KR101240658B1 - Display device and driving method thereof - Google Patents

Abstract

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a display device and a driving method thereof, the display device comprising: a driving transistor having a light emitting element, a capacitor, a control terminal and an input terminal and an output terminal, and supplying a driving current to the light emitting element so that the light emitting element emits light; A plurality of switches each comprising a first switching unit diode-connecting the driving transistor according to the signal and supplying a data voltage to the capacitor, and a second switching unit supplying the driving voltage to the driving transistor and connecting the capacitor to the driving transistor according to a light emission signal. It includes a pixel. In this case, the capacitor is connected to the driving transistor through the first switching unit to store a control voltage depending on the data voltage and the threshold voltage of the driving transistor, and is connected to the driving transistor through the second switching unit to supply the control voltage to the driving transistor. According to the present invention, even if the threshold voltages of the driving transistor and the organic light emitting diode are deteriorated, the degradation of the image quality can be prevented.

Description

Display device and driving method thereof {DISPLAY DEVICE AND DRIVING METHOD THEREOF}

The present invention relates to a display apparatus and a driving method thereof.

In recent years, with the reduction in weight and thickness of personal computers and televisions, display devices are also required to be lighter and thinner, and cathode ray tubes (CRTs) are being replaced by flat panel displays.

Such flat panel displays include liquid crystal displays (LCDs), field emission displays (FEDs), organic light emitting displays, plasma display panels (PDPs), and the like. There is this.

In general, in an active flat panel display, a plurality of pixels are arranged in a matrix form, and an image is displayed by controlling the light intensity of each pixel according to given luminance information. Among these, an organic light emitting display is a display device that displays an image by electrically exciting and emitting a fluorescent organic material. The organic light emitting display is a self-emission type, has a low power consumption, a wide viewing angle, and a fast response time of pixels. It is easy.

The organic light emitting display includes an organic light emitting diode (OLED) and a thin film transistor (TFT) driving the same. The thin film transistor is classified into a polysilicon thin film transistor and an amorphous silicon thin film transistor according to the type of the active layer. The organic light emitting diode display employing the polysilicon thin film transistor has many advantages, and thus is widely used. However, the manufacturing process of the thin film transistor is complicated and thus the cost increases. In addition, it is difficult to obtain a large screen with such an organic light emitting display device.

On the other hand, an organic light emitting display device employing an amorphous silicon thin film transistor is easy to obtain a large screen, and the number of manufacturing processes is relatively smaller than that of an organic light emitting display device employing a polysilicon thin film transistor. However, as the amorphous silicon thin film transistor continuously supplies a current to the organic light emitting diode, the threshold voltage V _th of the amorphous silicon thin film transistor itself may transition and deteriorate. This causes non-uniform current to flow through the organic light emitting element even when the same data voltage is applied, resulting in deterioration in image quality of the organic light emitting diode display.

The organic light emitting element also transitions its threshold voltage as a current flows for a long time. In the case of the n-type thin film transistor, the organic light emitting diode is positioned at the source side of the thin film transistor, and thus, when the threshold voltage of the organic light emitting diode is deteriorated, the source side voltage of the thin film transistor is changed. As a result, even when the same data voltage is applied to the gate of the thin film transistor, the voltage between the gate and the source of the thin film transistor is fluctuated so that an uneven current flows through the organic light emitting device. This also causes a deterioration in image quality of the OLED display.

On the other hand, when a large number of thin film transistors are connected to the current path between the driving voltage and the organic light emitting diode in order to compensate for the threshold voltage degradation of the driving transistor and the organic light emitting diode, the power is increased by them.

Accordingly, an aspect of the present invention is to provide a display device and a method of driving the same, including an amorphous silicon thin film transistor and compensating threshold voltage degradation of the amorphous silicon thin film transistor and the organic light emitting diode, and minimizing power loss. It is.

According to an aspect of the present invention, a display device includes a light emitting device, a capacitor, a control terminal, an input terminal, and an output terminal, and supplies a driving current to the light emitting device so that the light emitting device emits light. A transistor, a diode-connecting the driving transistor according to a scan signal, a first switching unit for supplying a data voltage to the capacitor, a driving voltage to the driving transistor according to a light emission signal, and connecting the capacitor to the driving transistor And a plurality of pixels, each pixel including a second switching unit, wherein the capacitor is connected to the driving transistor through the first switching unit to store a control voltage depending on the data voltage and the threshold voltage of the driving transistor. 2 through the switching unit to the driving transistor Is connected to supply the control voltage to the driving transistor.

