KR20110035442A - Organic electroluminescent display device and method of driving the same - Google Patents

Abstract

PURPOSE: An organic electroluminescent display device and a driving method thereof are provided to operate in a compensation mode when the same image is consecutively inputted during a threshold period of time, thereby reducing lowering of picture quality. CONSTITUTION: A gate line and a data line cross each other. A pixel comprises a switching transistor, a driving transistor, an organic light emitting diode and a detection transistor. A driving mode selecting unit(300) selects one of the driving mode, the normal mode, or the compensation mode of the same organic electroluminescent display device. A scan driving unit(320) shortens time for detecting a threshold voltage in the compensation mode compared to the normal mode. A data driving unit(330) outputs a data voltage in a compensation mode to a data line.

Description

Organic electroluminescent display device and method of driving the same {Organic electroluminescent display device and method of driving the same}

The present invention relates to an organic light emitting device, and more particularly, to an organic light emitting device and a driving method thereof.

As the information society develops, the demand for display devices for displaying images is increasing in various forms. Recently, liquid crystal displays (LCDs), plasma display panels (PDPs), organic fields Various flat display devices such as organic electroluminescent display devices (OELDs) are being utilized.

Among these flat panel display devices, the organic light emitting display device can be driven at low voltage, has a thin shape, is excellent in viewing angle, and has a fast response speed.

As the organic light emitting display device, an active matrix type organic light emitting display device in which a plurality of pixels are positioned in a matrix form and displays an image is widely used.

1 is a circuit diagram of a pixel of a general organic light emitting display device.

As shown in the figure, the organic light emitting diode has a gate wiring GL and a data wiring DL which cross each other to define the pixel P. As shown in FIG.

In the pixel P, a switching transistor T1, a driving transistor T2, and an organic light emitting diode OD are formed.

For the pixel P having such a configuration, when the gate wiring GL is scanned, the switching transistor T1 is turned on. In synchronization with this, the data voltage Vdata transferred through the data wiring DL is applied to the driving transistor T2. Accordingly, the light emitting current I _OD is applied to the organic light emitting diode OD through the driving transistor T2. As a result, the organic light emitting diode OD emits light to display an image.

The light emission current I _OD supplied to the organic light emitting diode OD is controlled by the data voltage Vdata applied to the gate electrode of the driving transistor T2. For example, the luminous current I _OD supplied to the organic light emitting diode OD is obtained through Equation 1 below.

I _OD = k (Vgs-Vth) ² = k (Vdata-Vss-Vth) ² ... (Equation 1)

Here, Vgs is a gate-source voltage as a voltage difference between the gate electrode and the source electrode of the driving transistor T2, Vth is a threshold voltage of the driving transistor T2, and k is a constant value.

As described above, the light emission current I _OD depends on the threshold voltage Vth of the driving transistor T2. However, the threshold voltage Vth of the driving transistor T2 is shifted according to the driving time. As a result, the luminous current I _OD is changed to change the luminance of the displayed image.

In order to improve this, a voltage compensation method for compensating for the variation of the threshold voltage Vth has been proposed. In the voltage compensation method, the threshold voltage Vth is detected before the light emitting period of the pixel P, and is reflected in advance on the gate electrode side. Accordingly, as shown in FIG. 2, even when the threshold voltage Vth is shifted, the shifted threshold voltage Vth can be detected. Therefore, the threshold voltage Vth component is canceled in Equation (1) above, so that the luminous current I _OD does not depend on the threshold voltage Vth. Therefore, it is possible to improve the brightness change of the image.

On the other hand, when the same image is displayed continuously, the same data voltage Vdata is continuously applied to the driving transistor T2. As a result, the driving transistor T2 deteriorates with time, and the threshold voltage Vth is shifted. Even when the threshold voltage Vth is shifted, as described above, if the shifted threshold voltage Vth is normally detected and reflected on the gate electrode, the image can be displayed normally.

However, due to factors such as process conditions, driving timing, driving environment, and the like, an error ΔVth may occur in the detection of the threshold voltage Vth. On the other hand, as the degree of degradation of the driving transistor T2 increases, the degree of detection error ΔVth increases. Therefore, as time passes, the luminance change of the image appears due to the detection error [Delta] Vth.

Meanwhile, the shift of the threshold voltage Vth is affected by the displayed image. For example, in a chess pattern image displayed in white and black, the shift of the threshold voltage Vth is greater in the portion where white is displayed than in the portion where black is displayed. In other words, the shift of the threshold voltage Vth has a gate bias tendency. Accordingly, if there is a detection error (ΔVth) in detecting the threshold voltage (Vth), the detection portion (ΔVth) will be larger in the white portion having a larger shift in the threshold voltage (Vth) than in the black portion. Further, the difference between the detection error [Delta] Vth and the detection error [Delta] Vth of the white portion and the black portion becomes larger as the time for displaying the chess pattern becomes longer.

