KR102189556B1 - Organic light emitting display device - Google Patents

Abstract

The present invention relates to an organic light-emitting display device, and in particular, an organic light-emitting display device capable of preventing a change in a current flowing to an organic light-emitting diode according to a change in a threshold voltage of a driving transistor and a change in characteristics of the organic light-emitting diode. To provide is a technical problem. To this end, the organic light-emitting display device according to the present invention includes a panel in which pixels including an organic light-emitting diode and a pixel driver driving the organic light-emitting diode are formed at each intersection area between data lines and gate lines, The pixel driver includes: a driving transistor connected between a first voltage supply line and a second voltage supply line to which the organic light emitting diode is connected; A first switching transistor configured to connect a first node connected to the first terminal of the driving transistor to the first voltage supply line in response to a first emission signal; A second switching transistor connecting a second node connected to the gate of the driving transistor to a data line in response to a first scan signal; A third switching transistor configured to connect a third node connected to the third terminal of the driving transistor to an initialization voltage supply line in response to a second scan signal; A storage capacitor connected between the second node and the third node; A driving capacitor connected between the driving transistor and the first voltage supply line; And a fourth switching transistor connecting the third node to the organic light emitting diode in response to a second emission signal.

Description

Organic light emitting display device{ORGANIC LIGHT EMITTING DISPLAY DEVICE}

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

In recent years, as the era develops into an information society, the importance of a flat panel display device (FPD) having excellent characteristics such as reduction in thickness, weight, and low power consumption is increasing. Flat panel display devices include a liquid crystal display device (LCD), a plasma display panel device (PDP), an organic light emitting display device (OLED), and more recently, electrophoresis. Electrophoretic display devices (EPDs) are also widely used.

Among them, a liquid crystal display device including a thin film transistor and an organic light emitting display device are excellent in resolution, color display, and image quality, and are widely commercialized as display devices for televisions, notebook computers, tablet computers, or desktop computers.

In particular, organic light-emitting display devices (OLEDs) are self-luminous devices, and are attracting attention as a next-generation flat panel display device because of their low power consumption, high response speed, high luminous expression, high brightness and wide viewing angle.

Each of the plurality of pixels constituting the organic light emitting display device independently comprises an organic light emitting diode (OLED) (hereinafter simply referred to as'OLED') and an OLED composed of an organic light emitting layer between the anode and the cathode. It includes a driving pixel circuit.

The pixel circuit includes a switching thin film transistor (hereinafter, simply referred to as'TFT'), a capacitor, and a driving TFT.

The switching TFT charges the data voltage to the capacitor in response to the scan pulse. The driving TFT controls the amount of light emitted by the OLED by controlling the amount of current supplied to the OLED according to the data voltage charged in the capacitor.

However, in the organic light emitting display device, due to reasons such as process variation, a difference in characteristics such as a threshold voltage (Vth) and mobility of a driving TFT occurs for each pixel, and a voltage drop of the high potential voltage (ELVDD) occurs. Occurs. Accordingly, for each pixel, the amount of current that drives the OLED varies, resulting in luminance deviation between pixels.

In general, differences in characteristics of driving TFTs that occur during initial driving of the organic light emitting display device cause spots or patterns on the screen.

When the organic light-emitting display device is continuously driven, a difference in characteristics due to deterioration of the driving TFT reduces the life of the organic light-emitting display panel or generates an afterimage. Accordingly, there is a need for a method capable of compensating for a characteristic difference due to deterioration of the driving TFT while the organic light emitting display device is continuously driven.

The present invention has been proposed in order to solve the above-described problems, and the organic light emitting display device capable of preventing the current flowing to the organic light emitting diode from being changed according to a change in a threshold voltage of a driving transistor and a characteristic change of the organic light emitting diode. It is a technical problem to provide

In the organic light-emitting display device according to the present invention for achieving the above-described technical problem, pixels comprising an organic light-emitting diode and a pixel driver driving the organic light-emitting diode are formed in each intersection area of data lines and gate lines. A driving transistor connected between a first voltage supply line and a second voltage supply line to which the organic light emitting diode is connected; A first switching transistor configured to connect a first node connected to the first terminal of the driving transistor to the first voltage supply line in response to a first emission signal; A second switching transistor connecting a second node connected to the gate of the driving transistor to a data line in response to a first scan signal; A third switching transistor configured to connect a third node connected to the third terminal of the driving transistor to an initialization voltage supply line in response to a second scan signal; A storage capacitor connected between the second node and the third node; A driving capacitor connected between the driving transistor and the first voltage supply line; And a fourth switching transistor connecting the third node to the organic light emitting diode in response to a second emission signal.

According to the present invention, even if the threshold voltage of the driving transistor driving the organic light-emitting diode and the characteristics of the organic light-emitting diode are changed, the luminance deviation between pixels may be reduced, and accordingly, the image quality of the organic light-emitting display device can be improved. have.

1 is a configuration diagram of an organic light emitting display device according to an embodiment of the present invention.
2 is a configuration diagram of a pixel applied to an organic light emitting display device according to the first embodiment of the present invention.
3 is a waveform diagram illustrating gate signals applied to the organic light emitting display device according to the first embodiment of the present invention.
4 is a configuration diagram of a pixel applied to an organic light emitting display device according to a second embodiment of the present invention.
5 is an exemplary view illustrating a method of operating the pixel driver during an initialization period (A) applied to the organic light emitting display device according to the second exemplary embodiment of the present invention.
6 is an exemplary view illustrating a method of operating the pixel driver during a sampling period (B) applied to an organic light emitting display device according to a second exemplary embodiment of the present invention.
7 is an exemplary view illustrating a method of operating the pixel driver during a programming period (C) applied to the organic light emitting display device according to the second embodiment of the present invention.
8 is an exemplary view illustrating a method of operating the pixel driver during a light emission period (D) applied to the organic light emitting display device according to the second exemplary embodiment of the present invention.
9 is an exemplary view showing a circuit configuration of a pixel and timing of gate signals applied to an organic light emitting display device according to a third embodiment of the present invention.
10 is a graph showing a state in which an amount of current flowing through an organic light-emitting diode applied to an organic light-emitting display device according to the present invention changes according to a change in capacitance of the organic light-emitting diode.

