KR100692861B1 - Electro-luminescensce dispaly panel and method of driving the same - Google Patents

Abstract

The present invention provides an EL display panel and a driving method thereof capable of compensating for a luminance difference due to nonuniform characteristics of a thin film transistor.

To this end, the EL display panel of the present invention is formed in a pixel region defined by the intersection of a gate line and a data line, and is connected between an EL cell connected with a first power supply electrode, and between the gate line and data line and the EL cell. A sub pixel including a cell driver connected to a second power line; A switch thin film transistor configured to supply a data signal of the data line to a first node in response to a scan signal of the gate line; A driving thin film transistor configured to control a current supplied from the second power line to the EL cell in response to a data signal of the first node; And a storage capacitor configured to charge the difference voltage between the gamma adjustment voltage supplied through the gamma adjustment line and the data signal of the first node to control the driving thin film transistor.

Description

ELECTROLUMINESCENSCE DISPALY PANEL AND METHOD OF DRIVING THE SAME             

1 is a diagram schematically showing a conventional organic EL display panel.

FIG. 2 is an equivalent view of the R, G, and B sub pixels shown in FIG. 1; FIG.

3 is an equivalent view of an organic EL display panel according to an exemplary embodiment of the present invention.

<Brief description of symbols for the main parts of the drawings>

20, 40: pixel matrix 22, 42: gate driver

24, 44: data driver 28, 54: sub pixel

30, 56: cell driver 48: R gamma adjustment voltage supply

50: G gamma adjustment voltage supply 52: B gamma adjustment voltage supply

32, 46: power

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electroluminescent display panel, and more particularly, to an EL display panel and a driving method thereof capable of compensating a difference in characteristics of a thin film transistor by gamma voltage adjustment.

Various flat panel display devices that can reduce weight and volume, which are disadvantages of cathode ray tubes, are emerging. Such flat panel displays include a liquid crystal display, a field emission display, a plasma display panel, and an electro-luminescence (hereinafter, EL). And a display panel.

Among them, an EL display panel is a self-luminous element that emits a phosphor by recombination of electrons and holes, and is classified roughly into an inorganic EL using an inorganic compound and an organic EL using an organic compound as the phosphor. Such EL display panels have many advantages such as low voltage driving, self-luminous, thin film type, wide viewing angle, fast response speed, and high contrast, and are expected to be the next generation display devices.

The organic EL element is usually composed of an electron injection layer, an electron transport layer, a light emitting layer, a hole transport layer, and a hole injection layer stacked between a cathode and an anode. In such an organic EL device, when a predetermined voltage is applied between the anode and the cathode, electrons generated from the cathode move to the light emitting layer through the electron injection layer and the electron transport layer, and holes generated from the anode move to the hole injection layer and the hole transport layer. Move toward the emitting layer through. Accordingly, the light emitting layer emits light by recombination of electrons and holes supplied from the electron transporting layer and the hole transporting layer.

As shown in FIG. 1, an active matrix EL display panel using such an organic EL element includes a pixel matrix including subpixels 28 arranged in regions defined by intersections of a gate line GL and a data line DL. 20, the gate driver 22 driving the gate lines GL of the pixel matrix 20, the data driver 24 driving the data lines DL of the pixel matrix 20, and the pixel. A power supply 32 and a ground power supply GND connected to the matrix 20 are provided.

The gate driver 22 sequentially drives the gate lines GL by supplying a scan pulse.

The data driver 24 supplies the R, G, and B data signals RD, GD, and BD to each data line DL every time a scan pulse is supplied. At this time, the data driver 24 converts the digital data input from the outside into an analog data signal and supplies the same. For example, the data driver 24 divides the gamma reference voltage input from the outside into a plurality of gamma voltage levels, selects a gamma voltage level corresponding to the input digital data, and supplies the same as an analog data signal.

Each of the R, G, and B sub-pixels 28 receives a data signal from the data line DL when a scan pulse is supplied to the gate line GL, and generates light corresponding to the data signal. The color of one pixel is realized by the combination of the R, G, and B sub-pixels 28.

Each of the R, G, and B sub-pixels 28 includes an EL cell 0EL, a gate line GL, a data line DL, and a power supply line, each having a cathode connected to a base power supply GND, as shown in FIG. It is provided with a cell driver 30 connected to the PL and connected to the anode of the EL cell 0EL to drive the EL cell 0EL.