In such a case, if the gray image is displayed after the chess pattern image is displayed for a long time, the detection error ΔVth generated in the chess pattern will be reflected in the gray image. Accordingly, a difference in luminance due to a difference in detection error DELTA Vth will occur between the portion where white is displayed and the portion where black is displayed. As a result, image quality deterioration such as an afterimage occurs in the gray image.

As such, in the conventional organic light emitting display device, image quality degradation such as an afterimage may be caused by a detection error.

The present invention has a problem to provide an organic light emitting display device and a driving method thereof capable of improving image quality.

In order to achieve the above object, the present invention, the gate wiring and data wiring intersecting with each other; A switching transistor connected to the gate wiring and a data wiring, a driving transistor receiving a data voltage through the switching transistor, an organic light emitting diode connected to the driving transistor, and a threshold voltage of the driving transistor to detect a threshold voltage of the driving transistor. A pixel including a detection transistor connected between the drain electrode and the gate electrode; A driving mode selection unit which counts the number of frames continuously inputted by the same image, and selects a normal mode when the count number is less than a threshold, and a compensation mode when the count number reaches a threshold; ; A scan driver for shortening the detection time of the threshold voltage in the compensation mode, compared to the normal mode; In the compensation mode, an organic light emitting diode comprising a data driver for outputting a data voltage to the data wiring to compensate for the difference between the threshold voltage detected in the normal mode and the compensation mode.

The driving mode selector may include an image comparator configured to compare whether an image of a previous frame and an image of a current frame are the same; If the image of the previous frame and the image of the current frame is the same, it may include a counter to increase the count number by one.

The data driver further includes a DAC circuit which generates gray voltages using gamma reference voltages, and outputs one of the gray voltages corresponding to the gray level of the input image data as a data voltage. The device may further include a gamma reference voltage generator configured to generate different gamma reference voltages in the normal mode and the compensation mode.

The data driver further includes a DAC circuit which generates gray voltages using gamma reference voltages, and outputs one of the gray voltages corresponding to the gray level of the input image data as a data voltage. The device includes a gamma reference voltage generator for generating the same gamma reference voltage in the normal mode and the compensation mode; The apparatus may further include a control unit outputting the image data input in the normal mode to the data driver, and converting the gradation level of the image data input in the compensation mode to output the image data to the data driver.

The pixel may include a capacitor connected between the drain electrode of the switching transistor and the gate electrode of the driving transistor; The display device may further include an initialization transistor connected to the gate electrode of the driving transistor and transferring an initialization voltage for initializing the voltage of the gate electrode of the driving transistor.

In another aspect, the present invention includes the steps of counting the number of frames of the same image is continuously input; Selecting a normal mode when the count number is less than a threshold value and a compensation mode when the count number reaches a threshold value as a driving mode of an organic light emitting display device; Detecting a threshold voltage of a driving transistor according to the driving mode; Applying a data voltage to a gate electrode of the driving transistor in which the detected threshold voltage is reflected according to the driving mode; Applying an emission current to the organic light emitting diode according to the applied data voltage to emit the organic light emitting diode, wherein the detection time of the threshold voltage in the compensation mode is shorter than that of the normal mode, The data voltage in the compensation mode provides an organic light emitting device driving method which is generated to compensate for the difference between the threshold voltage detected in the normal mode and the compensation mode.

In the data driver, generating grayscale voltages using gamma reference voltages; Outputting, by the data driver, one of the gray voltages corresponding to the gray level of the input image data as a data voltage; In the normal mode and the compensation mode, the method may further include generating different gamma reference voltages.

Generating, at the data driver, grayscale voltages using gamma reference voltages; Outputting, by the data driver, one of the gray voltages corresponding to the gray level of the input image data as a data voltage; Generating the same gamma reference voltage in the normal mode and the compensation mode; The method may further include outputting the image data input in the normal mode to the data driver, and converting the gradation level of the image data input in the compensation mode to output the image data to the data driver.

The compensation mode may be performed during the compensation setting time after the count reaches a threshold value, and counting the number of frames may be newly performed after the compensation setting time passes.

In the counting of the number of frames, if the image of the previous frame and the image of the current frame are the same, the count number is increased by one. If the image of the previous frame is different from the image of the current frame, the count number is counted. Can be initialized.