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

In the present invention, a thin film transistor (TFT) may be used as the transistor, and the transistor may be configured as a P type or an N type. In the following, for convenience of explanation, the present invention will be described using an N-type thin film transistor as an example of a transistor. Accordingly, the gate high voltage is a gate-on voltage for turning on the transistor, and the gate low voltage VGL is a gate-off voltage for turning off the transistor. In addition, in describing the pulse type signal, the gate high voltage is defined as a "high signal", and the gate low voltage is defined as a "low signal".

1 is a configuration diagram of an organic light emitting display device according to an embodiment of the present invention, and FIG. 2 is a configuration diagram of a pixel applied to an organic light emitting display device according to a first embodiment of the present invention.

The organic light-emitting display device according to the present invention drives the organic light-emitting diode and the organic light-emitting diode at each intersection area of the data lines DL1 to DLd and the gate lines GL1 to GLg, as shown in FIG. 1. The pixels P, which are formed of the pixel driver, are formed of the panel 100, the gate driver 200 for driving the gate lines, the data driver 3300 for driving the data lines, and an input image input from the outside. Data is aligned and the aligned image data (R, G, B) is supplied to the data driver 300, and the gate driver 200 and the gate driver 200 and the data control signal DCS are used. It includes a timing controller 200 that controls the data driver 300.

First, a pixel P is formed in the panel 100 in each area where a plurality of gate lines GL1 to GLg and data lines DL1 to DLd intersect.

Each pixel P, as shown in FIG. 2, includes an organic light-emitting diode OLED and a pixel driver 110 for driving the organic light-emitting diode. In addition, each pixel driver 110 is connected to a gate line GL, a data line DL, a first voltage supply line VL1, a second voltage supply line VL2, and an initialization voltage supply line VL3. .

The pixel driver 110 includes a driving transistor DR connected between a first voltage supply line VL1 and a second voltage supply line VL2 to which the organic light emitting diode is connected, and a first emission signal EM1. ) In response to, a first switching transistor T1 and a first scan signal SCAN1 connecting the first node N1 connected to the first terminal of the driving transistor DR to the first voltage supply line VL1. ) In response to the second switching transistor T2 connecting the second node N2 connected to the gate of the driving transistor DR with the data line DL, and in response to a second scan signal SCAN2 , A third switching transistor T3 connecting a third node N3 connected to the third terminal of the driving transistor DR to an initialization voltage supply line VL3, the second node N2 and the third node And a storage capacitor Cst connected between (N3) and a driving capacitor Colled' connected between the driving transistor DR and the first voltage supply line.

Here, a first voltage is supplied to the first voltage supply line VL1. When the driving transistor DR is an N-type as described above, the first voltage is a high potential voltage ELVDD. In addition, a second voltage is supplied to the second voltage supply line VL2. When the driving transistor DR is of the N type as described above, the second voltage is a low potential voltage VSS. The high potential voltage ELVDD has a relatively higher voltage than the low potential voltage VSS. The low potential voltage VSS may be a ground voltage. Hereinafter, for convenience of explanation, the present invention will be described with the case where the first voltage is the high potential voltage ELVDD and the second voltage is the low potential voltage VSS. An initialization voltage Vini is supplied to the initialization voltage supply line VL3. The initialization voltage Vinit has a voltage lower than the threshold voltage of the driving transistor DR of each pixel P.

The pixel driver 110 is configured to compensate for a characteristic of the driving transistor DR, in particular, a change in a threshold voltage and a voltage drop in the first voltage ELVDD, thereby reducing a luminance deviation between each pixel P. I can.

Second, the timing controller 400 includes a timing signal input from an external system (not shown), that is, a vertical synchronization signal (Vsync), a horizontal synchronization signal (Hsync), a data enable signal (DE), a clock (CLK), etc. Using, a gate control signal GCS for controlling an operation timing of the gate driver 200 and a data control signal DCS for controlling an operation timing of the data driver 300 are generated. In addition, the timing controller 200 arranges the input image data input from the external system according to the size and resolution of the panel 100, and transfers the aligned image data R, G, B to the data driver 300 ).

To this end, the timing controller 400 includes a receiving unit for receiving input image data and timing signals from the external system, a control signal generating unit for generating various control signals, and rearranging the input image data to rearrange the image. And a data alignment unit for generating data, and an output unit for outputting the control signals and the image data to the data driver 300 and the gate driver 200.

Third, the data driver 300 converts digital image data (R, G, B) transmitted from the timing controller 400 into an analog data voltage, and supplies the gate-on voltage to the gate line GL. The data voltage Vdata corresponding to one horizontal line is supplied to the data lines DL for each horizontal period.

The data driver 300 converts the image data R, G, B to the data voltage Vdata using gamma voltages supplied from a gamma voltage generator (not shown), and then converts the data A voltage Vdata is supplied to the data line DL. To this end, the data driver 300 includes a shift register unit, a latch unit, a digital-to-analog converter (DAC), and an output buffer.

The data driver 300 supplies the data voltage Vdata to the data line DL only during the programming period described below, and supplies the reference voltage Vref to the plurality of data lines DL during the remaining period. .

Fourth, the gate driver 200 may be connected to the panel 100 in the form of a chip-on-film (COF), and may be directly mounted on the panel or formed directly on the panel.

The gate driver 200 generates the gate-on voltage in response to the gate control signal input from the timing controller 400, and then sequentially applies the gate-on voltage to the gate lines GL1 to GLg. To be supplied. The second switching transistors T2 formed in each pixel of a corresponding horizontal line to which the gate-on voltage is input are turned on, so that an image may be output to each pixel P. The gate-on voltage is hereinafter referred to as a first scan signal SCAN1.

