Light-emitting device and method of driving the same

A light-emitting device avoids a cross-talk phenomenon. The device includes a precharge controlling circuit and a precharge circuit. The precharge controlling circuit provides a precharge controlling signal in accordance with display data input from an external source. The precharge circuit applies a precharge current corresponding to display data and a scan line resistance to the data lines in accordance with the precharge controlling signal transmitted from the precharge controlling circuit. As a result, precharge current is applied to data lines according to a pixel cathode voltage, and thus cross-talk occurs is eliminated or at least substantially reduced in the device.

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. 1shows a first related-art organic electroluminescent device. This device includes a panel100, a controlling circuit102, a scan driving circuit104, a discharge circuit106, a precharge circuit108, and a data driving circuit110.

The panel100includes a plurality of sub-pixels (E11to E44) formed in an area of crossed data lines (D1to D4) and scan lines (S1to S4). 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 circuit102receives display data input from an external source. The display data may, for example, be RGB data. Circuit102controls operation of the elements in the organic electroluminescent device by using the received display data. The scan driving circuit104is formed in one direction of the panel100, and transmits in sequence scan signals to the scan lines (S1to S4).

The discharge circuit106includes a switch (SW) and a zener diode (ZD). The switch (SW) is turned on or off by a control signal from the controlling circuit102. For example, when the data lines (D1to D4) are discharged, the switch (SW) is turned on. As a result, the data lines (D1to D4) are connected to the zener diode ZD, and a charge on the data lines (D1to D4) is discharged up to a zener voltage of the zener diode (ZD).

The precharge circuit108applies a precharge current corresponding to the display data to the data lines (D1to D4) in accordance with control of the controlling circuit102. The data driving circuit110applies a data current corresponding to the display data to the data lines (D1to D4) in accordance with control of the controlling circuit102.

FIG. 2AandFIG. 2Bshow circuits for driving the organic electroluminescent device ofFIG. 1,FIG. 2Cis a timing diagram showing how the pixels ofFIG. 2AandFIG. 2Bare 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 (E41) and pixel (E42) emits light having a brightness corresponding to the data current of 3 amps. Further, sub-pixels (E11, E21and E31) do not emit light. In addition, each of sub-pixels (E12, E22and E32) emit light having a brightness corresponding to the data current of 1 amp.

To cause sub-pixels E11to E41along scan line S1to emit light, precharge circuit108applies a precharge current corresponding to the display data to the E11to E41sub-pixels. (SeeFIG. 2A.) As a result, a charge corresponding to a second voltage (V2, default precharge voltage) is precharged to the E41sub-pixel during a first precharge time (pcha1), as shown inFIG. 2C.

Subsequently, data currents (I11to I41), which are 0, 0, 0, and 3 amps respectively, are applied to the data lines (D1to D4). In this case, an anode voltage (VA41) of the E41sub-pixel is increased up to a third voltage (V3), corresponding to the sum of a cathode voltage (VC41) and a voltage of 4V corresponding to a data current of 3 amps during T1time. Then, the anode voltage (VA41) reaches a stable third voltage (V3) after a certain time. Here, the cathode voltage (VC41) is the whole current (sum of 0, 0, 0 and 3 amps) passing through the first scan line (S1) times a resistor of the scan line (sum of 10, 2, 2 and 2Ω), i.e. 48V, and thus V3is 52V. Accordingly, the E41sub-pixel emits a light having gray scale corresponding to 4V, i.e., the difference between the anode voltage (VA41) and the cathode voltage (VC41).

As shown inFIG. 2B, the precharge circuit108applies a precharge current corresponding to the display data to the E12to E42sub-pixels. As a result, a charge corresponding to the second voltage (V2, default precharge voltage) is precharged to the E42sub-pixel during a second precharge time (pcha2), as further shown inFIG. 2C.

Subsequently, data currents (I12to I42), which respectively correspond to 1, 1, 1, and 3 amps, are applied to data lines (D1to D4). In this case, an anode voltage (VA42) of the E42pixel is increased up to a fourth voltage (V4) corresponding to the sum of a cathode voltage (VC42) and the voltage of 4V corresponding to the data current of 3 amps during T2time. Then, the anode voltage (VA42) reaches a stable fourth voltage (V4) after a certain time. Here, the cathode voltage (VC42) is the whole current (sum of 1, 1, 1 and 3 amps passing through the second scan line (S2) times the resistor of the scan line (sum of 10, 2, 2 and 2Ω), i.e. 96V, and thus V4is 100V.

