KR102084444B1 - Organic Light Emitting diode Display - Google Patents

Abstract

The present invention relates to an organic light emitting diode display.
The organic light emitting diode display according to the present invention includes a driving transistor supplied with driving power through a drain electrode and controlling the organic light emitting diode according to a potential difference between a gate and a source electrode, wherein the organic light emitting diode display includes a response to a scan signal. A first transistor supplying a data voltage to a gate electrode of the driving transistor; A second transistor supplying an initialization voltage to a source electrode of the driving transistor in response to a sense signal supplied to a gate electrode; And a third transistor configured to supply the sense signal to the gate electrode of the second transistor in response to the scan signal, and to turn off the first transistor to internally compensate for the mobility variation of the driving transistor. And a sensing period for turning on the third transistor and turning off the third transistor to raise the potential of the source electrode of the driving transistor.

Description

Organic Light Emitting Diode Display

The present invention relates to an organic light emitting diode display.

Flat panel displays (FPDs) are widely used not only for monitors of desktop computers but also for portable computers such as notebook computers and PDAs and mobile phone terminals due to advantages of miniaturization and light weight. Such flat panel displays include liquid crystal displays; LCD), plasma display panel (PDP), field emission display device (Field Emission Display; FED) and an organic light emitting diode display (OLED).

Among them, the organic light emitting diode display has a fast response speed, high luminance, high luminance, and a large viewing angle. In general, an organic light emitting diode display device applies a data voltage to a gate electrode of a driving transistor by using a switch transistor turned on by a scan signal, and emits an organic light emitting diode using the data voltage supplied to the driving transistor. . That is, the current supplied to the organic light emitting diode is controlled by the data voltage applied to the gate electrode of the driving transistor. However, due to the characteristics of the manufacturing process, each driving transistor formed in the pixels may have a deviation with respect to the threshold voltage Vth. Due to the deviation of the threshold voltage of the driving transistor, the current supplied to the organic light emitting diode may be provided with a value different from the designed value, and thus the luminance to emit light may be different from the desired value.

In order to improve this, the image quality compensation method of reducing the luminance unevenness by sensing characteristic parameters (threshold voltage, mobility) of the driving transistor from each pixel and appropriately correcting the input data according to the sensing result is used.

For example, the external compensation method disclosed in Korean Patent Laid-Open Publication No. 10-2013-0036659 (name: method for measuring transistor characteristics of an organic light emitting display device) places a current source outside a pixel, and the organic light emitting diode is connected to the organic light emitting diode through the current source. After applying a constant current, the voltage is measured accordingly to compensate for the deterioration deviation of the organic light emitting diode.

Commonly known image quality compensation techniques use a unique method to detect threshold voltage characteristics and mobility characteristics of a driving transistor, and each sensing method employs a different method and requires additional memory for storing offset values. .

Therefore, a new method for reducing memory while detecting threshold voltage characteristics and mobility characteristics of the driving transistor has been sought.

The present invention provides an organic light emitting diode display device capable of efficiently compensating data by detecting threshold voltage characteristics and mobility characteristics of a driving transistor.

The present invention is to provide an organic light emitting diode display that can reduce the time to detect the characteristics of the driving transistor while reducing the memory.

The organic light emitting diode display according to the present invention includes a driving transistor supplied with driving power through a drain electrode and controlling the organic light emitting diode according to a potential difference between a gate and a source electrode, wherein the organic light emitting diode display includes a response to a scan signal. A first transistor supplying a data voltage to a gate electrode of the driving transistor; A second transistor supplying an initialization voltage to a source electrode of the driving transistor in response to a sense signal supplied to a gate electrode; And a third transistor configured to supply the sense signal to the gate electrode of the second transistor in response to the scan signal, and to turn off the first transistor to internally compensate for the mobility variation of the driving transistor. And a sensing period for turning on the third transistor and turning off the third transistor to raise the potential of the source electrode of the driving transistor.

