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, particularly the pixel-driving circuit of active organic electroluminescent display and driving method thereof.
Background technology
Organic Light Emitting Diode (Organic Light Emitting Diode; OLED) display has frivolous; From main light emission, visible angle is big, the response time is short, low preparation cost, energy-conserving and environment-protective, be suitable for advantage such as flexible demonstration, is the display technique of future generation that has very much development potentiality.Along with development of technology; Display device begins to develop towards directions such as large scale, high resolving power, 3D; Original passive drive mode can't adapt to the demand of new display, and the novel active type of drive that the OLED of active driving (AMOLED) particularly has the pixel compensation ability has begun to become main flow.
Recent study personnel propose multiple drive scheme, mainly are divided into current programmed pattern and voltage-programming pattern.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 MM CAP and OLED itself, so can reduce the duration of charging greatly.According to the different processes route, pixel-driving circuit is divided into: end emitting structural and emission structure at top.
Adopt the pixel-driving circuit of emission structure at top,, cause having electric current easily and flow through in the improper glow phase of OLED because the anode of OLED is to be connected on the power vd D.So how avoiding electric current to flow through OLED in improper glow phase is the problem that the emission structure at top driving circuit must be considered.Technician such as Shinya ONO and Yoshinao KOBAYASHI (Four-Thin-Film-Transistor Pixel Circuit for Amorphous-Silicon Active-Matrix Organic Light-Emitting Diode Displays "; Journal of Applied Physics; VOL.43; NO.12; pp.7947-7952,2004.) emission structure at top voltage-programming type image element circuit is proposed, this image element circuit has four amorphous silicon transistors and a MM CAP to constitute.Technician such as Shinya ONO and Yoshinao KOBAYASHI point out that this image element circuit can effectively compensate the threshold voltage shift of drive TFT and the cut-in voltage of OLED is degenerated, and utilizes power lead VDD saltus step; The different phase varying level keeps non-glow phase not have electric current to flow through OLED; But power lead Vdd needs three kinds of level satisfy the certain time sequence requirement again, will guarantee enough current driving abilities simultaneously, and it is big that the peripheral driver chip implements difficulty; Consider the dead resistance on the power lead; In the saltus step process, possibly influence and flow through the OLED electric current, cause showing unstable.
Summary of the invention
For the shortcoming and deficiency that overcomes prior art; The object of the present invention is to provide a kind of pixel-driving circuit of active organic electroluminescent display; Can solve the situation that existing emission structure at top circuit power needs saltus step to make OLED not have electric current to flow through, reduce the difficulty of peripheral driver.Another object of the present invention is to provide the driving method of above-mentioned pixel-driving circuit.
The object of the invention is realized through following technical scheme:
A kind of pixel-driving circuit of active organic electroluminescent display comprises the first transistor, transistor seconds, the 3rd transistor, the 4th transistor, the 5th transistor, Organic Light Emitting Diode, coupling capacitance and MM CAP;
Each transistor comprises grid, first electrode and second electrode;
The grid of said the first transistor connects the first scan control line, and first electrode of said the first transistor connects the gradation data line, and second electrode of said the first transistor connects an end of said coupling capacitance; The other end of coupling capacitance connects an end of grid, the 3rd transistorized second electrode and the MM CAP of transistor seconds respectively;
First electrode of said transistor seconds connects the 3rd transistorized first electrode, the 4th transistorized second electrode respectively; Second electrode of transistor seconds connects the other end of the 5th transistorized first electrode and MM CAP respectively, and links to each other with power supply through Organic Light Emitting Diode;
The said the 3rd transistorized grid connects the second scan control line;
The said the 4th transistorized grid connects light emitting control line, the 4th transistorized first electrode grounding;
The said the 5th transistorized grid connects the first scan control line, and the 5th transistorized first electrode also is connected with the negative electrode of Organic Light Emitting Diode; The 5th transistorized second electrode is connected with the anode of Organic Light Emitting Diode.
Said first electrode is drain electrode, and second electrode is a source electrode.
Said first electrode is a source electrode, and second electrode is drain electrode.
Said the first transistor, transistor seconds, the 3rd transistor, the 4th transistor, the 5th transistor are P type thin film transistor (TFT).
