KR20060011038A - Light emitting display, light emitting panel and method thereof - Google Patents

Abstract

The present invention provides a light emitting display device that can extend the life of a light emitting device by applying a reverse bias to the light emitting device.

The pixel according to the present invention includes a pixel driver, a light emitting device, and first and second switching devices. The pixel driver receives a first power supply voltage and outputs a first current corresponding to the data signal in response to the selection signal, and the light emitting device emits light with light corresponding to the first current. The first switching device is electrically connected between the pixel driver and the light emitting device, and transmits a first current to the light emitting device when turned on. The second switching device applies a second current in a direction opposite to the first current to the light emitting device when the first switching device is turned off. In particular, the light emitting device includes a first electrode electrically connected to the second switching device and a second electrode to which a second power supply voltage lower than the first power supply is applied, and the first electrode of the light emitting device when the second switching device is turned on. A reverse bias voltage lower than the second power supply voltage may be applied to the second supply voltage.

Anode, Reverse bias, Light emitting element, Organic EL

Description

Light emitting display, light emitting panel and driving method thereof

1 is a diagram illustrating an equivalent circuit of a pixel of a conventional light emitting display panel.

2 is a plan view schematically illustrating a configuration of an organic EL display device according to an exemplary embodiment of the present invention.

3 is an equivalent circuit diagram of a pixel 110 of an organic EL display device according to a first embodiment of the present invention.

4 is a signal timing diagram of an organic EL display device according to a first embodiment of the present invention.

5 is a diagram schematically illustrating a configuration of an organic EL display device according to a second embodiment of the present invention.

6 is an equivalent circuit diagram illustrating a pixel 210 of an organic EL display device according to a second exemplary embodiment of the present invention.

7 is a signal timing diagram of an organic EL display device according to a second embodiment of the present invention.

8 is a diagram schematically illustrating a configuration of an organic EL display device according to a third embodiment of the present invention.

9 is a circuit diagram illustrating a pixel 310 of an organic EL display device according to a third exemplary embodiment of the present invention.

10 is a signal timing diagram of an organic EL display device according to a third embodiment of the present invention.

FIG. 11 is a diagram schematically illustrating a configuration of an organic EL display device according to a fourth embodiment of the present invention.

12 is a circuit diagram illustrating a pixel 410 of an organic EL display device according to a fourth embodiment of the present invention.

13 is a signal timing diagram of an organic EL display device according to a fourth embodiment of the present invention.

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a light emitting display device, and more particularly, to an organic EL display device using electroluminescence of organic materials (hereinafter referred to as "organic EL").

In general, a light emitting display device is an organic electroluminescence (EL) display device using electroluminescence of an organic material and displays an image by voltage driving or current driving N × M organic light emitting cells arranged in a matrix form.

The organic light emitting cell has a diode characteristic and is also called an organic light emitting diode (OLED), and has a structure of an anode (ITO), an organic thin film, and a cathode electrode layer (metal). The organic thin film has a multilayer structure including an emitting layer (EML), an electron transport layer (ETL), and a hole transport layer (HTL) to improve the emission efficiency by improving the balance between electrons and holes. It also includes a separate electron injecting layer (EIL) and a hole injecting layer (HIL). These organic light emitting cells are arranged in an N × M matrix to form an organic EL display panel.

The organic light emitting cell may be driven using a simple matrix method and an active matrix method using a thin film transistor (TFT) or a MOSFET. In the simple matrix method, the anode and the cathode are orthogonal and the line is selected and driven, whereas the active driving method connects a thin film transistor to each indium tin oxide (ITO) pixel electrode and is maintained by a capacitor capacitance connected to the gate of the thin film transistor. It is driven according to the voltage.

Hereinafter, a pixel of a general active driving organic EL display device will be described.

FIG. 1 is an equivalent circuit diagram of a pixel, and equivalently illustrates one of N × M pixels, that is, a pixel located in a first row and a first column.

As shown in FIG. 1, one pixel 10 is formed of three subpixels 10r, 10g, and 10b, and red (R) and green (G) are respectively present in the subpixels 10r, 10g, and 10b. And organic EL elements OLEDr, OLEDg, and OLEDb that emit light of blue (B). In the structure in which the subpixels are arranged in a stripe shape, the subpixels 10r, 10g, and 10b are connected to the separate data lines D1r, D1g, and D1b and the common scan line S1, respectively.

The red subpixel 10r includes two transistors M1r and M2r and a capacitor C1r for driving the organic EL element OLEDr. Similarly, the green subpixel 10g includes two transistors M1g and M2g and a capacitor C1g, and the blue subpixel 10b also includes two transistors M1b and M2b and a capacitor C1b. . Since the operations of these subpixels 10r, 10g, and 10b are all the same, one subpixel 10r will be described below as an example.

The driving transistor M1r is connected between the power supply voltage VDD and the anode of the organic EL element OLEDr to transfer a current for light emission to the organic EL element OLEDr, and the cathode of the organic EL element OECDr is the power supply voltage. It is connected to a voltage Vss lower than VDD. The amount of current in the driving transistor M1r is controlled by the data voltage applied through the switching transistor M2r. At this time, the capacitor C1r is connected between the source and the gate of the transistor M1r to maintain the applied voltage for a predetermined period. A scan line S1 for transmitting an on / off selection signal is connected to a gate of the transistor M2r, and a data line D1r for transmitting a data voltage corresponding to the red subpixel 10r is connected to a source side thereof. have.

Referring to the operation, when the switching transistor M2r is turned on in response to the selection signal applied to the gate, the data voltage V _DATA from the data line D1r is applied to the gate of the transistor M1r. Then, the current I _OLED flows through the transistor M1r in response to the voltage V _GS charged between the gate and the source by the capacitor C1r, and the organic EL element OLEDr corresponds to the current I _OLED . Emits light. At this time, the current I _OLED flowing through the organic EL device OLEDr is represented by Equation 1.

In the pixel shown in FIG. 1, a current corresponding to the data voltage is supplied to the organic EL element OLEDr, and the organic EL element OLEDr emits light at a luminance corresponding to the supplied current. In this case, the applied data voltage has a multi-level value in a predetermined range in order to express a predetermined gray level.