The first switching unit may include a first switching transistor connecting an input terminal and a control terminal of the driving transistor according to the scan signal, and a second switching transistor connecting the capacitor to the data voltage according to the scan signal. Can be.

The first switching unit may further include a third switching transistor connecting a common voltage to an output terminal of the driving transistor according to the scan signal.

The second switching unit may include: a fourth switching transistor connecting an input terminal of the driving transistor to the driving voltage according to the light emitting signal, and a fifth switching connecting the capacitor and an output terminal of the driving transistor according to the light emitting signal. It may include a transistor.

The control voltage may be a voltage obtained by subtracting the data voltage from the sum of the common voltage and the threshold voltage.

The data voltage may have a value of 0 or less.

The first to fifth switching transistors and the driving transistors may be amorphous silicon thin film transistors.

The first to fifth switching transistors and the driving transistors may be nMOS thin film transistors.

The light emitting device may include an organic light emitting layer.

In another embodiment, a display device includes a light emitting device, a first terminal connected to a first voltage, a second terminal connected to a light emitting device, and a driving transistor having a control terminal, and a second of the driving transistor. A capacitor connected between the terminal and the control terminal, the first switching element connected between the first terminal and the control terminal of the driving transistor, the first switching element operating in response to the scan signal, the capacitor and the data A second switching element connected between a voltage and a third switching element connected in response to the scan signal and connected between a second terminal and a second voltage of the driving transistor and operating in response to a light emission signal A fourth switching element connected between a voltage and a first terminal of the driving transistor, and responding to the light emitting signal And a fifth switching element connected between the capacitor and the second terminal of the driving transistor.

Among the first to fourth sections sequentially connected, the first to fifth transistors are turned on during the first period, and the first to third transistors are turned on during the second period, and the fourth and fourth transistors are turned on. A fifth transistor is turned off, the first to fifth transistors are turned off during the third period, the first to third transistors are turned off during the fourth period, and the fourth and fifth transistors are turned off. 5 transistors may be turned on.

The data voltage may have a value of 0 or less.

According to another exemplary embodiment of the present invention, there is provided a light emitting device, a driving transistor having a control terminal connected to the light emitting element, first and second terminals, and a capacitor connected to the control terminal of the driving transistor. The driving method includes connecting a control terminal and a first terminal of the driving transistor, connecting a second terminal of the driving transistor to a common voltage, connecting the capacitor to a data voltage, and connecting the capacitor to the driving transistor. Connecting between the control terminal and the second terminal of, and connecting the first terminal of the driving transistor to a driving voltage.

The method may further include charging the capacitor by applying a first voltage to a control terminal of the driving transistor.

The method may further include isolating a control terminal and a first terminal of the driving transistor connected to each other.

The method may further include isolating the capacitor and the driving transistor from an external signal source.

According to another exemplary embodiment of the present invention, there is provided a light emitting device, a driving transistor connected to the light emitting device, and a driving method including a capacitor connected to the driving transistor and the light emitting device. And charging by applying a data voltage, discharging the voltage charged in the capacitor toward the second voltage through the driving transistor, and applying the voltage after the discharge of the capacitor to the driving transistor to turn on the driving transistor. And emitting light by supplying a driving current to the light emitting device through the driving transistor.

As described above, according to the present invention, five switching transistors, one driving transistor, an organic light emitting element, and a capacitor are provided, and the driving transistor and the organic light emitting element are stored in the capacitor by storing a voltage depending on the data voltage and the threshold voltage of the driving transistor. Even if the threshold voltage of the deterioration is compensated for it can prevent the deterioration of the image quality.

In addition, display quality can be improved by preventing current flow through the organic light emitting device in a section other than the light emitting section, and power loss can be minimized by connecting only two transistors between the driving voltage and the organic light emitting device in the light emitting section.

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it is to be understood that the invention is not limited to the disclosed exemplary embodiments, Of the right.

