CN102903333B - Pixel circuit of organic light emitting display - Google Patents

Pixel circuit of organic light emitting display Download PDF

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Publication number
CN102903333B
CN102903333B CN201210414278.4A CN201210414278A CN102903333B CN 102903333 B CN102903333 B CN 102903333B CN 201210414278 A CN201210414278 A CN 201210414278A CN 102903333 B CN102903333 B CN 102903333B
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China
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transistor
connected
light emitting
organic light
drain electrode
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CN201210414278.4A
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Chinese (zh)
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CN102903333A (en
Inventor
张小宝
邱勇
黄秀颀
胡思明
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昆山工研院新型平板显示技术中心有限公司
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Publication of CN102903333A publication Critical patent/CN102903333A/en
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Abstract

The invention discloses a pixel circuit of an organic light emitting display, comprising a first power line, a second power line, a data line, a reference voltage, an organic light emitting diode, a storage capacitor and eight transistors T1-T8, wherein the data line is connected with a source electrode of the T1; a drain electrode of the T1 is connected with a drain electrode of the T2 and a source electrode of the T3; a source electrode of the T2 and a source electrode of the T7 are connected with the first power line; a drain electrode of the T3 is connected with a drain electrode of the T4 and a source electrode of the T5; a drain electrode of the T5 is connected with an anode electrode of the organic light emitting diode; a grid electrode of the T3 and a drain electrode of the T6 are connected with a first end of the storage capacitor; a drain electrode of the T7 and a drain electrode of the T8 are connected with a second end of the storage capacitor; a source electrode of the T8 is connected with the reference voltage; a source electrode of the T6 is connected with the second power line; a grid electrode of the T6 is connected with a first scanning control line; grid electrodes of the T2, the T5 and the T7 are connected with a control line; and grid electrodes of the T1, the T4 and the T8 are connected with a second scanning control line. The pixel circuit disclosed by the invention has the advantages that threshold shift of the driving transistors and the voltage fall of the power lines can be compensated, so that the brightness of the display is more uniform.

Description

The image element circuit of organic light emitting display

Technical field

The present invention relates to organic light emitting display technical field, particularly a kind of image element circuit of organic light emitting display, this image element circuit can make display brightness more even.

Background technology

Active organic electroluminescent display device part (AMOLED) is active illuminating device.Compare present main flow flat panel display Thin Film Transistor-LCD (TFT-LCD), AMOLED has high-contrast, wide viewing angle, low-power consumption, the advantages such as volume is thinner, being expected to the flat panel display of future generation become after LCD, is one of the maximum technology that receives publicity in current flat panel display.

The AMOLED device made on the glass substrate, has amorphous silicon (a-Si) thin film transistor (TFT) (TFT) and low temperature polycrystalline silicon (LTPS) TFT at present substantially; And LTPS TFT is because have higher carrier mobility, less device size, the peripheral drive circuit of display can also be integrated in glass substrate, so LTPS TFT becomes the developing direction of AMOLED technology.

Fig. 1 is traditional AMOLED pixel-driving circuit; Comprise switching transistor T1, memory capacitance Cst, driving transistors T2, Organic Light Emitting Diode OLED, power supply Vdd ', scan control line Scan, data line Vdata.Scan control line Scan opens switching transistor T1, and data line Vdata is stored into memory capacitance Cst via T1, thus controls driving transistors T2 generation current, drives Organic Light Emitting Diode OLED luminous.Now, the computing formula flowing through the electric current of OLED is:

I = 1 2 W L C ox u ( V sg - | V th | ) 2

I = 1 2 W L C ox u [ ( V dd - IR ) - V data - | V th | ] 2

Wherein, I is the electric current flowing through OLED, and W/L is the passage breadth length ratio of driving transistors, C oxfor the electric capacity between drive transistor gate and its passage, u represents the electron mobility of driving transistors, Vdd is external power source, and R is the impedance of the line producing the Vdd ' of image element circuit voltage Vdd to glass substrate from external power source chip, and Vth is the threshold voltage of pixel driven transistor T2.

