KR100994226B1 - Driving apparatus of organic electroluminescence device - Google Patents

Abstract

The present invention relates to a device for driving an organic light emitting display device, which compensates for variations in luminance between panels to increase luminance uniformity and adjusts luminance according to an external environment and a user's request.

An apparatus for driving an organic light emitting display device according to an embodiment of the present invention includes an organic light emitting display device that emits light according to a current; A memory in which a plurality of digital gamma data are stored; A controller for selecting digital gamma data; A gamma reference voltage generator for decoding the digital gamma data selected by the controller to generate an analog gamma voltage; And a column driver for driving the organic light emitting diode by using the analog gamma voltage from the gamma reference voltage generator, and selecting the digital gamma data by the user through the controller.

Description

Driving device for organic electroluminescent device {DRIVING APPARATUS OF ORGANIC ELECTROLUMINESCENCE DEVICE}             

1 is a cross-sectional view schematically showing a cross-sectional structure of a conventional organic light emitting display device.

2 is a plan view schematically illustrating a pixel arrangement of a conventional organic light emitting display device.

3 is an equivalent circuit diagram of a pixel shown in FIG.

FIG. 4 is a waveform diagram illustrating signals supplied to column lines and row lines shown in FIGS. 2 and 3.

5 is a view schematically showing a driving device of an organic light emitting display device according to an embodiment of the present invention.

6 is a plan view schematically illustrating a pixel arrangement of the organic light emitting display device illustrated in FIG. 5.

7 is an equivalent circuit diagram of the pixel shown in FIG.

8 is a schematic view of a driving device for driving an organic light emitting display device according to another embodiment of the present invention;

<Description of Symbols for Main Parts of Drawings>                 

1 glass substrate 2 anode electrode

3: hole injection layer 4: light emitting layer

5: electron injection layer 6: cathode electrode

12,32: Timing controller 20,44: Gamma reference voltage supply

16,36: column driver 18,38: organic light emitting panel

14,34: low driver DRV_TFT: driving thin film transistor

OLED: Electroluminescent Cell SW_TFT: Switched Thin Film Transistor

Cst: Capacitor RL: Lowline

CL: column line 15,44: power generator

22,40: external control unit 24,42: ROM

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an organic light emitting display device, and more particularly, to compensate for brightness fluctuations existing between panels to increase brightness uniformity, and to adjust brightness according to external environment and user's request. It is about.

Recently, various flat panel displays have been developed to reduce weight and volume, which are disadvantages of cathode ray tubes. Such flat panel displays include liquid crystal displays (hereinafter referred to as "LCDs"), field emission displays (FED) plasma display panels (hereinafter referred to as "PDPs") and electroluminescence. Electroluminescence Device and the like.

Among them, PDP is attracting attention as the most favorable display device for light and small size and large screen because of its simple structure and manufacturing process, but it has the disadvantages of low luminous efficiency, low luminance and high power consumption. On the other hand, active matrix LCDs with thin film transistors ("TFTs") as switching elements have difficulty in making large screens because they use semiconductor processes, but they are used as display elements in notebook computers. have. In contrast, the electroluminescent device is classified into an inorganic electroluminescent device and an organic electroluminescent device according to the material of the light emitting layer. The electroluminescent device is a self-light emitting device that emits light, and has a high response speed and high luminous efficiency, luminance, and viewing angle.

In the organic light emitting display device, the anode electrode 2 is formed on the glass substrate 1 using the transparent electrode pattern, and the hole injection layer 3, the light emitting layer 4, and the electron injection layer 5 are formed thereon. Are stacked. The cathode electrode 6 is formed on the electron injection layer 5 as a metal electrode.

When a driving voltage is applied to the anode electrode 2 and the cathode electrode 6, holes in the hole injection layer 3 and electrons in the electron injection layer 5 proceed toward the light emitting layer 33 to excite the light emitting layer 4. Causes the light emitting layer 4 to emit visible light. Thus, an image or an image is displayed by the visible light generated from the light emitting layer 4.

2 and 3, in the organic light emitting diode, m column lines CL1 to CLm and n row lines RL1 to RLn are formed to cross the column lines CL1 to CLm. Thus, m ㅧ n pixels are arranged in a matrix type.

In addition, the organic light emitting display device is formed at the intersection of the column lines CL1 to CLm and the row lines RL1 to RLn and serves as a switching element, the switch TFT SW_TFT, the cell driving voltage source VDD and the electric field. A driving TFT DRV_TFT is formed between the light emitting cells OLED to drive the electroluminescent cell OLED, and a capacitor Cst is connected between the switch TFT SW_TFT and the driving TFT DRV_TFT. The switch TFT (SW_TFT) and the driving TFT (DRV_TFT) are implemented with a P type MOS-FET.

