CN1312650C - Method and device capable of making active organic light-emitting diode display produce uniform image - Google Patents
Method and device capable of making active organic light-emitting diode display produce uniform image Download PDFInfo
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- CN1312650C CN1312650C CNB031091032A CN03109103A CN1312650C CN 1312650 C CN1312650 C CN 1312650C CN B031091032 A CNB031091032 A CN B031091032A CN 03109103 A CN03109103 A CN 03109103A CN 1312650 C CN1312650 C CN 1312650C
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- 238000000034 method Methods 0.000 title claims abstract description 17
- 239000010409 thin film Substances 0.000 claims description 25
- 229920001621 AMOLED Polymers 0.000 claims description 4
- 239000003990 capacitor Substances 0.000 claims description 3
- 238000003384 imaging method Methods 0.000 abstract 1
- 229910021420 polycrystalline silicon Inorganic materials 0.000 description 9
- 230000003247 decreasing effect Effects 0.000 description 6
- 229920005591 polysilicon Polymers 0.000 description 6
- 229910021417 amorphous silicon Inorganic materials 0.000 description 5
- 238000010586 diagram Methods 0.000 description 5
- 238000005516 engineering process Methods 0.000 description 4
- 238000004519 manufacturing process Methods 0.000 description 4
- 241001270131 Agaricus moelleri Species 0.000 description 3
- 239000004973 liquid crystal related substance Substances 0.000 description 3
- 238000005224 laser annealing Methods 0.000 description 2
- XUIMIQQOPSSXEZ-UHFFFAOYSA-N Silicon Chemical compound [Si] XUIMIQQOPSSXEZ-UHFFFAOYSA-N 0.000 description 1
- 239000013078 crystal Substances 0.000 description 1
- 230000000694 effects Effects 0.000 description 1
- 238000012986 modification Methods 0.000 description 1
- 230000004048 modification Effects 0.000 description 1
- 229910052710 silicon Inorganic materials 0.000 description 1
- 239000010703 silicon Substances 0.000 description 1
- 238000005496 tempering Methods 0.000 description 1
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Abstract
The present invention relates to a method and a device for uniformly imaging for an active organic light emitting diode display. The display is composed of a plurality of pixel devices, wherein each pixel device is provided with a driving unit which is used for driving an organic light emitting diode to be brightened. The cathode of the organic light emitting diode is connected with a positive power supply, and thereby, the positive power supply supplies the voltage to improve the electric potential of the organic light emitting diode. Further, when each driving unit acts, the Vsd (the voltage difference of a source electrode and a drain electrode) of the driving unit is reduced, and the Vsg (the voltage difference of the source electrode and a grid electrode) is unchanged. When each driving unit has different initial voltages because of the change of characteristics, the difference of the output current of each driving unit is reduced when the driving unit is conducted.
Description
Technical Field
The present invention relates to a method and apparatus for making an image uniform on an active matrix organic light emitting diode display, and more particularly, to a method and apparatus for preventing an output current of each Driving thin film transistor (Driving TFT) from being excessively changed by decreasing a Vsd (source-drain voltage difference) of the Driving thin film transistor (Driving TFT) and maintaining a Vsg (source-gate voltage difference) thereof.
Background
The known thin film transistor liquid crystal display (TFT LCD) technology is currently classified into an amorphous silicon thin film transistor (α -Si TFT) and a polycrystalline silicon thin film transistor (Poly-Si TFT), and the generally-called thin film transistor liquid crystal display (TFT LCD) refers to the amorphous silicon thin film transistor (α -Si TFT), and is mature in technology at present and is a mainstream product of the Liquid Crystal Display (LCD). The largest difference between the low-temperature polysilicon thin film transistor (LTPS TFT) and the amorphous silicon thin film transistor (alpha-Si TFT) is that the transistor of the low-temperature polysilicon (LTPS) needs to be further subjected to a laser tempering manufacturing step to convert the thin film of the amorphous silicon thin film transistor (alpha-SiTFT) into a polysilicon thin film layer, so that the arrangement of the low-temperature polysilicon (LTPS) on a silicon crystal structure is more ordered than that of the amorphous silicon thin film transistor (alpha-Si TFT), and the electron conduction rate can be improved to 200cm2V-sec. The Low Temperature Polysilicon (LTPS) technology can make the element smaller, and the whole TFT element area is reduced by more than 50%; and an aperture ratio (aperture ratio) is improved at the same size with respect to an alpha-Si TFT LCDHigher resolution can be produced with reduced power consumption. In addition, the low temperature polysilicon thin film transistor (LTPS TFT) has the advantages of power saving, high brightness, fine and light picture, few contacts (less than 200 contacts, increased yield, more than 3842 contacts for the α -Si TFT), and the like.
