CN101996579A - Pixel driving circuit and method of active organic electroluminescent display - Google Patents

Abstract

The invention discloses pixel driving circuit and method of an active organic electroluminescent display. The pixel driving circuit comprises a driving transistor, four switch transistors, a coupling capacitor, a storage capacitor and a light-emitting diode, wherein a drain electrode of the first transistor is connected with a data wire, a grid electrode of the first transistor is connected with a first scanning control wire, and a source electrode of the first transistor is connected with the C end of the coupling capacitor; a drain electrode of the second transistor is connected with source electrodes of the third transistor and the fourth transistor, a grid electrode of the second transistor is connected with the A ends of the coupling capacitor and the storage capacitor and a drain electrode of the third transistor, and a source electrode of the second transistor is connected with a drain electrode of the fifth transistor and the B end of the storage capacitor and is grounded through the organic light-emitting diode; a grid electrode of the third transistor is connected with a second scanning control wire; a drain electrode of the fourth transistor is connected with a power wire, and a grid electrode of the fourth transistor is connected with a light-emitting control wire; and a grid electrode of the fifth transistor is connected with the first scanning control wire, and a source electrode is grounded. The invention can effectively compensate the unevenness of threshold voltages of the transistors and the degradation of a start voltage of the OLED (Organic Light Emitting Diode), ensures that the brightness of an image displayed by the OLED is even and realizes high contrast.

Description

The pixel-driving circuit of active organic electroluminescent display and driving method thereof

Technical field

The present invention relates to the pixel drive technology of light emitting diode indicator, relate in particular to the pixel-driving circuit and the driving method thereof of active organic electroluminescent display.

Background technology

It is little that Organic Light Emitting Diode OLED display has a volume, from main light emission, advantage such as visible angle is big, the response time is short, and cost of manufacture is cheap, attracted more and more researchists' participation.The passive drive mode requires the efficient of OLED luminescent device and brightness very high, the pulse drive mode of high voltage or electric current makes the serviceable life that the work efficiency of luminescent device is very low and reduced OLED, and can't satisfy the requirement of high resolving power and large information capacity demonstration.Show for the giant-screen high resolving power, adopt active type of drive usually.

At present, the thin film transistor (TFT) that is applied to active OLED mainly contains amorphous silicon film transistor (a-Si TFT) and polycrystalline SiTFT (Poly-Si TFT).A-Si TFT carrier mobility is low, and size of devices is more much bigger than Poly-Si TFT, and driving voltage and signal voltage are all bigger, and these unfavorable factors can cause that the display screen matrix aperture opening ratio descends, the lost of life of OLED.Poly-Si TFT has higher carrier mobility, and than amorphous silicon technology, its device size can be accomplished littler, has increased the OLED aperture ratio of pixels, can also realize that the peripheral drive circuit with display is integrated in the periphery of display.Become the developing direction of following OLED display driver based on the active driving OLED technology of Poly-Si TFT.

In the production of reality, present technological level is difficult to guarantee that the threshold voltage of the driving tube TFT in each pixel is identical.In two traditional pipe unit drive schemes, because the unevenness of the threshold voltage of each pixel driven transistor will cause the unevenness of entire display screen brightness.Along with the increase of working time, the threshold voltage of driving transistors also can increase in addition, and the degeneration of OLED also can cause the rising of self cut-in voltage, thereby causes the decline of brightness of display screen.In order to compensate the unevenness of each pixel drive TFT threshold voltage, people have proposed many compensation schemes.These schemes mainly can be divided into current programmed type and voltage-programming type.In general, current programmed type pixel-driving circuit needs the very long duration of charging when low GTG shows, thereby has influenced its use in the giant-screen high resolution display.In voltage-programming type pixel-driving circuit, initial phase has the equivalent capacity charging of one very big electric current to memory capacitance and OLED itself, so can reduce the duration of charging greatly.Therefore in recent years the research of voltage-programming type pixel drive has been attracted more and more researchists' participation.

Summary of the invention

The objective of the invention is to overcome the shortcoming and defect of above-mentioned prior art, the pixel-driving circuit of active display of organic electroluminescence is provided, not only can effectively solve the unevenness of each pixel drive TFT threshold voltage in the active matrix OLED display, can also solve the problem that the OLED cut-in voltage is degenerated, thereby make that the brightness of OLED display lighting is even.

Another object of the present invention is to provide the driving method of the pixel-driving circuit of above-mentioned active organic electroluminescent display.