The switch TFT SW_TFT is turned on in response to the negative scan voltages from the low lines RL1 to RLn to conduct a current path between its source terminal and the drain terminal, as well as the low lines RL1 to RLn. When the voltage on the phase is below its threshold voltage (Vth), it is maintained off. In the on time period of the switch TFT SW_TFT, the data voltage Vcl from the column lines CL is connected to the gate terminal of the driving TFT DRV_TFT via the source terminal and the gate terminal of the switch TFT SW_TFT. Is applied to. On the contrary, in the off time period of the switch TFT SW_TFT, the current path between the source terminal and the drain terminal of the switch TFT SW_TFT is opened so that the data voltage Vcl is not applied to the driving TFT DRV_TFT.

The driving TFT DRV_TFT controls the current between the source terminal and the drain terminal according to the data voltage Vcl supplied to its gate terminal to emit the electroluminescent cell OLED at a brightness corresponding to the data voltage Vcl. .                         

The capacitor Cst stores the difference voltage between the data voltage Vcl and the cell driving voltage VDD to maintain a constant voltage applied to the gate terminal of the driving TFT DRV_TFT for one frame period, and also to display the electroluminescent cell. The current applied to the OLED is kept constant for one frame period.

4 illustrates a scan voltage and a data voltage applied to the organic light emitting diode of FIG. 2.

Referring to FIG. 4, a negative scan pulse scan is sequentially applied to the row lines RL1 to RLn and a data voltage data is synchronized to the scan pulse scan to the column lines CL1 to CLn. This is applied at the same time.

However, the conventional electroluminescent cell OLED has a problem in that the luminance of the electroluminescent cell OLED is lowered due to the threshold voltage Vth of the driving TFT DRV_TFT. This will be described in detail with reference to Equation 1 below.

 Here, W means the channel width of the TFT, and L means the channel length of the TFT. mu_P means mobility and C_OX means capacity per unit area. In addition, V_DD denotes a panel driving voltage, V_ {IN} denotes a voltage applied to the gate of the switch TFT SW_TFT, and V_TH denotes a threshold voltage of the driving TFT DRV_TFT.                         

As can be seen from Equation 1, the current I _OLED applied to the electroluminescent cell OLED is determined according to the gate voltage V _IN of the driving TFT DRV_TFT. At this time, when the threshold voltage V _TH of the inter-panel driving TFT DRV_TFT changes, the difference between the gate voltage V _IN determined according to the value of the gamma reference voltage changes (V _DD is fixed). The current through the driving TFT DRV_TFT and the current I _OLED applied to the electroluminescent cell _OLED are changed and cause luminance unevenness between panels. Accordingly, a method of compensating the threshold voltage of the driving TFT DRV_TFT is required to increase the luminance of the electroluminescent cell OLED.

Accordingly, an object of the present invention relates to a driving device of an organic light emitting device which compensates for a threshold voltage of an inter-panel TFT to increase luminance uniformity.

In order to achieve the above object, the driving device of the organic light emitting device according to an embodiment of the present invention includes an organic light emitting device for emitting light according to the current; A memory in which a plurality of digital gamma data are stored; A controller for selecting the digital gamma data; A gamma reference voltage generator for decoding the digital gamma data selected by the controller to generate an analog gamma voltage; And a column driver for driving the organic light emitting diode by using the analog gamma voltage from the gamma reference voltage generator, and selecting the digital gamma data by the user through the controller.

In the driving device of the organic light emitting device, the gamma reference voltage generator is embedded in the column driver.

The driving device of the organic light emitting display device includes a driving voltage source for generating a driving voltage, a column line supplied with the analog gamma voltage from the column driver, a low line crossing the column line, and a scan signal supplied thereto; A switch thin film transistor for switching the analog gamma voltage in response to a scan signal, a drive thin film transistor for switching a current path between the driving voltage source and the organic light emitting diode in response to the analog gamma voltage, and the drive voltage source And a storage capacitor connected between the gate terminal of the driving thin film transistor and maintaining a gate voltage of the driving thin film transistor constant.