However, since the Thin Film Transistor (TFT) manufactured in the low temperature poly-silicon (LTPS) manufacturing process is subjected to a laser annealing process, the threshold voltage (threshold voltage) and the drift rate (Mobility) of the TFT are often changed, so that the characteristics of each TFT element are different, and therefore, when the driving system uses an analog (analog) modulation method to represent gray scales, the TFTs have different characteristics after receiving the laser annealing manufacturing process, and even though the same voltage signal is written, the organic light emitting diodes of different pixels generate different currents to emit different brightness. This phenomenon may cause the oled panel to display an Image with a wrong gray scale, which may seriously damage the Image Uniformity (Image Uniformity).
The US patent US5684365 discloses a thin film display of an organic electroluminescent device, which proposes a pixel circuit composed of two thin film transistors and a capacitor, wherein when the pixel device scans image data, the switch unit is turned on, and then the image data enters the switch unit from a data line, and is stored in the storage unit (i.e. the storage unit is charged after the switch unit is turned on) after being scanned by the scan line, and the voltage difference of the storage unit provides Vsg (source and gate voltage difference) as a driving unit, so that the driving unit outputs current to the organic electroluminescent device, and the brightness emitted by the organic electroluminescent device is proportional to the current flowing through the device. However, if the device characteristics of the driving unit of such a pixel device vary due to the limitation of the manufacturing process, the organic electroluminescent device will emit light unevenly, and the image uniformity will be damaged.
Therefore, in order to improve the image uniformity of the display, some manufacturers develop a digital driving structure, and express gray scales by a Time Ratio (Time Ratio) modulation method, the operation principle is to control the ON/OFF of a Thin Film Transistor (TFT) to control the ON/OFF of an Organic Light Emitting Diode (OLED), and determine the gray scales of the image by the Ratio of the ON Time of the OLED to the Frame Time (Frame Time).
However, the following key technologies are still in need of breakthrough when the organic light emitting diode is driven in a digital manner:
when the thin film transistors on the display panel are in the on state, the difference of the output current magnitude must be small enough.
When each thin film transistor on the display panel is in an off state, it is necessary to ensure that all TFTs are completely off without any output.
Disclosure of Invention
Therefore, the main objective of the present invention is to solve the above-mentioned conventional drawbacks, and to avoid the drawbacks, the method and apparatus for equalizing the image of the active matrix organic light emitting diode display according to the present invention connect the cathode of each organic light emitting diode to a positive power source to increase the potential of the organic light emitting diode, so as to reduce the Vsd (source-drain voltage difference) of the driving TFT, and keep the Vsg (source-gate voltage difference) unchanged, so that the difference of the output current when each thin film transistor is in the on state is reduced.
In order to achieve the above object, the present invention adopts a method and a device for making an image of an active organic light emitting diode display uniform, wherein the display is composed of a plurality of pixel devices, each pixel device is provided with a driving unit for driving the organic light emitting diode to light, the cathode of the organic light emitting diode is connected with a positive power supply, so that the positive power supply provides Voltage to increase the potential of the organic light emitting diode, further the Vsd (source and drain Voltage difference) of the driving unit is reduced when the driving unit operates, and the Vsg (source and gate Voltage difference) is kept unchanged, so that when the driving units have different initial voltages (Threshold voltages) due to characteristic variations, the difference of output currents of the driving units when the driving units are conducted can be reduced.
Drawings
Fig. 1 is a circuit schematic of the present invention.
Fig. 2 is a current-voltage diagram of a driving unit.
Fig. 3 is a current-voltage diagram of the driving unit (two).
Detailed Description
The present invention will now be described in detail and with reference to the accompanying drawings, wherein:
fig. 1 is a schematic circuit diagram according to the present invention. As shown in the figure: the invention relates to a method and a device for homogenizing images of an active matrix organic light emitting diode display, wherein the display is composed of a plurality of pixel devices 10, each pixel device 10 is provided with a driving unit 2 for driving an organic light emitting diode 4 to light, the cathode of the organic light emitting diode 4 is connected with a positive power supply 5, so that the potential of the organic light emitting diode 4 is improved by the Voltage provided by the positive power supply 5, further, the Vsd (source and drain Voltage difference) of the driving unit 2 is reduced when the driving unit 2 acts, and the Vsg (source and gate Voltage difference) is kept unchanged, and when the driving unit 2 has different initial voltages (Threshold Voltage) due to characteristic variation, the difference of output currents of the driving unit 2 when the driving unit 2 is conducted can be reduced.
