Patent Publication Number: US-7714811-B2

Title: Light-emitting device and method of driving the same

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention generally relates to light-emitting devices, and more particularly to an electroluminescent device and a method of driving the same. 
   2. Description of the Related Art 
     FIG. 1  shows a first related-art organic electroluminescent device. This device includes a panel  100 , a controlling circuit  102 , a scan driving circuit  104 , a discharge circuit  106 , a precharge circuit  108 , and a data driving circuit  110 . 
   The panel  100  includes a plurality of sub-pixels (E 11  to E 44 ) formed in an area of crossed data lines (D 1  to D 4 ) and scan lines (S 1  to S 4 ). Each sub-pixel corresponds to a red sub-pixel, a green sub-pixel, or a blue sub-pixel, and each pixel comprises red, green, and blue (RGB) sub-pixels. 
   The controlling circuit  102  receives display data input from an external source. The display data may, for example, be RGB data. Circuit  102  controls operation of the elements in the organic electroluminescent device by using the received display data. The scan driving circuit  104  is formed in one direction of the panel  100 , and transmits in sequence scan signals to the scan lines (S 1  to S 4 ). 
   The discharge circuit  106  includes a switch (SW) and a zener diode (ZD). The switch (SW) is turned on or off by a control signal from the controlling circuit  102 . For example, when the data lines (D 1  to D 4 ) are discharged, the switch (SW) is turned on. As a result, the data lines (D 1  to D 4 ) are connected to the zener diode ZD, and a charge on the data lines (D 1  to D 4 ) is discharged up to a zener voltage of the zener diode (ZD). 
   The precharge circuit  108  applies a precharge current corresponding to the display data to the data lines (D 1  to D 4 ) in accordance with control of the controlling circuit  102 . The data driving circuit  110  applies a data current corresponding to the display data to the data lines (D 1  to D 4 ) in accordance with control of the controlling circuit  102 . 
     FIG. 2A  and  FIG. 2B  show circuits for driving the organic electroluminescent device of  FIG. 1 ,  FIG. 2C  is a timing diagram showing how the pixels of  FIG. 2A  and  FIG. 2B  are controlled to emit light. A first resistance (RS) between the outmost sub-pixel and ground has a value of 10Ω. A second resistor (RP) between sub-pixels has a value of 2Ω. Moreover, each of pixel (E 41 ) and pixel (E 42 ) emits light having a brightness corresponding to the data current of 3 amps. Further, sub-pixels (E 11 , E 21  and E 31 ) do not emit light. In addition, each of sub-pixels (E 12 , E 22  and E 32 ) emit light having a brightness corresponding to the data current of 1 amp. 
   To cause sub-pixels E 11  to E 41  along scan line S 1  to emit light, precharge circuit  108  applies a precharge current corresponding to the display data to the E 11  to E 41  sub-pixels. (See  FIG. 2A .) As a result, a charge corresponding to a second voltage (V 2 , default precharge voltage) is precharged to the E 41  sub-pixel during a first precharge time (pcha 1 ), as shown in  FIG. 2C . 
   Subsequently, data currents (I 11  to I 41 ), which are 0, 0, 0, and 3 amps respectively, are applied to the data lines (D 1  to D 4 ). In this case, an anode voltage (VA 41 ) of the E 41  sub-pixel is increased up to a third voltage (V 3 ), corresponding to the sum of a cathode voltage (VC 41 ) and a voltage of 4V corresponding to a data current of 3 amps during T 1  time. Then, the anode voltage (VA 41 ) reaches a stable third voltage (V 3 ) after a certain time. Here, the cathode voltage (VC 41 ) is the whole current (sum of 0, 0, 0 and 3 amps) passing through the first scan line (S 1 ) times a resistor of the scan line (sum of 10, 2, 2 and 2Ω), i.e. 48V, and thus V 3  is 52V. Accordingly, the E 41  sub-pixel emits a light having gray scale corresponding to 4V, i.e., the difference between the anode voltage (VA 41 ) and the cathode voltage (VC 41 ). 
   As shown in  FIG. 2B , the precharge circuit  108  applies a precharge current corresponding to the display data to the E 12  to E 42  sub-pixels. As a result, a charge corresponding to the second voltage (V 2 , default precharge voltage) is precharged to the E 42  sub-pixel during a second precharge time (pcha 2 ), as further shown in  FIG. 2C . 
