TWI249721B - Circuit and method for driving pixels of an organic light emitting display - Google Patents

Abstract

A circuit and a method for driving pixels of an organic light-emitting display are provided. The circuit comprises a thin-film transistor having a source terminal connected to a voltage source, a storage capacitor having a first terminal connected to a gate terminal of the thin-film transistor, and an organic light-emitting diode having a cathode connected to a ground. When the circuit is in a clamping phase, the gate terminal of the thin-film transistor is connected to a drain terminal of the thin-film transistor and a second terminal of the storage capacitor is connected to the ground. When the circuit is in a light-emitting phase, the second terminal of the storage capacitor is connected to a data line and an anode of the organic light-emitting diode is connected to the drain terminal of the thin-film transistor. When the circuit is in a reverse phase, the gate terminal of the thin-film transistor is connected to the drain terminal of the thin-film transistor, the second terminal of the storage capacitor is connected to the data line, and the anode of the organic light-emitting diode is connected to the drain terminal of the thin-film transistor.

Description

15897twf.doc/g

BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to a driving circuit and method for an organic light emitting display, and more particularly to a pixel driving circuit and method for an organic light emitting display. [Prior Art] An organic light emitting display using an organic light emitting diode has a problem of spontaneous high brightness, high contrast, wide viewing angle, and fast response speed. The unit is dedicated to the study of its characteristics and drive circuits. Although the organic light emitting display has the above advantages, there are still some problems to be solved. Fig. 1 is a basic driving circuit for driving an organic light emitting diode OLED constituting a pixel of an organic light emitting display. The circuit of FIG. i is a thin film transistor (brain _^ transistor 'bright for short) connected to a scan line SL. When the T2 is turned on, the data is stored in the storage valley Cs and then stored on the storage valley cs. The storage voltage determines the current through the thin film transistor T1&, which in turn determines the brightness of the organic light emitting diode OLED itself. Although this circuit is simple, it will face problems such as the drift of the gate voltage (10)^ voltage and the material lifetime of the organic light-emitting diode. The known gate voltage drift 'is the change of the gate voltage process and time of the drive switch, and thus affects the pass of the organic light-emitting diode. In this way, even if the pixels receive the same data signal, the degree of exemption will not be uniform. In response to this problem, Η. κ__ et al. 1249721 15897twf.doc/g proposed the driving circuit shown in Figure 2 in the paper "A 2.5_inch OLED Display with a Three-TFT Pixel Circuit for Clamped Inverter Driving" published in SID2004. . The circuit of FIG. 2 is a cuamping of the storage cell Cs by the thin film transistors T2 and T3, and the threshold voltage of the thin film transistor T1 (ie, vDD_Vth, where vth is the threshold voltage of the thin film transistor T1) ) Stored in the storage capacitor Cs. Thus, in the applied electric field period of the organic light emitting diode OLED (that is, the daylighting time), the voltage stored in the storage capacitor Cs can cancel the threshold voltage of the driving switch T1, thereby solving the brightness due to the threshold voltage drift. The problem of unevenness. In the material life part of the organic light-emitting diode, Dechun Zou et al. in the Japanese Journal 〇f Applied physics, v〇1 37, 卯1406 LI408, 1998 paper "impr〇vement 〇f Current-Voltage Characteristics in Organic Light Emitting Diodes by Application of Reversed_Bias v〇ltage, mentioned that polarization occurs in the applied electric field of the organic light-emitting diode. Please refer to FIG. 1 and FIG. 4. FIG. 3 shows the absence of the organic light-emitting diode. When the electric field is 扦 (that is, when it is not illuminating), the internal impurity ions are unevenly dispersed, and FIG. 4 shows the state of the applied electric field. When the galvanic period is applied, the organic illuminating diode is connected. The applied electric field E of the body will have the effect of separating the positive and negative charges of the internal = impurity ions, and thus has the internal reverse electric material generated against the externally added ,E, which is the polarization phenomenon. The polarization will not only shorten the organic light emission The material life of the polar body will reduce the circulation; the organic light-electron hole mobility of the polar body will cause the luminous efficiency to decrease. 6 1249721 15897twf.doc/g Phenomenon, Si Yujuan et al., IEEE Transactions on

Electron Devices, vol. 50, issue 4, ρρ· 1137-1141, April 2003 The paper "A Simple and Effective AC Pixel Driving Circuit for Active Matrix OLED" proposes a circuit as shown in Figure 5. The circuit of Figure 5 switches between 0V and a high potential with a voltage source.