The gate driver 200 generates a second scan signal SCAN2 and a first emission signal EM1 in response to the gate control signal input from the timing controller 400.

That is, the gate driver 200 supplies a plurality of gate signals according to the gate control signal GCS transmitted from the timing controller 200. The plurality of gate signals include the first scan signal SCAN1, the second scan signal SCAN2, and the first emission signal EN1. The gate signals are supplied to each pixel P.

3 is a waveform diagram illustrating gate signals applied to the organic light emitting display device according to the first embodiment of the present invention. Hereinafter, the configuration and operation method of the pixel driver applied to the organic light emitting display device according to the first embodiment of the present invention will be described in detail with reference to FIGS. 2 and 3.

The operation period of the pixel driver 110 is an initialization period (A) and sampling according to the pulse timing of the gate signals (SCAN1, SCAN2, EM1) supplied to the pixel (P), as shown in FIG. 3. It is divided into a period (B), a programming period (C), and a light emission period (D).

In the initialization period (A), the first scan signal SCAN1 and the second scan signal SCAN2 are high signals, and the first emission signal EM1 is a low signal.

In the sampling period B, the first scan signal SCAN1 and the first emission signal EM1 are high signals, and the second scan signal SCAN2 is a low signal.

In the programming period C, the first scan signal SCAN1 is a high signal, and the second scan signal SCAN2 and the first emission signal EM1 are low signals.

In the light emission period D, the first emission signal EM1 is a high signal, and the first scan signal SCAN1 and the second scan signal SCAN2 are low signals.

The data driver 300 supplies a data voltage Vdata to the data lines DL during the programming period C, and supplies a reference voltage Vref to the data lines DL during the remaining period. do.

As shown in FIG. 2, the pixel P includes the organic light emitting diode OLED, four transistors DR, T1, T2, T3, and two capacitors Cst and Coled1'. Thus, it includes the pixel driver 110 for driving the organic light emitting diode (OLED).

The driving transistor DR is connected between the first voltage supply line VL1 and the second voltage supply line VL2 together with the organic light emitting diode OLED, and in the light emitting period D, the organic Controls the amount of current flowing through the light-emitting diode (OLED).

The first switching transistor T1 is turned on or off according to the first emission signal EM1, and when turned on, the high potential voltage ELVDD is supplied to the first terminal of the driving transistor DR. do. For example, the first switching transistor T1 applies the high potential voltage ELVDD provided from the first voltage supply line VL1 to the driving transistor during the sampling period B and the light emission period D. Supply to the first terminal of (DR). When the driving transistor DR has an N-type configuration, among the three terminals of the driving transistor DR, the first terminal connected to the first voltage supply line VL1 is a drain, and the second voltage A third terminal connected to the supply line VL2 is a source, and a second terminal connected to the second switching transistor T2 is a gate.

The second switching transistor T2 is turned on or off according to the first scan signal SCAN1, and when turned on, a second node N2 connected to the gate of the driving transistor DR is connected to the data line ( DL). For example, the second switching transistor T2 receives the reference voltage Vref provided from the data line DL in the initialization period A and the sampling period B, and the second node ( Supply to N2). In addition, the second switching transistor T2 supplies the data voltage Vdata provided from the data line DL to the second node N2 during the programming period C.

The third switching transistor T3 is turned on or off according to the second scan signal SCAN2, and when turned on, the third node N3 connected to the third terminal of the driving transistor DR is It is connected to the initialization voltage supply line VL3. For example, the third switching transistor T3 supplies the initialization voltage Vinit supplied from the initialization voltage Vinit supply line to the third node N3 during the initialization period A. do.

The storage capacitor Cst is connected between the driving second node N2 and the third node N3. The storage capacitor Cst stores the threshold voltage Vth of the driving transistor DR in the sampling period B.

The driving capacitor Coled' is connected between the first voltage supply line VL1 and the third node N3. The driving capacitor Coled' is connected in series with the storage capacitor Cst and performs a function of relatively reducing a capacity ratio of the storage capacitor Cst. Accordingly, during the programming period C, the luminance of the organic light emitting diode OLED may be improved due to the data voltage Vdata applied to the second node N2. However, the driving capacitor Colled' may be connected between the initialization voltage supply line VL3 and the third node N3, and also, the second voltage supply line VL2 and the third node It may be connected between (N3).

Hereinafter, a driving method of the pixel driver 110 applied to the first embodiment of the present invention will be described with reference to FIGS. 1 to 3.

First, in the initialization period A, the second switching transistor T2 and the third switching transistor T3 are turned on. Accordingly, the reference voltage Vref is supplied to the second node N2 through the second switching transistor T2, and the initialization voltage Vinit is supplied to the third node N3, The pixel P is initialized.

Next, in the sampling period B, the first switching transistor T1 and the second switching transistor T2 are turned on. Accordingly, at the second node N2, the reference voltage Vref is maintained. In this case, the drain, which is the first terminal of the driving transistor DR, is floated with the first voltage ELVDD. Accordingly, when a current flows from the first terminal of the driving transistor DR to the source direction, which is the third terminal, and the voltage of the third terminal becomes "Vref-Vth", the driving transistor DR is turned. Is off. Here, "Vth" means a threshold voltage of the driving transistor DR.

Next, in the programming period C, the second switching transistor T2 is turned on. Accordingly, the data voltage Vdata is supplied to the second node N2 through the second switching transistor T2. In the third node N3, a coupling phenomenon occurs due to voltage distribution by a series capacitance between the storage capacitor Cst and the driving capacitor Colled'. Accordingly, the voltage of the third node N3 is changed to "Vref-Vth+C'(Vdata-Vref)". Here, C'means "Cstg/(Cstg+Coledg'+Coledg)", Cstg means a static capacitance of the storage capacitor (Cst), and Coledg' means the capacitance of the driving capacitor (Colde). And, Coled means a capacitance (capacitance) of the organic light-emitting diode (OLED). In the present invention, since the driving capacitor Colled' connected in series with the storage capacitor Cst is provided, the capacity ratio of the storage capacitor Cst can be relatively reduced. Accordingly, in the programming period C, the luminance of the organic light emitting diode OLED may be improved due to the data voltage Vdata applied to the second node N2.