   Subsequently, data currents (I 12  to I 42 ), which respectively correspond to 1, 1, 1, and 3 amps, are applied to data lines (D 1  to D 4 ). In this case, an anode voltage (VA 42 ) of the E 42  pixel is increased up to a fourth voltage (V 4 ) corresponding to the sum of a cathode voltage (VC 42 ) and the voltage of 4V corresponding to the data current of 3 amps during T 2  time. Then, the anode voltage (VA 42 ) reaches a stable fourth voltage (V 4 ) after a certain time. Here, the cathode voltage (VC 42 ) is the whole current (sum of 1, 1, 1 and 3 amps passing through the second scan line (S 2 ) times the resistor of the scan line (sum of 10, 2, 2 and 2Ω), i.e. 96V, and thus V 4  is 100V. 
   In summary, the difference of the stabilized anode voltage (VA 42 ) of the E 42  sub-pixel and the precharge voltage (V 2 ) is higher than that of the stabilized anode voltage (VA 41 ) and the precharge voltage (V 2 ). Hence, T 2  is bigger than T 1 . As a result, the consumed amount of charge to stabilize anode voltage (VA 42 ) in the E 42  sub-pixel is higher than is required to stabilize anode voltage (VA 41 ) in the E 41  sub-pixel, as shown in  FIG. 2C . Accordingly, the E 42  sub-pixel is designed to emit light at the same gray scale level as the E 41  sub-pixel, but in reality emits light having a gray scale level smaller than the E 41  sub-pixel. This phenomenon is often referred to as a cross-talk phenomenon. 
     FIG. 3  shows a second related-art organic electroluminescent device. This device includes a panel  300 , a controlling circuit  302 , a first scan driving circuit  304 , a second scan driving circuit  306 , a discharge circuit (e.g., a circuit to ground), a precharge circuit  310 , and a data driving circuit  312 . (Since the elements of this embodiment except the first scan driving circuit  304  and the second scan driving circuit  306  are the same as those of the first embodiment, any further detailed descriptions concerning the same elements will be omitted.) 
   The first scan driving circuit  304  transmits first scan signals to one group of scan lines (S 1  and S 3 ) in one direction of the panel. The second driving circuit  306  transmits second scan signals to remaining ones of the scan lines (S 2  and S 4 ) in other direction of the panel. As in the first related-art organic electroluminescent device, the cross-talk phenomenon occurs in the second related-art organic electroluminescent device. Also, the light-emitting process in the second device is similar to the device, and thus any further detailed descriptions concerning the process will be omitted. 
   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 
   Another object of the present invention is to prevent cross-talk. 
   These and other objects and advantages are achieved by providing a light-emitting device which, according to one embodiment of the present invention, includes a plurality of sub-pixels formed in areas of crossed data lines and scan lines, a precharge controlling circuit, and a precharge circuit. The precharge controlling circuit transmits a precharge controlling signal in accordance with display data inputted from an external source. The precharge circuit applies a precharge current corresponding to display data and resistance of the scan line to the data lines in accordance with the precharge controlling signal transmitted from the precharge controlling circuit. 
   Preferably, the amount of the precharge current equals the amount of current corresponding to the sum of a cathode voltage of pixel and a voltage corresponding to the display data. 
   Additionally, the light-emitting device may include a scan driving circuit for transmitting scan signals to the scan lines in one direction. 
   According to a variation, the light-emitting device may include a first scan driving circuit for transmitting first scan signals to a part of the scan lines and a second scan driving circuit for transmitting second scan signals to the other scan lines. 
   The precharge circuit may include a digital-analog converter (DAC). 
   Additionally, the precharge controlling circuit may store the scan line resistance, and calculate an amount of the precharge current through the scan line resistance and the display data. 
   In accordance with another embodiment, the present invention provides a light-emitting device having a plurality of sub-pixels formed in areas of crossed data lines and scan lines, a data converting circuit, and a data driving circuit. The data converting circuit converts display data inputted from the outside into conversion data corresponding to a resistance of the scan line. The data driving circuit applies data current corresponding to the conversion data transmitted from the data converting circuit to the data lines. 
   Additionally, the light-emitting device may include a discharge circuit for discharging the data lines to a certain discharge voltage. 
   According to one variation, the light-emitting device may include a discharge circuit for discharging the data lines to a discharge level corresponding to the conversion data. Such a discharge circuit may include a D/A converter for outputting a level voltage corresponding to the conversion data, and a buffer for buffering the level voltage output from the D/A converter to generate a discharge voltage. 
