KR100658631B1 - Organic light emitting diode display and driving method thereof - Google Patents

Abstract

An organic light emitting display device and a driving method thereof are provided to compensate the threshold voltage deviation of a driving transistor in a pixel circuit and to reduce the number of wires for transmitting voltage. An organic light emitting display device includes a data line for transmitting data voltage; a first scan line for transmitting selection signals(scan[i-1],scan[i]); an emission control line for transmitting an emission control signal(emit[i]); a signal line for transmitting a control signal; a first transistor(M1); a second transistor(M2) connected between a first wire(ELVDD) for transmitting a first voltage and a first electrode of the first transistor, and provided with a gate electrode connected to the emission control line; an OLED(Organic Light Emitting Diode) having a first electrode connected to a second wire(ELVSS) for transmitting a second voltage; a third transistor(M3) connected between a second electrode of the first transistor and a second electrode of the OLED, and provided with a gate electrode connected to the emission control line; a fourth transistor(M4) connected between the gate electrode and the first electrode of the first transistor, and provided with a gate electrode connected to the scan line; a fifth transistor(M5) connected between the data line and the second electrode of the first electrode, and provided with a gate electrode connected to the scan line; a sixth transistor(M6) connected between the gate electrode of the first transistor and the second wire, and provided with a gate electrode connected to the signal line; and a capacitor(Cst) connected between the first wire and the gate electrode of the first transistor.

Description

Organic light emitting display and driving method thereof {ORGANIC LIGHT EMITTING DIODE DISPLAY AND DRIVING METHOD THEREOF}

1 is a schematic plan view of an organic light emitting diode display according to an exemplary embodiment of the present invention.

2 is a schematic circuit diagram of a pixel circuit according to a first embodiment of the present invention,

3 is a signal timing diagram of the pixel circuit of FIG. 2;

4 is a schematic circuit diagram of a pixel circuit according to a second embodiment of the present invention.

The present invention relates to an organic light emitting diode display and a driving method thereof.

An organic light emitting diode display is a display device that electrically excites an organic compound to emit light, and may display an image by driving a plurality of organic light emitting diodes arranged in a matrix form. The organic light emitting diode has a diode characteristic and is called an organic light emitting diode (OLED), and generally has a structure of an anode electrode layer, an organic thin film, and a cathode electrode layer. In the organic light emitting diode, holes and electrons injected through the anode electrode and the cathode electrode are combined in the organic thin film to emit light. The method of driving the organic light emitting device is divided into a voltage programming method and a current programming method according to the type of the signal to be applied.

However, due to the nonuniformity of the manufacturing process, the variation of the threshold voltage occurs in the thin film transistor formed in the plurality of pixels in which the plurality of organic light emitting elements are formed. Then, the voltage writing method has a problem in that it is difficult to obtain a high gradation due to the variation of the threshold voltage of the thin film transistor. For example, when driving a transistor of a pixel at 3V, a voltage must be applied to the gate of the thin film transistor at intervals of about 12 mV (= 3 V / 256) in order to express an 8 bit 256 gray level. When the variation in the threshold voltage of the thin film transistor is 100 kΩ, it is difficult to express a high gray scale.

An object of the present invention is to provide an organic light emitting display device capable of compensating for variations in threshold voltages of driving transistors.

In order to solve this problem, according to an embodiment of the present invention, a data line for transmitting a data voltage, a first scanning line for transmitting a selection signal, an emission control line for transmitting an emission control signal, a signal line for transmitting a control signal, An organic light emitting display device including first to sixth transistors and a capacitor is provided. The second transistor is connected between the first wiring for transmitting the first voltage and the first electrode of the first transistor. The first electrode of the organic light emitting diode is connected to the second wiring which transmits the second voltage, and the third transistor is connected between the second electrode of the first transistor and the second electrode of the organic light emitting diode. The fourth transistor is connected between the first electrode and the gate electrode of the first transistor, and the fifth transistor is connected between the data line and the second electrode of the first transistor. Gate electrodes of the second and third transistors are connected to the emission control line, and gate electrodes of the fourth and fifth transistors are connected to the scan line. The sixth transistor is connected between the gate electrode of the first transistor and the second wiring, and the gate electrode of the sixth transistor is connected to the scan line. The capacitor is connected between the first wiring and the gate electrode of the first transistor.