The organic light emitting diode display according to the present invention compensates the threshold voltage of the driving transistor by an external compensation method, thereby simplifying the structure of the pixel and improving the aperture ratio.

In addition, the organic light emitting diode display according to the present invention compensates the mobility of the driving transistor in the pixel structure without adding a separate process, thereby compensating for the mobility deviation in real time without requiring an additional process or memory. have.

1 is a view showing an organic light emitting display device according to the present invention.
2 is a diagram showing a pixel structure according to the present invention.
3 is a diagram illustrating an external compensation period and an internal compensation period.
4 is a diagram illustrating waveforms of gate signals for internal compensation.
5A to 5C are diagrams showing equivalent circuits of pixels during an internal compensation period.
6 is a diagram illustrating waveforms of gate signals for external compensation.
7A and 7B illustrate an equivalent circuit of a pixel in a threshold voltage detection process.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings. Like numbers refer to like elements throughout. In the following description, when it is determined that a detailed description of known functions or configurations related to the present invention may unnecessarily obscure the subject matter of the present invention, the detailed description thereof will be omitted.

1 shows an organic light emitting diode display according to the present invention.

Referring to FIG. 1, the organic light emitting diode display according to the present invention includes a display panel 10, a data driver 12, a gate driver 13, and a timing controller 11 in which pixels P are arranged in a matrix form. It is provided.

The display panel 10 includes a plurality of pixels P, and is for displaying an image based on the gray scales of the pixels P. FIG. The pixels P are arranged in a matrix form in the display panel 10 by having a plurality of pixels arranged at regular intervals on each of the first to mth horizontal lines.

Each pixel P is disposed in an area where the data line 14 and the gate line 15 intersect each other at right angles. The data line unit 14 connected to each pixel P includes a data line 14a, a reference voltage line 14b, and a driving power supply line 14c, and the gate line unit 15 includes a scan line 15. And a sense line 15b. In this case, adjacent horizontal lines share one sense line 15a. That is, the first and second horizontal lines HL1 and HL2 share the first sense line 15a-1.

Each of the pixels P includes an organic light emitting diode OLED, a driving transistor DT, first to second transistors T1, T2, and T3, and a storage capacitor Cs. The driving transistor DT, the first and second transistors T1 and T2 may be implemented as an oxide thin film transistor (TFT) including an oxide semiconductor layer. The oxide TFT is advantageous for the large area of the display panel 10 in consideration of electron mobility, process variation, and the like. However, the present invention is not limited thereto, and the semiconductor layer of the TFT may be formed of amorphous silicon, polysilicon, or the like.

The timing controller 11 is for controlling the driving timing of the data driver 12 and the gate driver 13. To this end, the timing controller 11 rearranges the digital video data RGB input from the outside to the data driver 12 in accordance with the resolution of the display panel 10. The timing controller 11 operates the data driver 12 based on timing signals such as a vertical synchronization signal Vsync, a horizontal synchronization signal Hsync, a dot clock signal DCLK, and a data enable signal DE. The data control signal DDC for controlling timing and the gate control signal GDC for controlling the operation timing of the gate driver 13 are generated.

The data driver 12 is for driving the data line unit 14. To this end, the data driver 12 converts the digital video data RGB input from the timing controller 11 into an analog data voltage based on the data control signal DDC and supplies the converted data to the data lines 14. In addition, the data driver 12 includes an analog-digital converter (hereinafter, referred to as an ADC) for converting a sensing voltage fed back from each pixel P into sensing data.

The gate driver 13 drives the gate line unit 15 and generates a gate signal using the gate control signal GDC provided from the timing controller 11. The gate control signal GDC may include a gate start pulse GSP indicating a start scan line at which scanning starts, and a gate shift clock GSC for sequentially shifting the gate start pulse GSP. And a gate output enable (GOE) indicating the output of the gate driver.

FIG. 2 illustrates an example of the pixel P shown in FIG. 1. Referring to FIG. 2, a pixel P according to an exemplary embodiment may include an organic light emitting diode OLED, a driving transistor DT, first to third transistors T1, T2, and T3, and a storage capacitor Cs. ) And an auxiliary capacitor C1.

