KR102420485B1 - Organic light emitting display - Google Patents

Abstract

The present invention relates to an organic light emitting display device capable of preventing a change in the threshold voltage of a driving transistor of a sub-pixel that does not emit light for a long time. In the organic light emitting display according to the present invention, i (here, i is a natural number) of the sub-pixels, and the maximum (i-1) sub-pixels emit light during the first period, and restore data is supplied to the sub-pixels that did not emit light in the first period to emit light during the second period.

Description

Organic light emitting display device {ORGANIC LIGHT EMITTING DISPLAY}

The present invention relates to an organic light emitting display device, and more particularly, to an organic light emitting display device capable of preventing a change in a threshold voltage of a driving transistor of a sub-pixel that does not emit light for a long time.

A video display device that implements various information on a screen is a key technology in the information and communication era, and is developing in the direction of thinner, lighter, more portable and high-performance. Accordingly, as a flat panel display capable of reducing weight and volume, which are disadvantages of a cathode ray tube (CRT), an organic light emitting display device that displays an image by controlling the emission amount of an organic light emitting layer is in the spotlight.

In an organic light emitting diode display, a plurality of pixels are arranged in a matrix to display an image. Here, each pixel includes a light emitting element, at least a switching thin film transistor (TFT) for independently driving the light emitting element, and a pixel driving circuit including a storage capacitor and a driving TFT.

Such an organic light emitting diode display comprises red, green, and blue sub-pixels as one unit pixel, and displays images of various colors. Recently, each of the unit pixels further includes a white sub-pixel in addition to the red, green, and blue sub-pixels. Since the white sub-pixel does not require a color filter, transmittance is higher than that of other sub-pixels, thereby improving efficiency. In an organic light emitting diode display including such a white sub-pixel, the sub-pixel that does not emit light for a long time is exposed to light emitted from the sub-pixel that emits light, and the sub-pixel does not emit light due to negative bias temperature illumination stress (NBTiS). The threshold voltage of the driving transistor of the sub-pixel is shifted in a negative direction. In order to solve this problem, the data voltage can be externally compensated as much as the threshold voltage moves, but compensation is limited because the compensation range is limited. In particular, when the threshold voltage continues to move in the negative direction and out of the compensation range, there is a problem in that reliability is deteriorated.

SUMMARY OF THE INVENTION The present invention is to solve the above problem, and the present invention provides an organic light emitting diode display capable of preventing a change in a threshold voltage of a driving transistor of a sub-pixel that does not emit light for a long time.

In order to achieve the above object, in the organic light emitting display device according to the present invention, a maximum of (i-1) sub-pixels among i (where i is a natural number) sub-pixels that implement different colors emit light during a first period, , supplies the restored data to the sub-pixels that are not emitting light in the first period to emit light during the second period.

In the organic light emitting display device according to the present invention, a maximum of (i-1) sub-pixels among i (where i is a natural number) sub-pixels that implement different colors emit light during a display period that is a first period, and the first period Restored data is supplied to the non-light-emitting sub-pixel to emit light during the second period, which is the restoration period. Accordingly, since the threshold voltage of the driving transistor changed due to non-light emission in the first period is restored to its original state by the restored voltage supplied in the second period, shifting of the threshold voltage of the driving transistor can be prevented. As a result, in the organic light emitting diode display according to the present invention, stains, afterimages, and reliability are improved.

1 is a block diagram illustrating an organic light emitting diode display according to a first embodiment of the present invention.
FIG. 2 is a diagram for describing a sub-pixel of the organic light emitting diode display shown in FIG. 1 .
FIG. 3 is a diagram for explaining in detail the timing controller illustrated in FIG. 1 .
FIG. 4 is a waveform diagram illustrating a display period, a sensing period, and a restoration period of the organic light emitting diode display shown in FIG. 1 .
FIG. 5 is a flowchart illustrating a method of driving the organic light emitting diode display shown in FIG. 1 .
6 is a block diagram illustrating a timing controller of a flat panel display device according to a second exemplary embodiment of the present invention.
7 is a flowchart illustrating a method of driving a flat panel display device according to a second embodiment of the present invention.

Hereinafter, an embodiment according to the present invention will be described in detail with reference to the accompanying drawings.

