CN102222468A - Alternating-current pixel driving circuit and method for active organic light-emitting diode (OLED) display - Google Patents

Abstract

The invention discloses an alternating-current pixel driving circuit and method for an active organic light-emitting diode (OLED) display. The driving circuit comprises a driving transistor, a switch transistor, a storage capacitor and an OLED, wherein the drain of the first transistor is connected with a data wire; the grid of the first transistor is connected with a first scanning control wire; the source of the first transistor is connected with the end A of the storage capacitor; the drain of a second transistor is connected with the source of a third transistor; the grid of the second transistor is connected with the end A of the storage capacitor and the source of the first transistor; the source of the second transistor is connected with the drain of a four transistor and the end B of the storage capacitor, and is connected with the ground through the OLED; the drain of the third transistor is connected with a power wire; the grid of the third transistor is connected with a light-emitting control wire; the grid of the fourth transistor is connected with a second scanning control wire; and the source of the fourth transistor is connected with a reference potential. According to the driving circuit and method, the OLED works in an alternating-current driving mode, so that the characteristics of the OLED are recovered from degeneration state, the service life of the OLED is prolonged effectively, the threshold voltage drift of a thin film transistor and the degeneration of OLED cut-in voltage can be compensated effectively, and the uniformity of a display picture is enhanced.

Description

The active organic LED display exchanges pixel-driving circuit and driving method

Technical field

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

Background technology

Active matrix organic light emitting diode display (Active-Matrix Organic Light Emitting Diode:AMOLED) have volume little, simple in structure, from main light emission, brightness height, advantage such as visible angle is big, the response time is short, attracted to note widely.

At present, be applied to the thin film transistor (TFT) that AMOLED shows and mainly contain amorphous silicon film transistor (a-Si:H TFT) and polycrystalline SiTFT (Poly-Si TFT).Yet because the metastability of amorphous silicon material, serious drift takes place because of the effect of electric stress in the threshold voltage of a-Si:H TFTs in time.Because the stochastic distribution of grain boundary on the polycrystalline silicon material, the threshold voltage of Poly-Si TFTs skewness between pixel causes the viewing area GTG inhomogeneous.Become the problem that popular Zinc oxide-base TFT of research and organic tft also have similar threshold voltage shift gradually.Therefore, traditional electric capacity of two transistors (2T1C) image element circuit structure is not suitable for high-quality AMOLED demonstration.In addition, also need consider the performance degradation of OLED, the degeneration of OLED can cause the rising of self cut-in voltage, thereby causes the decline of brightness of display screen.The performance degradation of OLED can specifically be expressed as: one from electrology characteristic, and the electric current that the OLED two ends identical voltage source of loading is crossed OLED reduces; Two on optical characteristics, and OLED flows through the same galvanoluminescence brightness and descends.After the OLED device prepared, device architecture, organic material, electrode material and preparation technology determined that type of drive will produce material impact, the mission life of selecting good type of drive to help to prolong OLED to the reliably working of OLED.Many documents (as: 1.S.A.Van Slyke, C.H.Chen and C.W.Tang, Appl.Phys.Lett., 69 (15), Oct.1996:2160-2162 are arranged; 2.D.Zou, M.Yahiro and T.Tsutsui, Jpn.J.Appl.Phys., Vol.37 (1998): L1406-L1408; 3.D.Zou, M.Yahiro and T.Tsutsui, Appl.Phys.Lett., 72 (19), point out that May 1998:2484-2486.) pulse drive mode that comprises a reverse bias component can effectively improve the mission life of OLED, the AC driving mode of Here it is OLED.The reverse bias of OLED can reduce the electric charge accumulation of organic layer among the OLED, helps OLED to recover from degenerate, and can improve the I-E characteristic of OLED and improves energy utilization efficiency, but can not influence quantum efficiency.

At present, thus most AMOLED pixel circuit design or the AC driving that realizes OLED improves its mission life with the performance degradation that delays OLED, but fail to compensate TFT threshold voltage shift and OLED performance degradation; Realize compensation TFT threshold voltage shift and OLED performance degradation, but the AC driving of the OLED of being unrealized.The above analysis, a more satisfactory image element circuit topology is to comprise realization compensation TFT threshold voltage shift and OLED performance degradation on the AC driving mode basis of OLED.