In the production of reality, the threshold voltage that current technological level is difficult to the drive TFT ensureing each pixel is identical, and due to power supply Vdd different to the length of the line of each pixel, so impedance is also different; Therefore, even if the Vdata voltage of each pixel is the same, the electric current flowing through OLED is also different, and therefore brightness also have difference, thus causes the problem of organic light emitting display brightness irregularities.

Therefore, how the technical matters of above-mentioned existence is solved, be the research direction place of those skilled in the art.

Summary of the invention

Fundamental purpose of the present invention is to provide a kind of image element circuit of organic light emitting display, to solve the problem of the organic light emitting display brightness disproportionation caused because of driving transistors threshold value difference.

Secondary objective of the present invention is to provide a kind of image element circuit of organic light emitting display, to solve the problem of the organic light emitting display brightness disproportionation caused because of the pressure drop of power supply Vdd cabling.

In order to achieve the above object, the invention provides a kind of image element circuit of organic light emitting display, it comprises

One first power lead, a second source line, a data line, a reference voltage, an Organic Light Emitting Diode, a memory capacitance and 8 transistors, wherein:

Data line is connected with the source electrode of the first transistor, the drain electrode of the first transistor is connected with the source electrode of the drain electrode of transistor seconds and third transistor, the source electrode of transistor seconds is connected with the first power lead with the source electrode of the 7th crystal, the drain electrode of third transistor is connected with the source electrode of the drain electrode of the 4th transistor and the 5th transistor, the drain electrode of the 5th transistor is connected with the anode of described Organic Light Emitting Diode, the grid of third transistor, the drain electrode of the 6th transistor is connected with the first end of described memory capacitance, the drain electrode of the 7th transistor, the drain electrode of the 8th transistor is connected with the second end of described memory capacitance, the source electrode of the 8th transistor is connected with described reference voltage, the source electrode of the 6th transistor is connected with second source line, the grid of the 6th transistor is connected with one first scan control line, and the grid of transistor seconds, the 5th transistor, the 7th transistor is connected with a control line, and the grid of the first transistor, the 4th transistor, the 8th transistor is connected with one second scan control line.

Wherein, described the first transistor, transistor seconds, the 4th transistor, the 5th transistor, the 6th transistor, the 7th transistor, the 8th transistor are switching transistor.

Wherein, described third transistor is driving transistors.

Wherein, this image element circuit is divided into initial phase, capacitor charging stage and glow phase when realizing compensate function work.

Wherein, described image element circuit is when glow phase, and the electric current flowing through described Organic Light Emitting Diode is:

I = 1 2 W L C ox u ( V sg - | V th | ) 2

I = 1 2 W L C ox u [ V dd - V data + | V th | + ( V ref - V dd ) - | V th | ) ] 2 , Wherein: I is for flowing through

I = 1 2 W L C ox u [ V ref - V data ] 2

The electric current of Organic Light Emitting Diode, W/L is the passage breadth length ratio of driving transistors, C oxfor the electric capacity between drive transistor gate and its passage, u represents the electron mobility of driving transistors, and Vdd is external power source, and Vdata is data voltage, and Vref is reference voltage, and Vth is the threshold voltage of third transistor.

Compared with prior art, beneficial effect of the present invention is:

The image element circuit of organic light emitting display of the present invention can make up the difference of different pixels drive transistor threshold voltage, also can make up the difference of power supply Vdd to the impedance of each pixel line simultaneously, thus make the brightness of organic light emitting display more even.

Accompanying drawing explanation

In order to be illustrated more clearly in the embodiment of the present invention or technical scheme of the prior art, be briefly described to the accompanying drawing used required in embodiment or description of the prior art below, apparently, accompanying drawing in the following describes is only some embodiments of the present invention, for those of ordinary skill in the art, under the prerequisite not paying creative work, other accompanying drawing can also be obtained according to these accompanying drawings.