The method may further include applying an initialization voltage to the gate electrode of the driving transistor before detecting the threshold voltage.

In the present invention, when the same image is continuously input during the threshold time, it is driven in the compensation mode. When driving in such a compensation mode, the time for detecting the threshold voltage is forward compared to when driving in the normal mode. As a result, when a detection error with respect to a threshold voltage occurs, such a detection error can be reduced. As a result, when the image is changed after the same image is continuously input, it is possible to improve the deterioration of image quality such as an afterimage caused by a detection error.

Furthermore, as the detection time is shortened, a voltage difference detected during normal mode driving and compensation mode driving may occur, thereby generating a luminance difference of an image. The luminance difference of the image can be compensated by adjusting the data voltage.

Through the above method, the organic light emitting display device of the present invention can improve the image quality of the displayed image.

Hereinafter, with reference to the drawings will be described embodiments of the present invention.

3 is a view schematically showing an organic light emitting display device according to an embodiment of the present invention, FIG. 4 is an equivalent circuit diagram of a pixel of the organic light emitting display device according to an embodiment of the present invention, and FIG. FIG. 6 is a view illustrating waveforms of signals for driving an organic light emitting display device according to an embodiment, and FIG. 6 is a view illustrating a driving mode selection unit of an organic light emitting display device according to an embodiment of the present invention.

As shown, the organic light emitting display device 100 according to the embodiment of the present invention includes a display unit 200 and a driving circuit unit.

In the display unit 100, a plurality of gate lines GL extend in a first direction, for example, a row direction. A plurality of data lines DL extend in a second direction, for example, a column direction, which intersects with the first direction. As such, the gate lines GL and the data lines DL that cross each other define a plurality of pixels P arranged in a matrix form. On the other hand, the detection control wiring SCL and the initialization control wiring ICL extend in the first direction corresponding to the gate wiring GL.

Each pixel P of the display unit 100 may include a plurality of transistors T1 to T4, a capacitor C, and an organic light emitting diode OD.

As the plurality of transistors T1 to T4, a switching transistor T1, a driving transistor T2, an initialization transistor T3, and a detection transistor T4 may be used. As these transistors T1 to T4, for example, an N type transistor can be used.

The switching transistor T1 is connected to the corresponding gate line and data line GL and DL. The gate electrode and the source electrode of the switching transistor T1 are connected to the gate wiring and the data wiring GL and DL, respectively.

Meanwhile, a capacitor C may be connected between the driving transistor T2 and the switching transistor T1. The first and second electrodes of the capacitor C are connected to the drain electrode of the switching transistor T1 and the gate electrode of the driving transistor T2, respectively.

The organic light emitting diode OD is connected to the driving transistor T2. The cathode of the organic light emitting diode OD is connected to the drain electrode of the driving transistor T2. On the other hand, the anode electrode of the organic light emitting diode OD is connected to the first driving line PL1 to receive the first driving voltage Vdd. The source electrode of the driving transistor T2 is connected to the second driving wiring PL2 to receive the second driving voltage Vss. Here, the first driving voltage Vdd may have a higher potential than the second driving voltage Vss.

The gate electrode of the initialization transistor T3 is connected to the initialization control wiring ICL and switched on / off. The gate electrode of the detection transistor T4 is connected to the detection control wiring SCL and switched on / off.

In the pixel P having such a configuration, the initialization process, the threshold voltage detection process, the data writing process, and the light emission process are repeatedly performed at frame periods, which will be described with reference to FIG. 5.

In the initialization process, the pixel P emitting light according to the image data written in the previous frame is initialized using the initialization voltage Vini. For this purpose, the initialization control wiring ICL connected to the corresponding pixel P is selected and scanned. Accordingly, the initialization control voltage Vic having a turn-on voltage (for example, a high voltage) is applied to the initialization control wiring ICL, and thus the initialization transistor T3 is turned on. When the initialization transistor T3 is turned on, the initialization voltage Vint is applied to the gate electrode of the driving transistor T2. As the initialization voltage Vini, for example, when the driving transistor T2 is N type, a high voltage may be applied. The initialization voltage Vini may have a value sufficient to turn on the driving transistor T2. For example, the initialization voltage Vini may have a value equal to or greater than the second driving voltage Vss plus the threshold voltage Vth.