The organic light emitting diode OLED emits light by the driving current supplied from the driving transistor DT. A multilayer organic compound layer is formed between the anode electrode and the cathode electrode of the organic light emitting diode OLED. The organic compound layer includes a hole injection layer (HIL), a hole transport layer (HTL), an emission layer (EML), an electron transport layer (ETL) and an electron injection layer (Electron Injection layer, EIL). The anode electrode of the organic light emitting diode OLED is connected to the source electrode of the driving transistor DT, and the cathode electrode is connected to the low potential driving voltage VSS.

The driving transistor DT controls the driving current applied to the organic light emitting diode OLED with its gate-source voltage. For this purpose, the gate electrode of the driving transistor DT is connected to the input terminal of the data voltage Vdata, the drain electrode is connected to the input terminal of the driving voltage EVDD, and the source electrode is connected to the low voltage driving voltage VSS.

The first transistor T1 controls the current path between the data line 14a and the driving transistor DT in response to the scan signal Scan. To this end, the gate electrode of the first transistor ST1 is connected to the scan line 15a, the drain electrode is connected to the data line 14a, and the source electrode is connected to the first node N1 connected to the gate electrode of the driving transistor DT. Connected.

The second transistor T2 is positioned between the reference voltage line 14b and the second node N2 to receive an initialization voltage from the reference voltage line 14b and provide it to the second node N2. The gate electrode of the second transistor T2 is connected to the source electrode of the third transistor T3 in response to the scan signal. The drain electrode of the third transistor T3 is connected to the sense line. That is, the second transistor T2 operates only when the scan signal SCAN and the sense signal SENSE are turned on at the same time.

The storage capacitor Cst maintains the data voltage Vdata provided from the data line 14a for one frame so that the driving transistor DT maintains a constant voltage. To this end, the storage capacitor Cs is connected to the gate electrode and the source electrode of the driving transistor DT.

The data driver 12 is connected to the pixel P through the data line 14a and the reference voltage line 14b. The data driver 12 includes first and second digital-to-analog converters (DACs), analog-to-digital converters (ADCs), and a first switch SW1. do. The first DAC provides the compensation data MVdata with the digital video data RGB compensated through the data line 14a to the pixel, and the second DAC supplies the initialization voltage Vref to the pixel through the reference voltage line 14b. To provide. The ADC converts an analog sensing voltage into a digital sensing value during sensing operation using an external compensation method.

FIG. 3 is a diagram illustrating a period in which the threshold voltage change of the driving transistor DT is compensated by an external compensation scheme and a period in which the mobility change of the drive transistor DT is compensated by an internal compensation scheme.

As shown in FIG. 3, the change in mobility μ of the driving transistor DT may be compensated for in the image display period DP according to an internal compensation scheme. The change in the threshold voltage Vth of the driving transistor DT may include a second ratio disposed at a rear end of the first non-display period X1 and / or the image display period X0 disposed in front of the image display period DP. In the display period X2, the compensation may be performed according to an external compensation scheme. Here, the first non-display section X1 is defined as a section immediately after the driving power is applied and before the image is displayed, and the second non-display section X2 is the driving power EVDD immediately after the image display is finished. It can be defined as the interval until it is blocked.

4 is a diagram illustrating a timing of a driving waveform for performing mobility compensation on the pixel P according to the present invention, and FIGS. 5A to 5C illustrate an equivalent circuit of the pixel P using the driving waveform. Drawing. In this case, FIGS. 5A to 5C show solid lines indicating that the devices are activated, and dotted lines indicating that the devices are inactive.

Referring to FIG. 4, an internal compensation method for compensating the mobility μ of the driving transistor DT includes an initialization period Ti, a sensing period Ts, and a light emission period Te.