Realize the driving method of the pixel-driving circuit of above-mentioned active organic electroluminescent display, it is characterized in that, may further comprise the steps:
Reset phase: the first scan control line, the second scan control line and light emitting control line are in low level; Gradation data voltage is changed to zero; Electric current charges to MM CAP through the 5th transistor, transistor seconds and the 3rd transistor; The complete conducting of the 5th transistor makes that Organic Light Emitting Diode negative electrode and anode short circuit, the electric current that flows through organic light emitting diode are zero; The threshold voltage latch stage: the first scan control line, the second scan control line keep original low level, and gradation data voltage is changed to zero, and the light emitting control line skips to high level, and the voltage difference at MM CAP two ends equals the threshold voltage of transistor seconds at this moment;
Gradation data voltage write phase: the first scan control line is a low level; The second scan control line and light emitting control line are high level; Gradation data voltage is written to the grid point of transistor seconds through coupling capacitance, and this moment, the potential difference (PD) at storage capacitors two ends was threshold voltage and capacitor coupling voltage sum;
The Organic Light Emitting Diode glow phase: the first scan control line, the second scan control line are high level, and the light emitting control line is a low level, and the transistor seconds driving OLED is luminous, and the potential difference (PD) at storage capacitors two ends remains the magnitude of voltage of gradation data write phase.
Compared with prior art, the present invention has the following advantages and beneficial effect:
(1) circuit of the present invention not only can compensate the display brightness unevenness that transistorized threshold voltage difference between each pixel and OLED degenerate and cause; And because the type of drive that adopts; It is complete black to make pixel during inoperative, can realize, thereby has improved the contrast of display greatly.
(2) the present invention has adopted MM CAP and 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.
(3) the present invention adopts a transistor to be connected on OLED anode and negative electrode, solves the situation that the emission structure at top circuit power needs saltus step to make OLED not have electric current to flow through, and reduces the difficulty of peripheral driver, increases exhibit stabilization greatly.
(4) the present invention can effectively compensate the difference that each pixel drive TFT threshold voltage shift causes in the active matrix OLED display; Avoid pushing up the situation of emission driving circuit power supply saltus step; Can compensate simultaneously the influence of degeneration of OLED cut-in voltage and power supply cabling dead resistance; Improve AMOLED display brightness homogeneity and stability, prolonged the life-span of panel.
(5) the present invention adopts emission structure at top, makes light-emitting area and transistor size quantity irrelevant, and aperture opening ratio effectively improves, thereby increases the panel life-span effectively.
Description of drawings
Fig. 1 is the circuit theory diagrams of embodiment of the pixel-driving circuit of active organic electroluminescent display of the present invention.
Fig. 2 is the signal timing diagram of embodiment of the pixel-driving circuit of active organic electroluminescent display of the present invention.
Embodiment
Below in conjunction with embodiment and accompanying drawing, the present invention is done to specify further, but embodiment of the present invention is not limited thereto.
Embodiment
As shown in Figure 1; The pixel-driving circuit of active organic electroluminescent display comprises the first transistor T1, transistor seconds T2, the 3rd transistor T 3, the 4th transistor T 4, the 5th transistor T 5, Organic Light Emitting Diode OLED, coupling capacitance C1 and MM CAP C2;
Each transistor comprises grid, first electrode (drain electrode) and second electrode (source electrode); Be P type thin film transistor (TFT).
The grid of said the first transistor T1 connects the first scan control line Vscan1, and the source electrode of said the first transistor T1 connects data line, and the drain electrode of said the first transistor T1 connects the end of said coupling capacitance C1; The other end of coupling capacitance C1 connects the grid of transistor seconds T2, the source electrode of the 3rd transistor T 3 and the end of MM CAP C2 respectively;
The drain electrode of said transistor seconds T2 connects the drain electrode of the 3rd transistor T 3, the source electrode of the 4th transistor T 4 respectively; The source electrode of transistor seconds T2 connects the drain electrode of the 5th transistor T 5 and the other end of MM CAP C2 respectively, and links to each other with power vd D through Organic Light Emitting Diode OLED;
The grid of said the 3rd transistor T 3 connects the second scan control line Vscan2;
The grid of said the 4th transistor T 4 connects light emitting control line Vems, the 4th transistor drain ground connection;
The grid of said the 5th transistor T 5 connects the first scan control line, and the drain electrode of the 5th transistor T 5 also is connected with the negative electrode of Organic Light Emitting Diode OLED; The source electrode of the 5th transistor T 5 is connected with the anode of Organic Light Emitting Diode OLED.