As described above, in the organic EL display device, one pixel 10 includes three subpixels 10r, 10g, and 10b, and a driving transistor, a switching transistor, and a capacitor for driving the organic EL element for each subpixel are provided. Is formed. In addition, a data line for transmitting a data signal and a power supply line for transmitting a power supply voltage VDD are formed for each subpixel. As such, many wirings are required to drive the pixel, and thus, it is difficult to arrange all of them in the pixel region, and the aperture ratio corresponding to the region emitting light in the pixel region may be reduced. Therefore, there is a need for development of a pixel capable of reducing the number of wirings and the number of elements for driving the pixel.

SUMMARY OF THE INVENTION The present invention provides a light emitting display device in which a plurality of light emitting elements are connected to one pixel driver in common, thereby reducing the number of wirings and elements, thereby making it easy to utilize aperture ratio, yield, and panel space during design. It is.

Another object of the present invention is to provide a light emitting display device capable of extending the life of a light emitting device by applying a reverse bias to the light emitting device.

Another object of the present invention is to provide a method of driving a light emitting display device which can extend the life of the light emitting device by applying a reverse bias to the light emitting device.

In order to accomplish the above technical problem, a light emitting display device according to an aspect of the present invention includes a plurality of scan lines for transmitting a selection signal, a plurality of data lines for transmitting a data signal, and a plurality of scan lines for connecting the scan lines and the data lines, respectively. A light emitting display device comprising a plurality of pixels,

The pixel may include a pixel driver configured to receive a first power supply voltage and output a first current corresponding to the data signal in response to the selection signal; A light emitting device emitting light with light corresponding to the first current; A first switching device electrically connected between the pixel driver and the light emitting device and transferring a first current to the light emitting device when turned on; And a second switching device configured to apply a second current in a direction opposite to the first current to the light emitting device when the first switching device is turned off.

The light emitting device includes a first electrode electrically connected to the second switching device and a second electrode to which a second power supply voltage lower than the first power supply is applied, and the light emitting device is turned on when the second switching device is turned on. A reverse bias voltage lower than the second power supply voltage may be applied to the first electrode of the.

The second switching element may include a control electrode electrically connected to a signal line for transmitting a first control signal, a first main electrode electrically connected to a reverse bias power source applying the reverse bias voltage, and a second main electrode. It may be a transistor electrically connected to the first electrode of the light emitting device.

The plurality of scan lines may include first and second scan lines that transmit first and second selection signals, respectively, and the circuit driver includes a control electrode connected to the first scan line and a source electrically connected to the data line. A first transistor; A first capacitor applied with the first power supply voltage to one electrode, and the other electrode electrically connected to the drain of the first transistor; A second transistor having a control electrode connected to the second scan line and a source connected to one electrode of the first capacitor; A second capacitor having one electrode connected to the drain of the second transistor; A third transistor having a control electrode electrically connected to the other electrode of the first capacitor and having a first power supply voltage applied to a source; And a fourth transistor connected to the second scan line and diode-connected to the third transistor.

A light emitting display device according to another aspect of the present invention is a light emitting display device including a plurality of scanning lines for transmitting a selection signal, a plurality of data lines for transmitting a data signal, and a plurality of pixels respectively connected to the scanning lines and the data lines. ,

The pixel may include a pixel driver configured to output a first current corresponding to the data signal in response to the selection signal; First and second switching elements for selectively transferring the first current; First and second light emitting devices emitting light with light corresponding to the first current received from the first and second switching devices, respectively; And third and fourth switching devices applying reverse bias voltages to the first and second light emitting devices, respectively.

The third switching device may be turned on at the same time as the second switching device, and the fourth switching device may be turned on at the same time as the first switching device.

The first switching device is a transistor in which the control electrode is electrically connected to the first light emitting signal line for transmitting the first light emitting signal, and the second switching device is electrically connected to the second light emitting signal line in which the control electrode transmits the second light emitting signal. A third electrode connected to the second light emitting signal line, a first main electrode connected to a reverse bias power supply line applying a reverse bias voltage, and a second main electrode connected to the third switching element. The transistor is connected to a first light emitting device, and the fourth switching device has a control electrode connected to the first light emitting signal line, a first main electrode connected to a reverse bias power supply line applying a reverse bias voltage, and a second main electrode. The transistor may be connected to the second light emitting device.

A light emitting display panel according to another aspect of the present invention,

A plurality of scan lines sequentially transmitting selection signals; A plurality of data lines for transmitting data signals; A plurality of first and second light emitting signal lines respectively transmitting the first and second light emitting signals; A plurality of first power lines for supplying power of a first voltage; A plurality of second power lines for supplying power of a second voltage; A plurality of control signal lines for transmitting a control signal; And pixels connected to the scan line, the data line, the first and second emission signal lines, the first and second power supply lines, and the control signal line, respectively.

The pixel may include a plurality of pixel drivers configured to output a first current corresponding to the data signal in response to the selection signal; First and second transistors having control electrodes connected to the first and second light emitting signal lines, respectively, for transmitting the first current; First and second light emitting devices having a first electrode electrically connected to drains of the first and second transistors; And third and fourth transistors having control electrodes connected to the control signal lines, a source connected to the first electrodes of the first and second light emitting devices, respectively, and a drain connected to the second power line. do.

In the first and second light emitting devices, a third voltage lower than the first voltage may be applied to the second electrode.

The second voltage may be lower than the third voltage.

The circuit driver may include: a first transistor turned on in response to a current selection signal to transfer the data signal; A first capacitor storing a voltage corresponding to the data signal; A second transistor turned on in response to a previous selection signal and connected in parallel with the first capacitor; A third transistor outputting a current corresponding to the voltage stored in the first capacitor; A second capacitor connected to the gate of the third transistor to store a voltage corresponding to the threshold voltage of the third transistor; And a fourth transistor that is turned on in response to a previous selection signal to diode-connect the third transistor.

According to another aspect of the present invention, there is provided a method of driving a light emitting display device.

The light emitting display device may include a plurality of light emitting devices including first and second light emitting devices that emit light in response to an applied first current; And a plurality of pixel drivers configured to generate the first current based on a selection signal and a data signal.

