KR100627406B1 - Light emitting display and driving method thereof - Google Patents

Abstract

The present invention provides a light emitting display device in which the amount of current applied to the organic EL element is adjusted according to the ambient temperature by using a gamma correction value corresponding to the ambient temperature.

A light emitting display device according to an exemplary embodiment of the present invention is configured to display an image on a display panel including a plurality of scan lines for transmitting a selection signal, a plurality of data lines for transmitting a data signal, and a plurality of pixel circuits respectively connected to the scan lines and the data lines. The light emitting display device includes a temperature sensor, a gamma controller, and a data driver. The temperature detector outputs a detection signal corresponding to the ambient temperature, and the gamma controller outputs a gamma correction value corresponding to the detection signal. The data driver generates a gamma corrected data signal based on the gamma correction value and applies the data signal to a corresponding data line.

Light Emitting Display, OLED, Gamma Correction, Temperature Sensor

Description

Light emitting display and driving method thereof

1 is a view schematically showing the structure of an organic EL device.

2 is a diagram schematically illustrating a configuration of a light emitting display device according to an exemplary embodiment of the present invention.

3 is an equivalent circuit diagram illustrating an example of a pixel circuit 610 according to an exemplary embodiment of the present invention.

4 is a view showing in detail the configuration of the temperature sensing unit 100 and the gamma control unit 200 of FIG.

FIG. 5 is a graph for explaining an example of the gamma correction value stored in the gamma correction value storage unit 220 of FIG. 4.

The present invention relates to a light emitting display device, and more particularly, to a light emitting display device using light emission of an organic EL element.

In general, a light emitting display device is a display device using light emission 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.

Such an organic light emitting cell has a diode characteristic and is also called an organic light emitting diode (hereinafter referred to as an organic EL device).

1 is a view schematically showing the structure of an organic EL device.

As shown in FIG. 1, the organic EL device 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). The organic light emitting cells are arranged in an N × M matrix to form an organic EL display panel.

The organic EL display panel is driven by a simple matrix method and an active matrix method using a thin film transistor (hereinafter, referred to as TFT). 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. Such an active matrix method has a rather complicated pixel circuit, but has an advantage of low display current consumption and long light emission time, thereby improving display quality.

However, when the light emitting display device is driven in a high temperature environment, even if the same current is applied to the anode, the amount of current flowing in the organic EL element increases over time. In general, since the life of the organic EL element is determined by the amount of current flowing through the organic EL element, the life of the organic EL element is shortened as the amount of current flowing through the organic EL element increases. Therefore, when the temperature of the external environment is high, it is necessary to adjust the amount of current applied to the organic EL element by adjusting the data voltage value.

Accordingly, an object of the present invention is to solve the above-described problems, and an object of the present invention is to provide a light emitting display device in which an amount of current applied to an organic EL element is adjusted according to the ambient temperature by using a gamma correction value corresponding to the ambient temperature. It is.

It is also an object of the present invention to provide a light emitting display device capable of writing a suitable gamma correction value even after fabrication is completed by storing a gamma correction value using a programmable memory.

A light emitting display device according to an aspect of the present invention is a display having a plurality of scanning lines for transmitting a selection signal, a plurality of data lines for transmitting a data signal, and a plurality of pixel circuits respectively connected to the scanning lines and the data lines. A light emitting display for displaying an image on a panel,

A temperature sensing unit outputting a sensing signal corresponding to the ambient temperature;

A gamma control unit outputting a gamma correction value corresponding to the detection signal; And

A data driver generating a gamma corrected data signal based on the gamma correction value and applying the gamma corrected data signal to the corresponding data line;
The gamma correction value is an on voltage value corresponding to the gray of white; And a slope value indicating a degree of change of the slope of the gamma curve.

The temperature detection unit, a temperature sensor for outputting an analog detection signal corresponding to the ambient temperature; And an analog-to-digital converter for converting the analog sense signal into a digital sense signal.

The gamma control unit may include a detection signal processing unit outputting a storage unit control signal corresponding to the detection signal; And a gamma correction value storage unit for outputting a gamma correction value according to the storage unit control signal.

The gamma correction value storage unit may be a writable memory, and the writable memory may be any one of a PROM, an EPROM, an EEPROM, and a flash memory, and the gamma correction value storage unit may correspond to the detection signal in the form of a LUT. Can be saved.