When the pixel-driving circuit of the active organic electroluminescent display of present embodiment is worked; 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 is as shown in Figure 2.Pixel-driving circuit is driven by following steps at each frame:
Reset phase: the first scan control line Vscan1, the second scan control line Vscan2 and light emitting control line Vems are in low level, and gradation data voltage Vdata is zero.All transistors are all opened, and electric current to the point of the A among Fig. 1 (the A end of MM CAP C2) charging again, is charged to a certain fixed value through the 5th transistor T 5, transistor seconds T2 and the 3rd transistor T 3.Since this moment the opening of the 5th transistor T 5, the C point among Fig. 1 (the C end of MM CAP C2) current potential is charged to supply voltage VDD, makes OLED anode and cathode voltage equal, 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 low level, and light emitting control line Vems skips to high level, and gradation data voltage Vdata is zero.At this moment; It is constant that the C point is kept original current potential; A point current potential charges to the source electrode C point of transistor seconds T2 through the 5th transistor T 5, transistor seconds T2 and the 3rd transistor T 3, and the voltage difference at MM CAP C2 two ends is the threshold voltage vt h of transistor seconds T2, i.e. VA-VC=Vth (Vth < 0); Simultaneously the 5th transistor T 5 open that to make the OLED voltage still be zero, avoided OLED luminous in this stage.
Gradation data voltage write phase: the first scan control line Vscan1 is a low level; The second scan control line Vscan2 and light emitting control line Vems are high level; Gradation data voltage Vdata is a certain negative value from zero saltus step; Gradation data voltage is written to the grid A point of transistor seconds through coupling capacitance C1, the gradation data voltage that storage capacitors C2 storage simultaneously writes, and this moment, the potential difference (PD) at storage capacitors two ends was threshold voltage and capacitor coupling voltage sum; Opening of the 5th transistor T 5 makes the OLED voltage continue as zero at this moment, avoided OLED luminous in this stage;
The OLED glow phase: the first scan control line Vscan1, the second scan control line Vscan2 are high level; Light emitting control line Vems is a low level; The transistor seconds driving OLED is luminous, and the potential difference (PD) at storage capacitors two ends remains unchanged, and the potential difference (PD) that just A point and C are ordered among Fig. 1 remains unchanged.Specifically be; This stage: the first scan control line Vscan1, the second scan control line Vscan2 are high level, and light emitting control line Vems is a low level, and 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; MM CAP C2 voltage difference remains the magnitude of voltage of gradation data write phase in glow phase, make the current constant that flows through T2 and the influence that does not receive the OLED cut-in voltage, thereby it is constant to keep OLED brightness in a frame time.
The signal sequence of the pixel-driving circuit of active organic electroluminescent display of the present invention is as shown in Figure 2.
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 MM CAP C2 two ends (being the gate source voltage of transistor seconds T2) is fixed on
, and (Vdata < 0; Vth 0), and remain to next frame.For the different pixels point, the otherness of threshold voltage can cause the voltage difference at MM CAP C2 two ends different, but it is identical really to derive the electric current that flows through OLED by following formula:
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.This image element circuit is taked emission structure at top, can effectively increase aperture opening ratio, improves the life-span of panel; In addition, in non-glow phase, the OLED voltage is zero to avoid OLED luminous, thereby has improved the display contrast greatly; Power lead does not need saltus step in the course of the work, the harmful effect of avoiding the power supply saltus step to produce, the stability of increase display, the difficulty of minimizing peripheral driver.
The foregoing description is a preferred implementation of the present invention; But embodiment of the present invention is not limited by the examples; Other any do not deviate from change, the modification done under spirit of the present invention and the principle, substitutes, combination, simplify; All should be the substitute mode of equivalence, be included within protection scope of the present invention.