CN202957021U - Pixel unit driving circuit and display device - Google Patents
Pixel unit driving circuit and display device Download PDFInfo
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- CN202957021U CN202957021U CN2012206768139U CN201220676813U CN202957021U CN 202957021 U CN202957021 U CN 202957021U CN 2012206768139 U CN2012206768139 U CN 2012206768139U CN 201220676813 U CN201220676813 U CN 201220676813U CN 202957021 U CN202957021 U CN 202957021U
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Abstract
The utility model provides a pixel unit driving circuit and a display device. The circuit comprises four thin film transistors (TFT) and two capacitors. The display process comprises three processes of preflush, compensation and display respectively. Compared with the traditional pixel structure, the pixel unit driving circuit has the advantages that the threshold voltage shift, low uniformity and organic light emitting diode (OLED) voltage non-uniformity of an enhancement or depletion type TFT driving tube can be effectively compensated.
Description
Technical field
The utility model relates to the circuit structure of liquid crystal indicator, refers to especially a kind of pixel unit drive circuit and display device.
Background technology
Organic light emitting display diode (OLED) is applied in the high-performance demonstration more and more as a kind of current mode luminescent device.Traditional passive matrix organic light emitting display (Passive Matrix OLED), along with the increase of display size, needs the driving time of shorter single pixel, thereby needs to increase transient current, increases power consumption.The simultaneously application of large electric current can cause the ITO(tin indium oxide) on line pressure drop excessive, and make the OLED operating voltage too high, and then reduce its efficiency.And active matrix organic light-emitting shows that (Active Matrix OLED), by the switching tube input OLED electric current of lining by line scan, can address these problems well.
In the AMOLED back plate design, mainly needing the problem solved is the luminance nonuniformity between pixel and pixel.
At first, AMOLED adopts thin film transistor (TFT) (TFT) to build image element circuit and provides corresponding electric current for the OLED device.Low-temperature polysilicon film transistor (LTPS TFT) or the oxide thin film transistors (Oxide TFT) of adopting more.With general amorphous silicon film transistor (a-Si TFT), compare, LTPS TFT and Oxide TFT have higher mobility and more stable characteristic, are more suitable for being applied in the AMOLED demonstration.But the limitation due to crystallization process, the LTPS TFT made on the large-area glass substrate, usually on electrical parameters such as threshold voltage, mobility, there is heterogeneity, this heterogeneity can be converted into current difference and the luminance difference of OLED display device, and by the perception of human eye institute, i.e. mura phenomenon.Although the homogeneity of Oxide TFT technique is better, but similar with a-Si TFT, under long-time pressurization and high temperature, its threshold voltage there will be drift, due to the display frame difference, the threshold drift amount difference of panel each several part TFT, can cause display brightness difference, due to this species diversity with show before image-related, therefore often be rendered as ghost phenomena.
Secondly, in the large scale display application, because there is certain resistance in the backboard power lead, cause the supply voltage of close ARVDD Power supply position than the high IR of the being called Drop of supply voltage away from for electric position.IR Drop can cause the current difference of zones of different, and then produces mura when showing.
AMOLED is according to driving type can be divided into three major types: digital, current type and voltage-type.It is fast that the voltage-type driving has actuating speed, realizes simple advantage, is applicable to driving large size panel, but need to design extra TFT and capacitor element, compensate TFT heterogeneity, IR Drop and OLED heterogeneity.
Fig. 1 is the most traditional 2 TFT transistors of employing, 1 voltage driven type image element circuit structure (2T1C) that electric capacity forms.Wherein switching transistor T2 arrives the voltage transmission on data line the grid of driving transistors T1, driving transistors T1 is converted into corresponding electric current supply OLED device by this data voltage, when normal operation, driving transistors T1 should, in saturation region, provide steady current within the sweep time of a line.Its electric current can be expressed as:
μ wherein
nFor carrier mobility, C
OXFor gate oxide electric capacity, W/L is the transistor breadth length ratio, V
DATAFor the voltage of data line, Voled is the OLED operating voltage, for all pixel cells, shares, and Vth is transistorized threshold voltage, for enhancement mode TFT, Vth be on the occasion of, for depletion type TFT, Vth is negative value.From above formula, if the Vth difference between the different pixels unit, electric current there are differences.If the Vth of pixel drifts about in time, may cause first after-current difference, cause ghost.And, because OLED device heterogeneity causes OLED operating voltage difference, also can cause current difference.
Towards compensation Vth heterogeneity, drift and the heteropical dot structure of OLED, have a variety of, usually all adopt the mode that as shown in Figures 2 and 3 TFT is set to the diode connection to realize, but this structure is only applicable to the TFT of enhancement mode, the information of voltage of Vth can be do not contained in the voltage that depletion type TFT stores, thereby the Vth heterogeneity can't be compensated.