4 and 5A, during the initialization period Ti, a high level scan signal SCAN is provided through the scan line 15a, and a high level sense signal SENSE is provided through the sense line 15b. Is provided. Therefore, all of the first to third transistors T3 are turned on. The first transistor T1 is turned on in response to the scan signal SCAN and supplies the compensation data MVdata provided from the data line 14a to the gate electrode of the driving transistor DT. As the scan signal SCAN and the sense signal SENSE are simultaneously maintained at the high level, the third transistor T3 is turned on and the second transistor T2 connected to the source electrode of the third transistor T3 is also turned on. Is turned on. The second transistor T2 supplies an initialization voltage provided from the reference voltage line 14b to the source electrode of the driving transistor DT while being turned on. Accordingly, the potential between the gate and source electrodes of the driving transistor DT is initialized constantly.

4 and 5B, the scan signal SCAN maintains a high level and the sense signal SENSE becomes a low level during the sensing period Ts.

Accordingly, the first transistor T1 maintains the turn-on state to maintain the gate potential Vg of the driving transistor DT as the compensation data voltage MVdata.

The third transistor T3 does not operate even when the high level scan signal is provided to the gate electrode, since the drain electrode becomes low voltage by the sense signal SENSE. Therefore, the second transistor T2, in which the gate electrode is connected to the source electrode of the third transistor, also does not operate. In the driving transistor DT, a current corresponding to the potential difference Vgs between the gate and the source set in the initialization period Ti flows. Therefore, the source potential Vs of the driving transistor DT rises toward the data voltage MVdata applied to the gate electrode of the driving transistor DT, and thus the potential difference between the gate and the source of the driving transistor DT according to the desired gray level. Program (Vgs).

4 and 5C, the scan signal SCAN and the sense signal SENSE are both maintained at a low level during the light emission period Te. The gate potential Vg and the source potential Vs of the driving transistor DT are maintained after rising to a voltage level above the threshold voltage of the organic light emitting diode OLED while maintaining the programmed potential difference Vgs in the sensing period Ts. . A driving current corresponding to the gate-source potential difference Vgs of the programmed driving transistor DT flows through the organic light emitting diode OLED, and as a result, the organic light emitting diode OLED emits light to implement a desired gray scale.

As described above, the internal compensation scheme according to the present invention increases the source potential Vs of the driving transistor DT while the gate potential Vg of the driving transistor DT is fixed as the compensation data MVdata during the sensing period Ts. Let's do it. That is, the mobility difference between the driving transistors DT is compensated by varying the degree of increasing the source potential Vs in the process of the organic light emitting diode OLED along the operating point according to the mobility difference.

The driving current that determines the amount of light emission (luminance) of the pixel is determined by the mobility μ of the driving transistor DT (included in K or K ′ of the equation) and the driving transistor DT programmed in the sensing period Ts. It is proportional to the gate-source potential difference (Vgs). In the pixel with large mobility K, the source potential Vs of the driving transistor DT rises rapidly toward the higher gate potential Vg during the sensing period Ts so that the gate-source potential difference of the driving transistor DT is increased. In the case where the pixel Vgs is small and the mobility K 'is small, the source potential Vs of the driving transistor DT rises slowly toward the higher gate potential Vg during the sensing period Ts during the sensing period Ts. The gate-source potential difference Vgs of the transistor DT is largely programmed. As a result, the luminance deviation caused by the difference in the mobility μ is compensated.

6 is a diagram illustrating a timing of a driving waveform for performing the compensation of the threshold voltage Vth of the driving transistor DT of the pixel P of the present invention using an external compensation scheme, and FIGS. 7A to 7B illustrate the driving waveform. It is a figure which shows the equivalent circuit of the pixel P. FIG. 7A to 7B show solid lines indicating that the devices are activated, and dotted lines indicating that the devices are inactive.