The driving method,

a) applying the first current to the first light emitting device; And

b) electrically blocking the pixel driver and the first light emitting device, and applying a reverse bias to the first light emitting device.

During the step b), the first current may be applied to the second light emitting device.

During the step b), the pixel driver and the second light emitting device may be electrically blocked, and a reverse bias may be applied to the second light emitting device.

Step b) may proceed while the selection signal is applied.

The step a) may proceed during the first field and the step b) may proceed during the second field following the first field.

The light emitting display device may include a plurality of pixels, and each of the plurality of pixels may include the first and second light emitting devices and the pixel driver.

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.

Prior to the description, when a term relating to a scan line is defined, a scan line to which a current selection signal is to be transmitted is referred to as a "current scan line", and a scan line to which a selection signal is transmitted before the current selection signal is transmitted is referred to as a "previous scan line". In addition, the pixel which emits light based on the selection signal of the current scanning line is called "current pixel", and the pixel which emits light based on the selection signal of the previous scanning line is called "previous pixel".

2 is a diagram schematically illustrating a configuration of an organic EL display device according to a first embodiment of the present invention.

As shown in FIG. 2, the organic EL display device according to the first exemplary embodiment of the present invention includes a display panel 100, a selective scan driver 700, a light emitting scan driver 800, and a data driver 900. The display panel 100 includes a plurality of selective scan lines S [i] extending in a row direction, a plurality of light emitting scan lines E1 [i] and E2 [i], and a plurality of data lines D [extending in a column direction. j]), a plurality of power lines VDD, and a plurality of pixels 100. Here, 'i' is any natural number between 1 and n, and 'j' is any natural number between 1 and m.

The pixel 110 is defined by two neighboring arbitrary selection scan lines S [i-1] and S [i] and two neighboring data lines D [j-1] and D [j]. It is formed in the pixel region and includes two organic EL elements of a red (R) organic EL element, a green (G) organic EL element, and a blue (B) organic EL element. The pixel 110 configured as described above is one data by signals transmitted from the current selection scan line S [i], the light emission scan lines E1 [i], E2 [i], and the data line D [j]. The two organic EL elements are driven to time-divisionally emit light based on the data signal applied from the line D [j]. Particularly, in the organic EL display device according to the first embodiment of the present invention, two light emitting scan lines E1 [i] and E2 [i in order to time-emit light emitting two organic EL elements in one pixel 110. Light emission signals applied to each of the light emitting scan lines E1 [i] and E2 [i] are controlled to selectively emit two organic EL elements included in one pixel.

The selection scan driver 700 generates a selection signal for selecting a corresponding line so that a data signal can be applied to the pixels of the corresponding line, and sequentially transmits the selection signal to the selection scan lines S [1] to S [n]. The light emitting scan driver 800 generates a light emitting signal for controlling light emission of the organic EL elements OLED1 and OLED2 and sequentially transmits the light emitting signals to the light emitting scan lines E1 [i] and E2 [i]. Whenever the selection signal is applied, the data driver 900 applies a data signal corresponding to the pixel of the line to which the selection signal is applied to the data lines D [1] to D [m].

The selection scan driver 700, the light emitting scan driver 800, and the data driver 900 are electrically connected to the substrate on which the display panel 100 is formed. Alternatively, the selective scan driver 700, the light emitting scan driver 800, and / or the data driver 900 may be directly mounted on the glass substrate of the display panel 100, and the selective scan line may be mounted on the substrate of the display panel 100. It may be replaced by a driving circuit formed of the same layers as the light emitting scan line, the data line and the transistor. Alternatively, a tape carrier package (TCP), a flexible printed circuit (FPC), or the like, may be electrically bonded to the selective scan driver 700, the light emitting scan driver 800, and / or the data driver 900 to a substrate of the display panel 100. It can also be mounted in the form of a chip on TAB (tape automatic bonding).

In the first embodiment of the present invention, a frame is time-divided into two fields to drive two organic EL elements OLED1 and OLED2 included in one pixel, respectively. In the two fields, any two pieces of data of red, green, and blue data are written to emit light. To this end, the selection scan driver 700 sequentially transmits the selection signal to the selection scan line S [i] for each field, and the emission scan driver 800 has two organic EL elements included in one pixel during the corresponding field. The light emission signals are sequentially applied to the corresponding light emission scan lines E1 [i] and E2 [i] to emit light. The data driver 900 applies R, G, and B data signals to the corresponding data lines D [j] for each field.

Hereinafter, a pixel according to a first exemplary embodiment of the present invention will be described in detail with reference to FIG. 3.

3 is an equivalent circuit diagram illustrating a pixel 110 of an organic EL display device according to a first embodiment of the present invention. For convenience of explanation, the pixels of the pixel region formed in the scan line S [i] in the i-th row and the data line D [j] in the j-th column are shown as a representative. In the following description, for convenience of explanation, the codes of the light emission signals applied to the light emission scan lines E1 [i] and E2 [i] are also displayed as 'E1 [i], E2 [i]' as the light emission scan lines. The sign of the selection signal applied to the scan line S [i] is also denoted as 'S [i]'. The organic EL element OLED1 and the organic EL element OLED2 of the pixel 110 may be any one of a red (R) organic EL element, a green (G) organic EL element, and a blue (B) organic EL element. All transistors (DM, EM1, EM2, SM) of 110 are shown as p-channel transistors.

As shown in FIG. 3, the pixel 110 includes the pixel driver 111, two organic EL elements OLED1 and OLED2, and two organic EL elements OLED1 and OLED2 so as to selectively emit light. , EM2).

The pixel driver 111 is connected to the selection scan line S [i] and the data line D [j] and responds to the data signals transmitted through the data line D [j] and the organic EL elements OLED1 and OLED2. Generates a current to be applied. The pixel driver 111 according to the first embodiment includes two transistors and one capacitor, that is, a transistor SM, a transistor DM, and a capacitor Cst. Specifically, the transistor SM has a source connected to the data line D [j] and a gate connected to the selection scan line S [i]. The transistor DM is connected to the source of the power supply voltage VDD, the gate is connected to the drain of the transistor SM, and the capacitor Cst is connected between the gate and the source.

