CN102903333A - Pixel circuit of organic light emitting display - Google Patents

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 the 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 spare (AMOLED) is the 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 become the flat panel display of future generation after LCD, is one of the maximum technology that receives publicity in the present flat panel display.

At the AMOLED device that glass substrate is made, amorphous silicon (a-Si) thin film transistor (TFT) (TFT) and low temperature polycrystalline silicon (LTPS) TFT are arranged substantially at present; And LTPS TFT is because there is higher carrier mobility, and less device size can also be integrated in the peripheral drive circuit of display 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 stores memory capacitance Cst into via T1, thus control driving transistors T2 generation current, and it is luminous to drive Organic Light Emitting Diode OLED.At this moment, the flow through computing formula of electric current of OLED is:

$I=\frac{1}{2}\frac{W}{L}{C}_{\mathrm{ox}}u{(V_{\mathrm{sg}}-|V_{\mathrm{th}}\left|\right)}^2$

$I=\frac{1}{2}\frac{W}{L}{C}_{\mathrm{ox}}u{[(V_{\mathrm{dd}}-\mathrm{IR})-V_{\mathrm{data}}-|V_{\mathrm{th}}\left|\right]}^2$

Wherein, I is the electric current of OLED of flowing through, and W/L is the passage breadth length ratio of driving transistors, C _OxBe 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 that produces voltage Vdd line of the Vdd ' of image element circuit to the glass substrate from the external power source chip, and Vth is the threshold voltage of pixel driven transistor T2.

In the production of reality, the threshold voltage of the drive TFT of each pixel of the very difficult assurance of present technological level is identical, and because power supply Vdd is different to the length of the line of each pixel, so impedance is also different; Therefore, even the Vdata voltage of each pixel is the same, the electric current of the OLED that flows through is also different, and therefore brightness also have difference, thereby cause the problem of organic light emitting display brightness irregularities.

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

Summary of the invention

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

Secondary objective of the present invention provides a kind of image element circuit of organic light emitting display, to solve the problem of the organic light emitting display brightness disproportionation that causes 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 drain electrode of transistor seconds and the 3rd transistorized source electrode, the source electrode of transistor seconds is connected with the first power lead with the source electrode of the 7th crystal, the 3rd transistorized drain electrode is connected with the 5th transistorized source electrode with the 4th transistorized drain electrode, the anodic bonding of the 5th transistorized drain electrode and described Organic Light Emitting Diode, the 3rd transistorized grid, the 6th transistorized drain electrode is connected with the first end of described memory capacitance, the 7th transistorized drain electrode, the 8th transistorized drain electrode is connected with the second end of described memory capacitance, the 8th transistorized source electrode is connected with described reference voltage, and the 6th transistorized source electrode is connected with the second source line; The 6th transistorized grid is connected with one first scan control line, and transistor seconds, the 5th transistor, the 7th transistorized grid are connected with a control line, and the first transistor, the 4th transistor, the 8th transistorized grid are 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 the 3rd 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 of the described Organic Light Emitting Diode of flowing through is:

$I=\frac{1}{2}\frac{W}{L}{C}_{\mathrm{ox}}u{(V_{\mathrm{sg}}-|V_{\mathrm{th}}\left|\right)}^2$

$I=\frac{1}{2}\frac{W}{L}{C}_{\mathrm{ox}}u{[V_{\mathrm{dd}}-V_{\mathrm{data}}+|V_{\mathrm{th}}|+(V_{\mathrm{ref}}-V_{\mathrm{dd}})-\left|V_{\mathrm{th}}\right|)]}^2,$ Wherein: I is for flowing through

$I=\frac{1}{2}\frac{W}{L}{C}_{\mathrm{ox}}u{[V_{\mathrm{ref}}-V_{\mathrm{data}}]}^2$

The electric current of Organic Light Emitting Diode, W/L are the passage breadth length ratio of driving transistors, C _OxBe 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 3rd transistorized threshold voltage.

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 remedy the difference of different pixels drive transistor threshold voltage, also can remedy power supply Vdd simultaneously to the difference of the impedance of each pixel line, thereby make the brightness of organic light emitting display more even.

Description of drawings

In order to be illustrated more clearly in the embodiment of the invention or technical scheme of the prior art, the below will do to introduce simply to the accompanying drawing of required use in embodiment or the description of the Prior Art, apparently, accompanying drawing in the following describes only is some embodiments of the present invention, for those of ordinary skills, under the prerequisite of not paying creative work, can also obtain according to these accompanying drawings other accompanying drawing.

