KR20050064297A - Electro-luminescence display apparatus and driving method thereof - Google Patents

Abstract

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electro-luminescence display device capable of displaying an image of a desired gray scale by precharging pixel cells using a voltage when displaying an image of a low gray scale.

The electro-luminescence display device according to the present invention includes gate lines and data lines formed to intersect the gate lines, pixel cells formed at intersections of the gate lines and data lines, and one horizontal period unit. A gate driver for sequentially supplying a low gate signal to the gate lines, and gray level using only current when data supplied from the outside is high gray, and gray level using voltage and current when data is low gray. It includes a plurality of data integrated circuits for implementation.

Description

Electro-Luminescence Display Apparatus and Driving Method

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electro-luminescence display device and a driving method thereof, and more particularly to an electroluminescence display capable of displaying an image of a desired gradation by precharging pixel cells using a voltage when displaying an image of a low gradation. The present invention relates to a nessence display device and a driving method thereof.

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 a liquid crystal display, a field emission display, a plasma display panel, and an electro-luminescence (hereinafter, referred to as "EL"). Display).

Here, the EL display device is a self-luminous device that emits a fluorescent material by recombination of electrons and holes, and is roughly divided into inorganic EL and organic EL according to materials and structures. This EL display device has the advantage of having a fast response speed, such as a cathode ray tube, compared to a passive light emitting device that requires a separate light source like a liquid crystal display device.

1 is a cross-sectional view showing a general organic EL structure for explaining the light emission principle of an EL display device. Among the EL display devices, the organic EL includes an electron injection layer 4, an electron transport layer 6, a light emitting layer 8, a hole transport layer 10, and a hole injection layer 12 stacked between the cathode 2 and the anode 14. It is provided.

When a voltage is applied between the anode 14, which is a transparent electrode, and the cathode 2, which is a metal electrode, electrons generated from the cathode 2 are directed toward the light emitting layer 8 through the electron injection layer 4 and the electron transport layer 6. Move. In addition, holes generated from the anode 14 move toward the light emitting layer 8 through the hole injection layer 12 and the hole transport layer 10. Accordingly, in the light emitting layer 8, light is generated by collision between electrons and holes supplied from the electron transport layer 6 and the hole transport layer 10 and recombination, and the light is externally transmitted through the anode 14 which is a transparent electrode. Is emitted so that the image is displayed.

2 is a diagram showing a conventional Active Matrix Type EL display device.

Referring to FIG. 2, a conventional EL display device includes an EL cell including pixel cells 22 (hereinafter referred to as “PE”) arranged at each intersection of gate electrode lines GL and data electrode lines DL. The display panel 16, the gate driver 18 for driving the gate electrode lines GL, the data driver 20 for driving the data electrode lines DL, the gate driver 18, and the data. A timing controller 24 for controlling the driver 20 is provided.

The timing controller 24 controls the data driver 20 and the gate driver 18. To this end, the timing controller 24 supplies various control signals to the data driver 20 and the gate driver 18. The timing controller 24 rearranges the data and supplies the data to the data driver 20.

The gate driver 18 sequentially supplies gate signals to the gate electrode lines GL under the control of the timing controller 24. Here, the gate signal is supplied to have a width of one horizontal period (1H).

The data driver 20 supplies a video signal to the data electrode lines DL under the control of the timing controller 24. At this time, the data driver 20 supplies a video signal corresponding to one horizontal line to the data electrode lines DL during one horizontal period 1H during which the gate signal is supplied.

The PE cells 22 display an image corresponding to the video signal by emitting light corresponding to the video signal (i.e., current signal) supplied to the data electrode lines DL. 22 to the data electrode lines DL. For this purpose, each of the PE cells 22 is driven according to a driving signal supplied from each of the data electrode line DL and the gate electrode lines GL, as shown in FIG. A light emitting cell driving circuit 30 for driving the light emitting cell OLED, and a light emitting cell OLED connected between the light emitting cell driving circuit 30 and the ground voltage source GND.

The light emitting cell driving circuit 30 includes a first driving thin film transistor (TFT) connected between the voltage supply line VDD and the light emitting cell OLED, and a gate electrode line (T1). The first switching TFT T3 connected between the GL and the data electrode line DL, and the first switching TFT T3 and the voltage supply line VDD, are connected between the first driving TFT T1 and the current mirror. The second driving TFT (T2) forming the circuit, the second switching TFT (T4) connected between the gate electrode line (GL) and the second driving TFT (T2), and the first and second driving TFTs (T1, A storage capacitor Cst is connected between the node between T2) and the voltage supply line VDD. Here, the TFTs are P-type electron metal oxide semiconductor field effect transistors (MOSFETs).