The cell driver 30 includes a gate of the switch thin film transistor T1 having a gate terminal connected to the gate line GL, a source terminal connected to the data line DL, a drain terminal connected to the node N1, and a gate connected to the node N1. A driving thin film transistor T2 having a terminal connected to a source terminal to the power supply line PL and a drain terminal to the EL cell OEL, and a storage capacitor connected between the power supply line PL and the node N1. C).

The switch thin film transistor T1 is turned on when a scan pulse is supplied to the gate line GL, and supplies the data signal supplied to the data line DL to the gate terminal of the driving thin film transistor T2 through the node N1. do. In this case, the storage capacitor C charges the difference voltage between the driving voltage VDD supplied through the power line PL and the data signal supplied to the node N1. The driving thin film transistor T2 controls the amount of light emitted from the EL cell OEL by controlling the amount of current I supplied from the power supply line PL to the EL cell OEL in response to the voltage supplied to the node N1. . When the switch thin film transistor T1 is turned off, the driving thin film transistor T2 supplies a constant current I until the data signal of the next frame is supplied by the voltage charged in the storage capacitor C. The EL cell OEL keeps light emission.

As described above, the driving thin film transistor T2 of the cell driver 30 plays an important role of controlling the amount of light emitted from the EL cell OEL by adjusting the amount of current according to the input voltage. In other words, the current Ids supplied through the driving thin film transistor T2 is determined by Equation 1 below.

Where W and L are the channel width and length of the driving thin film transistor T2, Vgs is the voltage Vgs across the gate and source terminals of the driving thin film transistor T2, Vth is the threshold voltage, and μ is the mobility. Means. Referring to Equation 1, the current Ids supplied through the driving thin film transistor T2 is not only applied to the data voltage supplied to the gate terminal thereof, but also to the threshold voltage Vth and the mobility μ that determine its characteristics. It can be seen that also determined by. However, the driving thin film transistor T2 has non-uniform characteristics (ie, threshold voltage, mobility, etc.) depending on the position due to the laser crystallization process of crystallizing amorphous silicon (Amorphous-Si) to poly-silicon (Poly-Si). There is a problem with).

Specifically, in the manufacturing process of the thin film transistor, the amorphous-silicon thin film is crystallized to poly-silicon by a laser crystallization process of scanning a line beam in a horizontal or vertical direction using an excimer laser. When the amorphous-silicon thin film is crystallized into a poly-silicon thin film, the properties of the poly-silicon thin film are sensitive to the laser power output. However, as the output power of the excimer laser is unstable over time, the characteristics of the crystallized poly-silicon thin film become nonuniform along the scanning direction. Accordingly, there is a problem that a luminance deviation occurs due to a difference in characteristics of the thin film transistor between a plurality of EL display panels formed on one substrate.

Accordingly, it is an object of the present invention to provide an EL display panel and a driving method thereof capable of compensating for a luminance difference due to nonuniform characteristics of a thin film transistor.

In order to achieve the above object, an EL display panel according to the present invention is formed in a pixel region defined by the intersection of a gate line and a data line, and includes an EL cell connected to a first power supply electrode, the gate line and data line, and the EL. A sub-pixel connected between cells and including a cell driver connected to a second power supply line; A switch thin film transistor configured to supply a data signal of the data line to a first node in response to a scan signal of the gate line; A driving thin film transistor configured to control a current supplied from the second power line to the EL cell in response to a data signal of the first node; And a storage capacitor configured to charge the difference voltage between the gamma adjustment voltage supplied through the gamma adjustment line and the data signal of the first node to control the driving thin film transistor.

The gamma adjustment line supplies a gamma adjustment voltage to the storage capacitor to compensate for the threshold voltage deviation of the driving thin film transistor.

The sub-pixels are divided into red subpixels including red EL cells, green subpixels including green EL cells, and blue subpixels including blue EL cells; The gamma adjustment line includes first to third gamma adjustment lines separated and connected to each of the red, green, and blue sub-pixels.

The first to third gamma adjustment lines supply first to third gamma adjustment voltages capable of compensating light emission efficiency variations of the red, green, and blue EL cells, respectively.