The gamma correction value may further include an off voltage value corresponding to the gray of white.

delete

The storage control signal may be a signal indicating an address where a gamma correction value corresponding to the detection signal is stored.

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

a) measuring the ambient temperature;

b) determining a gamma correction value corresponding to the measured temperature;

c) generating a gamma corrected data signal based on the determined gamma correction value; And

d) displaying an image on a display unit according to the data signal;
The gamma correction value is an on voltage value corresponding to the gray of white; And a slope value indicating a degree of change of the slope of the gamma curve.

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

2 is a diagram schematically illustrating a configuration of a light emitting display device according to an exemplary embodiment of the present invention.

Referring to FIG. 2, the light emitting display device includes a temperature sensing unit 100, a gamma control unit 200, a gamma correction unit 300, a data driver 400, a scan driver 500, and a display unit 600.

The display unit 600 includes a plurality of data lines D1 -Dm extending in the column direction, a plurality of scan lines S1 -Sn extending in the row direction, and a plurality of pixel circuits 610. The data lines D1 -Dm transmit data signals representing the image signals to the pixel circuits, and the scan lines S1 -Sn transfer the selection signals to the pixel circuits. The pixel circuit is formed in a pixel region defined by two neighboring data lines D1 -Dm and two neighboring scan lines S1 -Sn. Therefore, the pixel 600 selected by the selection signal transmitted from the scan driver 500 emits light in response to the data signal transmitted from the data driver 400, so that the display 600 displays an image corresponding to the applied R, G, and B data. Is displayed.

3 is an equivalent circuit diagram illustrating an example of a pixel circuit 610 according to an exemplary embodiment of the present invention.

As shown in Fig. 3, the pixel circuit includes an organic EL element OLED, two transistors SM and DM and a capacitor Cst. The transistors SM and DM are formed of PMOS transistors.

In the switching transistor SM, the gate electrode is connected to the scan line Sn, the source electrode is connected to the data line Dm, and the drain electrode is connected to one end of the capacitor Cst and the gate electrode of the driving transistor DM. The other end of the capacitor Cst is connected to the power supply voltage VDD. The source electrode of the driving transistor DM is connected to the power supply voltage VDD, and the drain electrode is connected to the pixel electrode of the organic EL element OLED. The organic EL device OLED emits light based on a current of which the cathode is connected to the reference voltage Vss and is applied through the driving transistor DM. Here, the power supply VSS connected to the cathode of the organic EL element OLED is a voltage having a lower level than the power supply VDD, and a ground voltage or the like may be used.

Referring to the operation of the pixel circuit, first, when the selection signal is applied to the scan line Sn and the switching transistor SM is turned on, the data voltage is transferred to one end of the capacitor Cst and the gate electrode of the driving transistor DM. do. Therefore, the gate-source voltage V _GS of the driving transistor DM is maintained for a certain period by the capacitor Cst. In addition, the driving transistor DM applies a current I _OLED corresponding to the gate-source voltage V _GS to the pixel electrode of the organic EL element OLED, thereby emitting the organic EL element OLED. At this time, the current I _OLED flowing through the organic EL device _OLED is represented by Equation 1.

As shown in Equation 1, when the high data voltage V _DATA is transferred to the gate electrode of the driving transistor DM, the gate-source voltage V _GS of the driving transistor is lowered, so that a small amount of current I _OLED is transferred to the pixel electrode. When applied, the organic EL element OLED emits little light to display low gray scale. In addition, when the low data voltage V _DATA is transmitted, the gate-source voltage V _GS of the driving transistor is increased, and a large amount of current I _OLED is applied to the pixel electrode, so that the organic EL device emits a lot of light and thus high gray levels are generated. Will be displayed. The data voltage applied to each of the pixel circuits is determined based on the image data signal to be displayed, and the data voltage V _DATA level is determined, and the current amount I transmitted to the organic EL element OLED according to the data voltage V _DATA . _OLED ) is determined.

2, the temperature detector 100 measures the ambient temperature and outputs a detection signal corresponding to the ambient temperature to the gamma controller 200. The gamma control unit 200 outputs a gamma correction value corresponding to the detection signal received from the temperature detection unit 100 to the gamma correction unit 300. The gamma correction unit 300 generates a gamma correction signal corresponding to the gamma correction value received from the gamma control unit 200 and outputs the gamma correction signal to the data driver 400.