   Additionally, the data converting circuit may include a calculating circuit for calculating a cathode voltage of the pixel corresponding to the display data, and a look-up circuit for transmitting conversion data corresponding to the calculated cathode voltage to the data driving circuit. 
   Additionally, the light-emitting device may include a precharge circuit for applying a precharge current corresponding to the display data to the data lines, and a controlling circuit for controlling operation of the data converting circuit, the data driving circuit, and the precharge circuit. 
   A method of driving a light-emitting device having a plurality of sub-pixels formed in areas of crossed data lines and scan lines according to one embodiment of the present invention includes: calculating an amount of precharge current using display data input from an external source and a resistance of the scan line (scan line resistance), and applying precharge current based on the calculated amount to the data lines. Preferably, the amount of the precharge current equals the amount of current corresponding to the sum of a cathode voltage of sub-pixel and a voltage corresponding to the display data. 
   In accordance with another embodiment, the present invention provides a method of driving a light-emitting device including sub-pixels formed in areas of crossed data lines and scan lines includes: converting display data input from an external source into conversion data corresponding to a resistance of the scan line (scan line resistance), and applying data current corresponding to the conversion data to the data lines. 
   Additionally, the method may include discharging the data lines to a discharge level corresponding to the conversion data. The data lines may be discharged by outputting a level voltage corresponding to the conversion data and buffering the outputted level voltage to generate a discharge voltage. 
   Additionally, the converting the display data may include calculating a cathode voltage of sub-pixel corresponding to the display data and generating the conversion data corresponding to the calculated cathode voltage. The generated conversion data may correspond to the cathode voltage of data stored in a look-up table. 
   As described above, in a light-emitting device and a method of driving the same according to the present invention, a precharge current is applied to data lines based on the cathode voltage of pixels (or sub-pixels) and thus a cross-talk phenomenon is avoided in the panel. In addition, according to another embodiment, data current is applied to data lines based on the cathode voltage of pixels and thus cross-talk phenomenon is avoided in the panel. 
   Additional objects, advantages, 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 diagram showing first related-art light-emitting device; 
       FIG. 2A  and  FIG. 2B  are diagrams of circuits used in a process of driving the light-emitting device of  FIG. 1 , and  FIG. 2C  is a timing diagram showing a light-emitting process of the pixels of  FIG. 2A  and  FIG. 2B ; 
       FIG. 3  is a diagram showing a second related-art light-emitting device; 
       FIG. 4  is a diagram of a light-emitting device according to a first embodiment of the present invention; 
       FIG. 5A  is a circuit view relating to a process of driving the light-emitting device of  FIG. 4  according to one embodiment of the present invention,  FIG. 5B  is a circuit view relating to a process of driving the light-emitting device of  FIG. 4  according to another embodiment of the present invention, and  FIG. 5C  is a timing diagram relating to the light-emitting process in  FIG. 5A  and  FIG. 5B ; 
       FIG. 6  is a circuit view relating to a light-emitting process of the light emitting device of  FIG. 4  according to another embodiment of the present invention; 
       FIG. 7  is a diagram of a light-emitting device according to a second embodiment of the present invention; 
       FIG. 8  is a diagram of a light-emitting device according to a third embodiment of the present invention; 
       FIG. 9  is a diagram of a data converting circuit that may be included in the device of  FIG. 8 ; 
       FIG. 10A  is a circuit view relating to a process of driving the light-emitting device of  FIG. 8  according to one embodiment of the present invention,  FIG. 10B  is a circuit diagram relating to a process of driving the light-emitting device of  FIG. 8  according to another embodiment of the present invention, and  FIG. 10C  is a timing diagram relating to light-emitting process associated with  FIG. 10A  and  FIG. 10B ; 
       FIG. 11  is a diagram of a light-emitting device according to a fourth embodiment of the present invention; and 
       FIG. 12  is a diagram of a light-emitting device according to a fifth embodiment of the present invention. 
   

   DETAILED DESCRIPTION OF EMBODIMENTS AND/OR BEST MODE 
     FIG. 4  is a diagram of a light-emitting device, preferably an organic electroluminescent device, according to a first embodiment of the present invention. This device includes a panel  400 , a scan driving circuit  402 , a controlling circuit  404 , a precharge controlling circuit  406 , a precharge circuit  408 , and a data driving circuit  410 . The panel  400  includes a plurality of sub-pixels (E 11  to E 44 ) formed in areas of crossed data lines (D 1  to D 4 ) and scan lines (S 1  to S 4 ). The scan driving circuit  402  is formed along one side of the panel and transmits, preferably in sequence, scan signals to the scan lines (S 1  to S 4 ). 