Each of the first to third gamma adjustment lines is commonly connected to a corresponding color sub-pixel.

The first to third gamma adjustment voltages are set to have a relationship of second> first> third gamma adjustment voltages.

Each of the first to third gamma adjustment voltages is independently changed through a resistor.

In addition, the EL display panel of the present invention further includes first to third gamma adjustment voltage supply parts for supplying the first to third gamma adjustment voltages, respectively.

An EL display panel driving method according to the present invention is formed in a pixel region defined by the intersection of a gate line and a data line; An EL cell connected to a first power supply electrode, connected between the gate line and data line and the EL cell, and connected to a second power supply line; A switch thin film transistor having a gate terminal connected to the gate line, a source terminal connected to the data line, and a drain terminal connected to the node; A driving thin film transistor having a gate terminal connected to the node, a source terminal connected to a power supply line PL, and a drain terminal connected to an EL cell; Providing a cell driver having a storage capacitor connected between the gamma voltage regulation line and the node; Providing a sub-pixel including the cell driver; Supplying the data signal to the first node in response to a scan signal of the gate line by the switch thin film transistor; Charging, by the storage capacitor, a difference voltage between a gamma adjustment voltage and a data signal of the first node to compensate for a threshold voltage deviation of the driving thin film transistor; Controlling the current supplied from the second power line to the EL cell according to the difference voltage charged in the storage capacitor to light the EL cell, and maintaining it until the data signal of the next frame is supplied.

The gamma adjustment voltage includes first to third gamma adjustment voltages for compensating for variations in luminous efficiency of red, green, and blue EL cells, and the first to third gamma adjustment voltages are supplied by color.

Other objects and advantages of the present invention in addition to the above object will become apparent from the description of the preferred embodiment of the present invention with reference to the accompanying drawings.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to FIG. 3.

3 is an equivalent view of an EL display panel according to an embodiment of the present invention.

The EL display panel illustrated in FIG. 3 includes a pixel matrix 40 having subpixels 54 arranged in regions defined by intersections of the gate line GL and the data line DL, and the pixel matrix 40. A gate driver 42 for driving the gate lines GL of the gate lines, a data driver 44 for driving the data lines DL of the pixel matrix 40, and a power supply 46 connected to the pixel matrix 40. ) And a ground power source (GND). Further, the EL display panel shown in FIG. 3 further includes gamma adjustment voltage supply parts 48, 50, and 52 for supplying a gamma adjustment voltage to the pixel matrix 40 to compensate for the difference in characteristics of the thin film transistor.

The pixel matrix 40 includes R, G, and B subpixels 54 formed in each region defined by the intersection of the plurality of gate lines GL and the plurality of data lines DL, and includes three R, G, and B pixels. The color of one pixel is realized by the combination of the sub pixels 54. Each of the R, G, and B sub pixels 54 receives a data signal from the data line DL when a scan pulse is supplied to the gate line GL, and generates light corresponding to the data signal. To this end, each of the R, G, and B sub pixels 54 includes an EL cell 0EL connected to the base power supply GND through a cathode, a gate line GL, a data line DL, and a power supply line PL. Is connected to the anode of the EL cell (0EL), and has a cell driver 56 for driving the EL cell (0EL). The cell driver 56 is also connected to the gamma voltage adjustment line GCL.

Specifically, the cell driver 56 includes a switch thin film transistor T1 having a gate terminal connected to the gate line GL, a source terminal connected to the data line DL, and a drain terminal connected to the node N1, and a node ( A gate terminal is connected to N1, a source terminal is connected to power supply line PL, and a drain terminal is connected to EL cell OEL, and between gamma voltage adjustment line GCL and node N1. And a storage capacitor C connected to it.

Here, the storage capacitor C controls the driving thin film transistor T2 to supply a constant current to the EL cell OEL when the switch thin film transistor T1 is turned off. Accordingly, it can be seen that the current supplied to the EL cell OEL can be controlled via the driving thin film transistor T2 according to the voltage charged in the storage capacitor C. FIG. By using this, the voltage charged in the storage capacitor C is adjusted to compensate for the characteristic of the driving thin film transistor T2, for example, a difference in the threshold voltage Vth. To this end, a gamma adjustment voltage GCV is provided to the storage capacitor C to compensate for the deviation of the threshold voltage Vth of the driving thin film transistor T2 through the gamma adjustment line GCL.

