a pixel part which comprising a plurality of sub-pixels, supplying a data signals and charge signals comprising a charge value corresponding to the data signals to the pixel part selectively. Herein, the charge signals comprises a first charge signal and a second charge signal, and the first charge signal being a voltage signal selected from a plurality of preset voltage levels. The second charge signal is a current signal corresponding to the difference between the first charge signal and the charge value. 
     
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0012]    The invention will be described in detail with reference to the following drawings, in which like numerals refer to like elements: 
           [0013]      FIG. 1  is a plane view showing a flat panel display according to an embodiment of the present invention; 
           [0014]      FIG. 2  is a block view illustrating a data driver of the flat panel display according to the embodiment of the present invention; 
           [0015]      FIG. 3  is a waveform diagram based on driving methods of a flat panel display according to the embodiment of the present invention; 
           [0016]      FIGS. 4 and 5  are graphs illustrating the relationship between a pixel current and a pre-charge voltage to describe a driving method of a flat panel display according to the embodiment of the present invention; 
           [0017]      FIG. 6  is a block view describing a data driver of a flat panel display according to another embodiment of the present invention; and 
           [0018]      FIG. 7  is a graph illustrating the relationship between a pixel current and a pre-charge voltage to describe a driving method of a flat panel display according to the embodiment of the present invention. 
       
    
    
     DESCRIPTION OF EMBODIMENTS 
       [0019]    Referring to  FIG. 4 , a flat panel display  100  suggested in a first embodiment of the present invention comprises a pixel part  120  and a driving part  140  disposed on a substrate  110 . 
         [0020]    The pixel part  120  comprises a plurality of sub-pixels, each comprising an anode, a cathode, and an organic light emission layer interposed between the two electrodes. Although not shown, the sub-pixels are positioned in areas defined by intersection of scan lines and data lines. Each sub-pixel may comprise at least one transistor and capacitor connected to the anode. 
         [0021]    The driving part  140  comprises a scan driver  145  and a data driver  150 , and it supplies a driving signal to the pixel part  120  through scan lines  130 A and data lines  130 B upon receipt of a control signal from a controller (not shown). The driving part  140  comprises a scan driver  145  and a data driver  150  therein for the sake of convenience in description. However, the scan driver  145  and the data driver  150  may be realized in independent forms or they may be realized in multiple units, individually. 
         [0022]      FIG. 2  is a block view illustrating a data driver of a flat panel display according to an embodiment of the present invention. 
         [0023]    Referring to  FIG. 2 , the data driver  150  comprises a data output part  151 , a data processing part  152 , and a converter  155 . 
         [0024]    The data output part  151  receives digital data signals from the outside to the data processing part  152 . Herein, the data signals are values corresponding to gray scales to be represented in the pixel part  120 . 
         [0025]    The data processing part  152  processes the data signals transmitted from the data output part  151  and generate charge signals corresponding thereto. The charge signals are for exactly represent gray scales based on the data signals by satisfying a parasitic capacitance of the pixel part or for discharging charges charged in sub-pixels by data signals supplied in the previous frame. The charge signals comprise a first charge signal and a second charge signal. 
         [0026]    The charge signals may be applied before data signals are applied to the pixel part (P). Pre-charge signals may be acquired by processing the data signals and calculating the optimal values. 
         [0027]    Herein, the data processing part  152  may comprise a lookup table  153  and a first charge output part  154 . The lookup table  153  stores ideal charge values for data signals, and the first charge output part  154  comprises a plurality of preset voltage values. The data processing part  152  receives the data signals, determines an ideal charge value for the data signals based on the lookup table  153 , selects a voltage value which is smaller than the ideal voltage value and close to the ideal voltage value, and outputs a first charge signal. It also generates a second charge signal corresponding to the difference between the ideal charge value and the first charge signal. 
         [0028]    The converter  155  converts the data signals transmitted from the data processing part  152  or the second charge signal into current. In short, it converts digital signals into analog signals. 
         [0029]    The driving part  140  may further comprise a switch part  160 . The switch part  160  is connected to a controller (not shown) and the data driver  150  and optionally supplies the data signals, the first charge signal, and the second charge signal to the pixel part  120 . The switch part  160  comprises a first switch SW 1  and a second switch SW 2  between the converter  155  and the pixel part  120 . The data signals may be supplied to the pixel part  120  through the first switch SW 1 , whereas the second charge signal may be supplied to the pixel part  120  through the second switch SW 2 . Herein, the second switch SW 2  may further comprise a booster to thereby supply the second charge signal after boosting. 
         [0030]    The switch part  160  may comprise a third switch SW 3  interposed between the first charge output part  154  and the pixel part  120 . The third switch SW 3  may comprise a plurality of switches connected to a plurality of voltage values determined in the first charge output part  154 . 
