CN102890910A

CN102890910A - Synchronous and asynchronous bi-gate thin film transistor (TFT)-organic light emitting diode (OLED) pixel drive circuit and drive method thereof

Info

Publication number: CN102890910A
Application number: CN2012103897857A
Authority: CN
Inventors: 王漪; 王亮亮; 韩德栋; 蔡剑; 王薇; 耿友峰; 张盛东; 刘晓彦; 康晋锋
Original assignee: Peking University
Current assignee: BOE Technology Group Co Ltd
Priority date: 2012-10-15
Filing date: 2012-10-15
Publication date: 2013-01-23
Anticipated expiration: 2032-10-15
Also published as: CN102890910B

Abstract

The invention discloses a synchronous and asynchronous dual-gate TFT-OLED pixel driving circuit and a driving method thereof. The pixel driving circuit of the present invention includes: a first transistor, a second transistor, a storage capacitor and a light emitting diode; wherein, the first transistor is a synchronous double-gate thin film transistor, and the second transistor is an asynchronous double-gate thin film transistor. The pixel driving circuit of the present invention only introduces a synchronous double-gate structure and an asynchronous double-gate structure on the basis of the traditional 2T1C circuit, and adds a pre-charge voltage and a feedback line, which not only effectively increases the storage capacitance for data in the non-selection stage The effect of maintaining the voltage effectively realizes the compensation of the threshold voltage of the drive transistor, thereby ensuring the uniformity and stability of the luminance of the display. Compared with most pixel driving circuits used for data retention and threshold compensation, transistors, capacitors and control lines are saved, and the circuit structure is greatly simplified, thereby improving aperture ratio and resolution and reducing implementation costs.

Description

Synchronous and asynchronous double grid TFT-OLED pixel-driving circuit and driving method thereof

Technical field

The invention belongs to the flat pannel display field, be specifically related to a kind of synchronous and asynchronous double grid TFT-OLED pixel-driving circuit and driving method thereof.

Background technology

It is little that active matrix organic light-emitting diode (Active Matrix Organic Light-Emitting Diode) AMOLED has a volume, simple in structure, from main light emission, brightness is high, and image quality is good, and visible angle is large, low in energy consumption, the advantages such as the response time is short, thereby cause extensive concern, become most probably the display technique of future generation that replaces liquid crystal.

Current, the thin film transistor (TFT) TFT that is used for driving AMOLED mainly contains amorphous silicon film transistor, polycrystalline SiTFT.Because the characteristic of OLED current drives, amorphous silicon film transistor can't provide enough drive currents because carrier mobility is low, thereby polycrystalline SiTFT becomes the first-selection of driving OLED.In the prior art, usually adopt the pixel-driving circuit of the 2T1C of two transistor Ts 10 and T20 and a capacitor C to be used for driving OLED, as shown in Figure 1.But, on the one hand, owing to the threshold voltage of transistor T 20 can drift about along with the working time, thereby cause that OLED's is luminous unstable; On the other hand, because the existence of the leakage current of transistor T 10, so that the spread of voltage of capacitor C, thereby caused also that OLED's is luminous unstable.And, because the drift of the threshold voltage of the transistor T 20 of each pixel is different, increases or reduce, so that the non-uniform light between each pixel.Therefore, the pixel-driving circuit of a traditional electric capacity 2T1C of two transistors has been not suitable for the demonstration of high-quality AMOLED.In order to realize the threshold voltage compensation of driving tube, need the various novel circuit structures of research to drive better pixel cell.

Yet, the so far design of the pixel-driving circuit of most AMOLED or for realizing that good threshold voltage compensation adopts complicated circuit structure, or adopt simple circuit structure and fail well to realize valve value compensation.

Summary of the invention

For defective and the deficiency that overcomes above-mentioned prior art, the invention provides a kind of synchronous and asynchronous double grid TFT-OLED pixel-driving circuit and driving method thereof.

One object of the present invention is to provide a kind of synchronous and asynchronous double grid TFT-OLED pixel-driving circuit.

Pixel-driving circuit of the present invention comprises: the first transistor, transistor seconds, memory capacitance and light emitting diode; Wherein, transistor seconds is asynchronous double-gated transistor;

One end ground connection of memory capacitance;

The drain electrode of the first transistor connects data line, and grid connects the scan control line, and source electrode connects the ungrounded end of memory capacitance;

The drain electrode of transistor seconds is connected to the negative electrode of OLED and links to each other with power lead by Organic Light Emitting Diode, and the top grid connect the ungrounded end of memory capacitance, and source ground, bottom gate connect pre-charge voltage and link to each other with drain electrode by feedback line.

Transistor seconds is asynchronous double grid thin film transistor (TFT), and namely top grid and bottom gate are by different Control of Voltage, and the top grid connect the ungrounded end of memory capacitance, and bottom gate connects pre-charge voltage and links to each other with drain electrode by feedback line.Transistor seconds drives Organic Light Emitting Diode luminous as driving tube, and realizes valve value compensation by the feedback regulation effect of pre-charge voltage, makes each pixel luminous evenly constant.