Purpose of the present invention realizes by following proposal:

The pixel-driving circuit of active organic electroluminescent display, this driving circuit comprises:

The first transistor: its drain electrode connects data line, and grid connects the first scan control line, and source electrode connects the C end of coupling capacitance, and the grid that described the first transistor control coupling capacitance is a transistor seconds writes gradation data voltage;

Transistor seconds: its drain electrode connects the third and fourth transistorized source electrode, grid connects the A end and the 3rd transistor drain of coupling capacitance and memory capacitance, source electrode connects the B end of the 5th transistor drain and memory capacitance, and link to each other with ground wire by Organic Light Emitting Diode, described transistor seconds driving OLED is luminous;

The 3rd transistor: its grid connects the second scan control line, and described the 3rd transistor provides the charging path by the 4th transistor, provides discharge path by transistor seconds;

The 4th transistor: its drain electrode connects power lead, grid sending and receiving photocontrol line, and described the 4th transistor, by the 3rd transistor controls charging path, OLED is luminous by transistor seconds control;

The 5th transistor: its grid connects the first scan control line, the source ground line, and described the 5th transistor provides discharge path, avoids OLED luminous at the threshold voltage memory phase.

Above-mentioned the first transistor, transistor seconds, the 3rd transistor, the 4th transistor and the 5th transistor are any one transistor in polycrystalline SiTFT, amorphous silicon film transistor, Zinc oxide based film transistor or the OTFT.

During pixel-driving circuit work, the first transistor, the 3rd transistor, the 4th transistor and the 5th transistor all work in linear zone, and the transistor seconds that plays driving action is operated in the saturation region.The driving method of the pixel-driving circuit of above-mentioned active organic electroluminescent display comprises the following steps:

Reset phase: the first scan control line, the second scan control line and light emitting control line are in high level, and electric current charges to the A point again by the 3rd transistor and the 4th transistor;

The threshold voltage memory phase: the first scan control line, the second scan control line still keep original high level, the light emitting control line skips to low level, and A point current potential is discharged to the threshold voltage of transistor seconds by the 3rd transistor, transistor seconds and the 5th transistor;

Gradation data voltage write phase: the first scan control line is a high level, and the second scan control line and light emitting control line are low level, and data voltage is written to the grid A point of transistor seconds by coupling capacitance;

The OLED glow phase: the first scan control line, the second scan control line are low level, and the light emitting control line is a high level, and the transistor seconds driving OLED is luminous, and the voltage difference at storage capacitors two ends remains unchanged, and promptly A point and the B voltage difference of ordering remains unchanged;

Above-mentioned threshold voltage memory phase, the threshold voltage of storage capacitors storage transistor seconds; Above-mentioned data voltage write phase, the storage capacitors storage writes gradation data voltage;

Above-mentioned OLED glow phase, storage capacitors keep its two ends storage voltage constant, make the current constant that flows through and are not subjected to the influence of OLED cut-in voltage.

The present invention compared with prior art, advantage and effect are, (1) circuit of the present invention is simple and reliable, not only can compensate the display brightness unevenness that transistorized threshold voltage difference between each pixel and OLED degenerate and cause, and because the project organization that is adopted, it is complete black to make pixel can realize during inoperative, thereby has improved the contrast of display greatly; (2) the present invention has adopted a memory capacitance and a coupling capacitance, carries out thereby make the threshold voltage storage write to separate with gradation data, can improve the precision of pixel threshold voltage compensation, is fit to the large scale high-resolution display device.

Description of drawings

Fig. 1 is the pixel-driving circuit schematic diagram of active organic electroluminescent display of the present invention; Among the figure: the first transistor T1, transistor seconds T2, the 3rd transistor T 3, the 4th transistor T 4, the 5th transistor T 5, coupling capacitance C1, memory capacitance C2, the first scan control line Vscan1, the second scan control line Vscan2, light emitting control line Vems, power lead Vdd, ground wire Vss, data line Vdata, Organic Light Emitting Diode OLED.

Fig. 2 is the signal timing diagram of Fig. 1.

Embodiment

Below in conjunction with embodiment and accompanying drawing the present invention is described in further detail, but embodiments of the present invention are not limited thereto.

Embodiment

As shown in Figure 1, the pixel-driving circuit of active organic electroluminescent display of the present invention comprises, the first transistor T1, transistor seconds T2, the 3rd transistor T 3, the 4th transistor T 4, the 5th transistor T 5, coupling capacitance C1, memory capacitance C2, the first scan control line Vscan1, the second scan control line Vscan2, light emitting control line Vems, power lead Vdd, ground wire Vss, data line Vdata, Organic Light Emitting Diode OLED.