The transistor EM1 has a source connected to the drain of the transistor DM, a drain connected to the anode of the organic EL element OLED1, and a gate connected to the emission scan line E1 [i], thereby emitting the light emission signal E2 [i]. In response, the current is turned on to transmit the current output from the transistor DM to the anode of the organic EL element OLED1. The transistor EM2 which controls the light emission of the organic EL element OLED2 has a source connected to the drain of the transistor DM, a drain connected to the anode of the organic EL element OLED2, and a gate of the emission scan line E2 [i]. It is connected to and is turned on in response to the light emission signal E2 [i] to transmit a current output from the transistor DM to the anode of the organic EL element OLED2.

In the organic EL devices OLED1 and OLED2, an anode is connected to the drains of the transistors EM1 and EM2, respectively, and a cathode is connected to a reference voltage Vss lower than the power supply voltage VDD. As the power supply voltage Vss, a negative voltage or a ground voltage may be used.

Hereinafter, a method of driving an organic EL display device according to a first embodiment of the present invention will be described in detail with reference to FIG. 4. 4 is a signal timing diagram of an organic EL display device according to a first embodiment of the present invention.

As shown in FIG. 4, the organic EL display device according to the first exemplary embodiment of the present invention is driven by dividing one frame into two fields 1F and 2F, and selecting signals in each field 1F and 2F. S [1] to S [n]) are sequentially applied. The two organic EL elements OLED1 and OLED2 sharing the driving circuit section 111 emit light for a period corresponding to one field, respectively. The fields 1F and 2F are independently defined for each row. In FIG. 4, the two fields 1F and 2F are illustrated based on the selection scan line S [1] of the first row, and the selection scan line of the first row ( The operation will be described centering on S [1]).

First, in the first field 1F, while the low-level selection signal is applied to the current selection scan line S [1], the transistor SM is turned on to apply the data voltage applied from the data line D [j]. Vdata) is applied to the gate of the transistor DM, that is, one end of the capacitor C. Therefore, the capacitor C is charged with a voltage corresponding to the difference between the power supply voltage VDD and the data voltage Vdata, that is, the voltage V _GS charged between the gate and the source of the transistor DM, and the transistor DM The current I _OLED corresponding to the charged voltage V _GS flows to the drain.

Then, when the emission signal E1 [1] becomes low level, the transistor EM1 is turned on so that the current I _OLED flowing through the drain of the transistor DM is transferred to the anode of the organic EL element OLED1. The organic EL element OLED1 emits light corresponding to the current I _OLED . In this case, the current I _OLED flowing through the organic EL element OLED1 is represented by Equation 1 described above. On the other hand, while the light emission signal E1 [1] becomes low level in the first field 1F and the organic EL element OLED1 emits light, the light emission signal E2 [1] is maintained at a high level so that the transistor EM2 The current I _OLED is not transmitted to the organic EL element OLED2 by being turned off.

In the second field 2F, while the low-level selection signal is applied to the current selection scan line S [1], the transistor SM is turned on in the same manner as the first field 1F so that the data line D [j]. The data voltage Vdata applied from]) is applied to the gate of the transistor DM, that is, one end of the capacitor C. Therefore, the capacitor C is charged with a voltage corresponding to the difference between the power supply voltage VDD and the data voltage Vdata, that is, the voltage V _GS charged between the gate and the source of the transistor DM, and the transistor DM The current I _OLED corresponding to the charged voltage V _GS flows to the drain.

Then, when the light emission signal E2 [1] is at a low level, the transistor EM2 is turned on so that the current I _OLED flowing through the drain of the transistor DM is transferred to the anode of the organic EL element OLED2. The organic EL element OLED2 emits light corresponding to the current I _OLED . On the other hand, in the second field 2F, the light emission signal E2 [1] becomes low level while the light emission signal E1 [1] remains high while the current I _OLED is transmitted to the organic EL element OLED2. As a result, the transistor EM1 is turned off so that the current I _OLED is not transmitted to the organic EL element OLED2.

As described above, in the organic EL display device according to the first embodiment, current flows only in one direction from the anode to the cathode in the organic EL element OLED, and between the hole transport layer HTL and the emission layer EML of the organic layer, or Space charge is stored between the electron transport layer ETL and the light emitting layer EML. By accumulating such space charges, the life of the organic EL device OLED may be shortened.

Hereinafter, an organic EL display device and a driving method thereof according to the second embodiment of the present invention, which can prevent the above-described space charge from being stored in the organic EL device, will be described in detail.

5 is a diagram schematically illustrating a configuration of an organic EL display device according to a second embodiment of the present invention. The organic EL display device according to the second embodiment of the present invention differs from the first embodiment in that a power supply line for applying a bias voltage Vbias is added to each pixel.

As shown in FIG. 5, the organic EL display device according to the second exemplary embodiment of the present invention includes a display panel 200, a selective scan driver 700, a light emitting scan driver 800, and a data driver 900. In this case, since the selective scan driver 700, the light emitting scan driver 800, and the data driver 900 perform the same operations as those of the first embodiment, they are denoted by the same reference numerals and description thereof will be omitted.

The display panel 200 includes a plurality of selective scan lines S [i] extending in a row direction, a plurality of light emitting scan lines E1 [i] and E2 [i], and a plurality of data lines D [extending in a column direction. j]), a plurality of power lines VDD, a plurality of bias power lines Vbias, and a plurality of pixels 210. The pixel 210 is connected to the current selection scan line S [i], the emission scan lines E1 [i], E2 [i], and the data line D [j] by one signal. The two organic EL elements are driven to emit time-divisionally based on the data signal applied from D [j]). Here, the bias voltage Vbias is a voltage lower than the power supply voltage Vss applied to the cathodes of the organic EL elements OLED1 and OLED2 and is generally a negative bias voltage.

6 is an equivalent circuit diagram illustrating a pixel 210 of an organic EL display device according to a second exemplary embodiment of the present invention.

As illustrated in FIG. 6, the pixel 210 includes a transistor EM1, which controls the pixel driver 211, two organic EL elements OLED1 and OLED2, and two organic EL elements OLED1 and OLED2 to selectively emit light. EM2) and transistors BM1 and BM2 which control the two organic EL elements OLED1 and OLED2 to be selectively reverse biased, respectively.