1 is a block diagram of an organic light emitting diode display according to an exemplary embodiment of the present invention.
2 is an equivalent circuit diagram of one pixel of an organic light emitting diode display according to an exemplary embodiment of the present invention.
3 is a cross-sectional view illustrating a cross-section of a switching transistor and an organic light emitting diode of one pixel of an organic light emitting diode display according to an exemplary embodiment of the present invention.
4 is a schematic diagram of an organic light emitting diode of an organic light emitting diode display according to an exemplary embodiment.
5 is an example of a timing diagram illustrating driving signals of an organic light emitting diode display according to an exemplary embodiment of the present invention.
6A through 6D are equivalent circuit diagrams for one pixel in each section shown in FIG. 5.
7 is an example of a voltage waveform diagram displayed on each terminal of a driving transistor of an organic light emitting diode display according to an exemplary embodiment of the present invention.
8 is an example of a waveform diagram illustrating an output current according to a threshold voltage of a driving transistor of an organic light emitting diode display according to an exemplary embodiment of the present invention.
9 is an example of a waveform diagram illustrating an output current according to a threshold voltage of an organic light emitting diode of an organic light emitting diode display according to an exemplary embodiment.

DETAILED DESCRIPTION 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.

In the drawings, the thickness is enlarged to clearly represent the layers and regions. Like parts are designated with like reference numerals throughout the specification. When a portion of a layer, film, region, plate, etc. is said to be "on top" of another part, this includes not only when the other part is "right on" but also another part in the middle. Conversely, when a part is "directly over" another part, it means that there is no other part in the middle. In addition, when a part is connected to another part, this includes not only a case where the part is "directly" connected to another part but also a part "connected" through another part.

A display device and a driving method thereof according to an embodiment of the present invention will now be described in detail with reference to the accompanying drawings.

First, an organic light emitting diode display according to an exemplary embodiment of the present invention will be described with reference to FIGS. 1 to 7.

1 is a block diagram of an organic light emitting diode display according to an exemplary embodiment of the present invention, and FIG. 2 is an equivalent circuit diagram of one pixel of the organic light emitting diode display according to an exemplary embodiment of the present invention. 3 is a cross-sectional view illustrating a cross-sectional view of a switching transistor and an organic light emitting diode of one pixel of an organic light emitting diode display according to an exemplary embodiment of the present invention, and FIG. 4 illustrates an organic light emitting diode display according to an exemplary embodiment of the present invention. It is a schematic diagram of a light emitting element.

As shown in FIG. 1, an organic light emitting diode display according to an exemplary embodiment includes a display panel 300, a scan driver 400, a data driver 500, a light emission driver 700, and a display panel 300 connected thereto. And a signal controller 600 for controlling them.

The display panel 300 is connected to a plurality of signal lines G _{1 -} G _n , D _{1 -} D _m , S _{1 -} S _n , a plurality of driving voltage lines (not shown), and the like in an equivalent circuit. It includes a plurality of pixels arranged in the form of a matrix.

Signal line includes a plurality of scanning signal lines (G _1- G _n) and the data lines carrying data signals for transmitting the scan signals (D _{1 -} D _m), and a plurality of light-emitting signal lines (S _1- S _n to pass the flash signal ). The scan signal lines G _1- G _n and the light emission signal lines S _1- S _n extend approximately in the row direction, and are substantially parallel to each other, and the data lines D ₁ -D _m extend substantially in the column direction, and are substantially adjacent to each other. Parallel

The driving voltage line transfers the driving voltage Vdd and extends in the row or column direction.

As shown in FIG. 2, each pixel includes an organic light emitting element OLED, a driving transistor Qd, a capacitor Cst, and five switching transistors Qs1 to Qs5.

The driving transistor Qd has a control terminal ng, an input terminal nd, and an output terminal ns, and the input terminal nd is connected to the driving voltage Vdd. The capacitor Cst is connected between the control terminal ng and the output terminal ns of the driving transistor Qd, and the anode and the cathode of the organic light emitting diode OLED are each the driving transistor Qd. Is connected to the output terminal (ns) and the common voltage (Vss).

The organic light emitting diode OLED displays an image by emitting light at different intensities according to the magnitude of the current I _OLED supplied by the driving transistor Qd, and the magnitude of the current I _OLED is the size of the driving transistor Qd. It depends on the magnitude of the voltage V _gs between the control terminal ng and the output terminal ns.

The switching transistors Qs1 to Qs3 operate in response to the scan signal.

The switching transistor Qs1 is connected between the input terminal nd and the control terminal ng of the driving transistor Qd, and the switching transistor Qs2 is connected between the data voltage Vdata and the capacitor Cst. The switching transistor Qs3 is connected between the output terminal ns of the driving transistor Qd and the common voltage Vss.

The switching transistors Qs4 and Qs5 operate in response to the light emission signal.

The switching transistor Qs4 is connected between the input terminal nd of the driving transistor Qd and the driving voltage Vdd, and the switching transistor Qs5 is the output terminal ns of the capacitor Cst and the driving transistor Qd. ) Are connected.