To achieve the above method, the pixel (pixel) device 10 of the present invention comprises: a switch unit 1, a driving unit 2, a storage unit 3 and an organic light emitting diode 4; wherein,
the switch unit 1 is a Thin Film Transistor (TFT), and two input terminals 11 and 12 of the switch unit 1 are respectively connected to a Scan Line 60(Scan Line) and a Data Line 61(Data Line);
the driving unit 2 is a Thin Film Transistor (TFT), the input terminal 21 of the driving unit 2 is connected to a power Line 62(Supply Line), and the other input terminal 22 is connected to the output terminal 13 of the switching unit 1;
the storage unit 3 is composed of a capacitor, one end of which is connected with a power Line 62(Supply Line), and the other end of which is connected with the output end 13 of the switch unit 1;
the anode of the organic light emitting diode 4 is connected to the output terminal 23 of the driving unit 2, and the cathode thereof is connected to a positive power supply 5;
the positive power supply 5 provides a Voltage to increase the cathode and anode potentials of the oled 4, and also increases the potential of the output terminal 23 of the driving unit 2, so that Vsd (source-drain Voltage difference) of the driving unit 2 is decreased while Vsg (source-gate Voltage difference) is maintained during operation, and thus, when the driving units 2 have different Threshold voltages (Vth) due to characteristic changes, the difference of output currents of the driving units 2 during conduction is reduced.
In addition, to fully understand the effect achieved by the present disclosure, please refer to fig. 2, which is a schematic current-voltage diagram of the driving unit. As shown in the figure: when the input voltage Vdd of the power line 62 is 13V and the input voltage signal Vdd of the data line 61 is 0V, under the conventional pixel device structure, the driving unit 2 has a known load curve 71, so that the Vsd Operating Point (Operating Point) of the conventional driving unit is located at the intersection of the known load curve 71 and the characteristic curve one 72 of the driving unit 2 (when the input voltage Vdd of the power line is 13V and the input voltage signal Vdata of the data line is 0V).
Assuming that the Threshold Voltage (Vth) of the TFT device varies by + -1.5V due to the process limitation, it can be seen that when there is a variation of-1.5V in Vth, it will cause a variation of 23.3% in the output current of the conventional driving unit.
On the contrary, when the pixel device 10 of the present invention is used, assuming that the cathode potential of the Organic Light Emitting Diode (OLED) has a magnitude of 5V due to the voltage provided by the positive power source, the driving unit 2 has an inventive load curve 73, so that the Vsd operating point (operating point) of the driving unit 2 is located at the intersection of the inventive load curve 73 and the first characteristic curve 72 of the driving unit 2, and experiments prove that the output current of the driving unit 2 has only 13.6% variation when the threshold voltage (Vth) of the TFT element has a variation of-1.5V due to the process limitation.
Referring to fig. 3, a current-voltage diagram of the driving unit is shown. As shown in the figure: when the characteristic curve three 83 (when the input voltage (Vdd) of the power line 62 is 8V and the input voltage signal (Vdata) of the data line 61 is 0V), in the conventional pixel device structure, the Vsg of the conventional driving unit becomes smaller to 8V, and the Vsd Operating Point (Operating Point) of the conventional driving unit is located at the intersection of the load curve two 81 and the characteristic curve three 83(Vsg is 8V) of the driving unit 2. The variation of the output current of the conventional driving unit is 39.6% when the threshold voltage vth (threshold voltage) of the TFT device varies by ± 1.5V due to the process limitation.
However, when the driving apparatus of the present invention is used, since the common cathode potential of the Organic Light Emitting Diode (OLED) panel is equal to 5V, the input voltage (Vdd) is 13V, the input voltage signal (Vdata) of the data line 61 is 0V, and the Vsd Operating Point (Operating Point) of the driving unit 2 is located at the intersection of the load curve two 81 and the conventional driving unit characteristic curve two 82(Vsg is equal to 13V). The output current of the driving unit 2 has only 13.6% variation when the threshold voltage vth (threshold voltage) of the TFT device has ± 1.5V variation due to process limitation.
Therefore, in the conventional pixel device, when the power supply voltage (Vdd) is decreased, Vsd of the conventional driving unit can be decreased, but Vsg is also decreased, and instead, the influence of the characteristic change ON the output current of each conventional driving unit is increased, so that it is impossible to maintain Vsg at a constant value while decreasing Vsd of the driving unit 2 as in the present invention, and thus the output current is not influenced by the characteristic change of the TFT when the TFT is turned ON (ON).
The above description is only for the preferred embodiment of the present invention, and is not intended to limit the scope of the present invention. All the equivalent changes and modifications made according to the claims of the present invention are covered by the claims of the present invention.