The pixel driver 211 is connected to the selection scan line S [i] and the data line D [j], and responds to the data signals transmitted through the data line D [j] and the organic EL elements OLED1 and OLED2. Generates a current to be applied. The pixel driving circuit unit 211 according to the second embodiment includes two transistors and one capacitor, that is, a transistor SM, a transistor DM, and a capacitor Cst. In detail, the transistor SM has a source connected to the data line D [j] and a gate connected to the selection scan line S [i]. The transistor DM is connected to the source of the power supply voltage VDD, the gate is connected to the drain of the transistor SM, and the capacitor Cst is connected between the gate and the source.

The transistor EM1 has a source connected to the drain of the transistor DM, a drain connected to the anode of the organic EL element OLED1, and a gate connected to the emission scan line E1 [i], so that the light emission line E1 [i] The current is turned on in response to the light emission signal transmitted through the C1, and the current output from the transistor DM is transferred to the anode of the organic EL element OLED1. The transistor EM2 which controls the light emission of the organic EL element OLED2 has a source connected to the drain of the transistor DM, a drain connected to the anode of the organic EL element OLED2, and a gate of the emission scan line E2 [i]. It is connected to and is turned on in response to the light emission signal E2 [i] to transmit a current output from the transistor DM to the anode of the organic EL element OLED2.

In the organic EL devices OLED1 and OLED2, an anode is connected to the drains of the transistors EM1 and EM2, respectively, and a cathode is connected to a reference voltage Vss lower than the power supply voltage VDD.

The transistor BM1 has a drain connected to a power supply line Vbias to which a bias voltage is applied, a source connected to an anode of the organic EL element OLED1, and a gate connected to a light emitting scan line E2 [i] so that the light emitting scan line E2 is connected. The leakage current applied to the anode of the organic EL element OLED1 is turned on in response to the light emission signal transmitted through [i]) to the power line Vbias. In addition, the transistor BM2 has a drain connected to a power supply line Vbias to which a bias voltage is applied, a source connected to an anode of the organic EL element OLED2, and a gate connected to a light emitting scan line E1 [i]. In response to E1 [i]), a leakage current applied to the anode of the organic EL element OLED2 flows to the power supply line Vbias.

Hereinafter, a method of driving an organic EL display device according to a second exemplary embodiment of the present invention will be described in detail with reference to FIG. 7.

7 is a signal timing diagram of an organic EL display device according to a second embodiment of the present invention. The selection signal S [i] and the emission signals E1 [i] and E2 [i] applied to the pixel 210 according to the second embodiment are the pixels 110 according to the first embodiment shown in FIG. 4. Is basically the same as the signal applied to the signal, but after the predetermined time td elapses after the selection signal S [i] is converted from the low level to the high level, the light emission signal E1 [i] .E2 [i] ) Is the high level, which eliminates the effects of signal delay.

First, in the first field 1F, while the low level selection signal is applied to the current selection scan line S [1], the transistor SM is turned on and the data voltage applied from the data line D [j]. (Vdata) is applied to the gate of the transistor DM, that is, one end of the capacitor (C). Therefore, the capacitor C is charged with a voltage corresponding to the difference between the power supply voltage VDD and the data voltage Vdata, that is, the voltage V _GS charged between the gate and the source of the transistor DM, and the transistor DM The current I _OLED corresponding to the charged voltage V _GS flows to the drain. After the predetermined time td has elapsed after the low level selection signal S [1] is applied, the transistor EM1 is turned on when the light emission signal E1 [1] becomes low level. The current I _OLED flowing through the drain is delivered to the anode of the organic EL element OLED1, and the organic EL element OLED1 emits light corresponding to the current I _OLED . In this case, the current I _OLED flowing through the organic EL element OLED1 is represented by Equation 1 described above. On the other hand, while the light emission signal E1 [1] becomes low level in the first field 1F and the organic EL element OLED1 emits light, the light emission signal E2 [1] is maintained at a high level so that the transistor EM2 The current I _OLED is not transmitted to the organic EL element OLED2 by being turned off.

In addition, during the first field 1F, the transistor BM2 is turned on while the light emission signal E1 [i] is at a low level. Accordingly, a voltage having a lower level than that of the cathode is applied to the anode of the organic EL element OLED2, so that the reverse bias is applied to the organic EL element OLED2. Therefore, a reverse current flows through the organic EL element OLED2, so that the space charge stored between the hole transport layer HTL and the emission layer EML or between the electron transport layer ETL and the emission layer EML of the organic EL element OLED2. Is discharged, and the lifespan of the organic EL element OLED2 can be increased.

Then, in the second field 2F, while the low level selection signal is applied to the current selection scan line S [1], the transistor SM is turned on in the same manner as the first field 1F so that the data line ( The data voltage Vdata applied from D [j] is applied to the gate of the transistor DM, that is, one end of the capacitor C. Therefore, the capacitor C is charged with a voltage corresponding to the difference between the power supply voltage VDD and the data voltage Vdata, that is, the voltage V _GS charged between the gate and the source of the transistor DM, and the transistor DM The current I _OLED corresponding to the charged voltage V _GS flows to the drain. After the predetermined time td elapses after the low level selection signal S [1] is applied, when the light emission signal E2 [1] becomes low level, the transistor EM2 is turned on to turn on the transistor DM. The current I _OLED flowing through the drain is transferred to the anode of the organic EL element OLED2, and the organic EL element OLED2 emits light corresponding to the current I _OLED . On the other hand, in the second field 2F, the light emission signal E2 [1] becomes low level while the light emission signal E1 [1] remains high while the current I _OLED is transmitted to the organic EL element OLED2. As a result, the transistor EM1 is turned off so that the current I _OLED is not transmitted to the organic EL element OLED2.

In addition, during the second field 2F, the transistor BM1 is turned on while the light emission signal E2 [i] is at a low level. Therefore, a voltage having a lower level than that of the cathode is applied to the anode of the organic EL element OLED1, and the reverse bias is applied to the organic EL element OLED1. Accordingly, the reverse current flows through the organic EL element OLED1, so that the space charge stored between the hole transport layer HTL and the light emitting layer EML or between the electron transport layer ETL and the light emitting layer EML of the organic EL element OLED2. Is discharged, and the lifespan of the organic EL element OLED2 can be increased.