The gate terminal of the first driving TFT T1 is connected to the gate terminal of the second driving TFT T2, and the source terminal is connected to the voltage supply line VDD. The drain terminal of the first driving TFT T1 is connected to the light emitting cell OLED. The source terminal of the second driving TFT T2 is connected to the voltage supply line VDD, and the drain terminal is connected to the drain terminal of the first switching TFT T3 and the source terminal of the second switching TFT T4.

The source terminal of the first switching TFT T3 is connected to the data electrode line DL, and the gate terminal is connected to the gate electrode line GL. The drain terminal of the second switching TFT T4 is connected to the gate terminals of the first and second driving TFTs T1 and T2 and the storage capacitor Cst. The gate terminal of the second switching TFT T4 is connected to the gate electrode line GL.

Here, the first and second driving TFTs T1 and T2 are connected to form a current mirror. Therefore, assuming that the first and second driving TFTs T1 and T2 have the same channel width, the amount of current flowing through the first and second driving TFTs T1 and T2 is set the same.

Referring to the operation of the light emitting cell driving circuit 30, the gate signal is first supplied from the gate electrode line GL forming the horizontal line. When the gate signal is supplied, the first and second switching TFTs T3 and T4 are turned on. When the first and second switching TFTs T3 and T4 are turned on, the video signal from the data electrode line DL is first and second driving TFTs via the first and second switching TFTs T3 and T4. It is supplied to the gate terminals of (T1, T2). At this time, the first and second driving TFTs T1 and T2 supplied with the video signal are turned on. Here, the first driving TFT T1 adjusts the current flowing from its source terminal (ie, VDD) to the drain terminal according to the video signal supplied to its gate terminal and supplies the light to the light emitting cell OLED. OLED) so that light of brightness corresponding to the video signal is emitted.

At the same time, the second driving TFT T2 supplies the current id supplied from the voltage supply line VDD to the data electrode line DL via the first switching TFT T3. Here, since the first and second driving TFTs T1 and T2 form a current mirror circuit, the same current flows through the first and second driving TFTs T1 and T2. Meanwhile, the storage capacitor Cst stores the voltage from the voltage supply line VDD so as to correspond to the amount of current id flowing to the second driving TFT T2. The storage capacitor Cst turns on the first driving TFT T1 using a voltage stored therein when the gate signal is turned off so that the first and second switching TFTs T3 and T4 are turned off. By turning on, a current corresponding to the video signal is supplied to the light emitting cell OLED.

Here, the conventional data driver 20 controls the predetermined current to be supplied from the PE cell 22 in response to the data supplied from the timing controller 24. That is, the conventional data driver 20 drives the PE cells 22 by using a current.

To this end, the conventional data driver 20 includes a plurality of data driver integrated circuits (hereinafter referred to as " IC "), and each of the plurality of data driver ICs is configured as shown in FIG.

Referring to FIG. 4, the data driver IC includes a shift register 40, a first latch portion 42, a second latch portion 44, and a current driver 46.

The shift register unit 40 sequentially shifts the source start pulse SSP supplied from the timing controller 24 corresponding to the source sampling clock SSC to output a sampling signal.

The first latch unit 42 sequentially samples and latches data supplied from the timing controller 24 in predetermined units in response to a sampling signal from the shift register unit 40. To this end, the first latch unit 42 is composed of i latches for latching i (i is a natural number) of data, each of which has a size corresponding to the number of bits of the data. Have Data stored in the first latch unit 42 is supplied to the second latch unit 44.

The second latch unit 44 temporarily stores the data supplied from the first latch unit 42 and also stores the stored data in the source output enable SOE supplied from the timing controller 24. Output simultaneously in response to the signal.

The current driver 46 controls the current corresponding to the data input from the second latch unit 44 to be supplied from the PE cell 30. 5, each of the current drivers 46 includes a current driving block 48 for each channel (i.e., i). The current driving block 48 may receive data from the second latch unit 44 and a current id corresponding to the data from the PE cell 30 using the current gamma signal corresponding to the received data. To control. Accordingly, a predetermined current id corresponding to the video signal (ie, current) is supplied to each of the data lines DL, so that a predetermined image corresponding to the data is displayed.

As described above, the conventional EL display device drives the PE cell 30 using only current. However, when the PE cell 30 is driven using only current, a problem occurs in that an image of a desired gray scale is not displayed in the light emitting cell OLED when low gray scale is expressed. This will be described with reference to Equation 1.

t = C _total V _g / I

Here, "t" denotes a time when a voltage value corresponding to the video signal is applied to the gate terminal of the first driving TFT T1, and "C _total " denotes the capacitance of the storage capacitor Cst and the data electrode line DL. The sum of the parasitic capacitances of "V _g " represents a voltage value applied to the gate terminal of the first driving TFT (T1), and "I" represents a current driving block from the light emitting cell driving circuit 30 via the data electrode line DL. The value of current flowing into 48) is shown.