In summary, the difference of the stabilized anode voltage (VA42) of the E42sub-pixel and the precharge voltage (V2) is higher than that of the stabilized anode voltage (VA41) and the precharge voltage (V2). Hence, T2is bigger than T1. As a result, the consumed amount of charge to stabilize anode voltage (VA42) in the E42sub-pixel is higher than is required to stabilize anode voltage (VA41) in the E41sub-pixel, as shown inFIG. 2C. Accordingly, the E42sub-pixel is designed to emit light at the same gray scale level as the E41sub-pixel, but in reality emits light having a gray scale level smaller than the E41sub-pixel. This phenomenon is often referred to as a cross-talk phenomenon.

FIG. 3shows a second related-art organic electroluminescent device. This device includes a panel300, a controlling circuit302, a first scan driving circuit304, a second scan driving circuit306, a discharge circuit (e.g., a circuit to ground), a precharge circuit310, and a data driving circuit312. (Since the elements of this embodiment except the first scan driving circuit304and the second scan driving circuit306are the same as those of the first embodiment, any further detailed descriptions concerning the same elements will be omitted.)

The first scan driving circuit304transmits first scan signals to one group of scan lines (S1and S3) in one direction of the panel. The second driving circuit306transmits second scan signals to remaining ones of the scan lines (S2and S4) 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

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.

DETAILED DESCRIPTION OF EMBODIMENTS AND/OR BEST MODE

FIG. 4is 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 panel400, a scan driving circuit402, a controlling circuit404, a precharge controlling circuit406, a precharge circuit408, and a data driving circuit410. The panel400includes a plurality of sub-pixels (E11to E44) formed in areas of crossed data lines (D1to D4) and scan lines (S1to S4). The scan driving circuit402is formed along one side of the panel and transmits, preferably in sequence, scan signals to the scan lines (S1to S4).

The controlling circuit404stores display data input from an external source. This data may, for example, from the RGB data. The controlling circuit404controls operation of the scan driving circuit402, precharge controlling circuit406, precharge circuit408, and data driving circuit410using the stored display data. The precharge controlling circuit406calculates the amount of precharge current to be applied to the data lines (D1to D4) under control of the controlling circuit406, and transmits a precharge controlling signal having information of the calculated amount to the precharge circuit408.

The precharge circuit408applies the precharge current corresponding to the calculated amount to the data lines (D1to D4) in accordance with the precharge controlling signal transmitted from the precharge controlling circuit406. The precharge circuit408, 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 circuit410applies a data current corresponding to the display data transmitted from the controlling circuit404to the data lines (D1to D4). As a result, the sub-pixels (E11to E44) emit a light having a certain wavelength.

FIG. 5Ais a circuit view relating to a process of driving the light-emitting device ofFIG. 4according to one embodiment of the present invention.FIG. 5Bis a circuit view relating to a process of driving the light-emitting device ofFIG. 4according to another embodiment of the present invention, andFIG. 5Cis a timing diagram relating to the light-emitting process inFIG. 5AandFIG. 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 (E41) and sub-pixel (E42) emits light having a brightness corresponding to a predetermined data current, e.g., 3 amps. Non-selected sub-pixels (E11, E21and E31) do not emit light. In addition, each of sub-pixels (E12, E22and E32) emits light having a brightness corresponding to a predetermined data current, e.g., 1 amp.

A process of controlling sub-pixels (E11to E41) to emit light along first scan line (S1) will now be described. Referring toFIG. 5A, the precharge controlling circuit406calculates a cathode voltage (VC41) using information relating to resistors (RS and RP) stored therein and the display data transmitted from the controlling circuit404. In other words, the precharge controlling circuit406detects the magnitude of data currents (I11to I41) through the display data. Here, each of the detected data currents (I11to I41) may have the following non-limiting values, respectively: 0, 0, 0 and 3 amps. Subsequently, the precharge controlling circuit406calculates the cathode voltage (VC41, 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 circuit406transmits a precharge controlling signal having information relating to the calculated cathode voltage (VC41) to the precharge circuit408. Subsequently, the precharge circuit408applies a precharge current to sub-pixel (E41) through the fourth data line (D4) during a first precharge time (pcha1) in accordance with the transmitted precharge controlling signal. As a result, a charge corresponding to the sum (49V) of the cathode voltage (VC41, e.g., 48V) and default precharge current (for example, 1V) is precharged to the sub-pixel (E41). Here, the default precharge current may be related to a voltage corresponding to a precharge current in case the cathode voltage (VC41) and data current are 0V and 3A, respectively.