Fig. 1 is a kind of image element circuit figure of existing active matrix/organic light emitting display;

Fig. 2 is the image element circuit figure of organic light emitting display of the present invention;

Fig. 3 is the drive waveforms figure of Fig. 2 image element circuit figure.

Embodiment

Below in conjunction with the accompanying drawing in the embodiment of the present invention, be clearly and completely described the technical scheme in the embodiment of the present invention, obviously, described embodiment is only the present invention's part embodiment, instead of whole embodiments.Based on the embodiment in the present invention, those of ordinary skill in the art, not paying the every other embodiment obtained under creative work prerequisite, belong to the scope of protection of the invention.

Consult shown in Fig. 2, be the image element circuit figure of organic light emitting display of the present invention, the image element circuit figure of a kind of organic light emitting display provided by the invention comprises:

One first power lead Vdd; One second source line Vini; One reference voltage Vref;

One data line Vdata; One Organic Light Emitting Diode OLED;

One memory capacitance C; One driving transistors T 3 and 7 switching transistors T1, T2, T4, T5, T6, T7, T8;

Wherein, data line Vdata is connected with the source electrode of switching transistor T1, the drain electrode of switching transistor T1 is connected with the source electrode of the drain electrode of switching transistor T2 and driving transistors T3, the source electrode of switching transistor T2 is connected with power lead Vdd with the source electrode of switching transistor T7, the drain electrode of driving transistors T3 is connected with the source electrode of the drain electrode of switching transistor T4 and switching transistor T5, the drain electrode of switching transistor T5 is connected with the anode of Organic Light Emitting Diode OLED, the grid of driving transistors T3, the drain electrode of switching transistor T6 is connected with the first end of memory capacitance C, the drain electrode of switching transistor T 7, the drain electrode of switching transistor T8 is connected with second end of memory capacitance C, the source electrode of switching transistor T8 is connected with reference voltage Vref, the source electrode of switching transistor T6 is connected with power lead Vini, the grid of switching transistor T6 is connected with scan control line SCAN1, the grid of switching transistor T2, switching transistor T5, switching transistor T7 is connected with control line EM, and the grid of switching transistor T1, switching transistor T4, switching transistor T8 is connected with scan control line SCAN2.

As shown in Figure 3, be the drive waveforms figure of Fig. 2 image element circuit figure, image element circuit of the present invention realizes compensate function and is divided into 3 time periods, i.e. t1 time period, t2 time period, t3 time period, wherein:

The t1 time period is initial phase: scan control line SCAN1 is low level, and SCAN2 is high level; Switching transistor T6 is opened, and other transistor is all in closed condition, and node N voltage is initialized to Vini.

The t2 time period is the capacitor charging stage: scan control line SCAN2 is low level, and switching transistor T1, T4, T8 are opened; Vdata voltage charges to one end, the left side of memory capacitance C via T1, T3, T4; The voltage of node N is Vdata-|Vth|; Reference voltage Vref is charged to second end of memory capacitance C via switching transistor T8, and namely the voltage of node M is Vref.

The t3 time period is glow phase: scan control line SCAN1, SCAN2 are high level, and control line EM is low level; Switching transistor T2, T5, T7 open, and T1, T4, T6, T8 close; Second terminal voltage of memory capacitance C changes, and namely the voltage of node M becomes Vdd, so the first end voltage of memory capacitance C also saltus step can occur, namely the voltage jump of node N is Vdata-|Vth|-(Vref-Vdd);

Now flow through the electric current of OLED, namely the electric current of driving transistors T3 is:

I = 1 2 W L C ox u ( V sg - | V th | ) 2

I = 1 2 W L C ox u [ V dd - V data + | V th | + ( V ref - V dd ) - | V th | ) ] 2

I = 1 2 W L C ox u [ V ref - V data ] 2

I is the electric current flowing through Organic Light Emitting Diode, and W/L is the passage breadth length ratio of driving transistors, C oxfor the electric capacity between drive transistor gate and its passage, u represents the electron mobility of driving transistors, and Vdd is external power source, and Vdata is data voltage, and Vref is reference voltage, and Vth is the threshold voltage of driving transistors T 3.