The first transistor T1, its drain electrode meets data line Vdata, and grid meets the first scan control line Vscan1, and source electrode connects the C end of coupling capacitance C1, and the grid that described the first transistor control coupling capacitance is a transistor seconds writes gradation data voltage;

Transistor seconds T2, its drain electrode connects the source electrode of third and fourth transistor T 3, T4, grid connects the A end of coupling capacitance C1 and memory capacitance C2 and the drain electrode of the 3rd transistor T 3, source electrode connects the drain electrode of the 5th transistor T 5 and the B end of memory capacitance C2, and link to each other with ground wire Vss by Organic Light Emitting Diode, described transistor seconds driving OLED is luminous;

The 3rd transistor T 3, its grid meet the second scan control line Vscan2, and described the 3rd transistor provides the charging path by the 4th transistor, provides discharge path by transistor seconds;

The 4th transistor T 4, its drain electrode meets power lead Vdd, grid sending and receiving photocontrol line Vems, the 4th transistor, by the 3rd transistor controls charging path, OLED is luminous by transistor seconds control;

The 5th transistor, its grid meet the first scan control line Vscan1, source ground line Vss, and the 5th transistor provides discharge path, avoids OLED luminous at the threshold voltage memory phase.

Above-mentioned the first transistor T1, transistor seconds T2, the 3rd transistor T 3, the 4th transistor T 4 and the 5th transistor T 5 are any one transistor in polycrystalline SiTFT, amorphous silicon film transistor, Zinc oxide based film transistor or the OTFT.

During pixel-driving circuit work, the first transistor T1, the 3rd transistor T 3, the 4th transistor T 4 and the 5th transistor T 5 all work in linear zone, and the transistor seconds T2 that plays driving action is operated in the saturation region.The input of each signal wire as shown in Figure 2.Pixel-driving circuit has following steps to drive in each frame:

Reset phase: the first scan control line Vscan1, the second scan control line Vscan2 and light emitting control line Vems are in high level, and gradation data voltage Vdata is zero.All transistors are all opened, and electric current charge again by the 3rd transistor T 3 and 4 pairs of A points of the 4th transistor T, and when being charged to a certain fixed value, it is zero that the opening of while the 5th transistor T 5 makes the OLED anode voltage, has avoided OLED luminous in this stage;

The threshold voltage memory phase: the first scan control line Vscan1, the second scan control line Vscan2 still keep original high level, and light emitting control line Vems skips to low level, and gradation data voltage Vdata is zero.A point current potential is discharged to the threshold voltage of transistor seconds T2 by the 3rd transistor T 3, transistor seconds T2 and the 5th transistor T 5, simultaneously the 5th transistor T 5 open that to make the OLED anode voltage still be zero, avoided OLED luminous in this stage;

Gradation data voltage write phase: the first scan control line Vscan1 is a high level, the second scan control line Vscan2 and light emitting control line Vems are low level, gradation data voltage Vdata from zero saltus step be a certain on the occasion of, gradation data voltage is written to the grid A point of transistor seconds by coupling capacitance C1, opening of the 5th transistor T 5 makes the OLED anode voltage continue as zero simultaneously, avoided OLED luminous in this stage;

The OLED glow phase: the first scan control line Vscan1, the second scan control line Vscan2 are low level, light emitting control line Vems is a high level, the transistor seconds driving OLED is luminous, and the voltage difference at storage capacitors two ends remains unchanged, and just the voltage difference that A point and B are ordered among Fig. 1 remains unchanged.Specifically, this stage: the first scan control line Vscan1, the second scan control line Vscan2 are low level, light emitting control line Vems is a high level, the first transistor T1, the 3rd transistor T 3 and the 5th transistor T 5 are all closed, transistor seconds T2 driving OLED is luminous, memory capacitance C2 both end voltage difference remains unchanged in glow phase, thereby it is constant to keep OLED brightness in a frame time.

Above-mentioned threshold voltage memory phase, the threshold voltage of the storage capacitors C2 storage transistor seconds T2 in the pixel-driving circuit;

Above-mentioned gradation data voltage write phase, the storage capacitors C2 storage in the pixel-driving circuit writes gradation data voltage;

Above-mentioned OLED glow phase, the storage capacitors C2 in the pixel-driving circuit keeps its two ends storage voltage constant, makes the current constant that flows through T2 and the influence that is not subjected to the OLED cut-in voltage.

In pixel-driving circuit of the present invention, the heterogeneity of the threshold voltage vt h of each pixel and the degeneration of OLED can not have influence on the luminance difference of luminescent device OLED.The brightness of luminescent device OLED with flow through its size of current and be directly proportional.In the data voltage write phase, for each pixel, the voltage difference at its memory capacitance C2 two ends (being the gate source voltage of transistor seconds T2) is fixed on

(Vdata＞0), and remain to next frame.For the different pixels point, the otherness of threshold voltage can cause the voltage difference difference at memory capacitance C2 two ends, but it is identical really to derive the electric current that flows through OLED by following formula:

$I_{\mathrm{OLED}}=\mathrm{\β}{(V_{\mathrm{gs}}-V_{\mathrm{th}})}^2$

$=\mathrm{\&beta;}{(V_{\mathrm{th}}+\frac{C1}{\mathrm{<figure-callout\; id="1"\; label="C"\; filenames="HSA00000321824300012.png"\; state="\{\{state\}\}">C</figure-callout>}1+C2}{V}_{\mathrm{data}}-V_{\mathrm{th}})}^2$