In the threshold voltage detection process, the threshold voltage Vth of the driving transistor T2 is detected. To this end, the detection control wiring SCL connected to the corresponding pixel P is selected and scanned. As a result, the detection control voltage Vsc having the turn-on voltage (for example, a high voltage) is applied to the detection control wiring SCL, whereby the detection transistor T4 is turned on. Accordingly, the threshold voltage Vth of the driving transistor T2 is detected and reflected on the gate electrode of the driving transistor T2. Therefore, when the threshold voltage detection process is performed, the voltage Vg of the gate electrode becomes Vg = Vth + Vss. Such a voltage Vg is stored in the capacitor C. FIG.

When the threshold voltage detection is performed, data of the image to be expressed during the current frame is written to the pixel P through the data writing process. For this purpose, the gate wiring GL connected to the pixel P is selected and scanned. Accordingly, a gate voltage Vgl having a turn-on voltage (for example, a high voltage) is applied to the gate wiring GL, and thus the switching transistor T1 is turned on. In synchronization with this, the data voltage Vdata transferred to the data line DL is applied to the first electrode of the capacitor C through the switching transistor T1. Accordingly, the voltage of the second electrode of the capacitor C is boosted, that is, increased by the data voltage Vdata. For this reason, the voltage Vg of the gate electrode of the driving transistor T2 becomes Vg = Vdata + Vth + Vss.

When data is written to the pixel P through the data writing process, the organic light emitting diode OD of the pixel P emits light of luminance corresponding to the written data. That is, the luminous current I _OD applied to the organic light emitting diode OD is obtained through the following equation (2).

I _OD = k (Vgs-Vth) ² = k (Vdata + Vth + Vss-Vth) ² = k (Vdata + Vss) ² .... Equation (2)

Here, Vgs is a gate-source voltage as a voltage difference between the gate electrode and the source electrode of the driving transistor T2, and k is a constant value.

Accordingly, when the threshold voltage Vth is detected without a detection error, the organic light emitting diode OD emits light of luminance corresponding to the written data.

On the other hand, the capacitor C stores the voltage Vg of the gate electrode of the driving transistor T2. Accordingly, during the light emitting period, the light emitting current I _OD corresponding to the written data can continuously flow.

Meanwhile, in the embodiment of the present invention, the time for detecting the threshold voltage Vth is adjusted according to the driving mode, that is, driving in the normal mode or the compensation mode, which will be described later.

The driving circuit unit includes a driving mode selecting unit 300, a control unit 310, a scan driver 320, a data driver 330, and a gamma reference voltage generator 340.

The controller 310 supplies a data control signal DCS that controls the data driver 330 to the data driver 330. Furthermore, the image data Data supplied from the external system is sampled according to the data control signal SCS and supplied to the data driver 350. In addition, the controller 310 supplies a scan control signal SCS for controlling the scan driver 320 to the scan driver circuit 340.

The gamma reference voltage generator 340 generates gamma reference voltages Vgamma. The gamma reference voltages Vgamma generated as described above are supplied to the data driver 330.

The data driver 330 generates grayscale voltages using gamma reference voltages Vgamma. This may be performed in the digital-to-analog converter (DAC) circuit of the data driver 330 (see 331 of FIGS. 8 and 9). That is, the DAC circuit 331 receives the gamma reference voltage Vgamma and generates grayscale voltages using the gamma reference voltage Vgamma. To this end, the DAC circuit 331 may include a voltage divider resistance circuit. Each of the gray voltages generated in this way corresponds to gray levels that image data Data may have. Accordingly, the data driver 330 can output the grayscale voltage corresponding to the grayscale level as the data voltage Vdata with respect to the input image data Data in the digital format. In this way, the data driver 330 outputs the video data in the digital format as the video data in the analog format. The data voltage Vdata output as described above is applied to the corresponding data line DL and input to the corresponding pixel P.

The scan driver 320 scans the initialization control wiring ICL, the detection control wiring SCL, and the gate wiring GL in response to the scan control signal SCS supplied from the control unit 310. For example, each of the initialization control wiring ICL, the detection control wiring SCL, and the gate wiring GL is sequentially scanned every frame along the column direction. On the other hand, in each row line, the initialization control wiring ICL, the detection control wiring SCL, and the gate wiring GL are scanned in accordance with the drive timing of the corresponding row line. That is, the initialization control wiring ICL, the detection control wiring SCL, and the gate wiring GL are scanned according to the timing of the initialization process, the detection process, and the data write process. The scan driver 320 may sequentially select the initialization line IL and apply the initialization voltage Vini to the initialization line IL.

The driving mode selection unit 300 selects whether to drive the organic light emitting diode 100 in the normal mode and the compensation mode. To this end, the driving mode selector 300 includes an image comparator 301 and a counter 303 as shown in FIG. 6.