   The controlling circuit  404  stores display data input from an external source. This data may, for example, from the RGB data. The controlling circuit  404  controls operation of the scan driving circuit  402 , precharge controlling circuit  406 , precharge circuit  408 , and data driving circuit  410  using the stored display data. The precharge controlling circuit  406  calculates the amount of precharge current to be applied to the data lines (D 1  to D 4 ) under control of the controlling circuit  406 , and transmits a precharge controlling signal having information of the calculated amount to the precharge circuit  408 . 
   The precharge circuit  408  applies the precharge current corresponding to the calculated amount to the data lines (D 1  to D 4 ) in accordance with the precharge controlling signal transmitted from the precharge controlling circuit  406 . The precharge circuit  408 , according to one embodiment of the present invention, includes a digital-analog converter (DAC) and generates the precharge current having one of multi-levels by using the DAC. The data driving circuit  410  applies a data current corresponding to the display data transmitted from the controlling circuit  404  to the data lines (D 1  to D 4 ). As a result, the sub-pixels (E 11  to E 44 ) emit a light having a certain wavelength. 
     FIG. 5A  is a circuit view relating to a process of driving the light-emitting device of  FIG. 4  according to one embodiment of the present invention.  FIG. 5B  is a circuit view relating to a process of driving the light-emitting device of  FIG. 4  according to another embodiment of the present invention, and  FIG. 5C  is a timing diagram relating to the light-emitting process in  FIG. 5A  and  FIG. 5B . A first resistance (RS) between one sub-pixel and ground is assumed to have a predetermined value. For illustrative purposes, this value may be 10Ω. Also, the aforementioned sub-pixel will be assumed to be the outermost pixel, however another sub-pixel may alternatively be used in accordance with the present invention. 
   Additionally, a second resistor (RP) between sub-pixels is assumed to have a predetermined value, e.g., 2Ω. Each of sub-pixel (E 41 ) and sub-pixel (E 42 ) emits light having a brightness corresponding to a predetermined data current, e.g., 3 amps. Non-selected sub-pixels (E 11 , E 21  and E 31 ) do not emit light. In addition, each of sub-pixels (E 12 , E 22  and E 32 ) emits light having a brightness corresponding to a predetermined data current, e.g., 1 amp. 
   A process of controlling sub-pixels (E 11  to E 41 ) to emit light along first scan line (S 1 ) will now be described. Referring to  FIG. 5A , the precharge controlling circuit  406  calculates a cathode voltage (VC 41 ) using information relating to resistors (RS and RP) stored therein and the display data transmitted from the controlling circuit  404 . In other words, the precharge controlling circuit  406  detects the magnitude of data currents (I 11  to I 41 ) through the display data. Here, each of the detected data currents (I 11  to I 41 ) may have the following non-limiting values, respectively: 0, 0, 0 and 3 amps. Subsequently, the precharge controlling circuit  406  calculates the cathode voltage (VC 41 , e.g., 48V) which is the whole current (sum of 0, 0, 0 and 3A) times a resistance of the scan line (sum of 10, 2, 2 and 2Ω; hereinafter referred to as “scan line resistance”). 
   Then, the precharge controlling circuit  406  transmits a precharge controlling signal having information relating to the calculated cathode voltage (VC 41 ) to the precharge circuit  408 . Subsequently, the precharge circuit  408  applies a precharge current to sub-pixel (E 41 ) through the fourth data line (D 4 ) during a first precharge time (pcha 1 ) in accordance with the transmitted precharge controlling signal. As a result, a charge corresponding to the sum (49V) of the cathode voltage (VC 41 , e.g., 48V) and default precharge current (for example, 1V) is precharged to the sub-pixel (E 41 ). Here, the default precharge current may be related to a voltage corresponding to a precharge current in case the cathode voltage (VC 41 ) and data current are 0V and 3A, respectively. 
   Then, the data driving circuit  410  applies data currents (I 11  to I 41 ) corresponding to the display data transmitted from the controlling circuit  404  to the data lines (D 1  to D 4 ) during low logic time of a first scan signal (PS 1 ). As a result, an anode voltage (VA 41 ) of sub-pixel (E 41 ) is stabilized as 52V (e.g., saturation voltage) after T 1  time from finish of the precharge, as shown in  FIG. 5C . Accordingly, the sub-pixel (E 41 ) emits light having gray scale level corresponding to 4V (52V-48V). 
