KR102554099B1 - Organic light emitting diode display device with sensing mode - Google Patents

Abstract

The present invention relates to an OLED display device capable of efficiently performing a sensing operation for updating a compensation value, and a timing controller according to an embodiment determines whether a sensing mode is necessary by monitoring driving of a display module, and determines whether a sensing mode is required. If it is determined that is necessary, the sensing request state is transferred to the host set so that the host set sends a sensing command signal.

Description

Organic light emitting diode display having a sensing mode {ORGANIC LIGHT EMITTING DIODE DISPLAY DEVICE WITH SENSING MODE}

The present invention relates to an organic light emitting diode display capable of efficiently performing a sensing mode for updating a compensation value as needed.

Recently, flat panel display devices that display images using digital data include Liquid Crystal Display (LCD) using liquid crystal, OLED display device using Organic Light Emitting Diode (OLED), and electrophoretic particles. A typical example is an electrophoretic display (EPD) using.

Among them, an OLED display device is a self-emitting device that emits light through an organic light emitting layer through recombination of electrons and holes, and is expected as a next-generation display device because of its high luminance, low driving voltage, and ultra-thinning.

Each of a plurality of pixels or sub-pixels constituting the OLED display device includes an OLED element composed of an organic light emitting layer between an anode and a cathode, and a pixel circuit independently driving the OLED element.

The pixel circuit includes a switching thin film transistor (TFT) that supplies a data signal from a data line to a storage capacitor, and a driving TFT that controls current according to the voltage charged in the storage capacitor and supplies it to an OLED device. And, the OLED element generates light proportional to the current.

In the OLED display device, driving characteristics such as threshold voltage (hereinafter referred to as Vth) and mobility of TFTs for each sub-pixel are non-uniform depending on process variation, driving environment, driving time, etc., and thus driving current for the same voltage is different, which may cause luminance non-uniformity. .

In order to solve this problem, the OLED display device determines and stores a compensation value for compensating the characteristic deviation of each subpixel based on the result of sensing the driving characteristic of each subpixel, and stores the compensation value for each subpixel using the stored compensation value. An external compensation technology that compensates for the image data to be supplied is used.

However, in the conventional OLED display device, the OLED display module operates in the sensing mode and updates the compensation value only when the sensing mode is instructed according to a preset time in the host set, such as a power on/off time.

Because of this, the conventional OLED display device operates in a predetermined sensing mode even when a compensation value update is not required, which takes unnecessary time, or cannot operate in a sensing mode even when a compensation value update is required. There are vulnerabilities that cannot be effectively performed according to

The present invention provides an OLED display device capable of efficiently performing a sensing operation for updating a compensation value.

An OLED display device according to an embodiment includes a display module including a display panel, a panel driver, and a timing controller, and a host set that supplies an image source to the display module and instructs a sensing mode operation.

The timing controller according to an embodiment operates in a corresponding sensing mode when receiving a sensing command signal instructing a sensing mode operation from a host set, senses driving characteristics of each subpixel through a panel driver, and stores the sensing result in a memory. The compensation value of each subpixel is updated. In addition, the timing controller according to an embodiment determines whether the sensing mode is required by monitoring the driving of the display module, and when it is determined that the sensing mode is required, the sensing request state is transmitted to the host set so that the host set transmits a sensing command signal. do.

According to an exemplary embodiment, the timing controller analyzes accumulated image data to predict a characteristic change of the driving TFT, to perform sensing before or after a deterioration compensation step of an OLED device, or based on information on a sensing mode execution process stored in a memory. When an abnormal operation for the mode is confirmed, it is determined that the sensing mode is necessary, and the sensing request status is transmitted to the host set.

The timing controller according to an embodiment counts the number of times of entering the sensing mode in which the sensing mode is enabled in response to a sensing command signal supplied from the host set and the number of times of completion of the sensing mode after the completion of the sensing mode, respectively, and stores them in a memory. By comparing the number of entering the sensing mode and the number of completing the sensing mode stored in , it is checked whether there is an abnormal operation in the sensing mode.

The timing controller according to an embodiment stores a sensing request state in a memory when it is determined that the sensing mode is necessary, and a sensing non-request state when it is determined that the sensing mode is unnecessary. According to an exemplary embodiment, the host set reads the sensing request state stored in the memory and transfers the sensing command signal to the timing controller, and does not output the sensing command signal when the sensing non-request state is read.