The image comparison unit 301 compares, for example, whether the image of the previous frame and the image of the current frame are the same. The counter unit 303 increases the number of counts by one when the previous frame and the current frame are the same image according to the image comparison result of the image comparing unit 301. Meanwhile, when the previous frame and the current frame are not the same, the number of counts may be reset to an initial value.

According to the operations of the image comparator 301 and the counter 303 as described above, the driving mode selector 300 may count the number of frames in which the same image is continuously displayed. If the number of counts does not exceed the threshold, the drive mode selection unit 300 outputs a mode selection signal M corresponding to the normal mode.

On the other hand, when the number of counts reaches the threshold, the drive mode selection unit 300 outputs a mode selection signal M corresponding to the compensation mode. Furthermore, the mode selection signal M corresponding to the compensation mode may be output during a predetermined time set after the number of counts reaches the threshold, for example, the compensation setting time.

When the compensation setting time has passed, the number of counts is reset to an initial value, and the counting process may be performed again.

According to the mode selection signal M output as described above, the organic light emitting display device 100 can be selectively driven in the normal mode or the compensation mode.

Here, in detecting the threshold voltage Vth of the driving transistor T2 of the pixel P, when the detection error ΔVth occurs, the threshold is deteriorated in image quality due to the detection error ΔVth. Corresponds to a threshold time that can be recognized by the user. That is, when the same image is continuously input, if the image is changed before the threshold time elapses, the deterioration of the driving transistor T2 according to the same image input will not be significant. Accordingly, even if the detection error [Delta] Vth occurs, the detection error [Delta] Vth will not be large. In such a case, in displaying the changed image, the error of the gate-source voltage Vgs of the driving transistor T2 during the light emitting period is not large, and the afterimage will not be recognized by the user.

On the other hand, if the image is changed after the threshold time has elapsed, the driving transistor T2 will have a large deterioration. Accordingly, when the detection error [Delta] Vth occurs, the detection error [Delta] Vth becomes large. Also, in such a case, in displaying the changed image, the error of the gate-source voltage Vgs of the driving transistor T2 during the light emitting period becomes large, and the afterimage will be visually recognized by the user.

As described above, the threshold value corresponds to a threshold time that affects the image quality deterioration of the changed image when the detection error [Delta] Vth with respect to the threshold voltage Vth is changed when the same image that is continuously input is changed into another image.

Therefore, in the embodiment of the present invention, the organic light emitting display device 100 is normally driven before the time when the same image is continuously input reaches the threshold time. When the threshold time is reached, in order to compensate for the detection error ΔVth, the organic light emitting diode 100 is compensated for a predetermined time, that is, during the compensation setting time. The normal driving and the compensation driving of the organic light emitting diode 100 will be described with reference to FIGS. 7 to 9. In the following description, the case where the detection error ΔVth has a negative value, that is, a case where a voltage lower than the actual threshold voltage Vth is detected will be described as an example.

7 is a diagram illustrating a process of detecting a threshold voltage of a driving transistor when an organic light emitting diode is driven in a normal mode and a compensation mode according to an embodiment of the present invention. In FIG. 7, the first graph Vgsn illustrates the actual gate-source voltage of the driving transistor T2 in which the threshold voltage Vth is shifted with the long driving. The second graph Vgse represents the gate-source voltage of the drive transistor T2 detected during the detection time when the detection error ΔVth occurs.

8 and 9 illustrate a method of generating a data voltage of an organic light emitting display device according to an exemplary embodiment of the present invention.

When driving in the normal mode, the image data Data input to the organic light emitting diode 100 is input to the pixel P. That is, the image data Data of the digital format is transmitted to the data driver 330 through the controller 310. The image data Data transferred as described above is converted into image data, that is, data voltage Vdata, of an analog format having a gradation voltage corresponding to the gradation level through the DAC circuit 331 of the data driver 330. The data voltage Vdata converted as described above is output to the data line DL and written to the pixel P. Meanwhile, before the data writing process, the process of detecting the threshold voltage Vth of the driving transistor T2 is performed during the detection time set in the normal mode, that is, the normal detection time TS1.

Meanwhile, when driving in the compensation mode, a detection process of detecting the threshold voltage Vth of the driving transistor T2 is performed for a time shorter than the normal detection time TS1 set in the normal mode, that is, the compensation detection time TS2. .

Suppose that during the compensation mode driving, the detection process is performed during the normal detection time TS1 according to the timing in the normal mode. In such a case, at the end time t1 of the normal detection time TS1, the difference between Vgsn and Vgse is ΔV1. In other words, the detection error [Delta] Vth at the normal detection time TS1 corresponds to [Delta] V1.