Lastly, in the light emission period D, the first switching transistor T1 is turned on. Accordingly, the high potential voltage ELVDD is applied to the drain, which is the first terminal of the driving transistor, through the first switching transistor T1, and the driving transistor DR is applied to the organic light emitting diode. ). In this case, the formula for calculating the driving current Ioled supplied from the driving transistor DR to the organic light emitting diode OLED is as shown in [Equation 1].

Here, k = μ X (W/L) XC _GI . In addition, μ is the mobility of the driving transistor DR, C _GI is the parasitic capacitance of the driving transistor Tdr, W is the channel width of the driving transistor DR, and L is the driving transistor DR. Is a channel length of, Vdata is a data voltage supplied to the gate of the driving transistor DR, and Vref is the reference voltage supplied to the gate of the driving transistor DR.

According to [Equation 1], the current flowing through the organic light emitting diode is not affected by the threshold voltage Vth of the driving transistor DR and the high potential voltage ELVDD. Accordingly, in the first embodiment of the present invention, even if a characteristic variation occurs between the driving transistors DR formed in each pixel or a voltage drop of the high potential voltage ELVDD occurs, each pixel P ), the luminance deviation between them can be reduced. Further, in the first embodiment of the present invention, at the start of the light emission period D, the driving transistor DR is controlled by adjusting a rise time at which the first emission signal EM1 changes from a low signal to a high signal. ) May be compensated for the deviation of the mobility.

As described above, according to the first embodiment of the present invention, by compensating for a characteristic variation of the driving transistors and compensating for a voltage drop of the high potential voltage ELVDD, it is possible to improve image quality by reducing a luminance variation between pixels. have.

4 is a configuration diagram of a pixel applied to an organic light emitting display device according to a second embodiment of the present invention. In the following description, the same or similar content as described with reference to FIGS. 1 to 3 will be omitted or briefly described.

The organic light emitting display device according to the second embodiment of the present invention includes the panel 100, the gate driver 200, the data driver 3300, and the timing controller 200 as described with reference to FIG. 1. Includes.

Each pixel P, as shown in FIG. 4, includes an organic light emitting diode (OLED) and a pixel driver 110 driving the organic light emitting diode. In addition, each pixel driver 110 is connected to a gate line GL, a data line DL, a first voltage supply line VL1, a second voltage supply line VL2, and an initialization voltage supply line VL3. .

The pixel driver 110 includes a driving transistor DR connected between a first voltage supply line VL1 and a second voltage supply line VL2 to which the organic light emitting diode is connected, and a first emission signal EM1. ) In response to, a first switching transistor T1 and a first scan signal SCAN1 connecting the first node N1 connected to the first terminal of the driving transistor DR to the first voltage supply line VL1. ) In response to the second switching transistor T2 connecting the second node N2 connected to the gate of the driving transistor DR with the data line DL, and in response to a second scan signal SCAN2 , A third switching transistor T3 connecting a third node N3 connected to the third terminal of the driving transistor DR to an initialization voltage supply line VL3, the second node N2 and the third node In response to a storage capacitor Cst connected between (N3), a driving capacitor Colled' connected between the driving transistor DR and the first voltage supply line, and a second emission signal EM2, the And a fourth switching transistor T4 connecting the third node N3 to the organic light emitting diode OLED.

To further explain, comparing the pixel driving unit 110 applied to the second embodiment of the present invention and the pixel driving unit 110 applied to the first embodiment of the present invention, the second embodiment of the present invention The pixel driver 110 applied to the pixel further includes the fourth switching transistor T4.

In this case, the configuration and functions of the remaining components except for the fourth switching transistor T4 are the same as those described above. That is, the configuration and operation method of the pixel driving unit 110 applied to the organic light emitting display device according to the first embodiment of the present invention described with reference to FIGS. 2 and 3 is, in accordance with the second embodiment of the present invention. The configuration and operation method of the pixel driving unit 110 applied to the organic light emitting display device according to the present invention may be applied as it is.

Therefore, in the following, only the contents different from those mentioned in the description of the first embodiment of the present invention will be described in detail.

The operation period of the pixel driver 110 is an initialization period (A), a sampling period (B), and programming according to the pulse timing of the gate signals SCAN1, SCAN2, EM1, EM2 supplied to the pixel P. It is divided into a period (C) and a light emission period (D).

In the initialization period (A), the first scan signal SCAN1 and the second scan signal SCAN2 are high signals, the first emission signal EM1 is a low signal, and the second emission signal (EM2) is a high signal.

In the sampling period (B), the first scan signal SCAN1 and the first emission signal EM1 are high signals, and the second scan signal SCAN2 and the second emission signal EM2 are It is a low signal.

In the programming period (C), the first scan signal (SCAN1) is a high signal, the second scan signal (SCAN2) and the first emission signal (EM1) are low signals, and the second emission signal ( EM2) is a low signal.

In the light emission period D, the first emission signal EM1 is a high signal, the first scan signal SCAN1 and the second scan signal SCAN2 are low signals, and the second emission signal (EM2) is a high signal.

The fourth switching transistor T4 is turned on or off according to the second emission signal EM2, and when turned on, the third node N3 connected to the third terminal of the driving transistor DR is It is connected to the organic light emitting diode (OLED). For example, the fourth switching transistor T4 is turned on during the initialization period A and the light emission period D to connect the third node N3 with the organic light emitting diode OLED, It is turned off during the sampling period (B) and the programming period (C), thereby blocking the third node N3 from the organic light emitting diode OLED.