Further, the first transistor of the present invention is synchronous double grid thin film transistor (TFT), and namely top grid and bottom gate are by the same electrical pressure-controlled, and double grid connects same scan control line.The first transistor provides switch ways as switching tube for data voltage is written to the grid of transistor seconds and is stored in memory capacitance; Simultaneously, because the double grid synchro control of synchronous double-gated transistor has reduced leakage current effectively, so that the voltage of memory capacitance keeps stable.Utilize the little characteristics of leakage current of synchronous double-gated transistor, increase memory capacitance hold facility to data voltage during non-gating, thereby can reduce the size of required memory capacitance, save capacity area.

The first transistor and transistor seconds are polycrystalline SiTFT or zinc oxide thin-film transistor etc.

Another object of the present invention is to provide a kind of driving method of synchronous and asynchronous double grid TFT-OLED pixel-driving circuit.

The driving method of pixel-driving circuit of the present invention may further comprise the steps:

1) scanning and data voltage write phase: the scan control line is high level, and data line is significant level, and the first transistor is conducting state, and data voltage is written to the top grid of transistor seconds and remains to next frame by memory capacitance by the first transistor and upgrades;

2) the luminous and valve value compensation stage: the scan control line is low level, data line is inactive level, the first transistor is off state, the voltage that keeps on the memory capacitance makes the transistor seconds conducting, it is luminous that transistor seconds drives Organic Light Emitting Diode, the gate source voltage of glow phase transistor seconds remains unchanged, thereby it is constant until the next frame image update to keep Organic Light Emitting Diode brightness in a frame time.

When as the threshold voltage shift of the transistor seconds of driving tube, drive current changes in the opposite direction, and the pre-charge voltage of transistor seconds changes in the same direction with threshold voltage, because the threshold voltage of asynchronous double-gated transistor increases with pre-charge voltage and reduces, therefore the threshold voltage reverse excursion of transistor seconds, i.e. feedback regulation effect by pre-charge voltage has suppressed the drift as the threshold voltage of the transistor seconds of driving tube effectively, realize valve value compensation, thereby kept drive current and luminosity is evenly constant.

Pixel-driving circuit of the present invention is only introduced synchronous double-gate structure and an asynchronous double-gate structure on the basis of traditional 2T1C circuit, increase a pre-charge voltage and a feedback line, both effectively increased memory capacitance in the non-gating stage maintenance effect to data voltage, effectively realize again the threshold voltage compensation of driving transistors, thereby guaranteed homogeneity and the constancy of display lighting brightness.In other words, than 4T1C or the 4T2C pixel-driving circuit of major part for realizing that data maintenance and valve value compensation adopt, saved transistor, electric capacity and control line, greatly simplified circuit structure, thereby improved aperture opening ratio and resolution and reduced the realization cost.

Beneficial effect of the present invention:

The synchronous and asynchronous double grid pixel-driven structure that the present invention proposes, realize that data keep and valve value compensation with keep display brightness even constant in, saved the quantity of required transistor, electric capacity and control line, simplified circuit, saved cost, reduce the area of unit pixel, thereby can improve aperture opening ratio and display resolution.

Description of drawings

Fig. 1 is the circuit diagram of the pixel-driving circuit of 2T1C structure of the prior art;

Fig. 2 is the circuit diagram of the synchronous and asynchronous double grid TFT-OLED of the present invention pixel-driving circuit;

Fig. 3 be one embodiment of the present of invention signal timing diagram.

Embodiment

Below in conjunction with accompanying drawing, the present invention will be further described by example.

Embodiment

As shown in Figure 1, pixel-driving circuit of the present invention comprises: the first transistor T1, transistor seconds T2, memory capacitance C _ST, and Organic Light Emitting Diode OLED; Wherein, the first transistor T1 is synchronous double grid polycrystalline SiTFT, and transistor seconds T2 is asynchronous double grid polycrystalline SiTFT;

One end ground connection GND of memory capacitance;

The drain electrode of the first transistor T1 meets data line DATA, and double grid meets same scan control line SCAN, and source electrode meets the ungrounded end VG of memory capacitance, and the first transistor T1 is that data voltage is written to the top grid of transistor seconds T2 and is stored in memory capacitance C _STSwitch ways is provided;

The drain electrode of transistor seconds T2 is connected to the negative electrode VD of OLED OLED and links to each other with power lead VDD by OLED, and the top grid meet the ungrounded end VG of memory capacitance, and source ground, bottom gate meet pre-charge voltage VPRE and link to each other with drain electrode VD by feedback line Lf.

During pixel-driving circuit work, the first transistor T1 realizes the selection of pixel cell as switching tube, and transistor seconds T2 is responsible for driving and the valve value compensation of OLED as driving tube.