On the other hand, assume that the detection process is performed for a time shorter than the normal detection time TS1, that is, the compensation detection time TS2. In such a case, at the end time t2 of the compensation detection time TS2, the difference between Vgsn and Vgse is ΔV2. In other words, the detection error ΔVth detected by the compensation detection time TS2 corresponds to ΔV2.

As described above, if the detection process is performed for a short time TS2 compared to the normal detection time TS1 as described above, the detection error ΔVth is reduced from ΔV1 to ΔV2. Therefore, the error of the voltage reflected on the gate electrode of the driving transistor T2 is also reduced. Accordingly, the error of the light emission current I _OD is reduced, so that the error of luminance in the displayed image can be reduced.

Therefore, in the embodiment of the present invention, when driving in the compensation mode, the detection time is shortened to reduce the detection error [Delta] Vth. Accordingly, even when the image is changed during the driving of the compensation mode, it is possible to improve the deterioration of image quality such as an afterimage caused by the detection error ΔVth. In particular, in the embodiment of the present invention, it is preferable to reduce the compensation detection time TS2 such that the error of the image luminance due to the detection error [Delta] Vth is not perceived by the user as a deterioration in image quality such as an afterimage.

In this regard, when the image of the chess pattern of white and black is displayed for a threshold time and then converted into a gray image, the gray image is driven in a compensation mode according to an embodiment of the present invention as an example. In compensation mode, the detection time is reduced to reduce the detection error (ΔVth). Accordingly, both the detection error of the portion where white is displayed and the detection error of the portion where black is displayed will be smaller than in the prior art. Moreover, the difference between the detection error of the portion where white is displayed and the detection error of the portion where black is displayed will be reduced as compared with the prior art. As a result, when the gray image is displayed, image quality deterioration such as an afterimage may be improved.

In an embodiment of the present invention, the operation of adjusting the detection time between the normal detection time TS1 and the compensation detection time TS2 is performed by adjusting the scan control signal SCS of the control unit 310 in accordance with the Morse selection signal M. By adjusting. That is, as the scan control signal SCS is adjusted, the scan driver 320 may adjust the scan timing of the detection control wiring SCL in response thereto.

On the other hand, in the compensation mode driving, in order to reduce the detection error ΔVth, the detection time is reduced, whereby the voltage Vg of the gate electrode of the driving transistor T2 is changed. In this regard, referring to FIG. 7, the gate at the end time t2 of the compensation detection time TS2 is compared with the gate-source voltage Vgs1 at the end time t1 of the normal detection time TS1. The source voltage Vgs2 is high. That is, as the detection time is reduced, the detected voltage rises by ΔV3. As a result, when driving in the compensation mode, the brightness of the image is increased as compared with the driving in the normal mode.

As such, before and after applying the compensation mode, the luminance difference of the image may be induced. Therefore, in order to compensate for the luminance difference, the data voltage Vdata input to the pixel P is adjusted. For example, assume that image data Data having the same gradation level as in normal mode driving is input when driving in compensation mode. In such a case, the data voltage Vdata is lowered in the compensation mode driving mode than in the normal mode driving mode. Accordingly, in the compensation mode driving, the detected detection voltage can be canceled more than in the normal mode driving. Therefore, it is possible to compensate for the change in the luminance by changing the voltage detected by adjusting the detection time when driving the compensation mode.

Here, as the method of adjusting the data voltage Vdata when driving the compensation mode, a method of adjusting the gray scale voltage may be used. In this regard, a description will be given with reference to FIG. 8. Referring to FIG. 8, according to the mode selection signal M, the gamma reference voltage generator 340 adjusts the gamma reference voltage Vgamma. Accordingly, using the gamma reference voltage Vgamma, the gradation voltage generated in the DAC circuit 331 is adjusted. For example, for the image data Data having the same gradation level, the gradation voltage is adjusted to be lower than in the compensation mode driving and in the normal mode driving. Accordingly, the output data voltage Vdata can be adjusted. As such, in the present invention, different gamma reference voltages Vgamma can be used when driving the compensation mode and the normal mode. Here, the gray scale voltages may be adjusted by adjusting the maximum gamma reference voltage having the maximum value among the gamma reference voltages Vgamma according to the driving mode.