   A light-emitting process of sub-pixels (E 12  to E 42 ) corresponding to second scan line (S 2 ) will now be described. Referring to  FIG. 5B , the precharge controlling circuit  406  calculates a cathode voltage (VC 42 ) using information based on resistors (RS and RP) stored therein and the display data transmitted from the controlling circuit  404 . In other words, the precharge controlling circuit  406  detects the magnitude of data currents (I 12  to I 42 ) through the display data. Here, the detected data currents (I 12  to I 42 ) may be, for example, 1, 1, 1 and 3A respectively. Subsequently, the precharge controlling circuit  406  calculates the cathode voltage (VC 42 , e.g., 96V) which is the whole current (sum of 1, 1, 1 and 3A) times the scan line resistance (sum of 10, 2, 2 and 2Ω). 
   Then, the precharge controlling circuit  406  transmits a precharge controlling signal having information concerning the calculated cathode voltage (VC 42 ) to the precharge circuit  408 . Subsequently, the precharge circuit  408  applies a precharge current to sub-pixel (E 42 ) through the fourth data line (D 4 ) during a second precharge time (pcha 2 ) in accordance with the transmitted precharge controlling signal. As a result, a charge corresponding to the sum (97V) of the cathode voltage (VC 42 , e.g., 96V) and default precharge current (for example, 1V) is precharged to sub-pixel (E 42 ). Here, the default precharge current may relate to a voltage corresponding to a precharge current in case the cathode voltage (VC 42 ) and data current are 0V and 3A respectively. 
   Then, the data driving circuit  410  applies data currents (I 12  to I 42 ) corresponding to the display data transmitted from the controlling circuit  404  to the data lines (D 1  to D 4 ) during low logic time of a second scan signal (PS 2 ). Here, the cathode voltage (VC 42 ) is 96V, and thus the anode voltage (VA 42 ) should be augmented up to 100V as shown in  FIG. 5C , so that sub-pixel (E 42 ) emits light having gray scale level corresponding to 4V. In this case, since a precharge voltage (V 4 ) corresponding to sub-pixel (E 42 ) is 97V, the anode voltage (VA 42 ) is stabilized (e.g., reaches saturation voltage) after an increase of 3V. Accordingly, as in sub-pixel (E 41 ), the anode voltage (VA 42 ) is stabilized (e.g., reaches saturation voltage) after a T 1  time from the finish of the precharge. 
   In summary, in the light-emitting device of the present invention, sub-pixel (E 41 ) and sub-pixel (E 42 ) are stabilized (e.g., reach saturation or stabilization voltage) after a time T 1  taken from the finish of the precharge. Hence, in the light-emitting device of the present invention, the consumed amount of charge during dtl time is identical to that during dt 2  time, unlike the related-art. Accordingly, sub-pixel (E 41 ) and sub-pixel (E 42 ) have identical brightnesses, and therefore a cross-talk phenomenon does not occur in the light-emitting device of the present invention. 
     FIG. 6  is a circuit view relating to a light-emitting process performed for the light emitting device of  FIG. 4  according to another embodiment of the present invention. Here, the precharge voltage will be generalized with  FIG. 6 . 
   The following preferably sets forth the precharge voltages:
         (1) a first precharge voltage (V PRE-CHARGE-RED (n)) corresponding to red light may be given by V CR (n)+V default-precharge-red (DR(n));   (2) a second precharge voltage (V PRE-CHARGE-GREEN (n)) corresponding to green light may be given by V CG (n)+V default-precharge-green (DR(n)); and   (3) a third precharge voltage (V PRE-CHARGE-blue (n)) corresponding to blue light may be given by V CG (n)+V default-precharge-blue (DR(n)).       

   Here, V CR (n), V CG (n) and V CB (n) are cathode voltages corresponding to red, green and blue sub-pixel, respectively. Also, V default-precharge-red (DR(n)), V default-precharge-green (DR(n)) and V default-precharge-blue (DR(n)) are precharge voltages corresponding to red, green and blue display data, respectively, in case the cathode voltage is 0V. In other words, the light-emitting device of the present invention applies the precharge current to the data lines (D 1  to D 4 ) according to the cathode voltage. A method of calculating the cathode voltage is described through the examples in  FIG. 5A  to  FIG. 5C . 