Hereinafter, an organic EL display device and a driving method thereof according to a third embodiment of the present invention will be described in detail.

8 is a diagram schematically illustrating a configuration of an organic EL display device according to a third embodiment of the present invention. In the organic EL display device according to the third exemplary embodiment, a signal line RB [i] to which a reverse bias signal to be controlled is applied is added to each pixel in addition to a power supply line for applying a bias voltage Vbias. This is different from the second embodiment.

As shown in FIG. 8, the organic EL display device according to the third exemplary embodiment includes a display panel 300, a selective scan driver 710, a light emitting scan driver 800, and a data driver 900. Here, the light emitting scan driver 800 and the data driver 900 perform the same operations as those of the first embodiment, and are denoted by the same reference numerals, and description thereof will be omitted. The selection scan driver 710 sequentially generates the selection signal S [i] for each field. In addition, the selection scan driver 710 sequentially generates the reverse bias signal for each field and applies it to the corresponding signal line RB [i]. In the third embodiment, the reverse bias signal is generated by the selection scan driver 710, but the reverse bias signal may be generated by the light emission scan driver.

The display panel 300 includes a plurality of selective scan lines S [i], a plurality of emission scan lines E1 [i] and E2 [i], reverse bias signal lines RB [i], and a column direction that extend in a row direction. A plurality of data lines D [j], a plurality of power lines VDD, a plurality of bias power lines Vbias, and a plurality of pixels 310 extend to each other. The pixel 310 is formed from the previous selective scan line S [i-1], the current selective scan line S [i], the emission scan lines E1 [i], E2 [i], and the data line D [j]. By the transmitted signal, two organic EL elements are driven to emit time-divisionally based on a data signal applied from one data line D [j]. The bias voltage Vbias is set to a voltage lower than the power supply voltage Vss applied to the cathodes of the organic EL elements OLED1 and OLED2.

9 is a circuit diagram illustrating a pixel 310 of an organic EL display device according to a third exemplary embodiment of the present invention. All transistors M1, M21, M22, M3, M4, and M5 of the pixel 310 are illustrated as p-channel transistors.

As shown in FIG. 9, the pixel 310 controls the pixel driver 311, the two organic EL elements OLED1 and OLED2, and the two organic EL elements OLED1 and OLED2 to selectively emit light. M22), and transistors M61 and M62 for preventing leakage current from being transmitted to the two organic EL elements OLED1 and OLED2.

The pixel driver 311 is connected to the selection scan line S [i] and the data line D [j], and responds to the data signals transmitted through the data line D [j] and the organic EL elements OLED1 and OLED2. Generates a current to be applied. In the present embodiment, the pixel driver 311 includes four transistors and two capacitors, that is, a transistor M1, a transistor M3, a transistor M4, a transistor M5, a capacitor Cvth, and a capacitor Cst. do. However, the pixel driver according to the present invention is not limited to these four transistors and two capacitors, but a circuit for generating a current to be applied to the organic EL elements OLED1 and OLED2 is sufficient.

Specifically, the transistor M5 responds to the selection signal from the selection scan line S [i] with its gate connected to the current selection scan line S [i] and its source connected to the data line D [j]. The data voltage applied from the data line D [j] is transferred to the node B of the capacitor Cvth. The transistor M4 directly connects the node B of the capacitor Cvth to the power source VDD in response to the selection signal from the immediately preceding selection scan line S [i-1]. Transistor M3 diode-connects transistor M1 in response to a selection signal from immediately preceding scan line S [i-1]. The driving transistor M1 is a current whose gate is connected to the node A of the capacitor Cvth, the source is connected to the power supply VDD, and is applied to the organic EL elements OLED1 and OLED2 by a voltage applied to the gate. To control.

In addition, the capacitor Cst has one electrode connected to the power supply VDD, the other electrode connected to the drain electrode (node B) of the transistor M4, and the capacitor Cvth has one electrode connected to the other electrode of the capacitor Cst. Two capacitors are connected in series, and the other electrode is connected to the gate (node A) of the driving transistor M1.

Sources of the transistors M21 and M22 which control the organic EL elements OLED1 and OLED2 to selectively emit light are respectively connected to the drains of the driving transistors M1, and light emission is provided to the gates of the transistors M21 and M22, respectively. Scan lines E1 [i] and E2 [i] are connected. The anodes of the organic EL elements OLED1 and OLED2 are connected to the drains of the transistors M21 and M22, respectively. The transistors M61 and M62 have a source connected to the drains of the transistors M21 and M22, a drain connected to a power supply line Vbias, and a gate connected to a signal line RB [i].

Hereinafter, a method of driving an organic EL display device according to a third exemplary embodiment of the present invention will be described in detail with reference to FIG. 10. 10 is a signal timing diagram of an organic EL display device according to a third embodiment of the present invention. As shown in FIG. 10, the organic EL display device according to the third exemplary embodiment of the present invention is driven by dividing one frame into two fields 1F and 2F, and selecting signals in each field 1F and 2F. S [1] to S [n]) are sequentially applied.

In the first field 1F, the transistor M3 and the transistor M4 are turned on while the low level selection signal is applied to the immediately preceding selection scan line S [0]. Transistor M3 is turned on so that transistor M1 is in a diode-connected state. Therefore, the voltage difference between the gate and the source of the transistor M1 changes until the threshold voltage Vth of the transistor M1 becomes. At this time, since the source of the transistor M1 is connected to the power supply VDD, the voltage applied to the gate of the transistor M1, that is, the node A of the capacitor Cvth, is the power supply voltage VDD and the threshold voltage Vth. Is the sum of. In addition, since the transistor M4 is turned on and the power supply VDD is applied to the node B of the capacitor Cvth, the voltage V _Cvth charged in the capacitor _Cvth is expressed by Equation 2 below.