The switching and driving transistors Qs1 to Qs5 and Qd are formed of an n-channel metal oxide semiconductor (nMOS) transistor made of amorphous silicon or polycrystalline silicon. However, these transistors Qs1 to Qs5 and Qd may also be pMOS transistors. In this case, since the pMOS transistor and the nMOS transistor are complementary to each other, the operation, voltage, and current of the pMOS transistor are opposite to that of the nMOS transistor. do.

Next, the structure of the driving transistor Qd and the organic light emitting diode OLED of the organic light emitting diode display will be described.

As shown in FIG. 3, a control electrode 124 is formed on the insulating substrate 110. The control terminal electrode 124 is inclined with respect to the surface of the substrate 110 and its inclination angle is 20-80 °.

An insulating layer 140 made of silicon nitride (SiNx) is formed on the control terminal electrode 124.

A semiconductor 154 made of hydrogenated amorphous silicon (amorphous silicon is abbreviated a-Si), polycrystalline silicon, or the like is formed on the insulating layer 140.

On top of the semiconductor 154, ohmic contacts 163 and 165 made of a material such as n + hydrogenated amorphous silicon doped with a high concentration of silicide or n-type impurities are formed.

Side surfaces of the semiconductor 154 and the ohmic contacts 163 and 165 are inclined with an inclination angle of 30-80 degrees.

An output electrode 173 and an input electrode 175 are formed on the ohmic contacts 163 and 165 and the insulating layer 140.

The output terminal electrode 173 and the input terminal electrode 175 are separated from each other and positioned at both sides with respect to the control terminal electrode 124. The control terminal electrode 124, the output terminal electrode 173, and the input terminal electrode 175 together with the semiconductor 154 form a driving transistor Qd, the channel of which is the output terminal electrode 173 and the input terminal. It is formed in the semiconductor 154 between the electrodes 175.

Like the semiconductor 154 and the like, the output terminal electrode 173 and the input terminal electrode 175 are inclined at an angle of about 30-80 °, respectively.

On the output terminal electrode 173 and the input terminal electrode 175 and the portion of the exposed semiconductor 154, a-Si: C: O formed of organic material, plasma enhanced chemical vapor deposition (PECVD), A passivation layer 802 made of a low dielectric constant insulating material such as a-Si: O: F or silicon nitride (SiNx) or the like is formed. The material forming the passivation layer 802 may have planarization characteristics or photosensitivity.

In the passivation layer 802, a contact hole 183 exposing the output terminal electrode 173 is formed.

The pixel electrode 190 is formed on the passivation layer 802 and is physically and electrically connected to the output terminal electrode 173 through the contact hole 183. The pixel electrode 190 may be formed of a transparent conductive material such as indium tin oxide (ITO) or indium zinc oxide (IZO) or a material having excellent reflectivity of aluminum or a silver alloy.

An upper portion of the passivation layer 802 is formed of an organic insulating material or an inorganic insulating material, and a partition 803 is formed to separate the organic light emitting cells. The partition 803 surrounds the edge of the pixel electrode 190 to define a region in which the organic emission layer 70 is to be filled.

An organic emission layer 70 is formed in an area on the pixel electrode 190 surrounded by the partition 803.

As shown in FIG. 4, the organic light emitting layer 70 includes an electron transport layer (ETL) and a hole transport layer (ETL) in order to improve the light emission efficiency by improving the balance between electrons and holes in addition to the light emitting layer (EML). A multi-layered structure including a hole transport layer (HTL), and may also include a separate electron injecting layer (EIL) and a hole injecting layer (HIL).

An auxiliary electrode 272 is formed on the barrier rib 803 in the same pattern as the barrier rib 803 and made of a conductive material having a low specific resistance such as metal. The auxiliary electrode 272 contacts the common electrode 270 formed later, and serves to prevent the signal transmitted to the common electrode 270 from being distorted.

The common electrode 270 to which the common voltage Vss is applied is formed on the partition wall 803, the organic emission layer 70, and the auxiliary electrode 272. The common electrode 270 is made of a transparent conductive material such as ITO or IZO. If the pixel electrode 190 is transparent, the common electrode 270 may be made of a metal including calcium (Ca), barium (Ba), aluminum (Al), and the like.

The opaque pixel electrode 190 and the transparent common electrode 270 are applied to a top emission organic light emitting display device that displays an image in an upper direction of the display panel 300. The opaque common electrode 270 is applied to a bottom emission organic light emitting display device that displays an image in a downward direction of the display panel 300.

