CN1588520A - Method for improving current driving type display picture homogeneous degree - Google Patents

Abstract

The invention is a method of improving the picture uniformity of a current-driven display, including: providing a pixel group, where each pixel includes a driving transistor to drive a display component; and in the pixel group, all the driving transistors do not have the same standard size, and at least two of the driving transistors that are not of the standard size are situated on the same power supply line.

Description

Improve the method and the display thereof of current-driven display picture uniformity coefficient

Technical field

The present invention relates to a kind of current-driven display, and be particularly related to a kind of current-driven display, non-all driving transistorss are all same standard size in its driving transistors array.

Background technology

Organic light emitting diode display is one of fast-developing in recent years current-driven display, and it is combined by a large amount of pixels usually.Shown in Figure 1A, comprise one scan line (scanline) 102, a data line (data line) 104, power lead V in each pixel _DdAnd V _Ss, a switchgear T _Sw, a driving transistors T _Dr, a storage capacitors C _sWith an electroluminescence (electro-luminescence; EL) assembly 110, this switchgear T _SwComprise at least one transistor; In at present general application, switchgear T _SwWith driving transistors T _DrBe generally thin film transistor (TFT) (thin film transistor; And driving transistors T TFT), _DrNormal be P type MOS (metal-oxide-semiconductor) transistor, but it also can be N type MOS (metal-oxide-semiconductor) transistor, precisely because the framework of pixel need change slightly, shown in Figure 1B and 1C.

Because Organic Light Emitting Diode (organic luminescence emitting diode; OLED) brightness of the light that sends is proportional to the electric current that flows through, so the change of size of current just directly has influence on the picture homogeneous degree of organic light emitting diode display; V between pixel _DdPressure drop also can cause the uneven problem of picture, on its former because plain conductor a resistance must be arranged, when electric current flows, can cause voltage drop in lead, just cause the voltage difference of pixels in different positions in the lead.As shown in Figure 2, general normal will be with the power lead V of delegation's pixel _DdBe connected together, and in the picture element matrix outside with all the row power lead V _DdLink together; With regard to regard to the pixel of delegation, when showing same picture with the online pixel desire of data line, need a pixel voltage is write the gate terminal 202 of the driving transistors of each pixel, then have same current ideally and flow through Organic Light Emitting Diode in each pixel from power lead, make each pixel present identical brightness; Yet in fact, the existence of voltage drop in the power lead, make that the source voltage of driving transistors of each pixel is neither identical, thus, grid with the driving transistors of each pixel of delegation is also inequality with respect to the voltage of source electrode, therefore can not flow through identical electric current, and make the Organic Light Emitting Diode of each pixel demonstrate different brightness.

Summary of the invention

The invention provides a kind of method of improving current-driven display picture uniformity coefficient, this method comprises provides an array of pixels, and each pixel comprises a driving transistors, in order to drive a display module; Wherein, in this array of pixels, non-all driving transistorss are all same standard size, and non-in this standard-sized driving transistors in this array of pixels, have at least two to be positioned at same power supply and to supply online.

The present invention also provides a kind of current-driven display, comprises an array of pixels in this current-driven display, and each pixel comprises a driving transistors, in order to drive a display module; Wherein, in this array of pixels, non-these all driving transistorss are all same standard size, and in this array of pixels, and non-in this standard-sized these driving transistorss, have at least two to be positioned at same power supply and to supply online.

The present invention utilizes the size that changes driving transistors, and makes suitable compensation at the voltage drop in the power lead, so that the electric current that display module flow through in each pixel is roughly the same, and promotes the picture homogeneous degree of current-driven display.

For above and other objects of the present invention, feature and advantage can be become apparent, cited below particularlyly go out preferred embodiment, and conjunction with figs., be described in detail below.

Description of drawings

Figure 1A to 1C is the composition synoptic diagram of the single pixel of organic light emitting diode display.

Fig. 2 is the synoptic diagram of the problem of explanation organic light emitting diode display picture homogeneous degree.

Fig. 3 is the simple equivalent circuit figure with delegation's pixel.

When Fig. 4 is same standard size for all driving transistorss, the V of each pixel _DdVoltage is with the voltage distribution plan of position.

Fig. 5 is according to the size of the change driving transistors of one embodiment of the invention analog result figure with the organic light emitting diode display picture homogeneous degree that promotes.

Fig. 6 is according to the size of the change driving transistors of one embodiment of the invention analog result figure with the organic light emitting diode display picture homogeneous degree that promotes.