To this end, the fourth switching transistor T4 includes a first terminal connected to the third terminal of the driving transistor DR, a second terminal connected to the organic light emitting diode OLED, and the second emission. It includes a third terminal to which the signal EM2 is input. In this case, the third switching transistor T3 is a first terminal connected to the third node N3 between the second terminal of the fourth switching transistor T4 and the organic light emitting diode OLED, And a second terminal connected to the initialization voltage supply line VL3 and a third terminal to which the second scan signal SCAN2 is input.

5 is an exemplary diagram for explaining a method of operating the pixel driver during an initialization period (A) applied to an organic light emitting display device according to a second embodiment of the present invention, and FIG. 6 is a second embodiment of the present invention. Is an exemplary diagram for explaining a method of operating the pixel driver during the sampling period (B) applied to the organic light emitting display device according to FIG. 7, and FIG. 7 is a programming applied to the organic light emitting display device according to the second embodiment of the present invention. An exemplary view for explaining a method of operating the pixel driver during a period (C), and FIG. 8 is a diagram illustrating the pixel driver during a light emission period (D) applied to the organic light emitting display device according to the second embodiment of the present invention It is an exemplary diagram for explaining the operation method. In each drawing, (a) is an exemplary diagram showing the circuit configuration of the pixel driver, and (b) is a timing diagram of gate signals supplied to the pixel driver. Hereinafter, a driving method of the pixel driver 110 applied to the second embodiment of the present invention will be described with reference to FIGS. 5 to 8. In this case, the same or similar contents as the driving method of the pixel driver 110 described with reference to FIGS. 2 and 3 will be omitted or briefly described.

Before describing the second embodiment of the present invention, a brief summary of the first embodiment of the present invention is as follows.

The brightness of the organic light emitting diode (OLED) formed in each pixel of a general organic light emitting display device is proportional to the current Ioled flowing through the organic light emitting diode, as shown in [Equation 2] below. That is, the current Ioled flowing through the organic light emitting diode depends on the difference voltage V _GS between the gate voltage and the source voltage of the driving transistor controlling the organic light emitting diode and the threshold voltage V _TH of the driving transistor.

In [Equation 2], k = μ X (W/L) XC _GI . μ is the mobility of the driving transistor, C _GI is the parasitic capacitance of the driving transistor, W is the channel width of the driving transistor, L is the channel length of the driving transistor, and V _GS is the gate voltage of the driving transistor. The voltage difference between the source voltage and V _TH is the threshold voltage of the driving transistor Tdr. That is, in a general organic light emitting display device, the current Ioled flowing through the organic light emitting diode is affected by the threshold voltage Vth.

However, according to the first embodiment of the present invention, as described in [Equation 1], the current (Ioled) flowing through the organic light emitting diode (OLED) is a data voltage (Vdata) and the reference voltage (Vref ) Only. Therefore, even if the characteristic of the threshold voltage V _TH of the driving transistor DR is changed or a voltage drop of the high potential voltage ELVDD occurs, the current flowing through the organic light emitting diode is not affected by the change. .

However, in [Equation 1], C'= Cstg/(Cstg+Coledg+Coledg'). Here, Cstg is the capacitance of the storage capacitor Cst, Coledg' is the capacitance of the driving capacitor Colled', and Coledg is the capacitance of the organic light emitting diode (OLED).

That is, in the first embodiment of the present invention, the current Ioled flowing through the organic light emitting diode has a positive direction by the voltage drop of the threshold voltage Vth and the high potential voltage ELVDD of the driving transistor DR. However, it is affected by the change in the capacitance of the organic light emitting diode (Coledg).

To further explain, in the first embodiment of the present invention, by using the capacitance of the organic light emitting diode (Coledg), it is possible to increase the luminous efficiency of the organic light emitting diode. However, in the programming period C, the third terminal of the driving transistor DR, for example, the source, connected to the anode of the organic light emitting diode, is maintained in a floating state. Therefore, when the characteristics of the organic light-emitting diode (OLED) change according to temperature and deterioration, the capacitance (Coledg) of the organic light-emitting diode is changed, and accordingly, the amount of current (Ioled) flowing through the organic light-emitting diode is changed. can be changed.

However, according to the second embodiment of the present invention, the current Ioled flowing through the organic light emitting diode is not affected by a change in the capacitance of the organic light emitting diode (Coledg).

First, referring to FIG. 5, in the initialization period A, the second switching transistor T2, the third switching transistor T3, and the fourth switching transistor T4 are turned on. Accordingly, the reference voltage Vref is supplied to the second node N2 through the second switching transistor T2, and the initialization voltage Vinit is supplied to the third node N3, The pixel P is initialized. In this case, the first switching transistor T1 is turned off.

Next, referring to FIG. 6, in the sampling period (B), the first switching transistor T1 and the second switching transistor T2 are turned on, and the third switching transistor T3 and the fourth The switching transistors T4 are turned off. Accordingly, at the second node N2, the reference voltage Vref is maintained. In this case, the drain, which is the first terminal of the driving transistor DR, is floated with the first voltage ELVDD. Accordingly, when a current flows from the first terminal of the driving transistor DR to the source direction, which is the third terminal, and the voltage of the third terminal becomes "Vref-Vth", the driving transistor DR is turned. Is off. Here, "Vth" means a threshold voltage of the driving transistor DR.