The scan driver 500 sequentially transmits the selection signal to the scan lines S1 to Sn of the display unit 600. The data driver 400 receives the gamma correction signal from the gamma correction unit 300 and generates the gamma-corrected data voltage based on the gamma correction signal based on the input R, G, and B data, thereby generating a data line of the display unit 600. D1 to Dm). By using a gamma correction value corresponding to the sensing signal measured by the temperature sensing unit 100, the data voltage to be applied to the data lines D1 to Dm of the display unit 600 may be adjusted according to the ambient temperature.

4 is a view showing in detail the configuration of the temperature sensing unit 100 and the gamma control unit 200 of FIG.

The temperature sensing unit 100 includes a temperature sensor 110 and an A / D converter 120. The temperature sensor 110 measures the ambient temperature and outputs an analog detection signal. The analog sensing signal may be a voltage signal or a current signal. The A / D converter 120 converts the analog sense signal output from the temperature sensor 110 into a digital sense signal and outputs the digital sense signal.

The gamma control unit 200 outputs a gamma correction value corresponding to the detection signal output from the temperature detection unit 100 to the gamma correction unit 300. The gamma controller 200 includes a detection signal processor 210 and a gamma correction value storage unit 220. The detection signal processor 210 outputs a storage control signal for controlling the gamma correction value storage unit 220 to output a gamma correction value corresponding to the detection signal. The storage control signal may be an address in which a gamma correction value corresponding to the detected temperature is stored. The gamma correction value storage unit 220 stores a plurality of gamma correction values corresponding to the detection signal, and outputs the gamma correction value to the gamma correction unit 300 according to the storage control signal.

The gamma correction value storage unit 220 may store a separate gamma correction value for each of R, G, and B. The gamma correction value storage unit 220 may be a writable memory. Examples of writable memories include write once writeable PROM (Programmable Read Only Memory), rewritable erasable Programmable Read Only Memory (EPROM), electrically rewritable EEPROM (Electrically Erasable Programmable Read Only Memory), Flash memory. Writing of the gamma correction value storage unit 220 may be performed by the detection signal removing unit 210 or may be performed by a separate storage control unit (not shown). Since the gamma correction value storage unit 220 can write, the gamma correction value suitable for a user can be recorded on the manufactured and completed light emitting display device.

Specifically, since the characteristics of the manufactured display unit 600 are often affected by a small change in process conditions, each of the completed display units 600 may have different characteristics. Therefore, when a non-writable memory such as a mask ROM (mask ROM) is used, a fixed gamma correction value should be used for all the completed display parts. Therefore, the characteristics of the completed display part 600 may be changed. As it cannot reflect, proper gamma correction cannot be performed. Therefore, by writing a gamma correction value suitable for the completed display unit 600 using a writeable memory, it is possible to obtain a light emitting display device in which proper gamma correction is performed despite the difference in process conditions.

5 is a graph illustrating an example of a gamma correction value stored in the gamma correction value storage unit 220 of FIG. 4.

In FIG. 5, the horizontal axis represents the gray scale value, and the vertical axis represents the gray voltage. The graph expresses the gradation voltage corresponding to each gradation value, which is called a gamma curve. Gamma correction means correcting that the luminance of the display unit 600 has non-linear characteristics with respect to the R, G, and B data input to the data driver 400. The off voltage Voff is a voltage corresponding to black (gradation value 0), and the on voltage Von means a voltage corresponding to white (gradation value 15). The slope value represents the degree of change in the slope of the curve. The degree of change of the slope of the curve corresponding to C2 is larger than that of the curve corresponding to C1 and smaller than that of the curve corresponding to C3.

In FIG. 5, reference numeral C1 denotes a gamma curve corresponding to a detection signal when the ambient temperature is the lowest, reference numeral C2 denotes a gamma curve corresponding to the detection signal when the ambient temperature is somewhat low. Reference numeral C3 denotes a gamma curve corresponding to the detection signal when the ambient temperature is somewhat high, and reference numeral C4 denotes a gamma curve corresponding to the detection signal when the ambient temperature is the highest.