An embodiment of the present invention requests the sensing mode from the host set whenever the display module needs a sensing mode for updating a compensation value through bi-directional communication between the host set and the display module, and performs the sensing mode according to the host set's instructions. The operation timing of the sensing mode can be efficiently adjusted.

1 is a block diagram schematically illustrating the configuration of an OLED display device according to an embodiment of the present invention.
2 is an equivalent circuit diagram showing the configuration of one sub-pixel according to an embodiment of the present invention.
3 is a flowchart illustrating a process of performing a sensing mode by a timing controller in an OLED display device according to an embodiment of the present invention.
4 is a timing diagram illustrating transmission/reception waveforms in a sensing mode request state and an unrequested state in an OLED display device according to an embodiment of the present invention.

1 is a block diagram schematically showing the configuration of an OLED display device according to an embodiment of the present invention, and FIG. 2 is an equivalent circuit diagram showing the configuration of one subpixel according to an embodiment of the present invention.

Referring to FIG. 1 , an OLED display device according to an embodiment includes a host set 100 and a display module 200 that perform bi-directional communication. The host set 100 includes a System on Chip (hereinafter referred to as SoC) 110 and the like. The display module 200 includes a timing controller 210, a memory 212, a panel driver 220, a display panel 230, and the like. The panel driver 220 includes a data driver 222 and a gate driver 224 .

The host set 100 may be any one of a system of a portable terminal such as a computer, a TV system, a set-top box, a tablet or a mobile phone.

The SoC 110 has a built-in scaler to perform necessary image processing, such as scaling an image to be displayed on the display module 200 according to the resolution of the display module 200, and then image data for which image processing has been completed. is supplied to the timing controller 210 of the display module 200 along with the timing control signals. The timing control signals may include a dot clock, a data enable signal, a vertical sync signal, a horizontal sync signal, and the like.

The SoC 110 senses the characteristics (Vth of driving TFT, mobility, Vth of OLED, etc.) of each subpixel in the display module 200 through bi-directional communication with the timing controller 210, and stores the values in the memory 212. The RS mode is instructed to the display module 200 so as to efficiently perform the Real Sensing (RS) mode for updating the stored compensation value.

For example, when an RS request is received from the timing controller 210 because the display module 200 needs to operate in the RS mode, the SoC 110 transmits the RS command to the timing controller 210. so that the display module 200 operates in the RS mode. In addition, even if there is no RS request from the timing controller 210, the SoC 110 may periodically transmit an RS command to the timing controller 210 to instruct the display module 200 to operate in the RS mode. When the SoC 110 receives the RS done signal from the timing controller 210, it is determined that the RS operation of the display module 200 is completed.

The timing controller 210 controls driving timings of the panel driver 220, that is, the data driver 222 and the gate driver 224, respectively, using the timing control signals supplied from the SoC 110 during driving in the normal display mode. Data control signals and gate control signals are generated and supplied to the data driver 222 and the gate driver 224 . The timing controller 210 compensates for image data supplied from the SoC 110 using a compensation value stored in the memory 212 and supplies the compensated image data to the panel driver 220 .

When an RS command is received from the SoC 110 of the host set 100, the timing controller 210 drives the panel driving unit 220 and the display panel 230 in the RS mode to display each subpixel of the display panel 230. The characteristics (Vth of the driving TFT, mobility, Vth of the OLED, etc.) are sensed, and a compensation value for each subpixel stored in the memory 212 is updated using the sensing result.

Compensation information is preset and stored in the memory 212 together with various control information to be used in the timing controller 210 . The compensation information stored in the memory 212 includes a mobility compensation value of each subpixel for compensating for the mobility deviation of the driving TFT between subpixels and a Vth compensation value of each subpixel for compensating for the Vth of the driving TFT. and updated based on the sensing result of each subpixel obtained by the RS operation of the display module 200.

In the RS mode, the timing controller 210 supplies a data signal for sensing to the display panel 230 through the data driver 222 to drive a corresponding subpixel, and among the Vth and mobility of the driving TFT from the driven subpixel The compensation value stored in the memory 212 may be updated by sensing a signal having at least one characteristic, processing the sensing result through a predetermined operation, and converting the compensation value into a compensation value.