Then, the data driving circuit410applies data currents (I11to I41) corresponding to the display data transmitted from the controlling circuit404to the data lines (D1to D4) during low logic time of a first scan signal (PS1). As a result, an anode voltage (VA41) of sub-pixel (E41) is stabilized as 52V (e.g., saturation voltage) after T1time from finish of the precharge, as shown inFIG. 5C. Accordingly, the sub-pixel (E41) emits light having gray scale level corresponding to 4V (52V-48V).

A light-emitting process of sub-pixels (E12to E42) corresponding to second scan line (S2) will now be described. Referring toFIG. 5B, the precharge controlling circuit406calculates a cathode voltage (VC42) using information based on resistors (RS and RP) stored therein and the display data transmitted from the controlling circuit404. In other words, the precharge controlling circuit406detects the magnitude of data currents (I12to I42) through the display data. Here, the detected data currents (I12to I42) may be, for example, 1, 1, 1 and 3A respectively. Subsequently, the precharge controlling circuit406calculates the cathode voltage (VC42, 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 circuit406transmits a precharge controlling signal having information concerning the calculated cathode voltage (VC42) to the precharge circuit408. Subsequently, the precharge circuit408applies a precharge current to sub-pixel (E42) through the fourth data line (D4) during a second precharge time (pcha2) in accordance with the transmitted precharge controlling signal. As a result, a charge corresponding to the sum (97V) of the cathode voltage (VC42, e.g., 96V) and default precharge current (for example, 1V) is precharged to sub-pixel (E42). Here, the default precharge current may relate to a voltage corresponding to a precharge current in case the cathode voltage (VC42) and data current are 0V and 3A respectively.

Then, the data driving circuit410applies data currents (I12to I42) corresponding to the display data transmitted from the controlling circuit404to the data lines (D1to D4) during low logic time of a second scan signal (PS2). Here, the cathode voltage (VC42) is 96V, and thus the anode voltage (VA42) should be augmented up to 100V as shown inFIG. 5C, so that sub-pixel (E42) emits light having gray scale level corresponding to 4V. In this case, since a precharge voltage (V4) corresponding to sub-pixel (E42) is 97V, the anode voltage (VA42) is stabilized (e.g., reaches saturation voltage) after an increase of 3V. Accordingly, as in sub-pixel (E41), the anode voltage (VA42) is stabilized (e.g., reaches saturation voltage) after a T1time from the finish of the precharge.

In summary, in the light-emitting device of the present invention, sub-pixel (E41) and sub-pixel (E42) are stabilized (e.g., reach saturation or stabilization voltage) after a time T1taken 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 dt2time, unlike the related-art. Accordingly, sub-pixel (E41) and sub-pixel (E42) have identical brightnesses, and therefore a cross-talk phenomenon does not occur in the light-emitting device of the present invention.

FIG. 6is a circuit view relating to a light-emitting process performed for the light emitting device ofFIG. 4according to another embodiment of the present invention. Here, the precharge voltage will be generalized withFIG. 6.

The following preferably sets forth the precharge voltages:(1) a first precharge voltage (VPRE-CHARGE-RED(n)) corresponding to red light may be given by VCR(n)+Vdefault-precharge-red(DR(n));(2) a second precharge voltage (VPRE-CHARGE-GREEN(n)) corresponding to green light may be given by VCG(n)+Vdefault-precharge-green(DR(n)); and(3) a third precharge voltage (VPRE-CHARGE-blue(n)) corresponding to blue light may be given by VCG(n)+Vdefault-precharge-blue(DR(n)).

Here, VCR(n), VCG(n) and VCB(n) are cathode voltages corresponding to red, green and blue sub-pixel, respectively. Also, Vdefault-precharge-red(DR(n)), Vdefault-precharge-green(DR(n)) and Vdefault-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 (D1to D4) according to the cathode voltage. A method of calculating the cathode voltage is described through the examples inFIG. 5AtoFIG. 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. 7is 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 panel700, a first scan driving circuit702, a second scan driving circuit704, a controlling circuit706, a precharge controlling circuit708, a precharge circuit710, and a data driving circuit712. The elements of this embodiment, except the first scan driving circuit702and the second scan driving circuit704, is preferably the same as those in the first embodiment.