The sequential of each signal wire as shown in Figure 3, the control method of pixel-driving circuit of the present invention may further comprise the steps:

1) scanning writes (stage 1) with data voltage: scan control line SCAN voltage VSCAN is high level, data line DATA voltage VDATA is significant level, the first transistor T1 is the switch conduction state, and data voltage VDATA is written to the top grid of transistor seconds T2 by the first transistor T1 and by memory capacitance C _STRemaining to next frame upgrades;

2) luminous and valve value compensation (stage 2): scan control line SCAN voltage VSCAN is low level, and data line DATA voltage VDATA is inactive level, and the first transistor T1 is off state, memory capacitance C _STThe voltage of upper maintenance makes transistor seconds T2 conducting, it is luminous that transistor seconds T2 drives Organic Light Emitting Diode OLED, glow phase transistor seconds gate source voltage VG-GND=VDATA remains unchanged, thereby it is constant until the next frame image update to keep Organic Light Emitting Diode brightness in a frame time.

As the threshold voltage V as the transistor seconds T2 of driving tube _THDuring drift (increase or reduce), because asynchronous double-gated transistor threshold voltage V _THReduce with pre-charge voltage VPRE increase, therefore the threshold voltage reverse excursion of transistor seconds T2 has been realized valve value compensation.

Threshold voltage V as transistor seconds T2 _THDuring increase, drive current I _OLEDChange in the opposite direction, i.e. I _OLEDReduce driving voltage V _OLEDReduce, and the pre-charge voltage VPRE of driving tube T2 is with threshold voltage V _THChange in the same direction, i.e. pre-charge voltage VPRE=VD=VDD-V _OLEDIncrease, because asynchronous double-gated transistor threshold voltage V _THReduce with pre-charge voltage VPRE increase, therefore the threshold voltage V of transistor seconds T2 _THReverse excursion, i.e. V _THReduce; Threshold voltage V as transistor seconds T2 _THDrive current I when drift reduces _OLEDChange in the opposite direction, i.e. I _OLEDIncrease driving voltage V _OLEDIncrease, and the pre-charge voltage VPRE of driving tube T2 is with threshold voltage V _THChange in the same direction, i.e. VPRE=VD=VDD-V _OLEDReduce, because asynchronous double-gated transistor threshold voltage V _THReduce and increase with pre-charge voltage VPRE, therefore the threshold voltage V of transistor seconds T2 _THReverse excursion, i.e. V _THIncrease.The threshold voltage V that has effectively suppressed transistor seconds T2 by the feedback regulation effect of pre-charge voltage VPRE _THDrift, realized valve value compensation, thus keep drive current and luminosity evenly with constant.

In the pixel-driving circuit of the present invention, the heterogeneity of the threshold voltage of each pixel and drift can not affect the luminance difference of luminescent device OLED substantially.Luminescent device OLED brightness is directly proportional with the drive current size.At sweep phase, data voltage VDATA is stored in the maintenance capacitor C _STUntil next frame, and in glow phase, the threshold voltage difference of different pixels point and same pixel different time is compensated by the feedback regulation effect of pre-charge voltage.The size of current of each OLED is basic evenly constant therefore glow phase is flowed through, and namely each pixel luminosity is evenly constant.

It should be noted that at last, the purpose of publicizing and implementing mode is to help further to understand the present invention, but it will be appreciated by those skilled in the art that: without departing from the spirit and scope of the invention and the appended claims, various substitutions and modifications all are possible.Therefore, the present invention should not be limited to the disclosed content of embodiment, and the scope of protection of present invention is as the criterion with the scope that claims define.

Claims

1. A pixel driving circuit comprising: a first transistor T1, a second transistor T2, a storage capacitor C _ST , and an organic light emitting diode OLED; wherein, the second transistor T2 is an asynchronous double-gate polysilicon thin film transistor;

One end of the storage capacitor is grounded to GND;

The drain of the first transistor T1 is connected to the data line DATA, the gate is connected to the scan control line SCAN, and the source is connected to the non-ground terminal VG of the storage capacitor. The first transistor T1 is used for writing the data voltage into the second transistor. The top gate of T2 is stored in the storage capacitor C _ST to provide a switch path;

The drain of the second transistor T2 is connected to the cathode VD of the organic light emitting diode OLED and is connected to the power line VDD through the OLED, the top gate is connected to the non-ground terminal VG of the storage capacitor, the source is grounded, and the bottom gate is connected to the pre-charger The voltage VPRE is connected to the drain VD through the feedback line Lf.

2 . The pixel driving circuit according to claim 1 , wherein the first transistor T1 is a synchronous double-gate thin film transistor, and the double gates are connected to the same scanning control line. 3 .

3. The pixel driving circuit according to claim 1, wherein the first transistor T1 and the second transistor T2 are polysilicon thin film transistors or zinc oxide thin film transistors.

4. A driving method of the pixel driving circuit according to claim 1, wherein the driving method comprises the following steps:

1) Scanning and data voltage writing stage: the scanning control line is at high level, the data line is at active level, the first transistor is in a conducting state, and the data voltage is written into the top gate of the second transistor through the first transistor and is transmitted by The storage capacitor is kept until the next frame is updated;

2) Light emission and threshold compensation stage: the scanning control line is at low level, the data line is at inactive level, the first transistor is in an off state, the voltage held on the storage capacitor turns on the second transistor, and the second transistor drives organic light emitting The diode emits light, and the gate-source voltage of the second transistor remains unchanged during the light-emitting stage, so as to maintain the brightness of the organic light-emitting diode unchanged within one frame until the image of the next frame is updated.