$=\mathrm{\&beta;}{\left(\frac{C1}{\mathrm{<figure-callout\; id="1"\; label="C"\; filenames="HSA00000321824300012.png"\; state="\{\{state\}\}">C</figure-callout>}1+C2}{V}_{\mathrm{data}}\right)}^2$

Wherein I _OLEDFor the OLED glow phase flows through the electric current of transistor seconds T2, under the situation of other parameter constants, its size is only relevant with Vdata, and with the irrelevant formula of the forward voltage of Vth and OLED in, μ _nBe electron mobility; C _OXCapacitive dielectric layer for unit area; L and W are respectively channel length and the width of transistor seconds T2; Vth is the threshold voltage of transistor seconds T2; The gate source voltage of Vgs transistor seconds T2.In addition, this image element circuit is zero in inoperative stage OLED both end voltage, so inoperative stage image element circuit can be realized complete deceiving, thereby has improved the contrast of display greatly.

Certainly, those skilled in the art can also do suitably change to the pixel-driving circuit structure and the type of drive of the above-mentioned proposition of the present invention, for example suitably change the kind (P type or N type) of each switching transistor of image element circuit, with electrical connection exchange of each transistorized source electrode and drain electrode etc.

Just can realize the present invention preferably as mentioned above.

The foregoing description only is preferred implementation of the present invention; but embodiments of the present invention are not restricted to the described embodiments; other are any not to deviate from change, the modification done under spirit of the present invention and the principle, substitute, combination, simplify; all should be the substitute mode of equivalence, be included within protection scope of the present invention.

Claims (5)

1. the pixel-driving circuit of active organic electroluminescent display is characterized in that, this driving circuit comprises:

The first transistor: its drain electrode connects data line, and grid connects the first scan control line, and source electrode connects the C end of coupling capacitance, and the grid that described the first transistor control coupling capacitance is a transistor seconds writes gradation data voltage;

Transistor seconds: its drain electrode connects the third and fourth transistorized source electrode, grid connects the A end and the 3rd transistor drain of coupling capacitance and memory capacitance, source electrode connects the B end of the 5th transistor drain and memory capacitance, and link to each other with ground wire by Organic Light Emitting Diode, described transistor seconds driving OLED is luminous;

The 3rd transistor: its grid connects the second scan control line, and described the 3rd transistor provides the charging path by the 4th transistor, provides discharge path by transistor seconds;

The 4th transistor: its drain electrode connects power lead, grid sending and receiving photocontrol line, and described the 4th transistor, by the 3rd transistor controls charging path, OLED is luminous by transistor seconds control;

The 5th transistor: its grid connects the first scan control line, the source ground line, and described the 5th transistor provides discharge path, avoids OLED luminous at the threshold voltage memory phase.

2. the pixel-driving circuit of active organic electroluminescent display according to claim 1, it is characterized in that, described the first transistor, transistor seconds, the 3rd transistor, the 4th transistor and the 5th transistor are any one transistor in polycrystalline SiTFT, amorphous silicon film transistor, Zinc oxide based film transistor or the OTFT.

3. the driving method of the pixel-driving circuit of claim 1 or 2 described active organic electroluminescent displays is characterized in that, comprises the following steps:

Reset phase: the first scan control line, the second scan control line and light emitting control line are in high level, and electric current charges to the A point again by the 3rd transistor and the 4th transistor;

The threshold voltage memory phase: the first scan control line, the second scan control line still keep original high level, the light emitting control line skips to low level, and A point current potential is discharged to the threshold voltage of transistor seconds by the 3rd transistor, transistor seconds and the 5th transistor;

Gradation data voltage write phase: the first scan control line is a high level, and the second scan control line and light emitting control line are low level, and gradation data voltage is written to the grid A point of transistor seconds by coupling capacitance;

The OLED glow phase: the first scan control line, the second scan control line are low level, and the light emitting control line is a high level, and the transistor seconds driving OLED is luminous, and the voltage difference at storage capacitors two ends remains unchanged, and promptly A point and the B voltage difference of ordering remains unchanged;

4. driving method according to claim 3 is characterized in that described transistor seconds is operated in the saturation region, and the first transistor, the 3rd transistor, the 4th transistor, the 5th transistor are operated in linear zone.

5. driving method according to claim 3 is characterized in that,

Above-mentioned threshold voltage memory phase, the threshold voltage of storage capacitors storage transistor seconds;

Above-mentioned gradation data voltage write phase, the storage capacitors storage writes gradation data voltage;

Above-mentioned OLED glow phase, storage capacitors keep its two ends storage voltage constant, make the current constant that flows through and are not subjected to the influence of OLED cut-in voltage.

Images