For example, the timing controller 210 uses information obtained by sensing a linear section in which the source voltage increases due to the driving of the driving TFT in each subpixel to detect a change in mobility of the driving TFT that is sensitive to driving environments such as temperature and light. It is calculated, and the mobility compensation value of each subpixel stored in the memory 212 may be updated using the calculated result. The RS mode for updating the mobility compensation value corresponds to a fast mode in which the required time is relatively short, and is indicated by the SoC 110 in at least one of the power-on time and the vertical blank period of the display section. can be performed according to

In addition, the timing controller 210 senses the Vth of the driving TFT using information obtained by sensing the section in which the driving TFT is driven in each sub-pixel and reaches saturation, and uses the sensing result for each sub-pixel stored in the memory 212. The Vth compensation value of the pixel can be updated. The Vth compensation value may compensate for Vth deviation of the driving TFT between subpixels and compensate for Vth shifted due to deterioration due to electrical stress as the driving time elapses. The RS mode for updating the Vth compensation value corresponds to a slow mode requiring longer sensing time than the aforementioned fast mode, and may be performed according to instructions of the SoC 110 during power-off time.

The timing controller 210 performs an RS mode operation according to the instruction of the SoC 110 and transmits an RS completion signal to the SoC 110 when the update of the compensation value of the memory 212 is completed.

In particular, the timing controller 210 monitors the driving state of the display module 200, such as image data, sensing data, RS mode, etc., checks whether the RS mode for updating the compensation value is required, and determines that the RS mode is required. When the RS mode is requested to the SoC 110, the SoC 110 may instruct the timing controller 210 to perform an RS operation. In other words, the timing controller 210 can monitor the operating state of the display module 200 and, if necessary, efficiently adjust the operation timing of the RS mode through bi-directional communication with the host set 100 .

For example, the timing controller 210 may accumulate and analyze image data displayed on the display panel 230 or analyze sensing data to predict the Vth shift of the driving TFT. As a result of the analysis, if the Vth shift is predicted, RS When it is determined that an operation is necessary, the RS mode may be requested to the SoC 110 .

The timing controller 210 counts the driving time of the display module 200 and senses the OLED degradation of each subpixel for each set driving time, or predicts and senses the OLED degradation of each subpixel using the cumulative result of the image data. It is possible to compensate for afterimages and increase the lifespan of OLED devices by adjusting the luminance (luminance gain) of the image based on the deterioration information that has been or is predicted. The timing controller 210 may request an RS mode from the SoC 110 by determining that an RS operation is necessary before or after performing the degradation compensation algorithm. Accordingly, the timing controller 210 may improve compensation efficiency such as degradation compensation or Vth compensation by performing the RS mode before or after degradation compensation to update the Vth compensation value.

The timing controller 210 may request the RS mode from the SoC 110 even when a defective operation of the RS mode is recognized by checking whether the RS mode is normally performed. For example, the timing controller 210 counts the number of entries into the RS mode according to the RS command received from the SoC 110 and the number of RS completions when the operation of the RS mode is completed and outputs to the SoC 110, respectively. Stored in the memory 212, and the counted RS mode entry and completion counts are compared with each other, and if they do not match, it is determined that an unstable operation such as midway cancellation of the RS mode has occurred, and the RS mode can be requested from the SoC 110. there is.

The timing controller 210 may store an RS requested state or an RS unrequested state in the memory 212 after determining whether the aforementioned RS mode is required. When the SoC 110 reads the RS request state of the timing controller 210 stored in the memory 212 at a specific time such as power off, it can instruct the timing controller 210 with an RS command and read the RS unrequested state. , the RS command is not sent to the timing controller 210.

Even when the set board of the host set 100 is replaced, the replaced SoC 110 can grasp the operating state and history of the RS mode of the timing controller 210 stored in the memory 212 of the display module 200, If the RS request state stored in the memory 212 is read, the RS operation can be instructed to the display module 200 .

The SoC 110 may check the RS request state of the display module 200 by reading the RS state stored in the memory 212 of the display module 200 at a power on/off time or periodically.

In addition, the timing controller 210 may further perform various image processing for reducing power consumption, compensating for degradation of OLED devices, and the like. For example, the timing controller 210 may reduce power consumption by adjusting peak luminance (luminance gain) of an image according to an average picture level (APL) of the image.