   A light-emitting device, according to another embodiment of the present invention, is plasma display panel (PDP) or liquid crystal display (LCD) in which a precharge current is applied to data lines according to an electrode voltage for a cell. 
     FIG. 7  is a diagram of a light-emitting device, preferably an organic electroluminescent device, according to a second embodiment of the present invention. This device includes a panel  700 , a first scan driving circuit  702 , a second scan driving circuit  704 , a controlling circuit  706 , a precharge controlling circuit  708 , a precharge circuit  710 , and a data driving circuit  712 . The elements of this embodiment, except the first scan driving circuit  702  and the second scan driving circuit  704 , is preferably the same as those in the first embodiment. 
   In operation, the first scan driving circuit  702  provides first scan signals to one part (S 1  and S 3 ) of scan lines (S 1  to S 4 ) along one side or direction of the panel  700 . The second scan driving circuit  704  provides second scan signals to the other scan lines (S 2  and S 4 ) along another side or direction of the panel  700 . 
   As in the first embodiment, a precharge current may be applied to data lines (D 1  to D 4 ) according to a cathode voltage in the second embodiment. Also, the light-emitting process in the second embodiment may be similar to that in the first embodiment. 
     FIG. 8  is a diagram of a light-emitting device, preferably an organic electroluminescent device, according to a third embodiment of the present invention. This device includes a panel  800 , a controlling circuit  802 , a scan driving circuit  804 , a discharge circuit  806 , a precharge circuit  808 , a data converting circuit  810  and a data driving circuit  812 . The panel  800  includes a plurality of sub-pixels (E 11  to E 44 ) formed in areas of crossed data lines (D 1  to D 4 ) and scan lines (S 1  to S 4 ). 
   The controlling circuit  802  receives display data input from an external source, and controls operation of the elements in the light-emitting device. The display data may, for example, be RGB data. The scan driving circuit  804  is formed along one side or direction of the panel  800  and transmits, preferably in sequence, scan signals to the scan lines (S 1  to S 4 ) under control of the controlling circuit  802 . In other words, the scan driving circuit  804  may connect in sequence the scan lines (S 1  to S 4 ) to ground. 
   The discharge circuit  806  includes a switch (SW) and a discharge level circuitry  820 . The switch (SW) is turned on or off under control of the controlling circuit  802 . For example, the switch (SW) is turned on when data lines (D 1  to D 4 ) are discharged. As a result, data lines (D 1  to D 4 ) are connected to the discharge level circuitry  820 , and so a charge charged to the data lines (D 1  to D 4 ) is discharged to a certain level. The precharge circuit  808  applies a precharge current corresponding to the display data to data lines (D 1  to D 4 ) under control of the controlling circuit  802 . 
   The data converting circuit  810  converts the display data into conversion data corresponding to cathode voltages of sub-pixels (E 11  to E 44 ) under control of the controlling circuit  802 . In other words, since the cathode voltages of sub-pixels (E 11  to E 44 ) are affected by the scan line resistance of each of scan lines (S 1  to S 4 ), the data converting circuit  810  converts the display data into the conversion data in order to compensate the scan line resistance. In addition, the data converting circuit  810  provides the conversion data to the data driving circuit  812 . The data driving circuit  812  provides data current corresponding to the conversion data to the data lines (D 1  to D 4 ), and so the corresponding pixel to the data current emits a light. 
     FIG. 9  is a diagram of one type of data converting circuit that may be used in  FIG. 8 . This data converting circuit  810  includes calculating circuitry  900 , a memory  902 , and look-up circuitry  904 . The memory  902  stores resistances of the scan lines (S 1  to S 4 ). 
   The calculating circuitry  900  calculates a cathode voltage of a pixel corresponding to the scan line, and provides the calculated cathode voltage to the look-up circuitry  904 . Here, the cathode voltage is the scan line resistance times a data current corresponding to the display data. The look-up circuitry  904  includes a look-up table having at least one conversion data, and selects one of the conversion data included in the look-up table in accordance with the cathode voltage provided from the calculating circuitry  900 . Here, the selected data correspond to the cathode voltage. 
   Then, the look-up circuitry  904  provides the selected conversion data to the data driving circuit  812 . Here, the selected conversion data may not be precisely identical to the cathode voltage, and in that case, is most similar to the cathode voltage among the conversion data. Accordingly, the brightness of the pixels designed to emit the same brightness may be different according to scan lines, but such difference is not recognizable to a user of the panel  800 . 