As can be seen from above formula, the electric current flowing through Organic Light Emitting Diode OLED is only relevant with data voltage Vdata with reference voltage Vref, and has nothing to do with the threshold voltage of driving transistors T3, also has nothing to do with power supply Vdd.Even if the drive transistor threshold voltage of two pixels is different, and the power supply Vdd track lengths of two pixels is different, and the electric current flowing through Organic Light Emitting Diode OLED of two pixels is also the same, and namely the brightness of Organic Light Emitting Diode OLED is the same.

In sum, the image element circuit of organic light emitting display of the present invention can make up the difference of different pixels drive transistor threshold voltage, also can make up the difference of power supply Vdd to the impedance of each pixel line simultaneously, thus make the brightness of organic light emitting display more even.

Last it is noted that above embodiment is only in order to illustrate technical scheme of the present invention, be not intended to limit; Although with reference to previous embodiment to invention has been detailed description, those of ordinary skill in the art is to be understood that: it still can be modified to the technical scheme described in previous embodiment, or carries out equivalent replacement to wherein portion of techniques feature; And these amendments or replacement, do not make the essence of appropriate technical solution depart from the spirit and scope of embodiment of the present invention technical scheme.

Claims (5)

1. an image element circuit for organic light emitting display, is characterized in that, it comprises
One first power lead, a second source line, a data line, a reference voltage, an Organic Light Emitting Diode, a memory capacitance and 8 transistors, wherein:
Data line is connected with the source electrode of the first transistor, the drain electrode of the first transistor is connected with the source electrode of the drain electrode of transistor seconds and third transistor, the source electrode of transistor seconds is connected with the first power lead with the source electrode of the 7th crystal, the drain electrode of third transistor is connected with the source electrode of the drain electrode of the 4th transistor and the 5th transistor, the drain electrode of the 5th transistor is connected with the anode of described Organic Light Emitting Diode, the grid of third transistor, the drain electrode of the 6th transistor is connected with the first end of described memory capacitance, the drain electrode of the 7th transistor, the drain electrode of the 8th transistor is connected with the second end of described memory capacitance, the source electrode of the 8th transistor is connected with described reference voltage, the source electrode of the 6th transistor is connected with second source line, the grid of the 6th transistor is connected with one first scan control line, and the grid of transistor seconds, the 5th transistor, the 7th transistor is connected with a control line, and the grid of the first transistor, the 4th transistor, the 8th transistor is connected with one second scan control line.
2. the image element circuit of organic light emitting display according to claim 1, it is characterized in that, described the first transistor, transistor seconds, the 4th transistor, the 5th transistor, the 6th transistor, the 7th transistor, the 8th transistor are switching transistor.
3. the image element circuit of organic light emitting display according to claim 1, is characterized in that, described third transistor is driving transistors.
4. the image element circuit of organic light emitting display according to claim 1, is characterized in that, this image element circuit is divided into initial phase, capacitor charging stage and glow phase when realizing compensate function work.
5. the image element circuit of organic light emitting display according to claim 4, is characterized in that, described image element circuit is when glow phase, and the electric current flowing through described Organic Light Emitting Diode is:
I = 1 2 W L C ox u ( V sg - | V th | ) 2
I = 1 2 W L C ox u [ V dd - V data + | V th | + ( V ref - V dd ) - | V th | ] 2 , Wherein: I is for flowing through
I = 1 2 W L C ox u [ V ref - V data ] 2
The electric current of Organic Light Emitting Diode, described third transistor is driving transistors, and W/L is the passage breadth length ratio of driving transistors, C oxfor the electric capacity between drive transistor gate and its passage, u represents the electron mobility of driving transistors, and Vdd is external power source, and Vdata is data voltage, and Vref is reference voltage, and Vth is the threshold voltage of driving transistors.
CN201210414278.4A 2012-10-25 2012-10-25 Pixel circuit of organic light emitting display CN102903333B (en)

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