The data driver 222 converts the data supplied from the timing controller 210 into an analog data signal using the data control signal supplied from the timing controller 210 in each of the display mode and the RS mode to display the display panel 230. supply The data driver 222 converts digital data into an analog data voltage using the gamma voltage set supplied from the gamma voltage generator.

The data driver 222 converts the voltage (or current) sensed through the reference line from each subpixel of the display panel 50 in the sensing mode into digital sensing information and supplies it to the timing controller 210 .

The data driver 222 is composed of at least one data drive IC, is mounted on a circuit film such as a tape carrier package (TCP), a chip on film (COF), or a flexible printed circuit (FPC), and is mounted on a TAB on the display panel 230. It may be attached by a tape automatic bonding (Tape Automatic Bonding) method or mounted on a non-display area of the display panel 230 by a COG (Chip On Glass) method.

The gate driver 224 drives a plurality of gate lines of the display panel 230 using the gate control signal supplied from the timing controller 210 . The gate driver 224 supplies a scan pulse of a gate-on voltage in a corresponding scan period to each gate line using a gate control signal, and supplies a gate-off voltage in the remaining periods.

The gate driver 224 may be composed of at least one gate drive IC, mounted on a circuit film, and attached to the display panel 230 in a TAB method or mounted on a non-display area of the display panel 230 in a COG method. . In contrast, the gate driver 224 is formed in the non-display area of the TFT substrate together with the TFT array formed in the pixel array of the display panel 230, thereby forming a GIP (Gate In Panel) type embedded in the display panel 230. It can be.

The display panel 230 displays an image through a pixel array in which pixels are arranged in a matrix form. A basic pixel is at least three subpixels (W/R/G, B/W/ R, G/B/W, R/G/B, or W/R/G/B).

For example, as shown in FIG. 2 , each subpixel includes an OLED element, first and second switching TFTs ST1 and ST2 and a driving TFT DT and a storage capacitor Cst to independently drive the OLED element. ), but the configuration of each subpixel is various, so it is not limited to the configuration of FIG. 2 .

The first and second switching TFTs ST1 and ST2 and the driving TFT DT may be an amorphous silicon (a-Si) TFT, a poly-Si TFT, an oxide TFT, or an organic TFT. etc. can be used.

The OLED element includes an anode connected to the driving TFT (DT), a cathode connected to the low potential power supply voltage (EVSS), and a light emitting layer between the anode and the cathode. The anode is formed independently for each subpixel, but the cathode is formed to be shared by all subpixels. The light emitting layer may include a hole injection layer, a hole transport layer, an organic light emitting layer, an electron transport layer, an electron injection layer, etc. sequentially stacked between an anode and a cathode, and a functional layer for improving light emitting efficiency and/or lifetime of the organic light emitting layer. can include more. In the OLED device, when a positive voltage is applied between the anode and the cathode, electrons from the cathode are supplied to the organic light emitting layer via the electron injection layer and the electron transport layer, and holes from the anode are supplied to the organic light emitting layer via the hole injection layer and the hole transport layer. are supplied Accordingly, in the organic light emitting layer, light is generated in proportion to the amount of current supplied from the driving TFT (DT) by emitting a fluorescent or phosphorescent material by recombination of supplied electrons and holes.

The first and second switching TFTs ST1 and ST2 are driven by the scan signals of the gate lines GLn and GLn+1, respectively, to generate the data voltage Vdata from the corresponding data line DL and the corresponding reference line RL. ) is supplied to the gate and source nodes of the driving TFT (DT), respectively. The second switching TFT ST2 is further used as a path for outputting the current of the driving TFT DT to the reference line RL in the sensing mode.

The storage capacitor Cst is connected between the gate node and the source node of the driving TFT DT. The storage capacitor Cst has a difference between the data voltage Vdata supplied to the gate node through the first switching TFT ST1 and the reference voltage Vref supplied to the source node through the second switching TFT ST2 ( Vdata-Vref) is charged and supplied as the driving voltage (Vgs) of the driving TFT (DT).

The driving TFT (DT) controls the current supplied from the high-potential power supply voltage (EVDD) supply line PL according to the driving voltage Vgs supplied from the storage capacitor Cst, so that the current proportional to the driving voltage Vgs ( Ids) is supplied to the OLED element to cause the OLED element to emit light.