In operation, the first scan driving circuit702provides first scan signals to one part (S1and S3) of scan lines (S1to S4) along one side or direction of the panel700. The second scan driving circuit704provides second scan signals to the other scan lines (S2and S4) along another side or direction of the panel700.

As in the first embodiment, a precharge current may be applied to data lines (D1to D4) 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. 8is 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 panel800, a controlling circuit802, a scan driving circuit804, a discharge circuit806, a precharge circuit808, a data converting circuit810and a data driving circuit812. The panel800includes a plurality of sub-pixels (E11to E44) formed in areas of crossed data lines (D1to D4) and scan lines (S1to S4).

The controlling circuit802receives 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 circuit804is formed along one side or direction of the panel800and transmits, preferably in sequence, scan signals to the scan lines (S1to S4) under control of the controlling circuit802. In other words, the scan driving circuit804may connect in sequence the scan lines (S1to S4) to ground.

The discharge circuit806includes a switch (SW) and a discharge level circuitry820. The switch (SW) is turned on or off under control of the controlling circuit802. For example, the switch (SW) is turned on when data lines (D1to D4) are discharged. As a result, data lines (D1to D4) are connected to the discharge level circuitry820, and so a charge charged to the data lines (D1to D4) is discharged to a certain level. The precharge circuit808applies a precharge current corresponding to the display data to data lines (D1to D4) under control of the controlling circuit802.

The data converting circuit810converts the display data into conversion data corresponding to cathode voltages of sub-pixels (E11to E44) under control of the controlling circuit802. In other words, since the cathode voltages of sub-pixels (E11to E44) are affected by the scan line resistance of each of scan lines (S1to S4), the data converting circuit810converts the display data into the conversion data in order to compensate the scan line resistance. In addition, the data converting circuit810provides the conversion data to the data driving circuit812. The data driving circuit812provides data current corresponding to the conversion data to the data lines (D1to D4), and so the corresponding pixel to the data current emits a light.

FIG. 9is a diagram of one type of data converting circuit that may be used inFIG. 8. This data converting circuit810includes calculating circuitry900, a memory902, and look-up circuitry904. The memory902stores resistances of the scan lines (S1to S4).

The calculating circuitry900calculates a cathode voltage of a pixel corresponding to the scan line, and provides the calculated cathode voltage to the look-up circuitry904. Here, the cathode voltage is the scan line resistance times a data current corresponding to the display data. The look-up circuitry904includes 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 circuitry900. Here, the selected data correspond to the cathode voltage.

Then, the look-up circuitry904provides the selected conversion data to the data driving circuit812. 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 panel800.

FIG. 10Ais a circuit view relating to a process of driving the light-emitting device ofFIG. 8according to one embodiment of the present invention.FIG. 10Bis a circuit diagram relating to a process of driving the light-emitting device ofFIG. 8according to another embodiment of the present invention, andFIG. 10Cis a timing diagram relating to light-emitting process associated withFIG. 10AandFIG. 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 (E41) and sub-pixel (E42) emits light having brightness based on a predetermined data current, e.g., 3 amps. Further, sub-pixels (E11, E21and E31) may not emit light under certain circumstances, e.g., based on the video being displayed. In addition, each of sub-pixels (E12, E22and E32) emit light having brightness corresponding to a data current of, for example, 1 amp.

A process of emitting a light in sub-pixels (E11to E41) corresponding to a first scan line (S1) will now be described. Referring toFIG. 10A, the precharge circuit808applies a precharge current corresponding to the display data to the data lines (D1to D4). Thus, a charge corresponding to a second voltage (V2) is precharged to data lines (D1to D4).

Subsequently, calculating circuitry900calculates a cathode voltage (VC41) using information based on resistors (RS and RP) stored in memory902and the display data transmitted from the controlling circuit802. In other words, the calculating circuitry900detects data currents (I11to I41) through the display data. Here, each of the detected data currents (I11to141) is 0, 0, 0 and 3 amps.

Then, the calculating circuitry900calculates the cathode voltage (VC41, e.g., 48V) which is the whole current (sum of 0, 0, 0 and 3A) passing a first scan line (S1) times the scan line resistance (sum of 10, 2, 2 and 2Ω). Subsequently, calculating circuitry900transmits a first calculation signal having information of the calculated cathode voltage (VC41) to the look-up circuitry904. The look-up circuitry904then selects conversion data corresponding to the cathode voltage (VC41) in the look-up table and provides the selected conversion data to the data driving circuit812.