Meanwhile, when driving the compensation mode, a method of adjusting the data voltage Vdata may be used. In this regard, a description will be given with reference to FIG. 9. Referring to FIG. 9, the controller 310 is provided with a data converter 311. The data converter 311 adjusts the gradation level of the input image data Data_in according to the mode selection signal M. FIG. For example, when the mode selection signal M has a value corresponding to the compensation mode, the data driver controls the gray level of the input image data Data_in to convert the output image data Data_out whose gray level is converted. Output to 330. The DAC circuit 331 of the data driver 330 outputs the data voltage Vdata corresponding to the gradation level of the output image data Data_out. Here, the input gamma reference voltage Vgamma may correspond to the gamma reference voltage in the normal mode. Through this process, the data voltage Vdata can be adjusted. On the other hand, to convert the image data (Data), the data converter 311 may use a look-up table (look-up table).

Hereinafter, a method of driving an organic light emitting display device according to an embodiment of the present invention will be described with reference to FIG. 10.

First, the image comparison unit 301 compares whether the input image of the current frame is the same image as the image of the previous frame (S1).

If not the same image, the organic light emitting display device 100 is driven in the normal mode (S2). When driving in the normal mode, a process of detecting the threshold voltage Vth of the driving transistor T2 is performed during the set normal detection time TS1. Then, the data voltage Vdata corresponding to the gradation level of the image data Data of the input image is written in the pixel P. On the other hand, when it is not the same video, the count number CN of the counter unit 303 is reset to the initial value.

On the other hand, if it is the same image, the counter unit 303 increases the count CN by one and compares the count CN with the threshold CR (S3). The count number CN is increased according to a formula such as CN = CN + 1. If the count number CN does not reach the threshold CR, that is, CN <CR, the organic light emitting diode 100 is driven in the normal mode.

On the other hand, when the count number CN reaches the threshold value, that is, when CN = CR, the organic light emitting diode 100 is driven in the compensation mode (S4).

When driven in the compensation mode, a process of detecting the threshold voltage Vth for the compensation detection time TS2 shorter than the normal detection time TS1 is performed. In addition, since the detected voltage changes as the compensation detection time TS2 is shortened, the data voltage Vdata is adjusted to compensate for this. To this end, the gray voltage is adjusted, or the gray level of the input image data Data is adjusted.

Such compensation mode driving is performed during the compensation setting time. In other words, the drive mode selection unit 300 determines whether the time being driven in the compensation mode is equal to or less than the compensation setting time or has passed the compensation setting time (S5). If the compensation setting time has not been exceeded, driving continues in the compensation mode. On the other hand, when the compensation set time is exceeded, compensation mode driving is stopped, and image comparison is performed again. Here, when the compensation setting time is exceeded, the count number CN may be initialized. When the compensation set time has elapsed, the organic light emitting display device 100 is driven in the normal mode until the count number CN reaches a threshold value.

Therefore, after driving the compensation mode, the driving mode is driven in the normal mode, whereby the detection time returns to the normal detection time TS1. Then, the data voltage Vdata corresponding to the gradation level of the input image data Data is written in the pixel P.

As described above, in the embodiment of the present invention, when the same image is continuously input during the threshold time, it is driven in the compensation mode. When driving in such a compensation mode, the time for detecting the threshold voltage is forward compared to when driving in the normal mode. Accordingly, when a detection error with respect to the threshold voltage occurs, such a detection error can be reduced. As a result, when the image is changed after the same image is continuously input, it is possible to improve the deterioration of image quality such as an afterimage caused by a detection error.

Furthermore, as the detection time is shortened, a voltage difference detected during normal mode driving and compensation mode driving may occur, thereby generating a luminance difference of an image. The luminance difference of the image can be compensated by adjusting the data voltage.

Through the above method, the organic light emitting display device according to the embodiment of the present invention can improve the image quality of the displayed image.

Embodiment of the present invention described above is an example of the present invention, it is possible to change freely within the scope included in the spirit of the present invention. Accordingly, the invention includes modifications of the invention within the scope of the appended claims and their equivalents.

1 is a circuit diagram of a pixel of a general organic light emitting display device.

2 is a diagram illustrating a phenomenon in which a threshold voltage of a driving transistor is shifted.

3 is a view schematically showing an organic light emitting display device according to an embodiment of the present invention.

4 is a circuit diagram of a pixel of an organic light emitting display device according to an embodiment of the present invention.

5 illustrates waveforms of signals for driving an organic light emitting display device according to an exemplary embodiment of the present invention.

6 is a view showing a driving mode selection unit of an organic light emitting display device according to an embodiment of the present invention.

7 is a diagram illustrating a process of detecting a threshold voltage of a driving transistor when the organic light emitting diode is driven in a normal mode and a compensation mode according to an embodiment of the present invention.