The reference numeral explanation

The 102-sweep trace; The 104-data line; T _Sw-switchgear; T _Dr-driving transistors; C _s-storage capacitors; The 110-electroluminescence part; The gate terminal of 202-driving transistors; V _Pixel-pixel voltage; T _{Dr_1}To T _{Dr_N}-driving transistors; V _Dd-supply voltage; V _{Dd_1}To V _{Dd_N}-source voltage; R _PLThe resistance of-power lead.

Embodiment

The current-driven display that improves the method for current-driven display picture uniformity coefficient and use this method to make provided by the present invention will be example with organic light emitting diode display, the scope of right current type driving display is not limited thereto, it also can be other electroluminescent display

Before beginning to introduce embodiments of the invention, explain unevenness with the equivalent electrical circuit of pixel earlier.When desire shows same picture, needing with a pixel voltage V with the online pixel of data line (also all being connected to same power lead usually) _PixelWrite the gate terminal of the driving transistors of each pixel, existing equivalent electrical circuit with pixel is reduced to as shown in Figure 3, supposes the voltage V that power supply provides _DdBe 7 volts, each driving transistors (is T _{Dr_1}To T _{Dr_N}) size be all same standard size, for example, channel width is 6 microns, passage length is 24 microns, and the cathode voltage of Organic Light Emitting Diode is-4 volts, writes the pixel voltage V of grid of the driving transistors of each pixel _PixelBe 2 volts, and the resistance R of power lead _PLBe 0.918 nurse difficult to understand, then as shown in Figure 4, from simulating the source voltage (V of each pixel as can be seen _{Dd_1}, V _{Dd_2}V _{Dd_N}) distribute with the voltage of position, along with move gradually the pixel position, can find driving transistors T _{Dr_1}To T _{Dr_N}Source voltage also gradually change; As shown in Figure 5, the drive current of the Organic Light Emitting Diode of each pixel is flow through in heavy line representative, and it is also with the V of each pixel _DdVoltage and changing; If there are 240 pixels (N=240) in delegation, then the electric current in first pixel is about 2.35 micromicroamperes, to during the 240th pixel, drops to 2.2 micromicroamperes, and unevenness reaches about 6.58%.

The present invention is for reducing each current difference of transistorized, and utilization changes the size of driving transistors, make suitable compensation at the voltage drop in the power lead, so that the electric current that Organic Light Emitting Diode flow through in each pixel is roughly the same, and promote the picture homogeneous degree of organic light emitting diode display.One embodiment of the invention are that the channel width with the driving transistors of each pixel changes with the position, change in the mode that linearity increases if be, make channel width by linear the 240th pixel that increases of first pixel, continue aforesaid discussion unevenness for example, its V _DdDescending is about 6.58%, increases by 6.58% so channel width is just linear, and by the curve shown in the fine line of Fig. 5, this simulation result can see that electric current still drops to about 2.28 micromicroamperes from 2.36 micromicroamperes.

For voltage drop being done compensation more accurately, we can be at the V of Fig. 4 _DdWith the curve of change in location, getting its quadratic regression curve (with x represent pixel position) can get

V _dd(x)＝2.10 ^-6x ²-10 ^-3x+6.9944～2·10 ^-6x ²-10 ^-3x+7

As the electric current twisted effect (kink effect) of not considering thin film transistor (TFT), the drive current that driving transistors flow through of each pixel then, can simplify as follows:

$I_{\mathrm{dd}}\left(x\right)=\mathrm{\μ}{C}_{\mathrm{ox}}\frac{W}{2L}{(V_{\mathrm{gs}}-V_{\mathrm{th}})}^2=\mathrm{\μ}{C}_{\mathrm{ox}}\frac{W}{2L}{(V_{\mathrm{pixel}}-V_{\mathrm{dd}}\left(x\right)-V_{\mathrm{th}})}^2$

$I_{\mathrm{dd}}\left(x\right)=\mathrm{\μ}{C}_{\mathrm{ox}}\frac{W}{2L}{(2-(2\·{10}^{-6}{x}^2-{10}^{-3}x+7)-(-3))}^2$

$=\mathrm{\μ}{C}_{\mathrm{ox}}\frac{W}{2L}\·{(-2+{10}^{-3}x-2\·10^{-6}{x}^2)}^2$

$~\mathrm{\μ}{C}_{\mathrm{ox}}\frac{W}{2L}\·(4-4\·{10}^{-3}x+10\·10^{-6}{x}^2-4\·{10}^{-9}{x}^3)$

$=\μC_{\mathrm{ox}}\frac{W}{2L}\·4\·(1-{10}^{-3}x+2.5\·{10}^{-6}{x}^2-{10}^{-9}{x}^3)$