The pixel electrode 190, the organic emission layer 70, and the common electrode 270 form an organic light emitting diode (OLED) illustrated in FIG. 2, and the pixel electrode 190 is an anode, and the common electrode 270 is a cathode or a pixel electrode. Reference numeral 190 is a cathode, and the common electrode 270 is an anode. The organic light emitting diode OLED uniquely displays one of three primary colors, for example, red, green, and blue, depending on the organic material forming the emission layer EML, and displays a desired color as a spatial sum of these three primary colors.

Referring back to FIG. 1, the scan driver 400 is connected to the scan signal lines G _{1 -} G _n of the display panel 300 to turn on the high voltage Von and the turn-off that can turn on the switching transistors Qs 1 to Qs 3. a scanning signal (V _gi) which is a combination of a low voltage (Voff) capable of scanning signal lines _- is in the (G ₁ G _n) and may be formed of a plurality of integrated circuits.

The data driver 500 is connected to the data lines D ₁ -D _m of the display panel 300 to apply a data voltage Vdata representing an image signal to the pixels, and may be formed of a plurality of integrated circuits.

The light emission driver 700 is connected to the light emission signal lines S ₁ -S _n of the display panel 300, and the high voltage Von for turning on the switching transistors Qs4 and Qs5 and the low voltage Voff for turning off. The light emitting signal V _si may be applied to the light emitting signal lines S _1- S _n , and may be formed of a plurality of integrated circuits.

The signal controller 600 controls operations of the scan driver 400, the data driver 500, and the light emission driver 700.

The scan driver 400, the data driver 500, or the light emission driver 700 may be mounted on the display panel 300 in the form of a plurality of driving integrated circuit chips, or may be a flexible printed circuit film (not shown). It may be mounted on the display panel 300 in the form of a tape carrier package (TCP). Alternatively, the scan driver 400, the data driver 500, or the light emission driver 700 may be integrated on the display panel 300. The data driver 500 and the signal controller 600 may be integrated into one IC, also called a one-chip. In this case, the scan driver 400 and the light emission driver 700 may be selectively integrated into the IC.

Next, the display operation of the organic light emitting diode display will be described in detail with reference to FIGS. 5 to 7.

5 is an example of a timing diagram illustrating a driving signal of an organic light emitting diode display according to an exemplary embodiment of the present invention, and FIGS. 6A to 6D are equivalent circuit diagrams of one pixel in each section illustrated in FIG. 5. 7 is an example of a voltage waveform diagram displayed on each terminal of a driving transistor of an organic light emitting diode display according to an exemplary embodiment of the present invention.

The signal controller 600 may control the input image signals R, G, and B and their display from an external graphic controller (not shown), for example, a vertical sync signal V _sync and a horizontal sync signal. (H _sync ), a main clock (MCLK), a data enable signal (DE) is provided. The signal controller 600 properly processes the image signals R, G, and B according to the operating conditions of the display panel 300 based on the input image signals R, G, and B and the input control signal, and scan control signals CONT1. ), The data control signal CONT2 and the light emission control signal CONT3 are generated, and then the scan control signal CONT1 is sent to the scan driver 400, and the data control signal CONT2 and the processed image signal DAT are generated. The light emission control signal CONT3 is emitted to the data driver 500 and the light emission control signal CONT3 is emitted to the light emission driver 700.

The scan control signal CONT1 includes a vertical synchronization start signal STV for instructing the start of scanning of the high voltage Von and at least one clock signal for controlling the output of the high voltage Von.

The data control signal CONT2 is a load signal LOAD and a data clock signal HCLK for applying a corresponding data voltage to the horizontal synchronization start signal STH and the data lines D ₁ -D _m indicating data transmission of one pixel row. ), And the like.

First, the data driver 500 sequentially receives and shifts image data DAT for pixels in one row, for example, the i-th row, according to the data control signal CONT2 from the signal controller 600. The data voltage Vdata corresponding to the data DAT is applied to the data line D ₁ -D _m .

The scan driver 400 makes the voltage value of the scan signal V _gi applied to the scan signal line G _{i a} high voltage Von according to the scan control signal CONT1 from the signal controller 600, and thus the scan signal line G. _The switching transistors Qs1 to Qs3 connected to _i ) are turned on. In this case, the driving transistor Qd is diode connected.

Light-emitting driving part 700 to maintain the voltage value of the light emission signal (V _si) applied to the emit signal line (S _i) according to the emission control signal (CONT3) from the signal controller 600, a high voltage (Von), the light-emitting signal lines ( The switching transistors Qs4 and Qs5 connected to S _i are kept turned on.