Claims (5)
1. An apparatus for homogenizing an image of an active matrix organic light emitting diode display, said display comprising a plurality of pixel devices (10), wherein each pixel device (10) comprises:
a switch unit (1) having two input terminals (11), (12) and an output terminal (13), wherein the two input terminals (11), (12) are respectively connected to the scan line (60) and the data line (61);
a storage unit (3) having one end connected to a power line (62) and the other end connected to the output terminal (13) of the switch unit (1);
a driving unit (2) having two input terminals (21), (22) and an output terminal (23), wherein one input terminal (21) is connected to a power line (62), and the other input terminal (22) is connected to the output terminal (13) of the switching unit (1);
an organic light emitting diode (4) having an anode connected to the output terminal (23) of the driving unit (2) and a cathode connected to a positive power supply (5);
the positive power supply (5) provides voltage to increase the potentials of the cathode and the anode of the organic light emitting diode (4) and increase the potential of the output end (23) of the driving unit (2), so that the voltage difference between the source and the drain of the driving unit (2) is reduced and the voltage difference between the source and the gate is kept unchanged during action.
2. The device for image uniformity of an active organic light emitting diode display according to claim 1, wherein said switch unit (1) is a thin film transistor.
3. The device for image uniformity of an active organic light emitting diode display according to claim 1, wherein said driving unit (2) is a thin film transistor.
4. The device for image uniformity of an active organic light emitting diode display according to claim 1, wherein said storage unit (3) is formed by a capacitor.
5. A method for making image of active organic LED display uniform, the said display is mainly made up of multiple pixel devices, characterized by that, every said pixel device (10) has a driving unit (2) in order to drive the said organic LED (4) to shine, the negative pole of the said organic LED (4) is connected to a positive power supply (5), provide the voltage and improve the electric potential of the organic LED (4) through the said positive power supply (5), and then make the said driving unit (2) reduce its source, drain-source voltage difference when acting, and the source, grid voltage difference keeps unchanged, when the said each said driving unit (2) has different initial voltages because of characteristic variation, can make the difference of its output current of each said driving unit (2) reduce when turning on.
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| Application Number | Priority Date | Filing Date | Title |
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| CNB031091032A CN1312650C (en) | 2003-04-03 | 2003-04-03 | Method and device capable of making active organic light-emitting diode display produce uniform image |
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| CNB031091032A CN1312650C (en) | 2003-04-03 | 2003-04-03 | Method and device capable of making active organic light-emitting diode display produce uniform image |
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| CN1312650C true CN1312650C (en) | 2007-04-25 |
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| CN105118425A (en) * | 2015-10-14 | 2015-12-02 | 京东方科技集团股份有限公司 | Display panel and display control method thereof as well as display device |
Citations (7)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US5684365A (en) * | 1994-12-14 | 1997-11-04 | Eastman Kodak Company | TFT-el display panel using organic electroluminescent media |
| US5714968A (en) * | 1994-08-09 | 1998-02-03 | Nec Corporation | Current-dependent light-emitting element drive circuit for use in active matrix display device |
| CN1341915A (en) * | 2000-07-31 | 2002-03-27 | 三洋电机株式会社 | Active matrix self-luminous display device and active matrix organic EL display device |
| CN1369870A (en) * | 2001-02-08 | 2002-09-18 | 株式会社半导体能源研究所 | Light-emitting element and electronic appliance using such element |
| CN1369916A (en) * | 2001-01-29 | 2002-09-18 | 株式会社半导体能源研究所 | Light-emitting element |
| US20020180679A1 (en) * | 2001-02-23 | 2002-12-05 | Hiroshi Kageyama | Drive circuit and image display apparatus |
| JP2002358031A (en) * | 2001-06-01 | 2002-12-13 | Semiconductor Energy Lab Co Ltd | Light emitting device and its driving method |
-
2003
- 2003-04-03 CN CNB031091032A patent/CN1312650C/en not_active Expired - Fee Related
Patent Citations (7)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US5714968A (en) * | 1994-08-09 | 1998-02-03 | Nec Corporation | Current-dependent light-emitting element drive circuit for use in active matrix display device |
| US5684365A (en) * | 1994-12-14 | 1997-11-04 | Eastman Kodak Company | TFT-el display panel using organic electroluminescent media |
| CN1341915A (en) * | 2000-07-31 | 2002-03-27 | 三洋电机株式会社 | Active matrix self-luminous display device and active matrix organic EL display device |
| CN1369916A (en) * | 2001-01-29 | 2002-09-18 | 株式会社半导体能源研究所 | Light-emitting element |
| CN1369870A (en) * | 2001-02-08 | 2002-09-18 | 株式会社半导体能源研究所 | Light-emitting element and electronic appliance using such element |
| US20020180679A1 (en) * | 2001-02-23 | 2002-12-05 | Hiroshi Kageyama | Drive circuit and image display apparatus |
| JP2002358031A (en) * | 2001-06-01 | 2002-12-13 | Semiconductor Energy Lab Co Ltd | Light emitting device and its driving method |
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