3 is a flowchart illustrating a method of monitoring an RS mode in a timing controller of an OLED display device according to an embodiment of the present invention step by step.

At a specific point in time, such as when a power-off command is transmitted from the host set 100, the timing controller 210 checks the state of the display module 200 to determine whether the RS mode is required (S302), and determines that the RS operation is required. If it is determined, the RS request is transmitted to the host set 100 (S304), and if it is determined that it is unnecessary, the RS request is not transmitted. The timing controller 210 determines whether a Vth shift is predicted as a result of analyzing accumulated image data or sensing data, before or after performing a specific algorithm such as degradation compensation, or when the process of performing the RS mode stored in the memory 212 is in an abnormal state. (When the number of entry into the RS mode and the number of completion are different), it is determined that the RS operation is necessary and the RS request may be transmitted to the host set 100 .

In response to the RS request transmitted from the timing controller 210, the RS command, that is, the RS enable signal is received from the SoC 110 of the host set 100 (S306), and the number of RS entries according to the RS enable is counted. It is stored in the memory 212 (S308).

The timing controller 210 executes the RS mode, senses the Vth of each subpixel through the data driver 222, and updates the Vth compensation value stored in the memory 212 using the sensing result (S310).

When the operation in the RS mode is completed, the timing controller 210 counts the number of RS completions and stores them in the memory 212 (S312), transmits the RS completion signal to the host set 100, and ends (S314).

4 is a timing diagram illustrating transmission/reception waveforms in a case where a sensing mode is requested and not requested in an OLED display device according to an embodiment of the present invention.

Referring to FIG. 4(a) , when the RS request state stored in the memory 212 of the display module 200 is read (RD) from the host set 100, the RS command is transmitted (WR) to the display module 200. ), it can be seen that the display module 200 operates in the RS mode during the RS mode enable period, and when the RS operation is completed, the RS completion signal is transmitted to the host set 100. Referring to FIG. 4(b), it can be seen that when the host set 100 reads (RD) the RS unsolicited state stored in the memory 212 of the display module 200, the subsequent RS operation process is not performed. can

As described above, an embodiment of the present invention can efficiently adjust the operation timing of the RS mode whenever the RS mode is needed through bi-directional communication between the host set 100 and the display module 200.

According to an embodiment of the present invention, when the display module 200 displays an image under severe conditions with high luminance for a long time, such as a high dynamic range image, and a Vth shift is predicted, the host set In step 100, the RS operation may be instructed to the display module 200. In this case, the display module 200 senses the Vth of the driving TFT of each subpixel through the RS operation, and the Vth compensation value stored in the memory 212. Afterimages due to Vth shift can be prevented by updating .

In one embodiment of the present invention, even when the compensation algorithm is continuously updated due to the characteristics of the OLED display device, when an RS operation is required in conjunction with an algorithm updated in the timing controller 210, an RS request is additionally sent to the host set 100. Since the RS operation can be performed by transferring the RS operation, the RS operation can be efficiently performed in conjunction with various application technologies.

According to an embodiment of the present invention, the timing controller 210 stores both the number of RS entries and the number of RS completions in the memory 212, so that RS mode entry, completion, midway cancellation, etc. are performed using the information stored in the memory 212. It is possible to determine whether the RS mode is necessary by checking information, and RS mode execution information of the display module 200 stored in the memory 212 in the host set 100 can be checked and used for failure analysis.

An embodiment of the present invention requests the RS mode based on the RS mode execution information stored in the memory 212 of the display module 200 even if the host set 100 is replaced or the previous history disappears due to firmware update, etc. RS mode can be performed efficiently and stably.

Through the above description, those skilled in the art will understand that various changes and modifications are possible without departing from the spirit of the present invention. Therefore, the technical scope of the present invention should not be limited to the contents described in the detailed description of the specification, but should be determined by the claims.