The utility model content
The technical problems to be solved in the utility model is to provide a kind of pixel unit drive circuit and display device, can effectively compensate threshold voltage heterogeneity, threshold voltage shift and the OLED heterogeneity problem of N-shaped depletion type or enhancement mode TFT driving tube, promote display effect.
For solving the problems of the technologies described above, embodiment of the present utility model provides a kind of pixel unit drive circuit, for driving OLED, comprising:
The first transistor, transistor seconds, the 3rd transistor and the 4th transistor, the first electric capacity and the second electric capacity; Wherein,
The grid of described the first transistor is connected with the drain electrode of described transistor seconds, and its source electrode is connected respectively with the first end of described the second electric capacity, described the 4th transistorized drain electrode and described OLED, and its drain electrode is connected with the high level output end of power supply;
The grid of described transistor seconds is connected with the first control line, and its source electrode is connected with data line, and its drain electrode is connected with the grid of described the first transistor;
Described the 3rd transistorized grid is connected with the second control line, and its source electrode is connected with reference voltage input terminal, and its drain electrode is connected with the grid of described the first transistor;
Described the 4th transistorized grid is connected with described the first control line, and its source electrode is connected with the initial voltage input end, and its drain electrode is connected with the described first end of described the second electric capacity, and is connected with the source electrode of described the first transistor;
The second end of described the second electric capacity is connected with the first end of described the first electric capacity, and the second end of described the first electric capacity is connected with the grid of described the first transistor and is connected with the drain electrode of described transistor seconds;
Described reference voltage input terminal also is connected with the first end of described the first electric capacity and the second end of described the second electric capacity.
Wherein, described the first control line is first grid sweep signal control line, and described the second control line is second gate sweep signal control line;
In the pixel charging stage, described the first control line is high level, and described the second control line is low level;
In the pixel compensation stage, described the first control line and described the second control line are low level;
In the driving OLED luminescence display stage, described the first control line is low level, and described the second control line is high level.
Wherein, described the first transistor, described transistor seconds, described the 3rd transistor, described the 4th transistor is the N-type thin film transistor (TFT).
Wherein, described the first transistor, described transistor seconds, described the 3rd transistor, described the 4th transistor is the depletion type thin film transistor (TFT).
Embodiment of the present utility model also provides a kind of display device, comprises OLED, and pixel unit drive circuit as above; The source electrode of the first transistor that described pixel unit drive circuit comprises and the anodic bonding of described OLED, the negative electrode of described OLED is connected with earth terminal.
The beneficial effect of technique scheme of the present utility model is as follows:
In such scheme, the driving circuit of the pixel cell by adopting 4 transistors and 2 electric capacity, can effectively compensate threshold voltage heterogeneity, threshold voltage shift and the OLED heterogeneity problem of N-shaped depletion type or enhancement mode TFT driving tube, promote display effect, so applicability is wider.
The accompanying drawing explanation
Fig. 1 is 2 TFT transistors in prior art, 1 voltage driven type image element circuit schematic diagram that electric capacity forms;
Fig. 2 is the transistorized compensation pixel circuit structure of available technology adopting enhancement mode TFT;
Fig. 3 is the transistorized compensation pixel circuit structure of available technology adopting depletion type TFT;
The structural representation of the driving circuit that Fig. 4 is pixel cell of the present utility model;
The first control line that Fig. 5 is the circuit shown in Fig. 4 and the pulse sequence schematic diagram of the second control line.
Embodiment
For making the technical problems to be solved in the utility model, technical scheme and advantage clearer, be described in detail below in conjunction with the accompanying drawings and the specific embodiments.