An equivalent circuit of the pixel in this state is shown in FIG. 6A, and this section is called the precharge section T1. As shown in FIG. 6A, the switching transistors Qs4 and Qs5 may be represented by resistors r1 and r2, respectively.

Then, one terminal n1 of the capacitor Cst and the control terminal ng of the driving transistor Qd are connected to the driving voltage Vdd through the resistor r1, so that these voltages are at the driving voltage Vdd. It is a value obtained by subtracting the amount of voltage drop caused by the resistor r1, and the capacitor Cst serves to maintain this voltage. In this case, the driving voltage Vdd is preferably higher than the data voltage Vdata so that the driving transistor Qd can be turned on.

Therefore, the driving transistor Qd is turned on to flow an arbitrary current through the output terminal ns. However, since the current flows to the common voltage Vss and does not flow to the organic light emitting diode OLED, the organic light emitting diode OLED does not emit light. As a result, the display quality can be improved by preventing current flow through the organic light emitting element in this section T1.

Subsequently, the light emission driver 700 changes the light emission signal V _si to a low voltage Voff according to the light emission control signal CONT3 from the signal controller 600 to turn off the switching transistors Qs4 and Qs5 to thereby turn off the main charge period ( T2) begins. Since the scan signal V _gi continues to maintain the high voltage Von even in this period T2, the switching transistors Qs 1 to Qs 3 remain on.

Then, as shown in FIG. 6B, the driving transistor Qd is separated from the driving voltage Vdd while the control terminal ng and the input terminal nd are connected to each other, and the output terminal ns is It remains connected to the common voltage Vss. Since the control terminal voltage Vng of the driving transistor Qd is sufficiently high, the driving transistor Qd separated from the driving voltage Vdd remains turned on.

Accordingly, as shown in FIG. 7, the electric charge charged in the terminal n1 of the capacitor Cst charged to the predetermined level in the precharge section T1 starts to be discharged through the driving transistor Qd and accordingly the driving transistor ( The control terminal voltage Vng of Qd) is lowered. The voltage drop of the control terminal voltage Vng is equal to the threshold voltage Vth of the driving transistor Qd because the voltage Vgs between the control terminal ng and the output terminal ns of the driving transistor Qd is equal to the driving transistor Qd. It continues until (Qd) no longer flows current.

Therefore, the following Equation 1 is established in this section T2.

On the other hand, the data voltage Vdata is continuously applied to one terminal n2 of the capacitor Cst, and the voltage Vc charged in the capacitor Cst is the control terminal voltage Vng and the data voltage of the driving transistor Qd. Since Vdata) is different, Equation 2 is shown below.

From this, it can be seen that the capacitor Cst stores a voltage depending on the data voltage Vdata and the threshold voltage Vth of the driving transistor Qd.

However, since the voltage Vc determines the current I _OLED flowing in the organic light emitting element OLED in the emission period T4, the input data voltage Vdata has a value of 0 or less.

After the voltage Vc is charged to the capacitor Cst, the scan driver 400 changes the scan signal V _gi to a low voltage Voff according to the scan control signal CONT1 from the signal controller 600, thereby switching transistors. The interruption section T3 is started by turning off Qs1 to Qs3. Since the light emission signal V _si continues to maintain the low voltage Voff even in this period T3, the switching transistors Qs4 and Qs5 maintain the off state.

Then, as shown in FIG. 6C, the input terminal nd of the driving transistor Qd and the terminal n2 of the capacitor Cst are opened. Although the output terminal ns of the driving transistor Qd is connected to the organic light emitting diode OLED, since the driving transistor Qd does not flow current, the output terminal ns of the driving transistor Qd is the same as the open state. Do. Therefore, there is no outflow and inflow of charge in this circuit, and the capacitor Cst continues to maintain the charged voltage Vc in the main charging section T2.

After a predetermined time has elapsed while all the switching transistors Qs1 to Qs5 are turned off, the light emission driver 700 generates the light emission signal V _si according to the light emission control signal CONT3 from the signal controller 600. The light emission period T4 is started by turning on the switching transistors Qs4 and Qs5 by switching to Von. Since the scan signal V _gi keeps the low voltage Voff even in this period T4, the switching transistors Qs1 to Qs3 are kept in the off state.

Then, as shown in FIG. 6D, the capacitor Cst is connected between the control terminal ng and the output terminal ns of the driving transistor Qd, and the driving voltage (i) is applied to the input terminal nd of the driving transistor Qd. Vdd) is connected, and the organic light emitting diode OLED is connected to the output terminal ns of the driving transistor Qd.