     FIG. 10A  is a circuit view relating to a process of driving the light-emitting device of  FIG. 8  according to one embodiment of the present invention.  FIG. 10B  is a circuit diagram relating to a process of driving the light-emitting device of  FIG. 8  according to another embodiment of the present invention, and  FIG. 10C  is a timing diagram relating to light-emitting process associated with  FIG. 10A  and  FIG. 10B . In this circuit, a first resistor (RS) is located between one sub-pixel (e.g., the outermost sub-pixel) and ground and has a predetermined value, e.g., 10Ω. Additionally, a second resistor (RP) between sub-pixels has a predetermined value, e.g., 2Ω. Moreover, each of sub-pixel (E 41 ) and sub-pixel (E 42 ) emits light having brightness based on a predetermined data current, e.g., 3 amps. Further, sub-pixels (E 11 , E 21  and E 31 ) may not emit light under certain circumstances, e.g., based on the video being displayed. In addition, each of sub-pixels (E 12 , E 22  and E 32 ) emit light having brightness corresponding to a data current of, for example, 1 amp. 
   A process of emitting a light in sub-pixels (E 11  to E 41 ) corresponding to a first scan line (S 1 ) will now be described. Referring to  FIG. 10A , the precharge circuit  808  applies a precharge current corresponding to the display data to the data lines (D 1  to D 4 ). Thus, a charge corresponding to a second voltage (V 2 ) is precharged to data lines (D 1  to D 4 ). 
   Subsequently, calculating circuitry  900  calculates a cathode voltage (VC 41 ) using information based on resistors (RS and RP) stored in memory  902  and the display data transmitted from the controlling circuit  802 . In other words, the calculating circuitry  900  detects data currents (I 11  to I 41 ) through the display data. Here, each of the detected data currents (I 11  to  141 ) is 0, 0, 0 and 3 amps. 
   Then, the calculating circuitry  900  calculates the cathode voltage (VC 41 , e.g., 48V) which is the whole current (sum of 0, 0, 0 and 3A) passing a first scan line (S 1 ) times the scan line resistance (sum of 10, 2, 2 and 2Ω). Subsequently, calculating circuitry  900  transmits a first calculation signal having information of the calculated cathode voltage (VC 41 ) to the look-up circuitry  904 . The look-up circuitry  904  then selects conversion data corresponding to the cathode voltage (VC 41 ) in the look-up table and provides the selected conversion data to the data driving circuit  812 . 
   The data driving circuit  812  provides data currents (I 11  to I 41 ), corresponding to the conversion data provided from the look-up circuitry  904 , to the data lines (D 1  to D 4 ) during low logic time of a first scan signal (PS 1 ). As a result, an anode voltage (VA 41 ) of the sub-pixel (E 41 ) is stabilized to V 3  (e.g., reaches saturation voltage) after a certain time measured from the finish of the precharge, as shown in  FIG. 10C . In case the voltage corresponding to 3A is 4V, the anode voltage (VA 41 ) of sub-pixel (E 41 ) is stabilized to 52V, each reaches saturation voltage. Accordingly, the sub-pixel (E 41 ) may emit a light having a gray scale level corresponding to 4V (52V-48V). 
   A light-emitting process of sub-pixels (E 12  to E 42 ) corresponding to a second scan line (S 2 ) will now be described. Referring to  FIG. 10B , the precharge circuit  808  applies a precharge current corresponding to the display data to data lines (D 1  to D 4 ), and thus a charge corresponding to the second voltage (V 2 ) is precharged to data lines (D 1  to D 4 ). Subsequently, the calculating circuitry  900  calculates a cathode voltage (VC 42 ) using information based on resistors (RS and RP) stored in the memory  902  and the display data transmitted from the controlling circuit  802 . In other words, the calculating circuitry  900  detects data currents (I 12  to I 42 ) through the display data. Here, each of the detected data currents (I 12  to  142 ) may be 1, 1, 1 and 3 amps. 
   The calculating circuitry  900  calculates the cathode voltage (VC 42 , e.g., 96V) which is the whole current (sum of 1, 1, 1 and 3A) passing a second scan line (S 2 ) times the scan line resistance (sum of 10, 2, 2 and 2Ω). Subsequently, circuitry  900  provides a second calculation signal having information concerning the calculated cathode voltage (VC 42 ) to the look-up circuitry  904 . The look-up circuitry  904  selects conversion data corresponding to the cathode voltage (VC 42 ) in the look-up circuitry, and then transmits the selected conversion data to the data driving circuit  812 . 