Summary of the invention

The objective of the invention is to overcome the shortcoming and defect of above-mentioned prior art, provide active organic light emitting diode display to exchange pixel-driving circuit and driving method.The present invention exchanges pixel-driving circuit can promote Organic Light Emitting Diode recovery characteristics from degenerate, effectively improve the mission life of Organic Light Emitting Diode, and effectively compensate the degeneration of the threshold voltage shift and the light emitting diode cut-in voltage of driving transistors in the active organic LED display, thereby improve the homogeneity of light emitting diode indicator luminosity greatly.

Purpose of the present invention realizes by following proposal:

The active organic LED display exchanges pixel-driving circuit, and described driving circuit comprises: the first transistor, transistor seconds, the 3rd transistor, the 4th transistor, light emitting diode; These transistors are any one in polycrystalline SiTFT, amorphous silicon film transistor, Zinc oxide based film transistor or the OTFT.

The drain electrode of described the first transistor connects data line, and grid connects the first scan control line, and source electrode connects the A end of memory capacitance, and described the first transistor provides path for data voltage is written to the grid of transistor seconds and is stored in memory capacitance;

Described transistor seconds drain electrode connects the 3rd transistorized source electrode, grid connects the A end of memory capacitance, source electrode connects the B end of the 4th transistor drain and memory capacitance, and links to each other with ground by Organic Light Emitting Diode, and it is luminous that described transistor seconds drives Organic Light Emitting Diode;

Described the 3rd transistor drain connects power lead, grid sending and receiving photocontrol line, and described the 3rd transistor provides the charging path and the luminous path that provides of driving Organic Light Emitting Diode is provided for the storage of transistor seconds threshold voltage;

Described the 4th transistor gate connects the second scan control line, source electrode connects reference potential, described the 4th transistor provides the OLED discharge path makes B point potential drop to reference potential, impel the Organic Light Emitting Diode both end voltage reverse, and avoid Organic Light Emitting Diode luminous in the characteristic recovery stage.

Above-mentioned active organic LED display exchanges the driving method of pixel-driving circuit, comprises the following steps:

(1) characteristic is recovered the stage: the first scan control line, AC driving control line are in high level, the light emitting control line is in low level, data line is changed to the earth potential level, the first transistor and the 4th transistor turns, the 3rd transistor turn-offs, A point current potential is reset by the first transistor and is the earth potential level, and the discharge of anode charge stored equates with reference potential until its current potential; At this moment cathode potential is greater than anode potential, and the Organic Light Emitting Diode two ends are realized reverse bias and made Organic Light Emitting Diode be in the characteristic recovery stage thus, thereby realizes the AC driving of active organic LED pixel.In this stage, the 3rd transistor is in off state and causes transistor seconds can not flow through electric current, thereby can not influence the discharge of Organic Light Emitting Diode anode.

(2) threshold voltage memory phase: the first scan control line keeps original high level, the AC driving control line skips to low level, the light emitting control line skips to high level, data line and A point current potential are maintained the earth potential level, the first transistor and the 3rd transistor are in conducting state, the 4th transistor is in off state, power supply charges to Organic Light Emitting Diode anode B point by the 3rd transistor, transistor seconds and ends up to transistor seconds, at this moment, the memory capacitance both end voltage is the threshold voltage of transistor seconds.

(3) data voltage write phase: the first scan control line is a high level, AC driving control line and light emitting control line are low level, the first transistor is in conducting state, the 3rd transistor and the 4th transistor are in off state, and data voltage is written to the grid of transistor seconds and is retained to next frame by memory capacitance by the first transistor and upgrades.

(4) glow phase: the first scan control line, AC driving control line are low level, the light emitting control line is a high level, the first transistor and the 4th transistor are in off state, the 3rd transistor is in conducting state, it is luminous that transistor seconds drives Organic Light Emitting Diode, the gate source voltage of glow phase transistor seconds remains unchanged, thereby it is constant up to the next frame image refreshing to keep Organic Light Emitting Diode brightness in a frame time.