1 is a block diagram illustrating an organic light emitting diode display according to a first embodiment of the present invention.

The display device illustrated in FIG. 1 includes a data driver 104 , a scan driver 106 , a panel driver 108 including a timing controller 110 , and a light emitting display panel 102 .

The light emitting display panel 102 includes a plurality of unit pixels P including a red sub-pixel SPR, a green sub-pixel SPG, a blue sub-pixel SPB, and a white sub-pixel SPW. The arrangement of sub-pixels in each unit pixel P is very diverse, and the red sub-pixel SPR, white sub-pixel SPW, blue sub-pixel SPB, and green sub-pixel SPG shown in FIG. The order arrangement is only a specific example and is not limited thereto.

Each of the sub-pixels SPR, SPG, SPW, and SPB is formed in a pixel area provided at the intersection of the gate line GL and the data line DL, and each of the sub-pixels SPR, SPG, SPW, and SPB is shown in FIG. 2 As illustrated in FIG. 1 , a switching transistor Tr_Sw, a driving transistor Tr_D, a storage capacitor Cst, a sensing transistor Tr_Se, and an organic light emitting diode OLED are provided.

The organic light emitting diode OLED operates to emit light according to a driving current formed by the transistor Tr_D.

The switching transistor Tr_Sw performs a switching operation such that a data signal supplied through the data line DL is stored as a data voltage in the storage capacitor Cst in response to the first gate voltage supplied through the scan line SL.

The driving transistor Tr_D operates to flow a driving current between the high potential line VDD and the low potential line VSS according to the data voltage stored in the storage capacitor Cst.

The sensing transistor Tr_Se supplies the reference voltage Vref supplied to the reference line RL to the source electrode of the driving transistor Tr_D in response to the second gate voltage supplied through the sensing control line SCL. The threshold voltage and mobility of the driving transistor Tr_D are sensed through the sensing transistor Tr_Se and the reference line RL, and the data voltage is compensated in proportion to the difference between the sensed value S_Vth and the reference threshold voltage. . Since the configuration of the sensing transistor Tr_Se and the reference line RL is very diverse, the structure of FIG. 2 is only a specific example and is not limited thereto.

In the light emitting display panel 102 , two sub-pixels among the red sub-pixel SPR, the green sub-pixel SPG, and the blue sub-pixel SPB and the white sub-pixel SPW emit light during the display period, and the corresponding unit pixel (P) realizes white color, senses characteristics of the driving transistor of each sub-pixel during the sensing period, and supplies the restored data voltage to the gate terminal of the driving transistor whose threshold voltage is changed during the restoration period.

The scan driver 106 applies a first gate voltage in a high state or a low state to the scan lines SL1 to SLm formed in the light emitting display panel 102 in response to the gate control signal GCS from the timing controller 110 . and a second gate voltage of a high state or a low state is supplied to the sensing control lines SCL to SCLm.

The data driver 104 converts the digital pixel data into an analog data voltage using the data control signal DCS and the gamma voltage from the timing controller 110 in the display period, the sensing period, and the restoration period, and converts the changed pixel data into an analog data voltage. An analog data voltage is supplied to the data line DL. In addition, the data driver 104 converts the voltage (or current) sensed through the sensing transistor Tr_Se and the reference line RL into a digital sensing value S_Vth during the sensing period and supplies it to the timing controller 108 . do.

The timing control unit 108 includes a control signal generation unit 112 , a four-color data conversion unit 114 , a data processing unit 116 , and a memory 118 as shown in FIG. 3 .

The control signal generator 112 generates a gate control signal GCS and a data control signal DCS for controlling driving timings of the scan driver 106 and the data driver 104, respectively, based on a synchronization signal input from the outside. do. The generated gate control signal GCS is supplied to the scan driver 106 and the data control signal DCS is supplied to the data driver 104 .

The memory 118 stores compensation information set according to the characteristics of each sub-pixel. The compensation information includes a threshold voltage compensation value for compensating for the threshold voltage of the driving transistor Tr_D of each sub-pixel and a mobility compensation value for compensating for the mobility of the driving transistor Tr_D.