The organic light emitting diode display according to another exemplary embodiment of the present invention may further include first and second drivers. The first driver applies a control signal having a gate-on voltage to the signal line during the first period, and applies a selection signal having a gate-on voltage to the first scan line during the second period after the first period, and after the second period. An emission control signal having a gate-on voltage is applied to the emission control line during the third period. The second driver applies a data voltage to the data line during at least a part of the second period.

In this case, the signal line may include a second scan line transferring a selection signal having a gate-on voltage before the selection signal transmitted to the first scan line.

According to another embodiment of the present invention, a driving method of an organic light emitting display device including a plurality of pixel circuits is provided. Each of the pixel circuits includes a capacitor having a driving transistor, an organic light emitting diode, and a first electrode connected to a first wiring for transmitting a first voltage, and a second end connected to a gate electrode of the driving transistor. The driving method includes applying a second voltage of the second wiring to the second electrode of the capacitor, in a state in which the first electrode and the second electrode of the driving transistor are electrically disconnected from the first wiring and the second wiring, respectively. Connecting a first electrode and a gate electrode of the driving transistor and applying a data voltage to the second electrode of the driving transistor; and a first wiring, a first electrode of the driving transistor, a second electrode of the driving transistor, an organic light emitting element, and a first electrode. Forming a current path between the two wires.

DETAILED DESCRIPTION Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings so that those skilled in the art may easily implement the present invention. As those skilled in the art would realize, the described embodiments may be modified in various different ways, all without departing from the spirit or scope of the present invention. In the drawings, parts irrelevant to the description are omitted in order to clearly describe the present invention, and like reference numerals designate like parts throughout the specification.

Throughout the specification, when a part is "connected" to another part, this includes not only "directly connected" but also "electrically connected" with another element in between. . In addition, when a part is said to "include" a certain component, which means that it may further include other components, except to exclude other components unless otherwise stated.

An organic light emitting diode display and a driving method thereof according to an exemplary embodiment of the present invention will now be described in detail with reference to the accompanying drawings.

1 is a schematic plan view of an organic light emitting diode display according to an exemplary embodiment.

As illustrated in FIG. 1, the organic light emitting diode display includes a display area 100, a scan driver 200, a light emission control driver 300, and a data driver 400.

The display area 100 includes a plurality of data lines D ₁ -D _m , a plurality of scanning lines S ₁ -S _n , a plurality of emission control lines Em ₁ -E _{n n} , and a plurality of pixels 110. And they are formed on a substrate (not shown).

The plurality of data lines D ₁ -D _m extend in the column direction and transmit data voltages representing gray levels to the plurality of pixels 110, respectively, and the plurality of scan lines S ₁ -S _n and the plurality of emission control lines. Em ₁ -Em _n extend in the row direction and transmit the selection signal and the emission control signal to the plurality of pixels 110, respectively. Each pixel 110 is formed in a pixel region defined by a corresponding scan line among the plurality of scan lines S ₁ -S _n and a corresponding data line among the plurality of data lines D ₁ -D _m .

Meanwhile, in order to implement color display, each pixel uniquely displays one color of the primary colors or each pixel alternately displays the primary colors with time, so that a desired color is recognized by a spatial or temporal sum of these primary colors. Examples of primary colors include red (R), green (G), and blue (B). In this case, when colors are displayed by a time sum, R, G, and B colors are alternately displayed in one pixel to realize one color. In the case of displaying colors by spatial sum, one color is realized by three pixels of R, G, and B pixels, and each pixel is called a subpixel, and three R, G, and B subpixels are combined to form one color. It is also called a conch.

The data driver 400 is connected to the data lines D ₁ -D _m of the display area 100 to apply a data voltage to the data lines D ₁ -D _m . The scan driver 200 and the emission control driver 300 generate a selection signal and a light emission control signal including a combination of a gate on voltage and a gate off voltage, and respectively output the selection signal and the light emission control signal to the scan lines S ₁ -S _n . And light emission control lines Em ₁ -E _{m n} . In this case, when the selection signal and the emission control signal have the gate-on voltage, the transistor of the pixel 110 having the gate connected to the corresponding scan line and the emission control signal is turned on.