The data driving circuit812provides data currents (I11to I41), corresponding to the conversion data provided from the look-up circuitry904, to the data lines (D1to D4) during low logic time of a first scan signal (PS1). As a result, an anode voltage (VA41) of the sub-pixel (E41) is stabilized to V3(e.g., reaches saturation voltage) after a certain time measured from the finish of the precharge, as shown inFIG. 10C. In case the voltage corresponding to 3A is 4V, the anode voltage (VA41) of sub-pixel (E41) is stabilized to 52V, each reaches saturation voltage. Accordingly, the sub-pixel (E41) may emit a light having a gray scale level corresponding to 4V (52V-48V).

A light-emitting process of sub-pixels (E12to E42) corresponding to a second scan line (S2) will now be described. Referring toFIG. 10B, the precharge circuit808applies a precharge current corresponding to the display data to data lines (D1to D4), and thus a charge corresponding to the second voltage (V2) is precharged to data lines (D1to D4). Subsequently, the calculating circuitry900calculates a cathode voltage (VC42) using information based on resistors (RS and RP) stored in the memory902and the display data transmitted from the controlling circuit802. In other words, the calculating circuitry900detects data currents (I12to I42) through the display data. Here, each of the detected data currents (I12to142) may be 1, 1, 1 and 3 amps.

The calculating circuitry900calculates the cathode voltage (VC42, e.g., 96V) which is the whole current (sum of 1, 1, 1 and 3A) passing a second scan line (S2) times the scan line resistance (sum of 10, 2, 2 and 2Ω). Subsequently, circuitry900provides a second calculation signal having information concerning the calculated cathode voltage (VC42) to the look-up circuitry904. The look-up circuitry904selects conversion data corresponding to the cathode voltage (VC42) in the look-up circuitry, and then transmits the selected conversion data to the data driving circuit812.

The data driving circuit812applies data currents (I12to I42) corresponding to the conversion data transmitted from the look-up circuit904to the data lines (D1to D4) during low logic time of a second scan signal (PS2). As a result, an anode voltage (VA42) of sub-pixel (E42) is stabilized to V4(e.g., reaches saturation voltage) after a certain time measured from the finish of the precharge, as shown inFIG. 10C. In case the voltage corresponding to 3A is 4V, anode voltage (VA42) of pixel (E42) is stabilized to 100V, e.g., reaches saturation voltage. Here, the cathode voltage (VC42) is higher than the cathode voltage (VC41), and thus the data current (I42) higher than the data current (I41) is applied to the fourth data line (D4), as shown inFIG. 10C.

In other words, the slope of data current (I42) as shown in part B is higher than the slope of the data current (I41) as shown in part A. Hence, the consumed amount of charge for stabilizing the data current (I42) in the sub-pixel (E42) is the same as, or similar to, that needed to stabilize the data current (I41) in the sub-pixel (E41).

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. 11is 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 panel1000, a controlling circuit1102, a scan driving circuit1104, a discharge circuit1106, a precharge circuit1108, a data converting circuit1110and a data driving circuit1112. The elements of this embodiment, except the discharge circuit1106, may be the same as those of the third embodiment.

The discharge circuit1106includes a switch (SW), a digital-to-analog (D/A) converter1120, and a buffer1122. The switch (SW) is turned on during the discharge time. The D/A converter1120transmits a first discharge voltage corresponding to one level of a plurality of discharge levels to the buffer1122under control of the controlling circuit1102.

The buffer1122buffers the first discharge voltage transmitted from the D/A converter1120, to output a second discharge voltage of preferably a constant magnitude. As a result, a charge charged to the data lines (D1to D4) is discharged to the second discharge voltage during the discharge time. In other words, in the fourth embodiment, the discharge circuit1106has 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 (D1to D4). In this case, controlling circuit1106compensates the non-identical data current by adjusting the discharge voltage to a certain level of unit.

FIG. 12is 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 panel1200, a controlling circuit1202, a first scan driving circuit1204, a second scan driving circuit1206, a discharge circuit1208, a precharge circuit1210, a data converting circuit1212, and a data driving circuit1214. The elements of this embodiment, except the first scan driving circuit1204and the second scan driving circuit1206, may be the same as those in the second embodiment.

The first scan driving circuit1204provides first scan signals to some (S1and S3) of the scan lines (S1to S4) in one direction of the panel1200. The second scan driving circuit1206transmits second scan signals to remaining ones of the scan lines (S2and S4) in other direction of the panel1200. Like the third embodiment, data current is applied to data lines (D1to D4) 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.