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An apparatus for driving an organic light emitting display device according to an embodiment of the present invention includes a column line and a row line that cross each other; An organic light emitting display device emitting light according to an input current; A memory in which a plurality of digital gamma data are stored; A controller for selecting the digital gamma data; A gamma reference voltage generator for decoding the digital gamma data selected by the controller to generate an analog gamma voltage; A column driver supplying the analog gamma voltage to the column line; a row driver supplying a scan signal to the row line; A driving voltage source for generating a driving voltage; A thin film transistor for switching a current path between the organic light emitting element and the driving voltage source in response to the scan signal; Compensation for the change in the threshold voltage of the thin film transistor by the analog gamma voltage.

In the driving device of the organic light emitting diode, the thin film transistor includes a switch thin film transistor for switching the analog gamma voltage in response to the scan signal, and between the driving voltage source and the organic light emitting diode in response to the analog gamma voltage. A driving thin film transistor for switching a current path of the circuit is provided.

The driving device of the organic light emitting diode further includes a storage capacitor connected between the driving voltage source and the gate terminal of the driving thin film transistor to maintain a constant gate voltage of the driving thin film transistor.

In the driving device of the organic light emitting diode, the current I flowing through the driving thin film transistor is defined by Equation 1 below.

-- 식 1

Equation 1

Where W is the channel width of the driving thin film transistor, L is the channel length of the driving thin film transistor, μ _p is the mobility, C _OX is the capacitance per unit area, and V _DD is the organic electroluminescence The driving voltage of the device, V _IN is the gate voltage of the switch thin film transistor, V _TH is the threshold voltage of the driving thin film transistor, ΔV _TH is the variation of the threshold voltage of the driving thin film transistor, and ΔV _IN is the ΔV _TH . The gate voltage of the switch thin film transistor that changes according to the above.

In the driving device of the organic light emitting device, the driving thin film transistor is a polycrystalline silicon thin film transistor.

Hereinafter, exemplary embodiments of the present invention will be described with reference to FIGS. 5 to 8.

5 schematically shows a driving apparatus for driving an organic light emitting display device according to a first embodiment of the present invention.

Referring to FIG. 5, in the driving apparatus of the organic light emitting device according to the first embodiment of the present invention, m column lines CL1 to CLm and n row lines RL1 to RLn intersect each other and the column lines ( In the pixel area between CL1 to CLm and the row lines RL1 to RLn, an organic light emitting panel 18 in which m ㅧ n pixels are arranged in a matrix form, and column lines of the organic light emitting panel 18 ( A column driver 16 for supplying data to the CL1 to CLm, a low driver 14 for supplying scan pulses to the row lines RL1 to RLn of the organic light emitting panel 18, and a column driver 16, a timing controller 12 for controlling the gamma voltage supply unit 20 for supplying a gamma voltage to the column driver, a timing controller 12 for controlling the column driver 16 and the low driver 14, a panel driver 14, 16, and a timing controller. To generate the driving voltage, cell driving voltage (VDD) and initialization voltage (VI) necessary for (12). ROM (ROM, 24) for supplying gamma reference voltage information to the source generator (15), the external controller (22) for adjusting the luminance of the organic light emitting panel (18), and the gamma reference voltage supply (20). ).

The organic light emitting panel 18 includes an electroluminescent cell (OLED), a switch TFT (SW_TFT), a capacitor (Cst), a driving TFT (DRV_TFT), etc., in which an anode electrode, a hole injection layer, a light emitting layer, an electron injection layer, and a cathode electrode are stacked. M x n pixels (Pixel) including the formed on the glass substrate.

The organic light emitting panel 18 is formed at the intersection of the column lines CL1 to CLm and the row lines RL1 to RLn as shown in FIGS. 6 and 7 and serves as a switching element SW_TFT. And a driving TFT (DRV_TFT) formed between the cell driving voltage source (VDD) and the electroluminescent cell (OLED) to drive the electroluminescent cell (OLED), between the switch TFT (SW_TFT) and the driving TFT (DRV_TFT). The connected capacitor Cst is provided. The switch TFT (SW_TFT) and the driving TFT (DRV_TFT) are implemented with a P type MOS-FET.

The switch TFT SW_TFT is turned on in response to the negative scan voltages from the low lines RL1 to RLn to conduct a current path between its source terminal and the drain terminal, as well as on the low lines RL1 to RLn. When the voltage is below its threshold voltage (Vth), it is kept off. In the on time period of the switch TFT SW_TFT, the data voltage Vcl from the column lines CL is connected to the gate terminal of the driving TFT DRV_TFT via the source terminal and the gate terminal of the switch TFT SW_TFT. Is applied to. On the contrary, in the off time period of the switch TFT SW_TFT, the current path between the source terminal and the drain terminal of the switch TFT SW_TFT is opened so that the data voltage Vcl is not applied to the driving TFT DRV_TFT.                     