In this case, the scan driver 200, the emission control driver 300, and / or the data driver 400 may be directly mounted in the form of an integrated circuit on a substrate on which the display area 100 is formed. Alternatively, the scan driver 200, the emission control driver 300, and / or the data driver 400 may be formed on the substrate on which the display area 100 is formed, and the scan lines S ₁ -S _n and the emission control lines Em ₁ -Em _n . The data lines D ₁ -D _m may be formed of the same or similar layers as the layers forming the transistors of the pixel 110. Alternatively, a tape carrier package (TCP), a flexible printed circuit (FPC), or the like, may be bonded to the scan driver 200, the emission control driver 300, and / or the data driver 400 to a substrate on which the display area 100 is formed. It can also be mounted in the form of a chip on TAB (tape automatic bonding). 1, the scan driver 200 and the emission control driver 300 may be formed as one driver.

Next, the pixel circuit 111 formed in the pixel 110 of the organic light emitting diode display according to the first exemplary embodiment of the present invention will be described in detail with reference to FIG. 2.

FIG. 2 is a schematic circuit diagram of the pixel circuit 111 according to the first embodiment of the present invention, and FIG. 3 is a signal timing diagram of the pixel circuit 111 of FIG. 2 and 3 show only pixel circuits connected to the j th data line D _j and the i th scan line S _i for convenience of description (where j is an integer between 1 and m, and i is 1 and n). Is an integer between).

On the other hand, when a term for a scan line is defined in one pixel circuit, a scan line that transmits a selection signal for operating a transistor connected to the data line so as to transfer a data voltage is called a "current scan line", and the selection signal immediately before the current selection signal. The scan line that delivers is referred to as the "previous scan line". The selection signals transmitted by the current scan line and the immediately preceding scan line are called " current selection signal " and " previous selection signal ", respectively.

2, the pixel circuit 111 according to the first exemplary embodiment of the present invention includes transistors M1, M2, M3, M4, M5, and M6, a capacitor Cst, and an organic light emitting diode OLED. In FIG. 2, the transistors M1-M6 are illustrated as p-channel field effect transistors, in particular, p-channel metal oxide semiconductor (PMOS) transistors. These transistors M1-M6 have two electrodes and a gate electrode forming a source electrode and a drain electrode.

The first electrode of the transistor M2 is connected to the first wiring ELVDD transmitting the first voltage, and the second electrode of the transistor M2 is connected to the first electrode of the driving transistor M1. The first electrode of the transistor M3 is connected to the second electrode of the driving transistor M1, and the second electrode of the transistor M3 is connected to the anode electrode of the organic light emitting diode OLED. The emission control line Em _i is connected to the gate electrodes of the two transistors M2 and M3, and the cathode electrode of the organic light emitting diode OLED is connected to the second wiring ELVSS that transmits a voltage lower than the first voltage. It is. In this case, the positive voltage may be used as the first voltage ELVDD and the negative voltage or ground voltage may be used as the second voltage ELVSS.

The capacitor Cst has a first electrode connected to the first wiring ELVDD and a second electrode connected to the gate electrode of the driving transistor M1. Two electrodes of the transistor M4 are connected to the gate electrode of the transistor M1 (that is, the second electrode of the capacitor Cst) and the first electrode, and the second electrode and the data line D of the transistor M1 are respectively connected. _The transistor M5 is connected between _j ). And gate electrodes of the two transistors (M4, M5) is coupled to a current scan line (S _i). The transistor M6 is connected between the second electrode of the capacitor Cst (that is, the gate electrode of the driving transistor M1) and the third wiring V _INIT which transfers the initialization voltage V _INIT . The previous scanning line _Si-1 is connected to the gate electrode of M6.

In this case, two electrodes, electrodes and wirings (signal lines) connected to each other in the pixel circuit may be formed of the same electrode.

Next, the operation of the pixel circuit 111 of FIG. 2 will be described with reference to FIG. 3. Shows the before and the selection signal to the current scan line _{(S i-1, S i} ) is delivered in 3 to each scan [i-1] and scan [i], the emission control line (Em _i) emission control for the transmission The signal is shown as emit [i]. Since the transistors M2-M6 are PMOS transistors, the selection signal and the light emission control signal have the low level voltage as the gate on voltage and the high level voltage as the gate off voltage.