As shown in Figure 4, embodiment of the present utility model provides a kind of pixel unit drive circuit, for driving OLED, comprising: the first transistor T1, transistor seconds T2, the 3rd transistor T 3 and the 4th transistor T 4, the first capacitor C 1 and the second capacitor C 2; Wherein,
The grid of described the first transistor T1 is connected with the drain electrode of transistor seconds T2, the represented parts of D1 in the first end of its source electrode and the second capacitor C 2, the drain electrode of the 4th transistor T 4 and described OLED(accompanying drawing) be connected respectively, its drain electrode is connected with the high level output end ELVDD of power supply;
The grid of described transistor seconds T2 and the first control line SCAN(n) be connected, its source electrode is connected with data line DATA, and its drain electrode is connected with the grid of described the first transistor T1;
The grid of described the 3rd transistor T 3 and the second control line SCAN(n+2) be connected, its source electrode is connected with reference voltage input terminal VREF, and its drain electrode is connected with the grid of described the first transistor T1;
The grid of described the 4th transistor T 4 and described the first control line SCAN(n) be connected, its source electrode is connected with initial voltage input end VINIT, and its drain electrode is connected with the described first end J3 of described the second capacitor C 2, and is connected with the source electrode of the first transistor T1; Wherein, the initial voltage that initial voltage is used while resetting for compensation, be constant DC level value;
The second end J2 of described the second capacitor C 2 is connected with the first end of described the first capacitor C 1 (being the second end J2 of above-mentioned the second capacitor C 2), and the second end J1 of described the first capacitor C 1 is connected with the grid of described the first transistor T1 and is connected with the drain electrode of described transistor seconds T2;
Described reference voltage input terminal VREF also is connected with the first end J2 of described the first capacitor C 1 and the second end J2 of described the second capacitor C 2.Wherein, reference voltage is DC level;
Wherein, as shown in Figure 5, described the first control line SCAN(n) be first grid sweep signal control line, its pulse signal is: at t1, in the time period, being high level, is low level in the time period at t2, at t3, in the time period, is low level; Wherein, n is positive integer;
Described the second control line SCAN(n+2) be second gate sweep signal control line, its pulse signal is: at t1, in the time period, being low level, is low level in the time period at t2, at t3, in the time period, is high level; Wherein, the t1 time period is the pixel preliminary filling stage, t2 time period compensated stage, and the t3 time period is the luminescence display stage;
In addition, described the first transistor T1, described transistor seconds T2, described the 3rd transistor T 3, described the 4th transistor T 4 is the N-type thin film transistor (TFT).
In above-described embodiment, the course of work of the circuit that N-type TFT transistor T 1 ~ T4, memory capacitance C1, C2 etc. form is as follows: SCAN[n] and SCAN[n+2] be the line scanning control line, the control sequential of signal as shown in Figure 5:
The 1st stage was the preliminary filling stage, and fundamental purpose is to make source electrode J3 point and the J1 point of TFT pipe T1 rush in advance level, as shown in Figure 4 and Figure 5, control signal SCAN[n] be switch level VGH(high level), SCAN[n+2] be switch level VGL(low level), now T2 and T4 conducting, T3 turn-offs; Level on the DATA line is filled with second end (being node J1) of the first capacitor C 1, and the first end J3 of the second capacitor C 2 is charged to the VINIT level, and the first end J2 level of the second end of the second capacitor C 2 or the first capacitor C 1 is VREF; The VINIT level is enough low, makes on the one hand the OLED can be not luminous, makes on the other hand the conducting of T1 pipe; The use that capacitor C 1 and C2 are stored charge, guarantee the node stabilization of level.
The 2nd stage was compensated stage, as shown in Figure 4 and Figure 5, and SCAN[n] be switch level VGL(low level), SCAN[n+2] be switch level VGL(low level); Now TFT manages T2, T3, and T4 turn-offs; In this stage, the T1 pipe of the first end J3 point of the second capacitor C 2 by conducting is by the high level output end of ELVDD(power supply) charging, until voltage equals V
DATA-Vth; When compensated stage finishes, the voltage difference at memory capacitance C2 two ends is VREF-V
DATA+ Vth.
The 3rd stage was the maintenance glow phase, as shown in Figure 4 and Figure 5, in this stage, SCAN[n] be switch level VGL(low level), SCAN[n+2] be switch level VGH(high level), TFT pipe T3 conducting, TFT pipe T2, T4 turn-off; The second end of the first capacitor C 1 (node J1) is charged to VREF, due to the bootstrap effect of capacitor C 2, the grid of VGS(T1 and the voltage between source electrode) voltage becomes VREF-(V
DATA-Vth); The electric current that now flows through transistor T 1 is:
Wherein, μ
nFor carrier mobility, C
OXFor gate oxide electric capacity, W/L is the transistor breadth length ratio, V
DATAVoltage for data line, for all pixel cells, share, Vth is transistorized threshold voltage, from above formula, the independent from voltage at its electric current and threshold voltage and OLED two ends, therefore eliminated threshold voltage heterogeneity, drift and the heteropical impact of OLED electric property substantially.
Adopt the image element circuit of this structure, no matter for enhancement mode or the TFT of depletion type, can effectively compensate threshold voltage heterogeneity, threshold voltage shift and the OLED heterogeneity problem of N-shaped depletion type or enhancement mode TFT driving tube, promote display effect.
Embodiment of the present utility model also provides a kind of display device, comprises OLED, and pixel unit drive circuit as above; The source electrode of the first transistor that described pixel unit drive circuit comprises and the anodic bonding of described OLED, the negative electrode of described OLED is connected with earth terminal ELVSS.
This display device of the present utility model, adopt the image element circuit of this structure, no matter, for enhancement mode or the TFT of depletion type, can effectively compensate threshold voltage heterogeneity, threshold voltage shift and the OLED heterogeneity problem of N-shaped depletion type or enhancement mode TFT driving tube, promote display effect.