The driving TFT DRV_TFT adjusts the current between the source terminal and the drain terminal according to the data voltage Vcl supplied to its gate terminal to emit the electroluminescent cell OLED with brightness corresponding to the data voltage Vcl. do.

The capacitor Cst stores the difference voltage between the data voltage Vcl and the cell driving voltage VDD to maintain a constant voltage applied to the gate terminal of the driving TFT DRV_TFT for one frame period, and also to display the electroluminescent cell. The current applied to the OLED is kept constant for one frame period.

The timing controller 12 first receives a control signal including a synchronization signal HV and a clock signal together with data RGB from the outside. The timing controller 12 generates a column control signal CCS and samples data RGB from the outside according to the control signal, and the data RGB together with the column control signal CCS to the column driver 16. Supply. The column control signal CCS includes a shift clock, a latch signal, a multiplexer control signal, and the like of the column driver 16. In addition, the timing controller 12 generates a row control signal RCS including a start pulse for instructing the shift register to start operation, a shift clock of the shift register, and the like, and transmits the row control signal RCS to the low driver 14. Will be supplied.

The ROM 24 stores channel information about arbitrary luminance data and supplies the channel information CHx to the gamma reference voltage supply unit 20 under the control of the external controller 22. Here, the channel information CHx means a plurality of digital gamma data.

The external controller 22 selects any one of the plurality of digital gamma data stored in the ROM 24. The external control unit 22 is controlled to set the threshold voltage equally for each organic light emitting panel 18. Here, the external controller 22 may select any one of the plurality of digital gamma data that is externally controlled by the user and stored in the ROM 24.

The gamma reference voltage supply unit 20 generates digital gamma data using the channel information CHx supplied from the ROM 24 under the control of the external controller 22, and supplies the digital gamma data to the column driver 16. . Here, the digital gamma data is generated by the equation (2).

Here, V _H is the highest voltage of the gamma reference voltage supplied from the power generator 25 to the gamma reference voltage supply 20, and V _L is supplied from the power generator 25 to the gamma reference voltage supply 20. Represents the lowest voltage of the gamma reference voltage, and CHx represents the channel information output from the ROM 24. That is, the external control unit 22 selects any one of the digital gamma data among the digital gamma data stored in the ROM 24 and supplies it to the gamma reference voltage supply unit 20. The gamma reference voltage supply unit 20 decodes the digital gamma data generated by Equation 1 to generate an analog gamma voltage and supply the analog gamma voltage to the column driver 16.

The column driver 16 supplies the data RGB to the column lines CL1 to CLm in response to the column control signal CCS supplied from the timing controller 12. The column driver 16 samples the data RGB from the timing controller 12, latches the data, decodes the latched data, and sets the gamma voltage corresponding to the data value as the data voltage Vcl. Will be chosen. The data voltage Vcl generated from the column driver 85 is simultaneously supplied to the column lines CL1 to CLm in synchronization with the scan pulse generated from the low driver 14. In addition, the column driver 16 simultaneously supplies the initialization voltage VI to the column lines CL1 to CLm during the period allocated between the data supply periods.

The low driver 14 generates a scan pulse falling to a negative scan voltage in response to the row control signal RCS supplied from the timing controller 12, and the scan driver generates the scan pulses on the low line of the organic light emitting panel 18. To RL1 to RLn sequentially. The low driver 14 includes a shift register that sequentially generates negative scan pulses, and a level shifter for shifting the swing width of the scan voltage to a level suitable for driving the switch TFT (SW_TFT).

The power generator 25 supplies predetermined voltages to the gamma reference voltage supply 44, and also the driving voltage, the initialization voltage VI, and the cell driving voltage of the integrated circuit (IC) of the column driver 16. (VDD) and the like and supply the voltages to the column driver 16. In addition, the power generator 25 generates a negative scan voltage, and supplies the scan voltage to the low driver 14.                     

The driving device of the organic light emitting device according to the embodiment of the present invention is to change the driving voltage in response to the change in the threshold voltage (Vth) of the driving TFT (DRV_TFT) between each panel by flowing a constant current in the electroluminescent cell to the brightness between the panels It solves the nonuniformity. This will be described in detail with reference to Equation 3.

Here, W means the channel width of the TFT, and L means the channel length of the TFT. μ _p means mobility and C _OX means capacity per unit area. In addition, V _DD denotes a panel driving voltage, V _IN denotes a voltage applied to a gate of the switch TFT (SW_TFT), and V _TH denotes a threshold voltage of the driving TFT DRV_TFT.