Next, referring to FIG. 7, in the programming period (C), the second switching transistor T2 is turned on, and the first switching transistor T1, the third switching transistor T3, and the fourth switching transistor are switched on. The transistors T4 are turned off. Accordingly, the data voltage Vdata is supplied to the second node N2 through the second switching transistor T2. In the third node N3, a coupling phenomenon occurs due to voltage distribution by a series capacitance between the storage capacitor Cst and the driving capacitor Colled'. Accordingly, the voltage of the third node N3 is changed to "Vref-Vth+C'(Vdata-Vref)". Here, C'means "Cstg/(Cstg+Coledg')", Cstg means a fixed capacitance of the storage capacitor Cst, and Coledg' means a capacitance of the driving capacitor Colde. In the present invention, since the driving capacitor Colled' connected in series with the storage capacitor Cst is provided, the capacity ratio of the storage capacitor Cst can be relatively reduced. Accordingly, in the programming period C, the luminance of the organic light emitting diode OLED may be improved due to the data voltage Vdata applied to the second node N2. In addition, compared with the first embodiment of the present invention, it can be seen that Coledg, that is, the capacitance of the organic light emitting diode, is omitted in the calculation formula of C'. That is, in the programming period (C), the fourth switching transistor (T4) is turned off by the second emission signal (EM2), and accordingly, the characteristic of the organic light emitting diode (OLED) is the driving transistor (DR), the storage capacitor Cst and the driving capacitor Coled' are not affected.

As described above, in the programming period C, the data voltage Vdata is supplied to the gate as the second terminal of the driving transistor DR, and Vref− to the source as the third terminal of the driving transistor DR. Vth+C'(Vdata-Vref) is supplied. Substituting the above equations into [Equation 2] yields [Equation 3].

Finally, referring to FIG. 8, in the light emission period D, the first switching transistor T1 and the fourth switching transistor T4 are turned on, and the second switching transistor T2 and the third switching transistor T2 are turned on. The switching transistor T3 is turned off.

Accordingly, the high potential voltage ELVDD is applied to the drain, which is the first terminal of the driving transistor DR through the first switching transistor T1, and the driving transistor DR is driven to the organic light emitting diode. Supply current (Ioled). In this case, the driving current Ioled supplied from the driving transistor DR to the organic light emitting diode OLED is the same as the final equation of [Equation 3].

In the final formula of [Equation 3], C'means "Cstg/(Cstg+Coledg')" as described above. That is, according to the second embodiment of the present invention, as described in [Equation 3], the current Ioled flowing to the organic light emitting diode in the light emitting period D is Not only the threshold voltage Vth and the high potential voltage ELVDD, but also the capacitance of the organic light emitting diode Coledg are not affected.

Accordingly, in the second embodiment of the present invention, a characteristic variation occurs between the driving transistors DR formed in each pixel, a voltage drop of the high potential voltage ELVDD occurs, or the organic light emitting diode Even if the capacitance of the column is changed, the luminance deviation between the pixels P may be reduced.

Further, in the second embodiment of the present invention, at the start of the light emission period D, the driving transistor DR is controlled by adjusting a rise time at which the first emission signal EM1 changes from a low signal to a high signal. ) May be compensated for the deviation of the mobility.

The brief summary of the contents described above is as follows.

In the second embodiment of the present invention, in the initialization period (A), as shown in FIG. 5, the reference voltage Vref provided from the data line is supplied to the second node N2, and the third The switching transistor T3 supplies the initialization voltage Vini provided from the initialization voltage supply line VL3 to the third node N3. In the sampling period (B), as shown in FIG. 6, the reference voltage Vref provided from the data line is supplied to the second node N2, and the first voltage supplied from the first voltage supply line VL1. One voltage is supplied to the first terminal of the driving transistor DR, and the third node N3 and the organic light emitting diode OLED are cut off. In the programming period (C), as shown in FIG. 7, the data voltage (Vdata) provided from the data line is supplied to the second node (N2), and the third node (N3) and the organic light emitting diode (OLED) is blocked. In the light emission period D, as shown in FIG. 8, the first voltage provided from the first voltage supply line VL1 is supplied to the first terminal of the driving transistor DR, and the third The node N3 and the organic light emitting diode OLED are connected.

9 is an exemplary diagram showing a circuit configuration of a pixel and timing of gate signals applied to an organic light emitting display device according to a third embodiment of the present invention, (a) is an exemplary diagram showing the circuit configuration of the pixel, ( b) is a timing diagram of gate signals supplied to the pixels. In the following description, contents identical or similar to those described in the first and second embodiments of the present invention will be omitted or briefly described.

An organic light emitting display device according to a third embodiment of the present invention includes the panel 100, the gate driver 200, the data driver 3300, and the timing controller 200 as described with reference to FIG. 1. Includes.

Each pixel P includes an organic light emitting diode (OLED) and a pixel driver 110 driving the organic light emitting diode, as shown in FIG. 9A. In addition, each pixel driver 110 is connected to a gate line GL, a data line DL, a first voltage supply line VL1, a second voltage supply line VL2, and an initialization voltage supply line VL3. .

The pixel driver 110 includes a driving transistor DR, a first switching transistor T1, a second switching transistor T2, a third switching transistor T3, a storage capacitor Cst, and a driving capacitor Colled'. And a fourth switching transistor T4.

When comparing the second embodiment of the present invention with the third embodiment of the present invention, the connection position of the fourth switching transistor T4 applied to the pixel driver 110 applied to the third embodiment of the present invention is , It is different from the connection position of the fourth switching transistor T4 applied to the pixel driver 110 applied to the second embodiment of the present invention. In addition, the second emission signal EM2 driving the fourth switching transistor T4 applied to the second embodiment of the present invention is independent from the first emission signal EM2, but the present invention The second emission signal EM2 driving the fourth switching transistor T4 applied to the third embodiment of is the same signal as the first emission signal EM1.

In this case, the configuration and functions of the remaining components except for the fourth switching transistor T4 are the same as those described in the second embodiment. That is, the configuration and operation method of the pixel applied to the organic light emitting display device according to the second embodiment of the present invention described with reference to FIGS. 4 to 8 is an organic light emitting display according to the third embodiment of the present invention. The pixel configuration and operation method applied to the device can be applied as it is.

Therefore, in the following, only the contents different from those mentioned in the description of the second embodiment of the present invention will be described in detail.