In Equation 1, a time for which a desired voltage value is applied to the gate terminal of the first driving TFT T1 is inversely proportional to the current value I flowing from the light emitting cell driving circuit 30 to the current driving block 48. Therefore, in a high gradation where a certain high current flows, a voltage value corresponding to the video signal can be applied to the gate terminal of the first driving TFT T1 within a predetermined time 1H. (I.e., t is short because I is large. However, in a low gradation where a low current value flows, a voltage value corresponding to the video signal cannot be applied to the gate terminal of the first driving TFT T1 within a predetermined time (1H). That is, conventionally, a problem arises in that a desired luminance cannot be obtained when expressing low gradation.

Accordingly, an object of the present invention is to provide an electro-luminescence display device and a driving method thereof capable of displaying an image of a desired gradation by precharging pixel cells using a voltage when displaying an image of a low gradation. .

In order to achieve the above object, an electroluminescent display device of the present invention includes gate lines and data lines formed to intersect the gate lines, and pixel cells formed at intersections of the gate lines and the data lines. And a gate driver for sequentially supplying gate signals to the gate lines in units of one horizontal period, and realizing gradation using only current when data supplied from the outside is high gradation, and voltage and A plurality of data integrated circuits for implementing gray using currents are provided.

The low gradation is less than half of the gradation that can be expressed in the pixel cell.

Each of the data integrated circuits includes a current driver for controlling a current corresponding to data to be supplied from the pixel cells, a current driver for controlling a current corresponding to the data, and a voltage driver for generating a voltage value corresponding to the data; And a switching control block including first switches and second switches connected to the voltage driver, and a switch controller for turning on any one of the first and second switches in response to the grayscale value of the data.

When the data integrated circuit has i (i is a natural number) channels, the current driver and the voltage driver are provided for each i channel, and the first and second switches are provided in pairs for each channel to be common to one data line. Connected.

The switch controller turns on the first switch for one horizontal period when data of a specific channel is high gray.

The switch controller turns on the second switch for the first period of one horizontal period when the data of a specific channel is low gray, and turns on the first switch for the second period except the first period. .

The second period is a time longer than the first period.

A method of driving an electro-luminescence display device according to an embodiment of the present invention includes inputting data from an external source and driving a pixel cell using at least one of a current and a voltage corresponding to the gray level of the data.

When the gray level of the data is high gray scale, a current corresponding to the gray level of the data flows to the light emitting cell included in the pixel cell, thereby displaying an image having luminance corresponding to the data.

Supplying a voltage corresponding to the gray level of the data to the pixel cell when the gray level of the data is low, and controlling a current to correspond to the gray level of the data to the light emitting cell included in the pixel cell after the voltage is supplied. Displaying an image of luminance corresponding to the data.

The time for controlling the current to flow is set longer than the time for supplying the voltage.

Other objects and features of the present invention in addition to the above objects will become apparent from the description of the embodiments with reference to the accompanying drawings.

Hereinafter, exemplary embodiments of the present invention will be described with reference to FIGS. 6 to 9.

Fig. 6 is a diagram showing a data driver integrated circuit included in a large number of data drivers of an EL display device.

Referring to FIG. 6, a data driver IC according to an exemplary embodiment of the present invention may include a shift register unit 50, a first latch unit 52, a second latch unit 54, a current / voltage driver 56, and a switch controller. And 62 and a switching block 64.

The shift register unit 50 sequentially shifts the source start pulse SSP supplied from a timing controller (not shown) to correspond to the source sampling clock SSC to output a sampling signal. Here, the shift register section 50 includes i shift registers for outputting i sampling signals when the data driver IC has i (i is a natural number) channels.

The first latch unit 52 sequentially samples and latches data supplied from the timing controller in predetermined units in response to a sampling signal from the shift register unit 50. To this end, the first latch unit 52 is composed of i latches for latching i data, each of which has a size corresponding to the number of bits of the data. Data stored in the first latch unit 52 is supplied to the second latch unit 54.

The second latch unit 54 temporarily stores data supplied from the first latch unit 52 and responds to the source output enable signal SOE supplied from the timing controller. Output simultaneously.