As can be seen from Equation 3, when the data voltage is changed (ΔV _IN ) according to the variation (ΔV _TH ) of the threshold voltage of the driving TFT (DRV_TFT) existing between the panels, the electroluminescent cell OLED A constant current flows through it. As a result, the organic EL device can obtain uniform luminance for each panel. At this time, the data voltage (V _IN) range when using the gamma reference voltage supply 20, because they are made within the scope gamma reference voltages (V1 to VN) to adjust the gamma reference voltage data voltage (V _IN) of The range can be changed freely.

8 is a view schematically showing a driving device for driving an organic light emitting display device according to a second embodiment of the present invention.

Referring to FIG. 8, the driving device for driving the organic light emitting display device according to the second embodiment of the present invention is different from that in which the gamma reference voltage generator 44 is built in the column driver 36. It has the same configuration as in the first embodiment. For this reason, the description of the operation of each component will be omitted.

As described above, the driving device of the organic light emitting display device according to the present invention sets the optimal reference gamma voltage and adjusts the reference gamma voltage according to luminance information data and adjustment data by the user to compensate for the threshold voltage of the driving TFT. Since the decrease in the data voltage can be maintained at a high level of the current applied to the electroluminescent cell, the luminance uniformity of the organic electroluminescent device can be increased accordingly. Furthermore, the driving device and method of the organic light emitting device according to the present invention not only adjusts the brightness by user's control but also applies the logic concept to the gamma reference voltage generator instead of using a conventional resistor to consume power and the number of components. And circuit area can be reduced.

Those skilled in the art will appreciate that various changes and modifications can be made without departing from the technical spirit of the present invention. Therefore, the technical scope of the present invention should not be limited to the contents described in the detailed description of the specification but should be defined by the claims.

Claims (9)

An organic light emitting display device emitting light according to a current; A memory in which a plurality of digital gamma data are stored; A controller for selecting the digital gamma data; A gamma reference voltage generator for decoding the digital gamma data selected by the controller to generate an analog gamma voltage; A column driver for driving the organic light emitting diode by using the analog gamma voltage from the gamma reference voltage generator; The device of claim 1, wherein the digital gamma data can be selected by a user through the controller. The method of claim 1, The gamma reference voltage generator is the driving device of the organic light emitting device, characterized in that built in the column drive. The method of claim 1, A driving voltage source for generating a driving voltage; A column line to which the analog gamma voltage is supplied from the column driver; A low line crossing the column line and supplied with a scan signal; A switch thin film transistor for switching the analog gamma voltage in response to the scan signal; A driving thin film transistor for switching a current path between the driving voltage source and the organic light emitting diode in response to the analog gamma voltage; And a storage capacitor connected between the driving voltage source and the gate terminal of the driving thin film transistor to maintain a constant gate voltage of the driving thin film transistor. delete Column and row lines that cross each other; An organic light emitting display device emitting light according to an input current; A memory in which a plurality of digital gamma data are stored; A controller for selecting the digital gamma data; A gamma reference voltage generator for decoding the digital gamma data selected by the controller to generate an analog gamma voltage; A column driver supplying the analog gamma voltage to the column line; A row driver supplying a scan signal to the row line; A driving voltage source for generating a driving voltage; A thin film transistor for switching a current path between the organic light emitting element and the driving voltage source in response to the scan signal; And a device for compensating for the change in the threshold voltage of the thin film transistor by the analog gamma voltage. The method of claim 5, The thin film transistor, A switch thin film transistor for switching the analog gamma voltage in response to the scan signal; And a driving thin film transistor for switching a current path between the driving voltage source and the organic light emitting element in response to the analog gamma voltage. The method of claim 6, And a storage capacitor connected between the driving voltage source and the gate terminal of the driving thin film transistor to maintain a constant gate voltage of the driving thin film transistor. The method of claim 6, The current I flowing through the driving thin film transistor is defined by Equation 1 below.

Equation 1 Where W is the channel width of the driving thin film transistor, L is the channel length of the driving thin film transistor, μ _p is the mobility, C _OX is the capacitance per unit area, and V _DD is the organic electroluminescence The driving voltage of the device, V _IN is the gate voltage of the switch thin film transistor, V _TH is the threshold voltage of the driving thin film transistor, ΔV _TH is the variation of the threshold voltage of the driving thin film transistor, and ΔV _IN is the ΔV _TH . The gate voltage of the switch thin film transistor that changes according to the above. The method of claim 6, And the driving thin film transistor is a polycrystalline silicon thin film transistor.

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