   The data driving circuit  812  applies data currents (I 12  to I 42 ) corresponding to the conversion data transmitted from the look-up circuit  904  to the data lines (D 1  to D 4 ) during low logic time of a second scan signal (PS 2 ). As a result, an anode voltage (VA 42 ) of sub-pixel (E 42 ) is stabilized to V 4  (e.g., reaches saturation voltage) after a certain time measured from the finish of the precharge, as shown in  FIG. 10C . In case the voltage corresponding to 3A is 4V, anode voltage (VA 42 ) of pixel (E 42 ) is stabilized to 100V, e.g., reaches saturation voltage. Here, the cathode voltage (VC 42 ) is higher than the cathode voltage (VC 41 ), and thus the data current (I 42 ) higher than the data current (I 41 ) is applied to the fourth data line (D 4 ), as shown in  FIG. 10C . 
   In other words, the slope of data current (I 42 ) as shown in part B is higher than the slope of the data current (I 41 ) as shown in part A. Hence, the consumed amount of charge for stabilizing the data current (I 42 ) in the sub-pixel (E 42 ) is the same as, or similar to, that needed to stabilize the data current (I 41 ) in the sub-pixel (E 41 ). 
   In summary, in the light-emitting device of the present invention, the slope of the data current is changed in accordance with the cathode voltage of the pixel, and thus any difference of brightness does not occur between pixels designed to emit same brightness. Accordingly, unlike related-art light-emitting devices, a cross-talk phenomenon does not occur on the panel of the present light-emitting device. 
     FIG. 11  is a diagram of a light-emitting device, preferably an organic electroluminescent device, according to a fourth embodiment of the present invention. This device includes a panel  1000 , a controlling circuit  1102 , a scan driving circuit  1104 , a discharge circuit  1106 , a precharge circuit  1108 , a data converting circuit  1110  and a data driving circuit  1112 . The elements of this embodiment, except the discharge circuit  1106 , may be the same as those of the third embodiment. 
   The discharge circuit  1106  includes a switch (SW), a digital-to-analog (D/A) converter  1120 , and a buffer  1122 . The switch (SW) is turned on during the discharge time. The D/A converter  1120  transmits a first discharge voltage corresponding to one level of a plurality of discharge levels to the buffer  1122  under control of the controlling circuit  1102 . 
   The buffer  1122  buffers the first discharge voltage transmitted from the D/A converter  1120 , to output a second discharge voltage of preferably a constant magnitude. As a result, a charge charged to the data lines (D 1  to D 4 ) is discharged to the second discharge voltage during the discharge time. In other words, in the fourth embodiment, the discharge circuit  1106  has discharge levels unlike the third embodiment. 
   In summary, in the light-emitting device of the present invention, data current not precisely identical to the cathode voltage may be applied to the data lines (D 1  to D 4 ). In this case, controlling circuit  1106  compensates the non-identical data current by adjusting the discharge voltage to a certain level of unit. 
     FIG. 12  is a diagram of a light-emitting device, e.g., an organic electroluminescent device, according to a fifth embodiment of the present invention. This device includes a panel  1200 , a controlling circuit  1202 , a first scan driving circuit  1204 , a second scan driving circuit  1206 , a discharge circuit  1208 , a precharge circuit  1210 , a data converting circuit  1212 , and a data driving circuit  1214 . The elements of this embodiment, except the first scan driving circuit  1204  and the second scan driving circuit  1206 , may be the same as those in the second embodiment. 
   The first scan driving circuit  1204  provides first scan signals to some (S 1  and S 3 ) of the scan lines (S 1  to S 4 ) in one direction of the panel  1200 . The second scan driving circuit  1206  transmits second scan signals to remaining ones of the scan lines (S 2  and S 4 ) in other direction of the panel  1200 . Like the third embodiment, data current is applied to data lines (D 1  to D 4 ) according to the cathode voltage in the fifth embodiment. The light-emitting process of the fifth embodiment is similar to that of the third embodiment, and thus further detailed descriptions concerning the process will be omitted. 
   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. For example, the present invention may be used in or formed as a flexible display for electronic books, newspapers, magazines, etc., different types of portable devices, e.g., handsets, MP3 players, notebook computers, etc., vehicle audio applications, vehicle navigation applications, televisions, monitors, or other types of devices needing a display. 
   Further, 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.