First, in the T1 period, the light emission control signal emit [i] goes high and the immediately preceding selection signal scan [i-1] goes low. Then, the transistors M2 and M3 are turned off and the transistor M6 is turned on to initialize the second electrode voltage of the capacitor Cst to the initialization voltage V _INIT .

Next, in the state where the light emission control signal emit [i] is at a high level in the period T2, the previous selection signal scan [i-1] is at a high level and the current selection signal scan [i] is at a low level. . The data voltage V _DATA corresponding to the pixel circuit 111 is applied to the data line D _j during at least a part of the T2 period. The transistor M2 is then turned off and the transistors M4 and M5 are turned on so that the data voltage V _DATA from the data line D _j is applied to the second electrode of the transistor M1. At this time, since the first electrode and the gate electrode of the transistor M1 are connected by the turned-on transistor M4, that is, the transistor M1 is connected in the form of a diode, the first electrode voltage and the gate electrode voltage of the transistor M1 are The voltage V _DATA -V _TH corresponding to the difference between the second electrode voltage V _DATA of the transistor M1 and the threshold voltage V _TH of the transistor M1 is set. Therefore, the capacitor Cst stores the voltage ELVDD-V _DATA -V _TH corresponding to the difference between the first voltage ELVDD and the gate voltage V _DATA -V _TH of the transistor M1.

Subsequently, in the T3 period, the current selection signal scan [i] goes high and the light emission control signal emit [i] goes low. Then, the transistor M4 is turned off and the transistors M2 and M3 are turned on so that the first wiring ELVDD is connected to the first electrode of the driving transistor M1, and the second electrode of the driving transistor M1 is turned on. An anode electrode of the organic light emitting diode OLED is connected. Therefore, the voltage ELVDD-V _DATA -V _TH stored in the capacitor Cst becomes the voltage V _GS between the gate electrode and the first electrode (source electrode) of the driving transistor M1, thereby reducing the voltage of the driving transistor M1. A current I _OLED as shown in Equation 1 flows through the second electrode (drain electrode). In addition, the current I _OLED is transmitted to the organic light emitting diode OLED so that the organic light emitting diode OLED emits light with a brightness corresponding to the magnitude of the current I _OLED .

Here, k is a constant determined by the channel width, channel length, carrier mobility and oxide capacitance of the driving transistor M1.

In this case, since the current I _OLED transmitted to the organic light emitting diode OLED is determined only by the data voltage V _DATA regardless of the threshold voltage of the transistor M1, the deviation of the threshold voltage of the transistor M1 is compensated for. can do.

If the gate voltage of the driving transistor M1 (ie, the second electrode voltage of the capacitor Cst) is lower than the second electrode voltage of the driving transistor M1 (that is, the data voltage V _DATA ) in the T2 period, the diode The reverse voltage is applied to the driving transistor M1 connected in the form. Then, the second electrode voltage of the capacitor Cst is not changed to the voltage (V _DATA -V _TH ). Therefore, the initialization voltage V _INIT applied to the second electrode of the capacitor Cst during the T1 period is set to a voltage lower than the data voltage V _DATA .

Next, a pixel circuit of the organic light emitting diode display according to the second exemplary embodiment of the present invention will be described with reference to FIG. 4.

As shown in FIG. 4, the pixel circuit 112 according to the second embodiment of the present invention is similar to the first embodiment, but unlike the first embodiment, the second electrode of the transistor M6 transfers an initialization voltage. The third wiring V _INIT is connected to the second wiring ELVSS instead of the source. In this case, a contact hole may be formed in a layer formed between the second electrode and the second wiring ELVSS of the transistor M6 to connect the second electrode and the second wiring ELVSS.

The voltage of the second wiring ELVSS may be set to a voltage lower than the lowest data voltage applied to the data lines D ₁ -D _m . In general, since the data voltage is set to a positive voltage lower than the voltage of the anode power supply ELVDD, the voltage of the cathode power supply ELVSS may be set to a negative or ground voltage.

In this way, unlike the first embodiment, since a separate wiring for transmitting the initialization voltage V _INIT does not have to be formed in the pixel circuit 112, the wiring for transmitting the initialization voltage V _INIT in the pixel circuit 112 is performed. As much space can be used for opening ratio improvement. In addition, since a circuit (for example, a direct current (DC) / DC converter) for generating an initialization voltage V _INIT is not required to be separately formed in a power supply unit (not shown) of the organic light emitting diode display, the structure of the power supply unit may be simplified. Can be.