In this case, as shown in FIG. 5, when the off voltage Voff has a fixed voltage value, the gamma correction value is set to the on voltages Von1, Von2, Von3, and the corresponding gamma curves C1, C2, C3, and C4. Von4) and slope values of the gamma curves C1, C2, C3, and C4, and the gamma correction value is stored in the gamma correction value storage unit 220 in a LUT (lookup table) format together with the temperature.

In FIG. 5, the on voltages Von1, Von2, Von3, and Von4 corresponding to the gamma curves C1, C2, C3, and C4 and the slopes of the gamma curves C1, C2, C3, and C4 are stored as gamma correction values. Although shown for the case, otherwise, the gamma correction value stored in the gamma correction value storage unit 220 may be configured with all voltage values Von to Voff corresponding to each gray value. In this case, gamma correction can be easily performed using the gamma correction value, but since a large number of voltage values corresponding to all grayscale values must be stored, it takes up a lot of storage space. In addition, the gamma correction value stored in the gamma correction value storage unit 220 may be configured as a voltage value corresponding to a part of the gray scale value. In this case, the remaining voltage values can be obtained by interpolating the stored voltage values.

As such, the magnitude of the data voltage applied to the display unit 600 may be adjusted by measuring the ambient temperature and changing the gamma correction value according to the ambient temperature. Therefore, when the ambient temperature increases and the amount of current flowing through the organic EL element increases, the amount of current flowing through the organic EL element can be reduced by decreasing the magnitude of the data voltage.

Although the technical spirit of the present invention has been described in detail according to the above preferred embodiment, it should be noted that the above-described embodiment is for the purpose of description and not of limitation. In addition, it will be understood by those skilled in the art that various modifications are possible within the scope of the technical idea of the present invention.

In the light emitting display device and a control method thereof according to the present invention, by using a gamma correction value corresponding to the ambient temperature, the amount of current flowing through the organic EL element is adjusted according to the ambient temperature, thereby extending the life of the organic EL element and reducing power loss. .

In addition, the light emitting display device according to the present invention can write a gamma correction value suitable for a user or a manufactured image display part by storing the gamma correction value using a writable memory.

Claims (10)

A light emitting display device for displaying an image on a display panel including a plurality of scan lines for transmitting a selection signal, a plurality of data lines for transmitting a data signal, and a plurality of pixel circuits connected to the scan lines and the data lines, respectively. A temperature sensing unit sensing an ambient temperature and outputting a sensing signal corresponding to the sensed temperature; A gamma correction value controller outputting a gamma correction value based on the detection signal; And A data driver generating a gamma corrected data signal based on the gamma correction value and applying the gamma corrected data signal to the corresponding data line; The gamma correction value is, An on voltage value corresponding to the gray of white; And A light emitting display device comprising an inclination value representing a degree of change in the inclination of the gamma curve. The method of claim 1, The temperature sensing unit A temperature sensor for outputting an analog sensing signal corresponding to the ambient temperature; And A light emitting display device comprising an analog to digital converter for converting the analog sense signal into a digital sense signal. The method of claim 1, The gamma correction value control unit A gamma correction value storage unit for storing the gamma correction value; And And a detection signal processor configured to output a control signal for controlling a gamma correction value corresponding to the detection signal to be output among the gamma correction values stored in the gamma correction value storage unit. The method of claim 3, And the gamma correction value storing unit is a writable memory. The method of claim 4, wherein The writable memory may be any one of a PROM, an EPROM, an EEPROM, and a flash memory. The method of claim 3, The gamma correction value storage unit stores the gamma correction value to correspond to the detection signal in the form of an LUT. delete The method of claim 1, The gamma correction value further includes an off voltage value corresponding to a gray level of white. The method of claim 6, The control signal output to the gamma correction value storage unit And a signal indicating an address at which a gamma correction value corresponding to the detection signal is stored. In the method of driving a light emitting display device, a) measuring the ambient temperature; b) determining a gamma correction value corresponding to the measured temperature; c) generating a gamma corrected data signal based on the determined gamma correction value; And d) displaying an image on a display unit according to the data signal; Including; The gamma correction value, An on voltage value corresponding to the gray of white; And A driving method of a light emitting display device comprising an inclination value representing a degree of change in the inclination of a gamma curve.

Images