The present invention compared with prior art, advantage and effect are: the interchange pixel-driving circuit of the active organic LED display that the present invention proposes, when realizing the active organic LED AC driving, also effectively compensation transistor threshold voltage shift and Organic Light Emitting Diode cut-in voltage are degenerated, thereby improve the display frame brightness uniformity and the mission life thereof of active organic LED display.

Description of drawings

Fig. 1 is the interchange pixel-driving circuit figure of active organic LED display of the present invention;

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

Wherein: the first transistor T1, transistor seconds T2, the 3rd transistor T 3, the 4th transistor T 4, memory capacitance Cs, the first scan control line Vscan1, AC driving control line Vscan2, light emitting control line Vems, reference potential line Vref, power lead Vdd, ground wire Vss, data line Vdata, Organic Light Emitting Diode OLED.

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 interchange pixel-driving circuit figure of active organic LED display of the present invention comprises the first transistor T1, transistor seconds T2, the 3rd transistor T 3, the 4th transistor T 4, memory capacitance Cs, the first scan control line Vscan1, AC driving control line Vscan2, light emitting control line Vems, power lead Vdd, ground wire Vss, reference potential line Vref, data line Vdata, Organic Light Emitting Diode OLED (following only represent with OLED).Above-mentioned these transistors can adopt any one in polycrystalline SiTFT, amorphous silicon film transistor, Zinc oxide based film transistor or the OTFT.

The drain electrode of described the first transistor T1 meets data line Vdata, and grid meets the first scan control line Vscan1, and source electrode connects the A end of memory capacitance Cs, and described the first transistor T1 provides path for data voltage is written to the grid of transistor seconds T2 and is stored in Cs;

Described transistor seconds T2 drain electrode connects the source electrode of the 3rd transistor T 3, and grid connects the A end of memory capacitance Cs, and source electrode connects the drain electrode of the 4th transistor T 4 and the B end of memory capacitance, and links to each other with ground by OLED, and described transistor seconds T2 driving OLED is luminous;

Described the 3rd transistor T 3 drain electrode meets power lead Vdd, and grid sending and receiving photocontrol line Vems, described the 3rd transistor T 3 provide the charging path for the storage of transistor seconds T2 threshold voltage and path is provided for driving OLED is luminous;

Described the 4th transistor T 4 grids meet AC driving control line Vscan2, and source electrode meets reference potential Vref, and described the 4th transistor T 4 provides the OLED discharge path to make B point potential drop to reference potential Vref, and avoid OLED luminous in the characteristic recovery stage.

During pixel-driving circuit work, the first transistor T1, the 3rd transistor T 3 and the 4th transistor T 4 all work in linear zone, and the transistor seconds T2 that plays driving action is operated in the saturation region.The input timing of each signal wire as shown in Figure 2.This pixel-driving circuit step is by the following method realized:

(1) recovers the stage in characteristic, the first scan control line Vscan1, AC driving control line Vscan2 are in high level, light emitting control line Vems is in low level, data line is changed to earth potential level Vss, the first transistor T1 and 4 conductings of the 4th transistor T, the 3rd transistor T 3 turn-offs, and A point current potential is reset by the first transistor T1 and is Vss, and the discharge of OLED anode charge stored equates with reference potential Vref until its current potential; At this moment the cathode potential Vss of OLED is greater than anode potential Vref, and the OLED two ends are realized reverse bias and made OLED be in the characteristic recovery stage thus, thereby realizes the AC driving of active OLED pixel.Notice that in this stage, the 3rd transistor T 3 is in off state and causes transistor seconds T2 can not flow through electric current, thereby can not influence the discharge of OLED anode.