Compensation information is preset based on a sensed value that senses characteristics (threshold voltage and/or mobility) of each sub-pixel before shipment and is stored in the memory 118 . After the product is shipped, the compensation information stored in the memory 118 is updated by sensing the characteristics of each pixel again through the sensing mode every desired driving time. At least one desired driving time including a boot time at power-on, an end time at power-off, and a blanking period of each frame, the sensing mode may be executed to update compensation information stored in the memory 118 . In the present invention, an example in which the sensing mode is executed at the end time during power-off will be described.

The four-color data conversion unit 114 converts red, green, and blue input data RGB of each unit pixel input from the outside in frame units into red, green, blue, and white pixel data RGBW. . For example, the four-color data conversion unit 114 converts input data RGB having a minimum grayscale value (or a common grayscale value) from red, green, and blue input data RGB of a unit pixel to white pixel data ( W), and by reflecting the generated white pixel data W to the red, green, and blue input data RGB, respectively, red, green, and blue pixel data R, G, and B are generated. In this case, the four-color data conversion unit 114 subtracts the white pixel data W from each of the red, green, and blue input data RGB to obtain the red, green, and blue pixel data R, G, and B). You can create each of them.

The data processing unit 116 compensates image data input from the outside during the display period in which the power source Power1 of the organic light emitting display device is turned on and is in the power-on state, using compensation information of the memory 118 , and converts the compensated data to a data driver. (104) is output. In particular, the data processing unit 116 extracts data of red, white, and blue sub-pixels from the 4-color data of the unit pixel from the 4-color data conversion unit 114 and uses the extracted data as color coordinates according to the set target white luminance. is corrected with the white unit data R'W'B', and the corrected white unit data is supplied to the data driver 104 . In addition, the data processing unit 116 is configured to perform each sensing by the data driver 104 during a sensing period after the power source Power1 of the organic light emitting display device is turned off and before the power source Power2 of the panel driver 108 is turned off. The compensation information of the memory 118 is updated by processing the sensing information of the pixel according to a predetermined operation. In addition, the data processing unit 116 controls the sub-threshold voltage of the driving transistor Tr_D to be negatively shifted through sensing information sensed in the sensing period during the restoration period before the power source Power2 of the panel driver 108 is turned off. A pixel is extracted, and restored data to be supplied to the sub-pixel is supplied to the data driver 104 .

4 is a waveform diagram illustrating a method of driving an organic light emitting diode display according to a first embodiment of the present invention, and FIG. 5 is a diagram illustrating a driving method of an organic light emitting display according to the first embodiment of the present invention. It is a flow chart.

As shown in FIGS. 4 and 5 , a pixel data voltage is supplied to a sub-pixel to be emitted during the display period Td, and a black (off) data voltage Vblack is supplied to a sub-pixel to be non-emitted to realize an image. do. That is, during the display period Td, the black data voltage is supplied to the gate terminal of the driving transistor of the sub-pixel that is not emitting light. Thereafter, when the power source Power1 of the organic light emitting diode display is turned off by the user or other cause (step S11 ), the organic light emitting display device is sequentially switched to the sensing period Ts and the restoration period Tr. Here, in the sensing period Ts and the restoration period Tr, after the power source Power1 of the organic light emitting display device is turned off, the panel driver (Power2) of the panel driver 108 is actually turned off. 108) is maintained. In this case, the restoration period Tr is set shorter than the sensing period Ts to prevent the entire driving period from being lengthened due to the restoration period Tr.

During the sensing period Ts, the panel driver 108 receives the power Power2 of the panel driver 108 and supplies the sensing data voltage Vsen to each sub-pixel to sense the threshold voltage of each driving transistor Tr_D. (Step S12 ), a compensation value is generated through a predetermined association of the sensed threshold voltage, and the compensation value is updated in the memory 118 .