As the gamma adjustment voltage GCV, gamma adjustment voltages different for each of the R, G, and B sub-pixels 54 in consideration of R, G, and B EL cells 0EL_R, OEL_G, and OEL_B having different light emission efficiencies ( GCV_R, GCV_G, GCV_B) are supplied. In other words, different gamma adjustment voltages GCV_R, GCV_G, and GCV_B are supplied to the storage capacitor C for each of the R, G, and B sub-pixels 54, thereby compensating for variations in light emission efficiency of R, G, and B. To this end, the R subpixels 54 are commonly connected to the R gamma adjustment voltage GCV_R through the first gamma adjustment line GCL1, and the G subpixels 54 are connected to the second gamma adjustment line GCL2. The G gamma adjustment voltage GCV_G is commonly supplied to the B subpixels 54 and the B gamma adjustment voltage GCV_B is commonly supplied through the third gamma adjustment line GCL3. The R, G, and B gamma adjustment voltages GCV_R, GCV_G, and GCV_B are equal to the luminous efficiency of R, G, and B EL cells 0EL_R, OEL_G, and OEL_B having a relationship of G> R> B. Let GCV_B have a relationship. Accordingly, the difference voltage charged in the storage capacitor has a relationship opposite to the luminous efficiency of the R, G, and B EL cells 0EL_R, OEL_G, and OEL_B, thereby compensating for the variation in the luminous efficiency.

The switch thin film transistor T1 is turned on when a scan pulse is supplied to the gate line GL, and supplies the data signal supplied to the data line DL to the gate terminal of the driving thin film transistor T2 through the node N1. do. At this time, the storage capacitor C is connected to the corresponding gamma adjustment voltage GCV_R or GCV_G or GCV_B supplied through any one of the gamma voltage adjustment lines GCL1, GCL2, and GCL3 and the data signal supplied to the node N1. Charge the differential voltage. In particular, the storage capacitor C compensates for the threshold voltage Vth deviation of the driving thin film transistor T2 by the corresponding gamma adjustment voltage GCV_R or GCV_G or GCV_B, and the storage capacitor C of the R, G, and B EL cells OEL. Charge the difference voltage to compensate for the variation in luminous efficiency. The driving thin film transistor T2 controls the amount of current I supplied from the power supply line PL to the EL cells 0EL_R, OEL_G, and OEL_B in response to the voltage supplied to the node N1, so that the EL cells 0EL_R, OEL_G, The amount of light emitted by OEL_B) is adjusted. When the switch thin film transistor T1 is turned off, the driving thin film transistor T2 supplies a constant current I until the data signal of the next frame is supplied by the voltage charged in the storage capacitor C. The EL cells 0EL_R, OEL_G, and OEL_B keep light emission. In this case, since the deviation of the threshold voltage Vth of the driving thin film transistor T2 is compensated for by the difference voltage charged in the storage capacitor C, it is possible to prevent the luminance deviation due to the same luminance. In addition, since the light emission efficiency deviations of the R, G, and B EL cells 0EL_R, OEL_G, and OEL_B are compensated by the difference voltage charged in the storage capacitor C, the white balance can be improved.

The gate driver 42 sequentially drives the gate lines GL by supplying a scan pulse.

The data driver 44 supplies R, G, and B data signals RD, GD, and BD to each data line DL every time a scan pulse is supplied. At this time, the data driver 44 converts the digital data input from the outside into an analog data signal and supplies the same. For example, the data driver 44 divides the gamma reference voltage input from the gamma reference voltage generator (not shown) into a plurality of gamma voltage levels, selects a gamma voltage level corresponding to the input digital data, and selects analog data. Supply by signal.