         [0031]      FIG. 3  is a waveform diagram based on driving methods of a flat panel display according to the embodiment of the present invention, and  FIGS. 4 and 5  are graphs illustrating the relationship between a pixel current and a pre-charge voltage to describe a driving method of a flat panel display according to the embodiment of the present invention. 
         [0032]    For easy understanding, description will be provided with reference to  FIGS. 4 and 5  along with an example. Herein, it is assumed that the voltage value set in the first charge output part  154  has four steps, i.e., V 1st_charge0, 1, 2 and 3. 
         [0033]    When a control signal is supplied from the controller (not shown) to the driving part  140 , the scan driver  145  supplies a scan signal to the pixel part  120  through a scan line  130 A. The data output part  151  of the data driver  150  supplies the data signals transmitted from the outside to the data processing part  152 , and the data processing part  152  processes the received data signals to thereby generate the first and second charge signals corresponding to the data signals. 
         [0034]    To describe the generation of the first and second charge signals more in detail, when data signals are supplied from the data output part  151  to the data processing part  152 , the data processing part  152  determines an ideal charge value for the data signals based on the lookup table  153 . In  FIG. 4 , the ideal charge value is Vb. Subsequently, the data processing part  152  selects and outputs a value, which is smaller than the ideal charge value and most close to the ideal charge value in the first charge output part  154 . Accordingly, the first charge signal is determined to be V 1st_charge1. The data processing part  152  generates the second charge signal (ΔV) which corresponds to the difference between the ideal charge value and the first charge signal, i.e., Vb and V 1st_charge1. Referring to  FIG. 4  herein, the sub-pixels are charged to be Va by the data (n−1 data) supplied to the previous frame. Therefore, when the first and second charge signals are supplied, the pixel part  120  can be discharged to the optimal voltage value. 
         [0035]    Referring to  FIG. 5 , the ideal charge value is B and the first charge signal is V 1st_charge2. Thus, the data processing part  152  generates the second charge signal (ΔV) corresponding to the difference between the ideal charge value and the first charge signal, i.e., Vb and V 1st_charge2. Herein, the pixel part  120  is charged to be Va by the previous data (n−1 data). Therefore, when the first and second charge signals are supplied, the pixel part  120  can be pre-charged to the optimal voltage value. 
         [0036]    The data output part  151  outputs the data signals and the second charge signal to the converter  155  and outputs the first charge signal to the switch part  160  through the first charge output part  154 . 
         [0037]    The converter  155  converts the digital signals, i.e., the data signals and the second charge signal, into analog signals, i.e., current, and outputs it to the switch part  160  based on the control signal of the controller. 
         [0038]    When the third switch SW 3  is turned on based on the control signal of the controller, the first charge signal is supplied to the pixel part  120  through the first charge output part  154 . Herein, the controller can supply the first charge signal to the pixel part  120  by turning on a switch connected to a selected voltage value among the voltage values of the first charge output part  154 . Subsequently, when the second switch SW 2  is turned on, the second charge signal is supplied to the pixel part  120  and the pixel part  120  is charged with an ideal charge value. When the first switch SW 1  is turned on based on the control signal of the controller, data current is supplied to the pixel part  120 . Accordingly, the pixel part  120  can display image corresponding thereto. 
         [0039]    As described above, the flat panel display suggested in the first embodiment of the present invention can supply the optimal charge value corresponding to the data signal to the pixel part  120 . Therefore, power consumption is reduced, and exact image corresponding to the data signals can be represented to thereby improve image quality of a screen. 
         [0040]      FIG. 6  is a block view describing a data driver of a flat panel display according to another embodiment of the present invention. 
         [0041]    Referring to  FIG. 6 , the data driver  250  comprises a data output part  251 , a data processing part  252 , and a converter  255 . 
         [0042]    The data output part  251  receives digital data signals from the outside and transmits them to the data processing part  252 . The data processing part  252  processes the data signals transmitted from the data output part  251  to thereby generate charge signals. The charge signals comprise a first charge signal and the second charge signal. 
         [0043]    The charge signal may be supplied before the data signals are supplied to the pixel part (P). The pre-charge signal can be obtained by processing the data signals and calculating the optimal value. 
         [0044]    Herein, the data processing part  252  may comprise the lookup table  253  and a first charge output part  254 . The lookup table  253  stores ideal charge values corresponding to the data signals, and the first charge output part  254  comprises a plurality of preset voltage values. The data processing part  252  receives the data signals, determines an ideal charge value for data signals based on the lookup table  153 , selects a voltage value which is closest to the ideal voltage value in the first charge output part  254 , and outputs a first charge signal. Then, it generates a second charge signal corresponding to the difference between the ideal charge value and the first charge signal. 