During the restoration period Tr, the panel driver 108 calculates a difference ΔVth between the sensed threshold voltage and the reference threshold voltage, and selects sub-pixels in which the sensed threshold voltage is shifted in the negative direction (ΔVth<0). (Step S13). In particular, since the threshold voltage of a sub-pixel that has been non-emitted for a long time is shifted in a negative direction by the light of the sub-pixel that is emitted when an image is implemented, the sub-pixel that has not been lit for a long time is selected. Then, since the restored data voltage Vre is supplied to the selected non-emission sub-pixels, the restored data voltage Vre is supplied to the gate terminal of the driving transistor Tr_D through the turned-on switching transistor Tr_Sw. At this time, the restored data voltage Vre higher than the voltage Vs supplied to the source terminal of the driving transistor Tr_D is supplied to the gate terminal Vg of the driving transistor Tr_D (Vg-Vs=Vgs>0). . Accordingly, the threshold voltage Vth of the driving transistor Tr_D is moved in a positive direction due to positive bias temperature stress (PBTS), so that the threshold voltage of the driving transistor Tr_D can be restored to its original state. (Step S14). After the threshold voltage of the driving transistor Tr_D is restored to its original state, the power source Power 2 of the panel driver 108 of the organic light emitting diode display is actually turned off (step S15 ).

Meanwhile, the restored data voltage Vre supplied during the restoration period Tr of the organic light emitting diode display according to the first exemplary embodiment is higher than the sensing data voltage Vsen among voltages used when the organic light emitting display is driven. Use high voltage. For example, in the organic light emitting diode display according to the first embodiment of the present invention, the threshold voltage of the driving transistor can be restored to its original state in a short time by using the maximum grayscale voltage as the restored data voltage. In addition, in the organic light emitting diode display according to the first exemplary embodiment of the present invention, since the restored data voltage is supplied to the sub-pixels after the power of the panel driver 108 is turned off, the driving transistors do not affect the quality of the input image. The characteristic of (Tr_D) can be restored.

6 is a block diagram illustrating an organic light emitting display device according to a second exemplary embodiment of the present invention.

The organic light emitting diode display shown in FIG. 6 has the same components as the organic light emitting diode display according to the first embodiment, except that the image analyzer 120 is additionally included in the timing controller 110 . to provide Accordingly, detailed descriptions of the same components will be omitted.

The image analysis unit 120 analyzes digital video data of an image input from a host system (not shown) to determine whether the currently input image is a fixed/logo image or a moving image. To this end, the image analysis unit 120 includes a fixed image determination unit 122 and a logo image determination unit 124 .

The fixed image determination unit 122 detects a motion vector in units of frames and determines based on the motion vectors, or compares data in units of frames to obtain a fixed image (an image that is continuously output equally over the entire area of a screen) and a moving image. It is determined whether the entire image of one frame currently input is a fixed image or a moving image by using a known fixed/video determination algorithm for determining . When the input image is determined to be a fixed image, the fixed image determination unit 122 checks whether the fixed image is implemented for a long time enough to shift the threshold voltage of the driving transistor Tr_D in a negative direction.

The logo image determining unit 124 compares the image data of each frame in block units to determine whether there is a block including a logo image (an image that is continuously output in a certain area of a screen) in the entire image of one frame. judge When it is determined that the input image is a logo image, the logo image determining unit 124 checks whether the logo image is implemented for a long time enough to shift the threshold voltage of the driving transistor Tr_D in a negative direction.

Although the image analysis unit 120 has been described as being embedded in the timing control unit 110 as an example, it may also be embedded in the host system.

When the image currently input by the fixed image determination unit 122 of the image analysis unit determines that the image currently input is a fixed image, the data processing unit 116 extracts sub-pixels that are non-luminous for a long time from among the sub-pixels included in the fixed image, and the non-luminous sub-pixels The restored data Vre is supplied to the selected sub-pixels. In addition, when the logo image is included in the image currently input by the logo image determination unit 124 of the image analysis unit, the data processing unit 116 extracts sub-pixels that are not luminous for a long time from among the sub-pixels included in the logo image, , supplies the restored data Vre to the non-light-emitting sub-pixel. Here, the restored data Vre is a voltage higher than the black data voltage Vblack supplied to the non-emission sub-pixel and higher than the voltage supplied to the source terminal of the driving transistor Tr_D. In addition, the restored data voltage Vre level is set so that the organic light emitting diode (OLED) emits light at a level that is not recognized by the user (eg, 1 nit).

7 is a flowchart illustrating a method of driving an organic light emitting diode display according to a second exemplary embodiment of the present invention.