(2) at the threshold voltage memory phase, the first scan control line Vscan1 keeps original high level, AC driving control line Vscan2 skips to low level, light emitting control line Vems skips to high level, data line and A point current potential are maintained earth potential level Vss, the first transistor T1 and the 3rd transistor T 3 are in conducting state, the 4th transistor T 4 is in off state, power supply Vdd is by the 3rd transistor T 3, transistor seconds T2 charges to OLED anode B point and ends up to transistor seconds T2, at this moment, B point potential value deducts the threshold voltage V of transistor seconds T2 for the earth potential level _Th, i.e. V _B=-V _Th, then memory capacitance Cs both end voltage is the threshold voltage of transistor seconds T2.

(3) in the data voltage write phase, the first scan control line Vscan1 is a high level, AC driving control line Vscan2 and light emitting control line Vems are low level, the first transistor T1 is in conducting state, the 3rd transistor T 3 and the 4th transistor T 4 are in off state, and data voltage Vdata is written to the grid of transistor seconds T2 and is retained to next frame by memory capacitance Cs by the first transistor T1 and upgrades; At this moment be according to capacitance coupling effect B point current potential $V_B=-V_{\mathrm{th}}+\frac{C_S}{C_{\mathrm{OLED}}+C_S}{V}_{\mathrm{data}},$ C wherein _OLEDBe OLED self electric capacity when not luminous.

(4) in glow phase, the first scan control line Vscan1, AC driving control line Vscan2 are low level, light emitting control line Vems is a high level, the first transistor T1 and the 4th transistor T 4 are in off state, the 3rd transistor T 3 is in conducting state, the transistor seconds driving OLED is luminous, and the gate source voltage of glow phase transistor seconds T2 remains unchanged, thereby it is constant up to the next frame image refreshing to keep OLED brightness in a frame time.

The storage of above-mentioned steps (2) transistor seconds threshold voltage is by charging ends up to transistor seconds T2 to OLED, memory capacitance Cs two ends storage voltage is the threshold voltage of transistor seconds T2, in the data voltage write phase, this pixel-driving circuit has utilized the big electric capacity of OLED self and has made the terminal potential variation of transistor seconds T2 source less, can reduce the number that adds electric capacity, save wiring space.

In pixel-driving circuit of the present invention, each pixel threshold voltage V _ThHeterogeneity or drift 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, its memory capacitance Cs both end voltage (being the gate source voltage of transistor seconds T2) is fixed on $V_{\mathrm{gs}}=V_{\mathrm{data}}-({-V}_{\mathrm{th}}+\frac{C_S}{C_{\mathrm{OLED}}+C_S}{V}_{\mathrm{data}})=V_{\mathrm{th}}+\frac{C_{\mathrm{OLED}}}{C_{\mathrm{OLED}}+C_S}{V}_{\mathrm{data}}$ (V _Data＞0), and remain to next frame.For the different pixels point, the otherness of threshold voltage can cause the voltage difference at memory capacitance Cs two ends, but it is identical can deriving the electric current that flows through OLED by following formula:

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

$=\mathrm{\β}{(V_{\mathrm{th}}+\frac{C_{\mathrm{OLED}}}{C_{\mathrm{OLED}}+C_S}{V}_{\mathrm{data}}-V_{\mathrm{th}})}^2$

$=\mathrm{\β}{\left(\frac{C_{\mathrm{OLED}}}{C_{\mathrm{OLED}}+C_S}{V}_{\mathrm{data}}\right)}^2$

Wherein

I _OLEDFor 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 and V _ThAnd the forward voltage of OLED is irrelevant.In the formula, μ _nBe electron mobility; C _OXThin film transistor (TFT) capacitive dielectric layer for unit area; L and W are respectively length of effective channel and the width of transistor seconds T2; V _ThThreshold voltage for transistor seconds T2; V _GsThe gate source voltage of transistor seconds T2.