8 and 9 illustrate a method of generating a data voltage of an organic light emitting display device according to an embodiment of the present invention.

10 is a flowchart illustrating a method of driving an organic light emitting display device according to an embodiment of the present invention.

Description of the Related Art

100: organic light emitting display device 200: display unit

300: drive mode selection unit 310: control unit

320: scan driver 330: data driver

340: gamma reference voltage generator

Claims (11)

Gate wiring and data wiring intersecting with each other; A switching transistor connected to the gate wiring and a data wiring, a driving transistor receiving a data voltage through the switching transistor, an organic light emitting diode connected to the driving transistor, and a threshold voltage of the driving transistor to detect a threshold voltage of the driving transistor. A pixel including a detection transistor connected between the drain electrode and the gate electrode; A driving mode selection unit which counts the number of frames continuously inputted by the same image, and selects a normal mode when the count number is less than a threshold, and a compensation mode when the count number reaches a threshold; ; A scan driver for shortening the detection time of the threshold voltage in the compensation mode, compared to the normal mode; In the compensation mode, a data driver for outputting a data voltage to the data wiring to compensate for the difference between the threshold voltage detected in the normal mode and the compensation mode. Organic electroluminescent device comprising a. The method of claim 1, The drive mode selection unit, An image comparing unit for comparing whether an image of a previous frame and an image of a current frame are the same; If the image of the previous frame and the image of the current frame is the same, and includes a counter for increasing the count number by one Organic electroluminescent device. The method of claim 1, The data driver further includes a DAC circuit for generating gray voltages using gamma reference voltages and outputting one of the gray voltages corresponding to the gray level of the input image data as a data voltage. The organic light emitting diode further includes a gamma reference voltage generator for generating different gamma reference voltages in the normal mode and the compensation mode. Organic electroluminescent device. The method of claim 1, The data driver further includes a DAC circuit for generating gray voltages using gamma reference voltages and outputting one of the gray voltages corresponding to the gray level of the input image data as a data voltage. The organic light emitting display device includes: a gamma reference voltage generator for generating the same gamma reference voltage in the normal mode and the compensation mode; And a controller which outputs the image data input in the normal mode to the data driver, and converts the gradation level of the image data input in the compensation mode to output the image data to the data driver. Organic electroluminescent device. The method of claim 1, The pixel, A capacitor connected between the drain electrode of the switching transistor and the gate electrode of the driving transistor; And an initialization transistor connected to the gate electrode of the driving transistor, the initialization transistor transferring an initialization voltage for initializing the voltage of the gate electrode of the driving transistor. Organic electroluminescent device. Counting the number of frames in which the same image is continuously input; Selecting a normal mode when the count number is less than a threshold value and a compensation mode when the count number reaches a threshold value as a driving mode of an organic light emitting display device; Detecting a threshold voltage of a driving transistor according to the driving mode; Applying a data voltage to a gate electrode of the driving transistor in which the detected threshold voltage is reflected according to the driving mode; Applying a light emitting current to the organic light emitting diode according to the applied data voltage to emit the organic light emitting diode, The detection time of the threshold voltage in the compensation mode is shorter than that of the normal mode, The data voltage in the compensation mode is generated to compensate for the difference between the threshold voltages detected in the normal mode and the compensation mode. Organic electroluminescent device driving method. The method of claim 6, Generating, at the data driver, grayscale voltages using gamma reference voltages; Outputting, by the data driver, one of the gray voltages corresponding to the gray level of the input image data as a data voltage; Generating, in the normal mode and the compensation mode, different gamma reference voltages. Organic electroluminescent device driving method. The method of claim 6, Generating, at the data driver, grayscale voltages using gamma reference voltages; Outputting, by the data driver, one of the gray voltages corresponding to the gray level of the input image data as a data voltage; Generating the same gamma reference voltage in the normal mode and the compensation mode; Outputting the image data input in the normal mode to the data driver, converting the gradation level of the image data input in the compensation mode, and outputting the image data to the data driver. Organic electroluminescent device driving method. The method of claim 6, The compensation mode is performed for a compensation set time after the count reaches a threshold, After the compensation setting time has elapsed, the step of counting the number of frames is newly performed. Organic electroluminescent device driving method. The method of claim 6, Counting the number of frames, If the image of the previous frame and the image of the current frame are the same, the count is increased by one, If the image of the previous frame and the image of the current frame are different, the count is initialized. Organic electroluminescent device driving method. The method of claim 6, The method may further include applying an initialization voltage to a gate electrode of the driving transistor before detecting the threshold voltage. Organic electroluminescent device driving method.

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