Because the brightness of light that Organic Light Emitting Diode sends is proportional to the electric current that flows through, so when electric current that each Organic Light Emitting Diode flow through was identical, its brightness of sending was also identical, that is need are with I _Dd(x) be designed to certain value

$\frac{W}{L}\&CenterDot;(1-{10}^{-3}x+2.5\&CenterDot;{10}^{-6}{x}^2-{10}^{-9}{x}^3)=\frac{W_0}{{\mathrm{<figure-callout\; id="0"\; label="L"\; filenames="A20041006986000121.png,A20041006986000131.png"\; state="\{\{state\}\}">L</figure-callout>}}_0}$

W ₀With L ₀Be respectively the channel width and the channel length of the driving transistors of primary importance, if our a fixing wherein variables L is L ₀, that is the channel length of all driving transistorss is all L ₀, then can further design the channel width of the driving transistors of optional position, it is satisfied

W(x)·(1-10 ^-3x+2.5·10 ^-6x ²-10 ^-9x ³)＝W ₀

Then the channel width of each pixel should be

$W\left(x\right)=\frac{W_0}{(1-{10}^{-3}x+2.5\&CenterDot;{10}^{-6}{x}^2-{10}^{-9}{x}^3)}$

As shown in Figure 5, the curve of fine dotted line and thick dashed line representative is respectively the substitution analog result of getting twice formula and cubic expression tertiary, electric current significantly improves with successively decrease 6.58% situation of pixel position as can be seen, though even the analog result of cubic expression tertiary also demonstrate power supply V _DdDescend with the position, but electric current has been with having risen 0.67% on the position, hence one can see that, and method provided by the present invention can reduce the current difference between the driving transistors really.

In order to confirm feasibility of the present invention, suppose that all pixel operations are 3 volts GTG at pixel voltage, then Current Position with the simulation result of change in location as shown in Figure 6, when all driving transistorss are of a size of same standard size (shown in heavy line), the electric current that flows through Organic Light Emitting Diode descends 7.18% at most with the position, but, represent V with cubic expression tertiary if use method provided by the invention _DdVoltage, and changing the size of driving transistors according to this change in voltage, the electric current that then flows through Organic Light Emitting Diode can rise 3.48% at most with the position, and is shown in dotted line, hence one can see that, and method provided by the present invention can reduce the current difference between the driving transistors really.

In addition, the present invention also provides a kind of organic light emitting diode display, comprises an array of pixels in this organic light emitting diode display, and each pixel comprises a driving transistors, in order to drive an Organic Light Emitting Diode; Wherein, in this driving transistors array, non-these all driving transistorss are all same standard size, and in the array of pixels, and non-in this standard-sized these driving transistorss, have at least two to be positioned at same power supply and to supply online.

The present invention utilizes the size that changes driving transistors, and makes suitable compensation at the voltage drop in the power lead, so that the electric current that Organic Light Emitting Diode flow through in each pixel is roughly the same, and promotes the picture homogeneous degree of organic light emitting diode display.

Though the present invention discloses as above with preferred embodiment; right its is not in order to limit the present invention; anyly have the knack of this skill person; without departing from the spirit and scope of the present invention; when can doing a little change and retouching, so protection scope of the present invention is as the criterion when looking accompanying the claim person of defining.

Claims (8)

1. current-driven display comprises in this current-driven display:

One array of pixels, each pixel comprises a driving transistors, in order to drive a display module; Wherein, in this array of pixels, non-these all driving transistorss are all same standard size, and in this array of pixels, and non-in this standard-sized these driving transistorss, have at least two to be positioned at same power supply and to supply online.

2. current-driven display as claimed in claim 1, wherein, these are positioned at, and power supply supply is online and non-to be standard-sized these driving transistorss, its size gradually changes in regular turn along the direction of power lead.

3. current-driven display as claimed in claim 2, wherein, these are positioned at, and power supply supply is online and non-to be standard-sized these driving transistorss, its size is linear change along the direction of power lead.

4. current-driven display as claimed in claim 1, wherein, this display module is an electroluminescence part.

5. current-driven display as claimed in claim 4, wherein, this electroluminescence part is an Organic Light Emitting Diode.

6. current-driven display as claimed in claim 1, wherein, the channel length difference of the driving transistors of these off-standard sizes.

7. current-driven display as claimed in claim 1, wherein, the channel width difference of the driving transistors of these off-standard sizes.

8. current-driven display as claimed in claim 1, wherein, the channel length of the driving transistors of these off-standard sizes and channel width difference.

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