The R, G, and B gamma adjustment voltage supply units 48, 50, and 52 compensate for the deviation of the threshold voltage Vth of the driving thin film transistor T2 formed in the pixel matrix 40, and also R, G, and B EL cells ( R, G, and B gamma adjustment voltages GCV_R, GCV_G, and GCV_B are generated, respectively, to compensate for variations in the light emission efficiency of the OEL. In addition, the resistors R1, R2, and R3 connected to the output terminals of the R, G, and B gamma adjustment voltage supply parts 48, 50, and 52 are adjusted to respectively adjust the R, G, and B gamma adjustment voltages GCV_R, GCV_G, and GCV_B. This can be variable. The R, G, and B gamma adjustment voltage supply parts 48, 50, and 52 are embedded in peripheral circuits of the EL display panel, such as the gate driver 42 and the data driver 44, or external printed circuit boards (PCBs). Is mounted on.

As described above, the EL display panel and its driving method according to the present invention can compensate for the threshold voltage deviation of the thin film transistor by using the gamma adjustment voltage supplied through the gamma adjustment line connected to the storage capacitor. As a result, it is possible to prevent the luminance variation compared with the same luminance between the EL display panels due to the variation of the threshold voltage of the thin film transistor.

In addition, the EL display panel and the driving method thereof according to the present invention can compensate for the variation in the light emission efficiency of the R, G, and B EL cells by separately supplying the gamma adjustment voltage supplied to the storage capacitor for each of R, G, and B. . Accordingly, it is possible to improve the white balance due to the variation in the luminous efficiency of the R, G, and B EL cells.

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 (11)

An EL cell connected to a first power supply electrode and a cell driver connected between the gate line and the data line and the EL cell and connected to a second power line; A sub-pixel that includes; The cell driver A switch thin film transistor configured to supply a data signal of the data line to a first node in response to a scan signal of the gate line; A driving thin film transistor configured to control a current supplied from the second power line to the EL cell in response to a data signal of the first node; And a storage capacitor configured to charge the difference voltage between the gamma adjustment voltage supplied through the gamma adjustment line and the data signal of the first node to control the driving thin film transistor. The method of claim 1, The gamma adjustment line And a gamma adjustment voltage for compensating for the threshold voltage deviation of the driving thin film transistor to the storage capacitor. The method of claim 2, The sub-pixels are divided into red subpixels including red EL cells, green subpixels including green EL cells, and blue subpixels including blue EL cells; And the gamma adjustment line includes first to third gamma adjustment lines separated and connected to each of the red, green, and blue sub-pixels. The method of claim 3, wherein And the first to third gamma adjustment lines supply first to third gamma adjustment voltages for compensating for variations in luminous efficiency of the red, green, and blue EL cells, respectively. The method of claim 4, wherein And each of the first to third gamma adjustment lines is commonly connected to a corresponding color sub-pixel. The method of claim 4, wherein And the first to third gamma adjustment voltages are set to have a relationship of second> first> third gamma adjustment voltages. The method of claim 4, wherein And each of the first to third gamma adjustment voltages is independently changed through a resistor. The method of claim 4, wherein And an additional first to third gamma adjustment voltage supply sections for supplying the first to third gamma adjustment voltages, respectively. A pixel region defined by the intersection of the gate line and the data line; An EL cell connected to a first power supply electrode, connected between the gate line and data line and the EL cell, and connected to a second power supply line; A switch thin film transistor having a gate terminal connected to the gate line, a source terminal connected to the data line, and a drain terminal connected to the node; A driving thin film transistor having a gate terminal connected to the node, a source terminal connected to a power supply line PL, and a drain terminal connected to an EL cell; Providing a cell driver having a storage capacitor connected between the gamma voltage regulation line and the node; Providing a sub-pixel including the cell driver; Supplying the data signal to the first node in response to a scan signal of the gate line by the switch thin film transistor; Charging, by the storage capacitor, a difference voltage between a gamma adjustment voltage and a data signal of the first node to compensate for a threshold voltage deviation of the driving thin film transistor; Controlling the current supplied from the second power line to the EL cell according to the difference voltage charged in the storage capacitor to light the EL cell, and maintaining it until the data signal of the next frame is supplied. A driving method of an EL display panel. The method of claim 9, The gamma adjustment voltage includes first to third gamma adjustment voltages to compensate for light emission efficiency variations of red, green, and blue EL cells. And the first to third gamma adjustment voltages are supplied according to the corresponding color. The method of claim 10, And the first to third gamma adjustment voltages are set to have a relationship of second> first> third gamma adjustment voltages.

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