6 and 7A, during the initialization period Ti, a high level scan signal SCAN is provided through the scan line 15a and a high level sense signal SENSE through the sense line 15b. ) Is provided. Therefore, all of the first to third transistors T3 are turned on. The first transistor T1 is turned on in response to the scan signal SCAN and supplies the compensation data MVdata provided from the data line 14a to the gate electrode of the driving transistor DT. As the scan signal SCAN and the sense signal SENSE are simultaneously maintained at the high level, the third transistor T3 is turned on and the second transistor T2 connected to the source electrode of the third transistor T3 is also turned on. Is turned on. The second transistor T2 supplies an initialization voltage provided from the reference voltage line 14b to the source electrode of the driving transistor DT while being turned on. Accordingly, the potential between the gate and source electrodes of the driving transistor DT is initialized constantly.

6 and 7B, the scan signal SCAN and the sense signal SENSE maintain the high level during the sensing period Ts. Then, the first switch SW1 is turned off to connect the reference voltage line 14b to the ADC. As the first switch SW1 is turned off, the source electrode of the driving transistor DT is floated. Since the driving transistor DT is operated by the operation of the initialization period Ti while the source electrode of the driving transistor DT is floated, the source electrode is passed from the driving power supply EVDD via the drain electrode of the driving transistor DT. Current flows. Therefore, the source electrode is saturated with a potential corresponding to the difference between the data voltage Vdata and the threshold voltage Vth. As such, the potential accumulated at the source electrode of the driving transistor DT is sensed through the ADC, and the change of the threshold voltage is compensated based on the sensed voltage.

The method for compensating the threshold voltage Vth characteristic of the driving transistor DT may be performed among the non-display periods X1 and X2 illustrated in FIG. 3 because the sensing period takes a long time. In addition, a separate section may be set to sense the threshold voltage Vth.

Those skilled in the art will appreciate that various changes and modifications can be made without departing from the technical 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 defined by the claims.

10: display panel 11: timing controller
12: data driver 13: gate driver
14: data line portion 15: gate line portion

Claims (8)

In the organic light emitting diode display device comprising a plurality of pixels, each of the pixels is supplied with a driving power through a drain electrode and a driving transistor for controlling the organic light emitting diode according to the potential difference between the gate and the source electrode,
A first node connected between a data line to which a data voltage is supplied and a first node connected to a gate electrode of the driving transistor, and turned on according to a scan signal supplied from a scan line to supply a data voltage to the gate electrode of the driving transistor; transistor;
It is connected between a reference voltage line to which an initialization voltage is supplied and a second node connected to a source electrode of the driving transistor, and is turned on according to a sense signal supplied from a sense line to supply the initialization voltage to the source electrode of the driving transistor. A second transistor; And
And a third transistor connected between the gate electrode of the second transistor and the sense line and turned on according to the scan signal to supply the sense signal to the gate electrode of the second transistor.
Two pixels disposed in adjacent horizontal lines and vertically adjacent to each other share the sense line,
In the sensing period for compensating for the variation in mobility of the driving transistor internally, the first transistor is turned on and the third transistor is turned off, thereby shifting the potential of the source electrode of the driving transistor to the movement of the driving transistor. An organic light emitting diode display which rises differently according to FIG.
delete The method of claim 1,
And a sensing period of the driving transistor is performed in a display period in which the organic light emitting diode displays an image.
The method of claim 1,
And operating the driving transistor by initializing a potential between the gate and source electrodes of the driving transistor by maintaining both the scan signal and the sense signal at a high level before the sensing period.
The method of claim 1,
And turning off the scan signal and the sense signal to emit the organic light emitting diode according to a driving current programmed in the sensing period.
The method of claim 1,
The organic light emitting diode may be characterized by supplying the driving power in a state in which the source electrode of the driving transistor is floated, saturating the source electrode, and detecting a threshold voltage characteristic of the driving transistor by detecting a potential of the saturated source electrode. Diode display.
The method of claim 6,
And detecting the threshold voltage characteristic of the driving transistor in a non-display period. The method of claim 1,
In the pixel where the mobility of the driving transistor is relatively high, the gate-source voltage of the driving transistor is programmed to a first value within the sensing period, and in the pixel where the mobility of the driving transistor is relatively small, within the sensing period. Wherein the gate-source voltage of the driving transistor is programmed to a second value greater than the first value.

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