Accordingly, as shown in FIG. 7, since the terminal n1 of the capacitor Cst is isolated, the voltage Vgs between the control terminal voltage Vng and the output terminal voltage Vns of the driving transistor Qd is determined by the capacitor ( The voltage Vc stored in Cst is equal to (Vgs = Vc), and the driving transistor Qd emits organic light through the output terminal ns, output current I _OLED controlled by the voltage Vgs. Supply to the device OLED. Accordingly, the organic light emitting diode OLED emits light of varying intensity depending on the size of the output current I _OLED to display a corresponding image.

However, since the capacitor Cst keeps the voltage Vc stored in the main charging section T2 regardless of the load caused by the organic light emitting element OLED (Vc = Vss + Vth−Vdata), the output current I _OLED is It can be expressed as:

Where k is a constant depending on the characteristics of the thin film transistor, where k = μ C _{siNx OW} / L, μ is the field effect mobility, C _SiNx is the capacitance of the insulating layer, W is the channel width of the thin film transistor, and L is The channel length of the thin film transistor is shown.

As shown in Equation 3, the output current I _OLED in the light emission period T4 is determined only by the data voltage Vdata and the common voltage Vss. Therefore, the output current I _OLED is not affected by the change of the threshold voltage Vth of the driving transistor Qd. In addition, the output current I _OLED is not affected by the change in the threshold voltage Vth_ _OLED of the organic light emitting diode OLED. That is, even if the threshold voltage Vth_ _OLED of the organic light emitting diode OLED is changed so that the output terminal voltage Vns of the driving transistor Qd changes accordingly, the voltage Vc stored in the capacitor Cst does not change. The voltage Vgs does not change. After the organic light emitting display device according to this embodiment, even if the deterioration of a threshold voltage (Vth_ _OLED) of threshold voltage (Vth) and the organic light emitting device (OLED) a driving transistor (Qd) can be compensated.

In addition, since only the switching transistor Qs4 and the driving transistor Qd are connected between the driving voltage Vdd and the organic light emitting diode OLED in the emission period T4, power loss is low.

On the other hand, if the light emission section T4 continues immediately after the main charging section T2 ends, the switching transistor Qs4 may be turned on before the switching transistor Qs1 is turned off. Then, charge may flow from the driving voltage Vdd and the voltage value charged in the capacitor Cst may change. Therefore, it is necessary to turn off the switching transistor Qs1 after the switching transistor Qs1 is reliably turned off by providing the blocking period T3 between the main charging section T2 and the light emitting section T4.

The light emission section T4 continues until the precharge section T1 for the pixels in the i-th row starts again in the next frame, and the operation in each of the sections T1 to T4 described above is also performed for the pixels in the next row. Repeat the same. However, for example, the precharge section T1 of the (i + 1) th row starts after the main charging section T2 of the i th row ends. In this way, all the scanning signal _{line-sequentially} performs the interval (T1~T4) control with respect to (G ₁ G _n) and the emission signal lines (S _1- S _n) and to display the corresponding image on all the pixels.

The length of each section T1-T4 can be adjusted as needed.

The common voltage Vss may be set to 0V, for example. The drive voltage Vdd is preferably set to a voltage high enough to supply sufficient charge to the capacitor Cst and allow the drive transistor Qd to flow the output current I _OLED , for example, 15V. The data voltage Vdata has a negative sign as described above, and the larger the absolute value thereof, the larger the output current I _OLED corresponding thereto.

Next, the simulation test result according to the change of the threshold voltage in the organic light emitting diode display according to the exemplary embodiment of the present invention will be described with reference to FIGS. 8 and 9.

8 is an example of a waveform diagram illustrating an output current according to a change in a threshold voltage of a driving transistor of an organic light emitting diode display according to an exemplary embodiment of the present invention, and FIG. 9 is an example of the organic light emitting diode display according to an exemplary embodiment of the present invention. An example of a waveform diagram showing an output current according to a change in a threshold voltage of an organic light emitting diode is shown.