The data output from the second latch unit 54 is supplied to the switch controller 62 and the current / voltage driver 56. The current / voltage driver 56 includes a current driver 58 and a voltage driver 60 provided for each channel as shown in FIG. 7 (that is, i channels include i current drivers and i voltage drivers). The current driver 58 controls the current corresponding to the data to be supplied from the PE cell toward itself. The voltage driver 60 supplies a voltage corresponding to the data to the PE cell.

In practice, the current driver 58 selects one current gamma signal corresponding to data among a plurality of current gamma signals supplied from the outside, and controls the current so that the current corresponding to the selected current gamma signal is supplied from the PE cell toward itself. The predetermined image corresponding to the gray scale is displayed in the cell.

The voltage driver 60 receives a plurality of voltage gamma signals from a gamma voltage unit (not shown). In practice, the voltage driver 60 selects one voltage gamma signal corresponding to data from among the plurality of voltage gamma signals supplied from the gamma voltage unit, and supplies a voltage corresponding to the selected voltage gamma signal to the PE cell.

The switching block 64 has first and second switches SW1 and SW2 provided for each channel. Here, the first and second switches SW1 and SW2 are provided in pairs for each channel and commonly connected to one data line DL. The first switch SW1 is installed between the current driver 58 and the data line DL to be turned on by the control of the switch controller 62. The second switch SW2 is installed between the voltage driver 60 and the data line DL to be turned on by the control of the switch controller 62.

The switch controller 62 turns the switch SW1 or SW2 of any one of the first and second switches SW1 and SW2 included in each channel in response to the data supplied from the second latch unit 54. Turn on In detail, first, the switch controller 62 turns on the first switch SW1 installed in the specific channel for one horizontal period 1H as shown in FIG. 8A when the data of the specific channel is high gray. Then, the current value of high gradation is supplied from the PE cell to the current driver 58 to display an image corresponding to the high gradation. Here, in high gradation, since a high current value flows, a desired image can be displayed in a PE cell.

On the other hand, if the data of a specific channel is low gradation (for example, less than half of the gradation that can be expressed), the switch controller 62 switches the second switch during the first period T1 of one horizontal period 1H as shown in FIG. 8B. Turn on (SW2). When the second switch SW2 is turned on, a voltage value corresponding to the low gray level is supplied to the PE cell so that the voltage corresponding to the low gray level is precharged to the storage capacitor Cst of the PE cell. The switch controller 62 turns on the first switch SW1 for the second period T2: T2> T1, which is a period other than the first period T1 of the one horizontal period 1H. At this time, the second period T2 is set to a longer time (or wider width) than the first period T1. When the first switch SW1 is turned on, a current value corresponding to the low gray level is supplied from the PE cell to the current driver 58 so that an image corresponding to the low gray level is displayed on the PE cell. Here, when driven at a low gradation, a desired image can be displayed in the PE cell by first driving the PE cell using the voltage value.

Such a process of displaying an image with low gradation in the EL display device of the present invention will be described in detail with reference to FIG.

First, a gate signal is supplied from the gate driver 72 to select a PE cell 70 formed on a specific horizontal line. Here, the detailed driving of the PE cell 70 is the same as that of FIG. When the gate signal is supplied, the first and second switching TFTs T3 and T4 are turned on.

On the other hand, when expressing low gradation, the second switch SW2 is turned on under the control of the switch controller 62. When the second switch SW2 is turned on, a voltage value (ie, a voltage gamma signal) corresponding to data is supplied from the voltage driver 60 to the data line DL. At this time, since the first and second switching TFTs T3 and T4 are turned on, the voltage values supplied to the data line DL may include the storage capacitor Cst, the first driving TFT T1, and the second driving TFT ( It is supplied to the gate terminal of T2). At this time, the storage capacitor Cst is charged with a voltage value corresponding to the data.

Thereafter, the second switch SW2 is turned off and the first switch SW1 is turned on under the control of the switch controller 62. When the first switch SW1 is turned on, a current corresponding to data flows to the data line DL under the control of the current driver 58. In other words, when the first switch SW1 is turned on, the current corresponding to the data is driven from the voltage supply line VDD via the second driving TFT T2 and the first switching TFT T3. 58). At this time, the same current also flows through the second driving TFT T2 and the first driving TFT T1 forming the current mirror. Therefore, the light emitting cell OLED emits light of brightness corresponding to the current supplied from the first driving TFT T1 so that a predetermined image is displayed on the panel 74. The storage capacitor Cst stores a predetermined voltage so as to correspond to the amount of current flowing to the second driving TFT T2. Here, since the voltage of the data is precharged during the first time T1, the storage capacitor Cst is charged with a sufficient voltage corresponding to the amount of current. The storage capacitor Cst turns on the first driving TFT T1 using a voltage stored therein when the gate signal is turned off so that the first and second switching TFTs T3 and T4 are turned off. By turning on, a current corresponding to the video signal is supplied to the light emitting cell OLED.