The operation period of the pixel driver 110 is an initialization period A, a sampling period B, and a programming period according to the pulse timing of the gate signals SCAN1, SCAN2, EM1 supplied to the pixel P. It is divided into C) and light emission period (D).

In the initialization period (A), the first scan signal SCAN1 and the second scan signal SCAN2 are high signals, and the first emission signal EM1 is a low signal.

In the sampling period B, the first scan signal SCAN1 and the first emission signal EM1 are high signals, and the second scan signal SCAN2 is a low signal.

In the programming period C, the first scan signal SCAN1 is a high signal, and the second scan signal SCAN2 and the first emission signal EM1 are low signals.

In the light emission period D, the first emission signal EM1 is a high signal, and the first scan signal SCAN1 and the second scan signal SCAN2 are low signals.

The fourth switching transistor T4 is turned on or off according to the first emission signal EM1, and when turned on, the third node N3 connected to the third terminal of the driving transistor DR is It is connected to the organic light emitting diode (OLED). For example, the fourth switching transistor T4 is turned on during the sampling period B and the light emission period D to connect the third node N3 to the organic light emitting diode OLED, It is turned off during the initialization period (A) and the programming period (C) to block the third node (N3) from the organic light emitting diode (OLED).

To this end, the fourth switching transistor T4 includes a first terminal connected to the third terminal of the driving transistor DR, a second terminal connected to the organic light emitting diode, and the second emission signal. Includes a third terminal to be used. In this case, the third switching transistor T3 is a first terminal connected to the third node N3 between the first terminal of the fourth switching transistor T4 and the third terminal of the driving transistor And a second terminal connected to the initialization voltage supply line VL3 and a third terminal to which the second scan signal is input. As described above, in the third embodiment, the fourth switching transistor T4 is turned on or off by the first emission signal EM1 for turning on or off the first switching transistor T1. do. That is, the second emission signal for driving the fourth switching transistor is the same as the first emission signal for driving the first switching transistor.

Hereinafter, a method of driving the pixel driver 110 applied to the third embodiment of the present invention will be described. In this case, the same or similar contents as the driving method of the pixel driver 110 described in the third embodiment of the present invention will be omitted or briefly described.

First, in the initialization period A, the second switching transistor T2 and the third switching transistor T3 are turned on. Accordingly, the reference voltage Vref is supplied to the second node N2 through the second switching transistor T2, and the initialization voltage Vinit is supplied to the third node N3, The pixel P is initialized. In this case, the first switching transistor T1 is turned off by the first emission signal EM1 which is a low signal. Further, since the first emission signal EM1, which is a low signal, is also supplied to the gate of the fourth switching transistor T4, the fourth switching transistor T4 is also turned off. In the second embodiment, the fourth switching transistor T4 is turned on during the initialization period A, but in the third embodiment, the fourth switching transistor T4 is turned off during the initialization period A. . To further explain, in the second embodiment, the initialization voltage Vini is supplied to the third node N3 by turning on the fourth switching transistor T4, but in the third embodiment, the fourth switching transistor T4 is turned on. When the switching transistor T4 is turned off, the initialization voltage Vini may be supplied to the third node N3.

Next, in the sampling period (B), the first switching transistor (T1), the second switching transistor (T2), and the fourth switching transistor (T4) are turned on, and the third switching transistor (T3) is It is turned off. Accordingly, in the second node N2, the reference voltage Vref is maintained. In this case, the drain, which is the first terminal of the driving transistor DR, is floated with the first voltage ELVDD. Accordingly, when a current flows from the first terminal of the driving transistor DR to the source direction, which is the third terminal, and the voltage of the third terminal becomes "Vref-Vth", the driving transistor DR is turned. Is off. Here, "Vth" means a threshold voltage of the driving transistor DR. In this case, even when the fourth switching transistor T4 is turned on, a current and voltage capable of turning on the organic light emitting diode OLED are not supplied to the organic light emitting diode OLED. Accordingly, the method of operating the pixel driver 110 in the state in which the fourth switching transistor T4 is turned on in the sampling period (B) of the third exemplary embodiment is, in the sampling period (B) of the second exemplary embodiment. It is the same as the method of operating the pixel driver 110 when the fourth switching transistor T4 is turned off. To further explain, in the third embodiment, the third node and the organic light emitting diode are electrically cut off during the sampling period (B).

Next, in the programming period (C), the second switching transistor T2 is turned on, and the first switching transistor T1, the third switching transistor T3, and the fourth switching transistor T4 are turned on. Is off.

The operating method of the pixel driver 110 in the programming period (C) of the third embodiment is the same as that of the pixel driver (110) in the programming period (C) of the second embodiment.

Finally, in the light-emitting period (D), the first switching transistor T1 and the fourth switching transistor T4 are turned on, and the second switching transistor T2 and the third switching transistor T3 are turned on. It is turned off.

The operating method of the pixel driver 110 in the light emission period D according to the third embodiment is the same as the operation method of the pixel driver 110 in the light emission period D according to the second embodiment.

Accordingly, the high potential voltage ELVDD is applied to the drain, which is the first terminal of the driving transistor DR through the first switching transistor T1, and the driving transistor DR is driven to the organic light emitting diode. Supply current (Ioled). In this case, the driving current Ioled supplied from the driving transistor DR to the organic light emitting diode OLED is the same as the final equation of [Equation 3].

Therefore, as in the second embodiment, in the third embodiment of the present invention, a characteristic variation occurs between the driving transistors DR formed in each pixel, or a voltage drop of the high potential voltage ELVDD Even if is generated or the capacitance of the organic light emitting diode (Coledg) is changed, luminance deviation between the pixels P may be reduced.

The brief summary of the contents described above is as follows.