The waveform diagram shown in FIG. 8 shows the amount of change in the output current I _OLED when the threshold voltage Vth of the driving transistor Qd is changed from 2.0V to 3.0V. Simulations were performed using SPICE. As simulation conditions, the driving voltage Vdd was set to 15V, the common voltage Vss was set to 0V, and the data voltage Vdata was set to -4.5V. As a result of measuring the output current I _OLED flowing through the organic light emitting diode OLED under these experimental conditions, as shown in FIG. 8, the output current I _OLED was 1.394 mA when the threshold voltage Vth was 2.0 V. When the threshold voltage Vth was 3.0V, the voltage was 1.375 mA. Therefore, when the threshold voltage Vth of the driving transistor Qd is increased by 1V, the amount of change in the current is 19 mA, and 1.363% of the current before the change is changed. The variation of the output current I _OLED is negligible compared to the variation of the output current due to the change in the threshold voltage of the driving transistor in the pixel having two conventional thin film transistors.

9 shows the amount of change in output current I _OLED when the threshold voltage Vth_ _OLED of the organic light emitting diode OLED changes from 2.8V to 3.3V. As a result of measuring the output current (I _OLED ) flowing through the organic light emitting device (OLED) under the same experimental conditions as the previous experimental condition, as shown in FIG. 9, the output current (I _OLED ) has a threshold voltage (Vth_ _OLED ) of 2.8 V. It was the case 1.306㎂, was 1.291㎂ when the threshold voltage (Vth_ _OLED) is 3.3V. Therefore, the amount of change in current when the threshold voltage Vth_ _OLED of the organic light emitting diode OLED increased by 0.5 V was 15 mA, and 1.149% of the current before deterioration was changed. The variation of the output current I _OLED is negligible compared to the variation of the output current due to the deterioration of the threshold voltage of the organic light emitting diode in the pixel having two conventional thin film transistors.

This simulation result shows that the organic light emitting display device according to this embodiment is, even if the deterioration threshold voltage (Vth_ _OLED) of threshold voltage (Vth) and the organic light emitting device (OLED) a driving transistor (Qd) for example to compensate for this .

400 scan drivers
500 data driver
600 signal controller

Claims (7)

The light-
A driving transistor having a first terminal connected to a first voltage, a second terminal connected to the light emitting element, and a control terminal;
A capacitor connected between the second terminal and the control terminal of the driving transistor,
A first switching element operating in response to a scan signal and connected between a first terminal and a control terminal of the driving transistor,
A second switching element operating in response to the scan signal and connected between a first terminal of the capacitor and a data voltage;
A third switching element operating in response to the scan signal and connected between a second terminal of the driving transistor and a second voltage;
A fourth switching element operating in response to a light emission signal and connected between the first voltage and the first terminal of the driving transistor, and
A fifth switching element operated in response to the light emission signal and connected between a first terminal of the capacitor and a second terminal of the driving transistor
. In claim 1,
Among the first to fourth sections that are in turn,
The first to fifth transistors are turned on during the first period,
The first to third transistors are turned on during the second period, and the fourth and fifth transistors are turned off.
The first to fifth transistors are turned off during the third period,
The first to third transistors are turned off and the fourth and fifth transistors are turned on during the fourth period.
Display device. In claim 2,
The data voltage has a value less than or equal to zero. A light emitting element, a driving transistor having a control terminal as a three terminal element, a first terminal, and a second terminal connected to the light emitting element, a first terminal connected to the control terminal of the driving transistor, and the first terminal A driving method of a display device including a capacitor including an opposite second terminal,
Connecting the control terminal and the first terminal of the driving transistor;
Coupling a second terminal of the driving transistor to a common voltage,
Coupling a second terminal of the capacitor to a data voltage,
Connecting the capacitor between a control terminal and a second terminal of the driving transistor, and
Coupling a first terminal of the driving transistor to a driving voltage
Method of driving a display device comprising a. 5. The method of claim 4,
And charging the capacitor by applying a first voltage to the control terminal of the driving transistor, and then isolating the control terminal and the first terminal of the driving transistor connected to each other. The method of claim 5,
And isolating the capacitor and the driving transistor from an external signal source after isolating the control terminal and the first terminal of the driving transistor connected to each other. A light emitting element, a driving transistor having a control terminal as a three terminal element, a first terminal, and a second terminal connected to the light emitting element, a first terminal connected to the control terminal of the driving transistor, and the first terminal A driving method of a display device including a capacitor including an opposite second terminal,
Charging the capacitor by applying a first voltage to a first terminal of the capacitor and a data voltage to a second terminal of the capacitor;
Discharging the voltage charged in the capacitor toward the second voltage through the driving transistor;
Applying a voltage after discharge of the capacitor to the driving transistor to turn on the driving transistor, and
Emitting light by supplying a driving current to the light emitting device through the driving transistor;
Method of driving a display device comprising a.

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