That is, in the present invention, the PE cell 70 is charged with a voltage value corresponding to the data for a part of one horizontal period 1H, and the data is stored in the PE cell 70 for the remaining period of the first horizontal period 1H. By controlling the corresponding current value to flow, sufficient luminance can be obtained at low gradation, thereby improving the display quality of the image.

As described above, according to the electro-luminescence display device and the driving method thereof according to the present invention, an image is displayed by controlling only a current when displaying a high gradation, and an image using voltage and current when displaying a low gradation. Will be displayed. Here, in the low gradation, an image having a sufficient brightness corresponding to the low gradation can be displayed by supplying a voltage value corresponding to the data to precharge the storage capacitor, and then controlling the current value to display the image.

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.

1 is a cross-sectional view showing an organic light emitting cell of a general electroluminescent display panel.

2 shows a conventional electro-luminescence display.

FIG. 3 is an equivalent circuit diagram of the pixel cells PE shown in FIG. 2.

FIG. 4 is a diagram illustrating a data integrated circuit included in the data driver shown in FIG. 2. FIG.

FIG. 5 is a diagram illustrating a configuration of the current driver shown in FIG. 4. FIG.

6 is a view showing an electro luminescence display device according to an embodiment of the present invention.

FIG. 7 is a diagram illustrating the current / voltage driver and the switching block illustrated in FIG. 6.

8A and 8B are waveform diagrams illustrating an operation process of the switching controller illustrated in FIG. 6.

9 is a diagram illustrating a current driver and a voltage driver connected to a pixel cell.

<Description of Symbols for Main Parts of Drawings>

2: cathode 4: electron injection layer

6: electron transport layer 8: light emitting layer

10 hole transport layer 12 hole injection layer

14: anode 16,74: EL display panel

18,72: Gate Driver 20: Data Driver

22,70: pixel cell 24: timing controller

30: light emitting cell driving circuit 40, 50: shift register section

42, 44, 52, 54: latch portion 46, 58: current drive portion

48: current drive block 56: current / voltage drive unit

60: voltage driver 62: switch controller

64: switching block

Claims (11)

Gate lines and data lines formed to intersect the gate lines; Pixel cells formed at intersections of the gate lines and data lines; A gate driver for sequentially supplying a gate signal to the gate lines in units of one horizontal period; When the data supplied from the outside is a high gradation to implement the gradation using only the current, and when the data is a low gradation is characterized in that it comprises a plurality of data integrated circuit for implementing the gradation using the voltage and current -Luminescence display. The method of claim 1, And the low gradation is less than half of the gradation that can be expressed in the pixel cell. The method of claim 1, Each of the data integrated circuits A current / voltage driver including a current driver for controlling a current corresponding to the data to be supplied from the pixel cells, and a voltage driver for generating a voltage value corresponding to the data; A switching block including first switches connected to each of the current drivers and second switches connected to each of the voltage drivers; And a switch control unit for turning on any one of the first and second switches in response to the gray scale value of the data. The method of claim 3, wherein When the data integrated circuit has i (i is a natural number) channels, the current driver and the voltage driver are provided for each of the i channels, and the first and second switches are provided in pairs for each of the channels to provide one data. An electroluminescent display device, characterized in that connected to a line in common. The method of claim 3, wherein And the switch control unit turns on the first switch during the one horizontal period when the data of a specific channel is high gray level. The method of claim 3, wherein The switch control unit turns on the second switch for the first period of the first horizontal period when the data of a specific channel is low gray, and operates the first switch for a second period other than the first period. An electro-luminescence display device, characterized in that turned on. The method of claim 6, And wherein the second period of time is longer than the first period of time. Inputting data from the outside, And driving the pixel cell using at least one of a current and a voltage corresponding to the gray level of the data. The method of claim 8, If the gray level of the data is a high gray level, the electroluminescence is characterized by displaying an image having a luminance corresponding to the data by controlling a current corresponding to the gray level of the data to flow to a light emitting cell included in the pixel cell. Method of driving display device. The method of claim 8, When the gradation of the data is low gradation Supplying a voltage corresponding to the gray level of the data to the pixel cell; And controlling an electric current corresponding to the gray level of the data to flow to the light emitting cell included in the pixel cell after the voltage is supplied, thereby displaying an image having a luminance corresponding to the data. Method of driving the nessence display device. The method of claim 10, And a time for controlling the current to flow longer than the time for supplying the voltage.