In the third embodiment of the present invention, in the initialization period A, the reference voltage Vref provided from the data line is supplied to the second node N2, and the third switching transistor T3 is initialized. The initialization voltage Vini provided from the voltage supply line VL3 is supplied to the third node N3. In the sampling period B, the reference voltage Vref provided from the data line is supplied to the second node N2, and the first voltage provided from the first voltage supply line VL1 is the driving transistor DR ) Is supplied to the first terminal, and the third node N3 and the organic light emitting diode OLED are substantially blocked. In the programming period C, the data voltage Vdata provided from the data line is supplied to the second node N2, and the third node N3 and the organic light emitting diode OLED are cut off. In the light emission period D, the first voltage provided from the first voltage supply line VL1 is supplied to the first terminal of the driving transistor DR, and the third node N3 and the organic light emission The diode (OLED) is connected.

10 is a graph illustrating a state in which an amount of current flowing through an organic light-emitting diode applied to an organic light-emitting display device according to the present invention changes according to a change in capacitance of the organic light-emitting diode. In FIG. 10, a graph indicated by a solid line indicates a change in current in the present invention, and a graph indicated by a dotted line indicates a change in conventional current.

According to the present invention, even if the characteristics of the organic light-emitting diode (OLED) are changed and the capacitance of the organic light-emitting diode (OLED) is changed, the amount of current flowing through the organic light-emitting diode (OLED) is compared with the conventional one. , It can be seen that there is no significant change.

That is, according to the present invention, as described in [Equation 3], the current (Ioled) flowing to the organic light emitting diode during the light emission period (D) affects the capacitance of the organic light emitting diode (Coledg). Do not receive.

Those skilled in the art to which the present invention pertains will appreciate that the present invention can be implemented in other specific forms without changing the technical spirit or essential features thereof. Therefore, it should be understood that the embodiments described above are illustrative in all respects and not limiting. The scope of the present invention is indicated by the claims to be described later rather than the detailed description, and all changes or modified forms derived from the meaning and scope of the claims and their equivalent concepts should be interpreted as being included in the scope of the present invention. do.

100: panel 200: panel driver
300: data driver 400: timing controller

Claims (9)

Each crossing area between the data lines and the gate lines includes a panel in which pixels are formed, including an organic light emitting diode and a pixel driver driving the organic light emitting diode,
The pixel driver,
A driving transistor connected between a first voltage supply line and a second voltage supply line to which the organic light emitting diode is connected;
A first switching transistor configured to connect a first node connected to the first terminal of the driving transistor to the first voltage supply line in response to a first emission signal;
A second switching transistor connecting a second node connected to the gate of the driving transistor to a data line in response to a first scan signal;
A third switching transistor configured to connect a third node connected to the third terminal of the driving transistor to an initialization voltage supply line in response to a second scan signal;
A storage capacitor connected between the second node and the third node;
A driving capacitor connected while one side is connected to the first voltage supply line and the other side is connected to the third terminal of the driving transistor; And
In response to a second emission signal, an organic light emitting display device comprising a fourth switching transistor connecting the third node to the organic light emitting diode. The method of claim 1,
In the initialization period, the second switching transistor and the third switching transistor are turned on, the first switching transistor is turned off,
In the sampling period, the first switching transistor and the second switching transistor are turned on, and the third switching transistor is turned off,
During the programming period, the second switching transistor is turned on, and the first switching transistor, the third switching transistor, and the fourth switching transistor are turned off.
And the first switching transistor and the fourth switching transistor are turned on, and the second and third switching transistors are turned off during the light emission period. The method of claim 2,
In the initialization period, the reference voltage provided from the data line is supplied to the second node, and the third switching transistor supplies the initialization voltage provided from the initialization voltage supply line to the third node. Display device. The method of claim 2,
In the sampling period, a reference voltage provided from the data line is supplied to the second node, and a first voltage provided from the first voltage supply line is supplied to the first terminal of the driving transistor, and the third node and The organic light-emitting display device, wherein the organic light-emitting diode is blocked. The method of claim 2,
And the data voltage provided from the data line is supplied to the second node during the programming period, and the third node and the organic light emitting diode are cut off. The method of claim 2,
An organic light emitting display device, wherein the first voltage provided from the first voltage supply line is supplied to the first terminal of the driving transistor during the light emission period, and the third node and the organic light emitting diode are connected to each other. . Each crossing area between the data lines and the gate lines includes a panel in which pixels are formed, including an organic light emitting diode and a pixel driver driving the organic light emitting diode,
The pixel driver,
A driving transistor connected between a first voltage supply line and a second voltage supply line to which the organic light emitting diode is connected;
A first switching transistor configured to connect a first node connected to the first terminal of the driving transistor to the first voltage supply line in response to a first emission signal;
A second switching transistor connecting a second node connected to the gate of the driving transistor to a data line in response to the first scan signal;
A storage capacitor connected between the second node and a third terminal of the driving transistor;
A driving capacitor connected between one side connected to the first voltage supply line and the other side connected to the third terminal of the driving transistor;
A fourth switching transistor connecting a third terminal of the driving transistor to the organic light emitting diode in response to a second emission signal; And
In response to a second scan signal, a third switching transistor connecting a third node between the fourth switching transistor and the organic light emitting diode to an initialization voltage supply line, and
The fourth switching transistor includes a first terminal connected to the third terminal of the driving transistor, a second terminal connected to the organic light emitting diode, and a third terminal to which the second emission signal is input,
The third switching transistor may include a first terminal connected to the third node between the second terminal of the fourth switching transistor and the organic light emitting diode, a second terminal connected to the initialization voltage supply line, and the second terminal. An organic light emitting display device including a third terminal to which a scan signal is input. The method of claim 1,
The fourth switching transistor includes a first terminal connected to the third terminal of the driving transistor, a second terminal connected to the organic light emitting diode, and a third terminal to which the second emission signal is input,
The third switching transistor may include a first terminal connected to the third node between the first terminal of the fourth switching transistor and the third terminal of the driving transistor, and a second terminal connected to the initialization voltage supply line And a third terminal to which the second scan signal is input. The method of claim 8,
The second emission signal is the same as the first emission signal.

Images