         [0045]    The converter  255  converts the data signals transmitted from the data processing part  252  or the second charge signal into current. In short, it converts digital signals into analog signals. 
         [0046]    The driving part  240  may further comprise a switch part  260 . The switch part  260  is connected to a controller (not shown) and the data driver  250  and optionally supplies the data signals, the first charge signal, and the second charge signal to the pixel part  220 . The switch part  260  comprises a first switch SW 1  and a second switch SW 2  between the converter  255  and the pixel part  220 . The data signals may be supplied to the pixel part  220  through the first switch SW 1 , whereas the second charge signal may be supplied to the pixel part  220  through the second switch SW 2 . The switch part  260  may comprise a current mirror  265  and a third switch SW 3  interposed between the current mirror  265  and the pixel part  220 . The current mirror  265  is connected to one end of the second switch SW 2  and one end of the third switch SW 3 . 
         [0047]    Herein, the third switch SW 3  can discharge pixel parts as much as the second charge signal by comprising the current mirror  265  connected to a ground voltage. 
         [0048]    The second and third switches SW 2  and SW 3  may comprise a booster to thereby quickly perform pre-charging or discharging. The switch part  260  may further comprise a fourth switch SW 4  interposed between the first charge output part  254  and the pixel part  220 . The fourth switch SW 4  may comprise a plurality of switches connected to a plurality of voltage values determined in the first charge output part  254 . 
         [0049]      FIG. 7  is a graph illustrating the relationship between a pixel current and a pre-charge voltage to describe a driving method of a flat panel display according to an embodiment of the present invention. The driving method of a flat panel display suggested in the embodiment of the present invention will be described with reference to  FIGS. 3 ,  6  and  7  hereinafter. Herein, it is assumed that the voltage value set in the first charge output part  254  has four steps, i.e., V 1st_charge0, 1, 2 and 3. 
         [0050]    When a control signal is supplied from the controller (not shown) to the driving part  240 , the scan driver  245  supplies a scan signal to the pixel part  220  through a scan line  230 A. The data output part  251  of the data driver  250  supplies the data signals transmitted from the outside to the data processing part  252 , and the data processing part  252  processes the received data signals to thereby generate the first and second charge signals corresponding to the data signals. 
         [0051]    To describe the generation of the first and second charge signals more in detail, when data signals are supplied from the data output part  251  to the data processing part  252 , the data processing part  252  determines an ideal charge value for the data signals based on the lookup table  253 . In  FIG. 7 , the ideal charge value is Vb. Subsequently, the data processing part  252  selects and outputs a value which is smaller than the ideal charge value and closest to the ideal charge value in the first charge output part  254 . Accordingly, the first charge signal is determined to be V 1st_charge3. The data processing part  252  generates the second charge signal (ΔV) which corresponds to the difference between the ideal charge value and the first charge signal, i.e., Vb and V 1st_charge3. Referring to  FIG. 7  herein, the sub-pixels are charged to be Va by the data (n−1 data) supplied to the previous frame. Therefore, when the first and second charge signals are supplied, the pixel part  220  can be discharged to the optimal voltage value. 
         [0052]    The data output part  251  outputs the data signals and the second charge signal to the converter  255  and outputs the first charge signal to the switch part  260  through the first charge output part  254 . 
         [0053]    The converter  255  converts the digital signals, i.e., the data signals and the second charge signal, into analog signals, i.e., current, and outputs it to the switch part  260  based on the control signal of the controller. 
         [0054]    When the fourth switch SW 4  is turned on based on the control signal of the controller, the first charge signal is supplied to the pixel part  220  through the first charge output part  254 . Herein, the controller can supply the first charge signal to the pixel part  220  by turning on a switch connected to a selected voltage value among the voltage values of the first charge output part  254 . Subsequently, when the third switch SW 3  is turned on, the second charge signal is supplied to the current mirror  265  and thus the pixel part  220  is discharged as much as an amount corresponding to the second charge signal through the third switch SW 3 . Herein, since the first charge signal is larger than the ideal charge value, the second charge signal becomes a discharge signal. 
         [0055]    When the ideal charge value is larger than the first charge signal, the second charge signal becomes a pre-charge signal. In this case, the second switch SW 2  is turned on and current corresponding to the second charge signal is supplied to the pixel part  220 . 
         [0056]    Subsequently, when the first switch SW 1  is turned on based on a control signal of the controller, data current is supplied to the pixel part  220  and the pixel part  220  represents image corresponding to the data current. 
         [0057]    As described above, the flat panel display suggested in the second embodiment of the present invention can supply the ideal charge value corresponding to the data signal through the data processing part  252 . Therefore, power consumption is reduced, and exact image corresponding to the data signals can be represented to thereby improve image quality of a screen.