100: host set 110: system on chip (SoC)
200: display module 210: timing controller
212: memory 220: panel driving unit
222: data driver 224: gate driver
230: display panel

Claims (9)

a display panel having a plurality of sub-pixels, each sub-pixel including an OLED element and a driving TFT for driving the OLED element;
a panel driver for driving the display panel;
a display module including a timing controller controlling the panel driver;
a host set supplying an image source to the display module and instructing a sensing mode operation;
The host set periodically transfers a sensing command signal instructing the sensing mode operation to the timing controller, or transfers the sensing command signal to the timing controller if there is a request from the timing controller. The method of claim 1,
The timing controller
A change in the characteristics of the driving TFT is predicted by analyzing the accumulated image data, or
Before or after the deterioration compensation step of the OLED device,
When an abnormal operation of the sensing mode is confirmed based on information on the execution process of the sensing mode stored in the memory,
An OLED display device that determines that the sensing mode is required and transfers the sensing request state to the host set. The method of claim 2,
The timing controller
In response to the sensing command signal supplied from the host set, counting the number of times of entering the sensing mode enabling the sensing mode and the number of completions of the sensing mode after completion of the sensing mode are respectively counted and stored in the memory;
An OLED display device that compares the number of entering the sensing mode and the number of completion of the sensing mode stored in the memory to determine whether an abnormal operation in the sensing mode occurs. The method of claim 3,
The timing controller
Storing the sensing request state in the memory when it is determined that the sensing mode is necessary and a sensing non-request state when it is determined that the sensing mode is unnecessary;
wherein the host set reads the sensing request state stored in the memory and transmits the sensing command signal to the timing controller, and does not output the sensing command signal when the sensing non-request state is read. The method of claim 1,
The timing controller
When a sensing command signal instructing an operation of the sensing mode is supplied from the host set, it operates in the corresponding sensing mode, senses the driving characteristics of each subpixel through the panel driver, and uses the sensing result to determine the values of the subpixels stored in the memory. update the reward value,
An OLED display device that monitors driving of the display module to determine whether the sensing mode is required, and transmits a sensing request state to the host set so that the host set transmits the sensing command signal when it is determined that the sensing mode is required. . A display panel having a plurality of sub-pixels, each sub-pixel including an OLED element and a driving TFT for driving the OLED element;
a panel driver for driving the display panel;
a display module including a timing controller controlling the panel driver;
a host set supplying an image source to the display module and instructing a sensing mode operation;
The timing controller calculates a change in mobility of the driving TFT using information obtained by sensing a linear section in which a source voltage increases due to driving of the driving TFT in each subpixel, and stores the result in a memory using the calculated result. Updating the mobility compensation value of each subpixel, the OLED display device. a display panel having a plurality of sub-pixels, each sub-pixel including an OLED element and a driving TFT for driving the OLED element;
a panel driver for driving the display panel;
a display module including a timing controller controlling the panel driver;
a host set supplying an image source to the display module and instructing a sensing mode operation;
The timing controller calculates a change in mobility of the driving TFT using information obtained by sensing a linear section in which a source voltage increases due to driving of the driving TFT in each subpixel, and stores the result in a memory using the calculated result. Updating a mobility compensation value of each subpixel;
The sensing mode for updating the mobility compensation value performs the sensing mode operation in at least one period of a power-on time corresponding to a relatively short fast mode or a vertical blank period of a display section. An OLED display device that is performed according to an instructing sensing command signal. a display panel having a plurality of sub-pixels, each sub-pixel including an OLED element and a driving TFT for driving the OLED element;
a panel driver for driving the display panel;
a display module including a timing controller controlling the panel driver;
a host set supplying an image source to the display module and instructing a sensing mode operation;
The timing controller senses the threshold voltage (Vth) of the driving TFT by using information obtained by sensing a section in which the driving TFT is driven to reach a saturation state in each subpixel, and uses the sensing result to detect the threshold voltage Vth stored in a memory. An OLED display device for updating a threshold voltage (Vth) compensation value of each subpixel. a display panel having a plurality of sub-pixels, each sub-pixel including an OLED element and a driving TFT for driving the OLED element;
a panel driver for driving the display panel;
a display module including a timing controller controlling the panel driver;
a host set supplying an image source to the display module and instructing a sensing mode operation;
The timing controller senses the threshold voltage (Vth) of the driving TFT by using information obtained by sensing a section in which the driving TFT is driven to reach a saturation state in each subpixel, and uses the sensing result to detect the threshold voltage Vth stored in a memory. Updating the threshold voltage compensation value of each subpixel;
The sensing mode for updating the threshold voltage compensation value is performed according to a sensing command signal instructing the sensing mode operation at a power-off time corresponding to a slow mode in which sensing time is long, OLED display device .

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