The above is preferred implementation of the present utility model; should be understood that; for those skilled in the art; under the prerequisite that does not break away from principle described in the utility model; can also make some improvements and modifications, these improvements and modifications also should be considered as protection domain of the present utility model.
Claims (5)
1. a pixel unit drive circuit, for driving OLED, is characterized in that, comprising:
The first transistor, transistor seconds, the 3rd transistor and the 4th transistor, the first electric capacity and the second electric capacity; Wherein,
The grid of described the first transistor is connected with the drain electrode of described transistor seconds, and its source electrode is connected respectively with the first end of described the second electric capacity, described the 4th transistorized drain electrode and described OLED, and its drain electrode is connected with the high level output end of power supply;
The grid of described transistor seconds is connected with the first control line, and its source electrode is connected with data line, and its drain electrode is connected with the grid of described the first transistor;
Described the 3rd transistorized grid is connected with the second control line, and its source electrode is connected with reference voltage input terminal, and its drain electrode is connected with the grid of described the first transistor;
Described the 4th transistorized grid is connected with described the first control line, and its source electrode is connected with the initial voltage input end, and its drain electrode is connected with the described first end of described the second electric capacity, and is connected with the source electrode of described the first transistor;
The second end of described the second electric capacity is connected with the first end of described the first electric capacity, and the second end of described the first electric capacity is connected with the grid of described the first transistor and is connected with the drain electrode of described transistor seconds;
Described reference voltage input terminal also is connected with the first end of described the first electric capacity and the second end of described the second electric capacity.
2. pixel unit drive circuit according to claim 1, is characterized in that,
Described the first control line is first grid sweep signal control line, and described the second control line is second gate sweep signal control line;
In the pixel charging stage, described the first control line is high level, and described the second control line is low level;
In the pixel compensation stage, described the first control line and described the second control line are low level;
In the driving OLED luminescence display stage, described the first control line is low level, and described the second control line is high level.
3. pixel unit drive circuit according to claim 1 and 2, is characterized in that, described the first transistor, and described transistor seconds, described the 3rd transistor, described the 4th transistor is the N-type thin film transistor (TFT).
4. pixel unit drive circuit according to claim 1 and 2, is characterized in that, described the first transistor, and described transistor seconds, described the 3rd transistor, described the 4th transistor is the depletion type thin film transistor (TFT).
5. a display device, is characterized in that, comprises OLED, and as the described pixel unit drive circuit of claim 1-4 any one;
The source electrode of the first transistor that described pixel unit drive circuit comprises and the anodic bonding of described OLED, the negative electrode of described OLED is connected with earth terminal.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CN2012206768139U CN202957021U (en) | 2012-12-10 | 2012-12-10 | Pixel unit driving circuit and display device |
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| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CN2012206768139U CN202957021U (en) | 2012-12-10 | 2012-12-10 | Pixel unit driving circuit and display device |
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| CN202957021U true CN202957021U (en) | 2013-05-29 |
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| CN2012206768139U Withdrawn - After Issue CN202957021U (en) | 2012-12-10 | 2012-12-10 | Pixel unit driving circuit and display device |
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Cited By (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN102982767A (en) * | 2012-12-10 | 2013-03-20 | 京东方科技集团股份有限公司 | Pixel unit driving circuit, driving method and display device |
| WO2016155087A1 (en) * | 2015-03-27 | 2016-10-06 | 深圳市华星光电技术有限公司 | Amoled pixel drive circuit and pixel drive method |
| CN111261112A (en) * | 2020-03-20 | 2020-06-09 | 合肥京东方卓印科技有限公司 | Pixel driving circuit, display panel, display device and pixel driving method |
-
2012
- 2012-12-10 CN CN2012206768139U patent/CN202957021U/en not_active Withdrawn - After Issue
Cited By (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN102982767A (en) * | 2012-12-10 | 2013-03-20 | 京东方科技集团股份有限公司 | Pixel unit driving circuit, driving method and display device |
| US9214506B2 (en) | 2012-12-10 | 2015-12-15 | Boe Technology Group Co., Ltd. | Pixel unit driving circuit, method for driving pixel unit driving circuit and display device |
| WO2016155087A1 (en) * | 2015-03-27 | 2016-10-06 | 深圳市华星光电技术有限公司 | Amoled pixel drive circuit and pixel drive method |
| CN111261112A (en) * | 2020-03-20 | 2020-06-09 | 合肥京东方卓印科技有限公司 | Pixel driving circuit, display panel, display device and pixel driving method |
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Granted publication date: 20130529 Effective date of abandoning: 20150225 |
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| RGAV | Abandon patent right to avoid regrant |