Here, V _Cvth is the voltage applied to the node (B) of the voltage applied to the node (A) of a voltage that is charged in the capacitor (Cvth), and, V _CvthA a capacitor (Cvth), V _CvthB a capacitor (Cvth) Means.

While the low level selection signal is applied to the current selection scan line S [1], the transistor M5 is turned on to apply the data voltage Vdata applied from the data line D1 to the node B. In addition, since the capacitor Cvth is charged with a voltage corresponding to the threshold voltage Vth of the transistor M1, the gate of the transistor M1 is charged with the data voltage Vdata and the threshold voltage Vth of the transistor M1. The voltage corresponding to the sum is applied. That is, the gate-source voltage Vgs of the transistor M1 is expressed by Equation 3 below.

In the first field 1F, while the low level selection signal is applied to the previous selection scan line S [0] and the current selection scan line S [1], the light emission signal E1 [1] and the light emission signal ( E2 [1] is all at the high level and both transistors M21 and M22 are turned off, thereby preventing leakage current from flowing to the organic EL elements OLED2 and OLED2. In addition, while the low-level selection signal is applied to the previous selection scan line S [0] and the current selection scan line S [1], the signal RB [1] becomes low level so that the transistors M61 and M62. Are turned on, and reverse bias is applied to both the organic EL elements OLED1 and OLED2. Therefore, the space charges stored in the organic EL elements OLED1 and OLED2 are all discharged to extend the life of the organic EL elements OLED1 and OLED2.

Then, when the current selection scan line S [1] is at a high level, a low level light emission signal is applied to the light emission control line E1 [1] to turn on the transistor M21 so that the gate of the transistor M1 is turned on. The current I _OLED corresponding to the source voltage V _GS is supplied to the organic EL element OLED1, and the organic EL element OLED1 emits light. The current I _{OLED is} shown in Equation 4.

Where I _OLED is the current flowing through the organic EL element OLED1, Vgs is the voltage between the source and gate of transistor M1, Vth is the threshold voltage of transistor M1, Vdata is the data voltage, and β is a constant value. Indicates.

In the second field 2F, while the low level selection signal is applied to the immediately preceding selection scan line S [0], the voltage V _Cvth is charged to the capacitor Cvth as in the first field 1F. do. Then, while the low level select signal is applied to the current select scan line S [1], the transistor M5 is turned on to apply the data voltage Vdata applied from the data line D1 to the node B. .

In the second field 2F, while the low level selection signal is applied to the immediately previous selection scan line S [0] and the current selection scan line S [1], the light emission signal E1 [1] and the light emission signal ( E2 [1] is all at the high level and both transistors M21 and M22 are turned off, thereby preventing leakage current from flowing to the organic EL elements OLED2 and OLED2. In addition, while the low-level selection signal is applied to the previous selection scan line S [0] and the current selection scan line S [1], the signal RB [1] becomes low level so that the transistors M61 and M62. Are turned on, and reverse bias is applied to both the organic EL elements OLED1 and OLED2. Therefore, the space charges stored in the organic EL elements OLED1 and OLED2 are all discharged to extend the life of the organic EL elements OLED1 and OLED2.

When a high level signal is applied to the current selection scan line S [1], a low level light emission signal is applied to the emission control line E2 [1] to turn on the transistor M22 so that the gate of the transistor M1 is turned on. A current I _OLED corresponding to the source voltage V _GS is supplied to the organic EL element OLED2, and the organic EL element OLED2 emits light.

As described above, according to the third exemplary embodiment of the present invention, while the light emission signals E1 [i] and E2 [i] are all high level, the low level signal RB [i] is applied to the organic EL elements OLED2, The reverse bias is applied to OLED2 to discharge all the space charges stored in the organic EL devices OLED1 and OLED2, thereby extending the life of the organic EL devices OLED1 and OLED2.

Next, an organic EL display device according to a fourth exemplary embodiment of the present invention will be described with reference to FIGS. 11 to 13. The organic EL display device according to the fourth exemplary embodiment differs from the third exemplary embodiment in that one organic EL element is included in one pixel, and a separate independent field is provided to apply reverse bias to the organic EL element.

FIG. 11 is a diagram schematically illustrating a configuration of an organic EL display device according to a fourth embodiment of the present invention. The selective scan driver 710 and the data driver 900 are the same as in the third embodiment. The light emitting scan driver 810 sequentially generates and outputs one light emitting signal E [i] unlike the light emitting scan driver 800 of the third embodiment, which generates and outputs two light emitting signals.

The display panel 400 includes a plurality of selective scan lines S [i], a plurality of emission scan lines E [i], a reverse bias signal line RB [i], and a plurality of columns extending in a column direction. A data line D [j], a plurality of power lines VDD, a plurality of bias power lines Vbias, and a plurality of pixels 410 are included. The pixel 410 is driven by signals transmitted from the previous selective scan line S [i-1], the current selective scan line S [i], the emission scan line E [i], and the data line D [j]. The organic EL element is driven to emit light.

12 is a circuit diagram illustrating a pixel 410 of an organic EL display device according to a fourth embodiment of the present invention. The pixel 410 differs from the pixel 310 of the third embodiment in that each of the organic EL elements OLED and the transistor M2 is one.

The pixel 410 includes a transistor M2 for controlling light emission of the pixel driver 411, the organic EL element OLED, and the organic EL element OLED, and a transistor M6 for controlling reverse bias to the organic EL element OLED. It includes.

13 is a signal timing diagram of an organic EL display device according to a fourth embodiment of the present invention. According to the fourth embodiment as in FIG. 13, one frame is driven by two fields.

During the first field 1F, it operates in the same manner as the first field 1F of the third embodiment.

During the second field 2F, the reverse bias signal RB [1] becomes low level so that the transistor M6 is turned on to electrically connect the anode of the organic EL element OLED and the power line Vbias. In this way, by applying reverse bias to the organic EL elements OLED1 and OLED2 for a relatively long time, the space charges stored in the organic EL elements can be more reliably discharged, thereby extending the life of the organic EL elements OLED1 and OLED2.

Although the embodiments of the present invention have been described above, the present invention is not limited thereto, and the scope of the present invention is not limited to the same structures as the embodiments, and various skilled artisans using the basic concepts of the present invention defined in the claims are provided. Modifications and improvements are also within the scope of the present invention.