As shown in FIG. 7 , an image is realized by supplying a pixel data voltage to a sub-pixel to be emitted during the display period and a black (off) data voltage Vblack to a sub-pixel to be non-emissive during the display period (step S21). At this time, it is determined whether the currently input image is a logo/fixed image or a moving image (step S22). When it is determined that the currently implemented image is a fixed image, after checking the implementation time of the fixed image (step S23), sub-pixels that are not luminous for a long time are extracted from sub-pixels included in the fixed image, and the non-light-emitting sub-pixels are extracted. The restored data is supplied to the pixel (step S24). And, when a logo image is included in the currently input image, after checking the implementation time of the logo image (step S25), sub-pixels that do not emit light for a long time from among the sub-pixels included in the logo image are extracted, and the The restored data is supplied to the non-light-emitting sub-pixel (step S26).

For example, in the second embodiment of the present invention, after a logo image or a fixed image in which the green sub does not emit light among the red, green, blue, and white sub-pixels is realized for a long period of time for a first period, the non-light-emitting green sub-pixel is displayed. A logo image or a fixed image is implemented during the second period by supplying the restored data Vre and supplying pixel data to the remaining red, blue, and white sub-pixels. Due to the restoration data, the threshold voltage of the driving transistor Tr_D of the green sub-pixel that has not been lit for a long time is shifted in a positive direction, so that the threshold voltage of the driving transistor Tr_D of the non-light-emitting green sub-pixel is restored to its original state. can

The above description is merely illustrative of the present invention, and various modifications may be made by those of ordinary skill in the art to which the present invention pertains without departing from the technical spirit of the present invention. Therefore, the embodiments disclosed in the specification of the present invention do not limit the present invention. The scope of the present invention should be interpreted by the following claims, and all technologies within the scope equivalent thereto should be construed as being included in the scope of the present invention.

102: display panel 104: data driver
106: gate driver 108: panel driver
110: timing control

Claims (6)

A display panel comprising: a display panel including a unit pixel including i (where i is a natural number) sub-pixels implementing different colors;
and a panel driver for driving the display panel;
The panel driver
displaying an image on the display panel for a first period, and selecting sub-pixels that are not emitting light during the first period;
supplying a restored data voltage to the sub-pixels that are not lit during the selected first period to emit light during a second period;
and the restored data voltage is higher than a voltage supplied to a gate terminal of a driving transistor of the non-light-emitting sub-pixel in the first period. The method of claim 1,
The panel driver
A sensing data voltage is supplied to each sub-pixel to sense a threshold voltage of a driving transistor of each sub-pixel, and a difference between the sensed threshold voltage and a reference threshold voltage is calculated, and the sub-pixel that is not lit during the first period An organic light emitting diode display comprising: a data processing unit that selects the selected sub-pixels and supplies the restored data voltage to the selected sub-pixels. 3. The method of claim 2,
The panel driver senses the threshold voltage and supplies the restored data voltage after the light emitting cell of each sub-pixel is turned off and before the panel driver turns off. 3. The method of claim 2,
The organic light emitting diode display device of claim 1, wherein a restoration period that is a supply period of the restored data voltage is shorter than a sensing period of the threshold voltage. A display panel comprising: a display panel including a unit pixel including i (where i is a natural number) sub-pixels implementing different colors;
and a panel driver for driving the display panel;
The panel driver
an image analysis unit that analyzes the input image to be input to the display panel, determines whether the input image is a fixed image or whether the input image includes a logo image, and determines whether the fixed image and the logo image are driven for a long time;
When the input image includes a logo image, a restored data voltage is supplied to a non-emission sub-pixel among sub-pixels included in the logo image, and when the input image is a fixed image, a sub-pixel included in the fixed image An organic light emitting diode display including a data processing unit that supplies the restored data voltage to non-emission sub-pixels among them. 6. The method according to claim 2 or 5,
The data processing unit
When the threshold voltage of the driving transistor is changed in the negative direction, the restored data voltage higher than the black data voltage and higher than the voltage supplied to the source terminal of the driving transistor is applied to the sub-pixel in which the threshold voltage is changed in the negative direction. supplying organic light emitting display devices.

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