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 invention, the technical scheme in the embodiment of the invention is clearly and completely described, obviously, described embodiment only is the present invention's part embodiment, rather than whole embodiment.Based on the embodiment among the present invention, those of ordinary skills belong to the scope of protection of the invention not paying the every other embodiment that obtains under the creative work prerequisite.

Consult shown in Figure 2ly, 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 transistor 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 drain electrode of switching transistor T2 and the source electrode of 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 and the drain electrode of switching transistor T4 are connected source electrode and are connected with switching transistor T5, the anodic bonding of the drain electrode of switching transistor T5 and 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 the second end of memory capacitance C, the source electrode of switching transistor T8 is connected with reference voltage Vref, and 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 that compensate function 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 all is 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 the left side one end of memory capacitance C via T1, T3, T4; The voltage of node N is Vdata-|Vth|; Reference voltage Vref is charged to the 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; The 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);

The flow through this moment electric current of OLED, namely the electric current of driving transistors T3 is:

$I=\frac{1}{2}\frac{W}{L}{C}_{\mathrm{ox}}u{(V_{\mathrm{sg}}-|V_{\mathrm{th}}\left|\right)}^2$

$I=\frac{1}{2}\frac{W}{L}{C}_{\mathrm{ox}}u{[V_{\mathrm{dd}}-V_{\mathrm{data}}+|V_{\mathrm{th}}|+(V_{\mathrm{ref}}-V_{\mathrm{dd}})-\left|V_{\mathrm{th}}\right|)]}^2$

$I=\frac{1}{2}\frac{W}{L}{C}_{\mathrm{ox}}u{[V_{\mathrm{ref}}-V_{\mathrm{data}}]}^2$

I is the electric current of Organic Light Emitting Diode of flowing through, and W/L is the passage breadth length ratio of driving transistors, C _OxBe 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.

Can find out that from above formula the electric current of the Organic Light Emitting Diode OLED that flows through is only relevant with data voltage Vdata with reference voltage Vref, and irrelevant with the threshold voltage of driving transistors T3, also irrelevant with power supply Vdd.Even 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 of the Organic Light Emitting Diode OLED that flows through of two pixels also is the same, i.e. 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 remedy the difference of different pixels drive transistor threshold voltage, also can remedy simultaneously power supply Vdd to the difference of the impedance of each pixel line, thereby make the brightness of organic light emitting display more even.

It should be noted that at last: above embodiment only in order to technical scheme of the present invention to be described, is not intended to limit; Although with reference to previous embodiment the present invention is had been described in detail, those of ordinary skill in the art is to be understood that: it still can be made amendment to the technical scheme that previous embodiment is put down in writing, and perhaps part technical characterictic wherein is equal to replacement; And these modifications or replacement do not make the essence of appropriate technical solution break away from the spirit and scope of embodiment of the invention technical scheme.

Claims (5)

1. the image element circuit of an 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 drain electrode of transistor seconds and the 3rd transistorized source electrode, the source electrode of transistor seconds is connected with the first power lead with the source electrode of the 7th crystal, the 3rd transistorized drain electrode is connected with the 5th transistorized source electrode with the 4th transistorized drain electrode, the anodic bonding of the 5th transistorized drain electrode and described Organic Light Emitting Diode, the 3rd transistorized grid, the 6th transistorized drain electrode is connected with the first end of described memory capacitance, the 7th transistorized drain electrode, the 8th transistorized drain electrode is connected with the second end of described memory capacitance, the 8th transistorized source electrode is connected with described reference voltage, and the 6th transistorized source electrode is connected with the second source line; The 6th transistorized grid is connected with one first scan control line, and transistor seconds, the 5th transistor, the 7th transistorized grid are connected with a control line, and the first transistor, the 4th transistor, the 8th transistorized grid are 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 the 3rd 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 of the described Organic Light Emitting Diode of flowing through is:

$I=\frac{1}{2}\frac{W}{L}{C}_{\mathrm{ox}}u{(V_{\mathrm{sg}}-|V_{\mathrm{th}}\left|\right)}^2$

$I=\frac{1}{2}\frac{W}{L}{C}_{\mathrm{ox}}u{[V_{\mathrm{dd}}-V_{\mathrm{data}}+|V_{\mathrm{th}}|+(V_{\mathrm{ref}}-V_{\mathrm{dd}})-\left|V_{\mathrm{th}}\right|)]}^2,$ Wherein: I is for flowing through

$I=\frac{1}{2}\frac{W}{L}{C}_{\mathrm{ox}}u{[V_{\mathrm{ref}}-V_{\mathrm{data}}]}^2$

The electric current of Organic Light Emitting Diode, W/L are the passage breadth length ratio of driving transistors, C _OxBe 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 3rd transistorized threshold voltage.

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