It is pointed out that the storage of desiring successfully to realize threshold voltage, must satisfy-V at the threshold voltage memory phase _Ref＞V _ThDesire to make image element circuit not luminous at non-glow phase OLED, the OLED both end voltage need be lower than its cut-in voltage, so only need to satisfy $-V_{\mathrm{th}}+\frac{C_S}{C_{\mathrm{OLED}}+C_S}{V}_{\mathrm{data}}<V_{\mathrm{OLED}\_\mathrm{th}},$ V _{OLED_th}It is the cut-in voltage of OLED.Like this, non-glow phase pixel can be realized complete black, thereby has improved the contrast of display greatly.No matter micromolecule light emitting diode or polymer LED, the unit-area capacitance of himself is about 25nF/cm ², for a typical 200um*100um light-emitting area, its capacitance is about 5pF.And the Cs capacitance is generally less than 1pF.In the data voltage write phase, this pixel-driving circuit has utilized the big electric capacity of OLED self and has made B point potential change less, and therefore above-mentioned condition is easy to satisfy.

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 (3)

1. the interchange pixel-driving circuit of active organic LED display, this driving circuit comprises:

The first transistor, transistor seconds, the 3rd transistor, the 4th transistor, memory capacitance, the first scan control line, AC driving control line, light emitting control line, power lead, ground wire, reference potential line, data line, Organic Light Emitting Diode;

The drain electrode of described the first transistor connects data line, and grid connects the first scan control line, and source electrode connects the A end of memory capacitance, and described the first transistor provides path for data voltage is written to the grid of transistor seconds and is stored in memory capacitance;

Described transistor seconds drain electrode connects the 3rd transistorized source electrode, grid connects the A end of memory capacitance, source electrode connects the B end of the 4th transistor drain and memory capacitance, and links to each other with ground by Organic Light Emitting Diode, and it is luminous that described transistor seconds drives Organic Light Emitting Diode;

Described the 3rd transistor drain connects power lead, grid sending and receiving photocontrol line, and described the 3rd transistor provides the charging path and the luminous path that provides of driving Organic Light Emitting Diode is provided for the storage of transistor seconds threshold voltage;

Described the 4th transistor gate connects the AC driving control line, and source electrode connects reference potential, and described the 4th transistor provides discharge path to make B point potential drop to reference potential, and avoids luminous in the characteristic recovery stage.

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

3. according to the driving method of the interchange pixel-driving circuit of the described active organic LED display of claim 1 to 2, it is characterized in that, comprise the following steps:

(1) characteristic is recovered the stage: the first scan control line, AC driving control line are in high level, the light emitting control line is in low level, data line is changed to the earth potential level, the first transistor and the 4th transistor turns, the 3rd transistor turn-offs, A point current potential is reset by the first transistor and is earth potential, and the discharge of Organic Light Emitting Diode anode charge stored equates with reference potential until its current potential; At this moment the cathode potential of Organic Light Emitting Diode is greater than anode potential, and the Organic Light Emitting Diode two ends are realized reverse bias and made Organic Light Emitting Diode be in the characteristic recovery stage thus, realize the AC driving of active organic LED pixel; In this stage, the 3rd transistor is in off state and causes transistor seconds can not flow through electric current, can not influence the discharge of OLED anode;

(2) threshold voltage memory phase: the first scan control line keeps original high level, the AC driving control line skips to low level, the light emitting control line skips to high level, data line and A point current potential are maintained the earth potential level, the first transistor and the 3rd transistor are in conducting state, the 4th transistor is in off state, power supply charges and ends up to transistor seconds by the 3rd transistor, transistor seconds antianode B point, at this moment, the memory capacitance both end voltage is the threshold voltage of transistor seconds;

(3) data voltage write phase: the first scan control line is a high level, AC driving control line and light emitting control line are low level, the first transistor is in conducting state, the 3rd transistor and the 4th transistor are in off state, and data voltage is written to the grid of transistor seconds and is retained to next frame by memory capacitance by the first transistor and upgrades;

(4) glow phase: the first scan control line, AC driving control line are low level, the light emitting control line is a high level, the first transistor and the 4th transistor are in off state, the 3rd transistor is in conducting state, it is luminous that transistor seconds drives Organic Light Emitting Diode, the gate source voltage of glow phase transistor seconds remains unchanged, thereby it is constant up to the next frame image refreshing to keep Organic Light Emitting Diode brightness in a frame time.

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