As described above, the driving transistor M1 is described as a PMOS transistor in the first and second embodiments of the present invention, but the driving transistor M1 may be formed as an n-channel transistor. In this case, the first voltage ELVDD is set to a voltage lower than the second voltage ELVSS, and the anode electrode and the cathode electrode of the organic light emitting diode OLED are formed oppositely. The transistor M2-M6 may be formed as an n-channel transistor. In this case, the high level voltage may be used as the gate on voltage and the low level voltage may be used as the gate off voltage.

Although the embodiments of the present invention have been described in detail above, the scope of the present invention is not limited thereto, and various modifications and improvements of those skilled in the art using the basic concepts of the present invention defined in the following claims are also provided. It belongs to the scope of rights.

As described above, according to the exemplary embodiment of the present invention, the deviation of the threshold voltage of the driving transistor may be compensated for in the pixel circuit. Further, according to another exemplary embodiment of the present invention, the number of wirings for transmitting voltage in the pixel circuit can be reduced.

Claims (11)

A data line carrying a data voltage, A first scan line for transmitting a selection signal, A light emission control line for transmitting a light emission control signal, Signal lines for transmitting control signals, First transistor, A second transistor connected between a first wiring transferring a first voltage and a first electrode of the first transistor, and a gate electrode connected to the emission control line; An organic light emitting diode having a first electrode connected to a second wiring for transmitting a second voltage; A third transistor connected between the second electrode of the first transistor and the second electrode of the organic light emitting diode and having a gate electrode connected to the emission control line; A fourth transistor connected between the first electrode and the gate electrode of the first transistor and having a gate electrode connected to the scan line; A fifth transistor connected between the data line and the second electrode of the first transistor and having a gate electrode connected to the scan line; A sixth transistor connected between the gate electrode of the first transistor and the second wiring, and a gate electrode connected to the signal line; and A capacitor connected between the first wiring and the gate electrode of the first transistor An organic light emitting display device comprising a. The method of claim 1, Applying the control signal having a gate-on voltage to the signal line during a first period, applying the selection signal having a gate-on voltage to the first scan line during a second period after the first period, and applying the second period A first driver for applying the light emission control signal having a gate-on voltage to the light emission control line during a third period thereafter; and A second driver configured to apply the data voltage to the data line during at least a part of the second period An organic light emitting display device further comprising. The method of claim 1, And the signal line includes a second scan line which transfers a selection signal having a gate-on voltage before the selection signal transmitted to the first signal line. The method according to any one of claims 1 to 3, The first transistor comprises a p-channel transistor, And the first voltage is higher than the second voltage. The method of claim 4, wherein The second to sixth transistors each include a p-channel transistor. The method according to any one of claims 1 to 3, The first transistor includes an n-channel transistor, And the first voltage is lower than the second voltage. The method of claim 6, The second to sixth transistors each include an n-channel transistor. A plurality of pixel circuits, each of the plurality of pixel circuits being connected to a driving transistor, an organic light emitting element, and a first wiring through which a first electrode transfers a first voltage, and a second electrode connected to a gate electrode of the driving transistor; A method of driving an organic light emitting display device including a capacitor connected thereto, Applying a second voltage of a second wiring to a second end of the capacitor, The first electrode and the gate electrode of the driving transistor are connected to each other while the first electrode and the second electrode of the driving transistor are electrically disconnected from the first wiring and the second wiring, respectively, and the second electrode of the driving transistor is connected. Applying a data voltage to, and Forming a current path between the first wiring, the first electrode of the driving transistor, the second electrode of the driving transistor, the organic light emitting element, and the second wiring. Driving method comprising a. The method of claim 8, The driving transistor comprises a p-channel transistor, And the first voltage is higher than the second voltage. The method of claim 8, The driving transistor includes an n-channel transistor, And the first voltage is lower than the second voltage. The method according to any one of claims 8 to 10, Forming the current path, The first wiring is connected to the first electrode of the driving transistor, the second electrode of the driving transistor is connected to the first electrode of the organic light emitting diode, and the second electrode of the organic light emitting diode is connected to the second wiring. Driving method comprising the step of connecting.

Images