According to the present invention, the reverse bias is applied to the organic EL element for a predetermined time to prevent the organic EL element from flowing current in only one direction. Therefore, a current flows only in one direction to the organic EL device OLED, thereby sufficiently discharging the space charge stored between the hole transport layer HTL and the light emitting layer EML or between the electron transport layer ETL and the light emitting layer EML. The life of the organic EL element OLED can be extended.

Claims (17)

A light emitting display device comprising a plurality of scan lines for transmitting a selection signal, a plurality of data lines for transmitting a data signal, and a plurality of pixels connected to the scan lines and the data lines, respectively. The pixel, A pixel driver configured to receive a first power supply voltage and output a first current corresponding to the data signal in response to the selection signal; A light emitting device emitting light with light corresponding to the first current; A first switching device electrically connected between the pixel driver and the light emitting device and transferring a first current to the light emitting device when turned on; And And a second switching element configured to apply a second current in a direction opposite to the first current to the light emitting element when the first switching element is turned off. The method of claim 1, The light emitting device includes a first electrode electrically connected to the second switching device, and a second electrode to which a second power supply voltage lower than the first power supply is applied. And a reverse bias voltage lower than the second power supply voltage is applied to the first electrode of the light emitting device when the second switching device is turned on. The method of claim 2, The second switching device, The control electrode is electrically connected to the signal line for transmitting the first control signal, the first main electrode is electrically connected to the reverse bias power source for applying the reverse bias voltage, and the second main electrode is the first electrode of the light emitting device. A light emitting display device which is a transistor electrically connected to the. The method according to any one of claims 1 to 3, The plurality of scan lines includes first and second scan lines that respectively transmit first and second selection signals. The circuit driving unit, A first transistor having a control electrode connected to the first scan line and a source electrically connected to the data line; A first capacitor applied with the first power supply voltage to one electrode, and the other electrode electrically connected to the drain of the first transistor; A second transistor having a control electrode connected to the second scan line and a source connected to one electrode of the first capacitor; A second capacitor having one electrode connected to the drain of the second transistor; A third transistor having a control electrode electrically connected to the other electrode of the first capacitor and having a first power supply voltage applied to a source; And And a fourth transistor connected to the second scan line and diode-connected to the third transistor. A light emitting display device comprising a plurality of scan lines for transmitting a selection signal, a plurality of data lines for transmitting a data signal, and a plurality of pixels connected to the scan lines and the data lines, respectively. The pixel, A pixel driver outputting a first current corresponding to the data signal in response to the selection signal; First and second switching elements for selectively transferring the first current; First and second light emitting devices emitting light with light corresponding to the first current received from the first and second switching devices, respectively; And And third and fourth switching elements configured to apply a reverse bias voltage to the first and second light emitting elements, respectively. The method of claim 5, The third switching device is turned on simultaneously with the second switching device, and the fourth switching device is turned on simultaneously with the first switching device. The method of claim 6, The first switching element is a transistor in which the control electrode is electrically connected to the first light emitting signal line for transmitting the first light emitting signal, The second switching element is a transistor in which a control electrode is electrically connected to a second light emitting signal line for transmitting a second light emitting signal, In the third switching device, a control electrode is connected to the second light emitting signal line, a first main electrode is connected to a reverse bias power line applying a reverse bias voltage, and a second main electrode is connected to the first light emitting device. Transistors, In the fourth switching device, a control electrode is connected to the first light emitting signal line, a first main electrode is connected to a reverse bias power line applying a reverse bias voltage, and a second main electrode is connected to the second light emitting device. A light emitting display device which is a transistor. A plurality of scan lines sequentially transmitting selection signals; A plurality of data lines for transmitting data signals; A plurality of first and second light emitting signal lines respectively transmitting the first and second light emitting signals; A plurality of first power lines for supplying power of a first voltage; A plurality of second power lines for supplying power of a second voltage; A plurality of control signal lines for transmitting a control signal; And A pixel connected to the scan line, the data line, the first and second light emission signal lines, the first and second power supply lines, and the control signal line, respectively; The pixel, A plurality of pixel drivers outputting a first current corresponding to the data signal in response to the selection signal; First and second transistors having control electrodes connected to the first and second light emitting signal lines, respectively, for transmitting the first current; First and second light emitting devices having a first electrode electrically connected to drains of the first and second transistors; And A control electrode connected to the control signal line, a source connected to each of the first electrodes of the first and second light emitting devices, and a drain connected to the second power line, respectively; LED display panel. The method of claim 8, The first and second light emitting devices are configured to apply a third voltage lower than the first voltage to a second electrode. The method of claim 9, The second voltage is lower than the third voltage. The method of claim 8, The circuit driving unit, A first transistor turned on in response to a current selection signal to transfer the data signal; A first capacitor storing a voltage corresponding to the data signal; A second transistor turned on in response to a previous selection signal and connected in parallel with the first capacitor; A third transistor outputting a current corresponding to the voltage stored in the first capacitor; A second capacitor connected to the gate of the third transistor to store a voltage corresponding to the threshold voltage of the third transistor; And And a fourth transistor that is turned on in response to a previous selection signal to diode-connect the third transistor. In the method of driving a light emitting display device, The light emitting display device, A plurality of light emitting devices including first and second light emitting devices that emit light corresponding to the first current applied thereto; And A plurality of pixel drivers configured to generate the first current based on a selection signal and a data signal; The driving method, a) applying the first current to the first light emitting device; And b) electrically blocking the pixel driver and the first light emitting device, and applying a reverse bias to the first light emitting device Method of driving a light emitting display device comprising a. The method of claim 12, And applying the first current to the second light emitting device while step b) is performed. The method of claim 12, And b) electrically blocking the pixel driver and the second light emitting device and applying a reverse bias to the second light emitting device while step b) is performed. The method according to any one of claims 12 to 14, And b) is performed while the selection signal is applied. The method according to any one of claims 12 to 14, The step a) proceeds during the first field And b) is performed during a second field following the first field. The method of claim 12, The light emitting display device includes a plurality of pixels. Each of the plurality of pixels includes the first and second light emitting elements and the pixel driver.

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