The organic light emitting diode OLED can have a period of reverse bias. This reverse bias can push the separated positive and negative impurity ions in the opposite direction to eliminate the polarization phenomenon, thereby increasing the material lifetime of the organic light-emitting diode and the mobility of the internal electron hole, and the luminous efficiency naturally increases. It can be seen from the above description that the current technology can only solve the phenomenon of gate-sand voltage drift and polarization, and there is no technology to balance the two. The object of the present invention is to solve both problems at the same time. SUMMARY OF THE INVENTION The purpose of the present invention is to provide an organic light-emitting display pixel drive = two: organic light-emitting diode material: life = Ming's other purpose is to provide "organic light-emitting display" + =; = 2 = _ Following the level action indicator ΐ ί · ί ΐ 'the invention proposed - an organic luminescence - organic hair: two, a thin film transistor, a storage capacitor, with a DC voltage source == = electricity ^ The source (--) is connected to - the younger end of Shibuya is connected to the thin film transistor _ 7

Medium 12497 benefits - (gate), the cathode of the organic light-emitting diode (cath〇de) is connected to a ground. Wherein, when the OLED driving circuit of the OLED display is in a clamping stage, the gate of the thin film transistor is connected to the drain. The second end of the storage capacitor is connected to the ground. When the above organic light emission is displayed as a pixel driving circuit in a light emitting phase, the two ends of the storage capacitor are connected to a data line, and the anode of the organic light emitting diode is connected to the drain of the thin film transistor. . Finally, when the organic light-emitting display element driving circuit is in a reverse phase, the thin film transistor=gate is connected to the drain, and the second end of the storage capacitor is connected to the anode of the light-emitting diode of the data line machine. The drain of a thin film transistor. In an embodiment, when the illuminating circuit of the OLED display is in the illuminating stage, a data voltage is received from the data line, and the voltage is “computed by the data voltage and the reference voltage (4) of the film transistor ^ The above-mentioned organic light emitting display pixel driving circuit has a triangular wave voltage every reference voltage. The above-mentioned organic light emitting device halogen driving circuit receives a negative voltage from the data line at a power. - μ know from another point of view 'The present invention further proposes an organic light-emitting display denier driving method' which is characterized in that the gate-voltage voltage of the thin film transistor is stored before the device connected to the _scan line is turned on. For capacitors. In the above method for driving an organic light-emitting display, the above-mentioned thin film transistor drives an organic light-emitting diode. 8 1249721 15897twf.doc/g The above-mentioned organic light-emitting display halogen driving method includes, in one implementation, a conduction time of a data voltage and a reference voltage, and also >. The above-mentioned organic light-emitting display pixel driving method of the shoulder-and-metal film is further included in the above-mentioned organic light-emitting diode without an applied electric field plus a reverse bias to the above-mentioned organic light-emitting diode body. / The invention stores the threshold voltage of the driving switch in the storage emperor to cancel the threshold voltage of the driving switch itself, and the brightness is uneven. At the same time, the invention also benefits: reverse bias and increase the mobility of electron holes. In addition, the present invention completes the driving and closing of the door (4) clamping action, and does not require the postal organic body to apply the electric field. The reduced relaxation is controlled by __ to make the above and other objects, features and advantages of the present invention more obvious. The preferred embodiments of the present invention are described in detail below and are described in detail below. "Illustration" [Embodiment] An organic light-emitting display device that drives an embodiment of the present invention

Ql~Q5, storage ° — _ transistor crystal cavity life day electric valley Cs, and organic light-emitting diode 〇 LED. And ΪΓ ΪΓ ΓΓ ΓΓ ΓΓ 接 接 接 接 接 接 接 接 接 接 接 接 接 接 接 接 接 接 接 接 接 接 接 接 接 接 接 接 接 接 接 接 接 接 接 接 接 接 接 接 接 接 接 接 接 接 阴极 阴极 阴极 阴极 阴极 阴极 阴极 阴极Turning on or off the second end of the storage capacitor Cs and the data line DL·. The thin film electrical aa body Q3 is connected between the gate and the drain of the thin film transistor. The thin film capacitor Q4 is connected between the second end of the storage capacitor CS and the ground line GND. The thin film transistor Q5 is connected between the drain of the thin film transistor Qi and the anode of the organic light emitting diode OLED. In this embodiment, ^ is also referred to as a drive switch. The LED is driven by Qi. A two-example drive circuit is continuously circulated in three phases of operation, which are the clamp phase, the illumination phase, and the reverse phase. Fig. 7 is a diagram showing the evolution of the voltage of the driving switch ^ in the three operating phases among the driving circuits of the embodiment. For details, see the following description. At the otT stage, the thin film transistors Ql, Q3, and Q4 are turned on, and the volume of the film transistor Qi is connected to the drain, and the memory is connected to the ground and the line GND. The conduction state is as shown in FIG. When the real 8^5, ° ^ drive switch Ql can be equivalent to - diode, and ^ / on the diagram is the equivalent circuit as shown in Figure 9. The voltage across the diode Q1 is the thin film transistor Q; the storage capacitor Cw (five) Vth, and connected to the electric house of the two knows, sink is the gate surface VG of (VDD_Vth) Q!, as shown in Fig. 7 Electric Japanese 曰 曰 因子 v v v v v v v v v v v v v v v v At this point, the kneading capacitor ΓΓ position has been completed, that is, when the gate is pinched, “the memory transistor Qi, Q2, Q5 is turned on, and the Q film Q4 is turned off, so that the storage capacitor Cs Y is Q3 organic light-emitting diode 硖 orpn A spoon is connected to the lean line Dl, the pole, the conductive anode is connected to the thin film transistor Qi is not high, as shown in the solid line of Figure 〖. This stage will = 1249721 15897twf.doc/g

The line DL feeds the data voltage Vdata and the reference voltage Vsweep, so that the gate voltage ▽(} rises to (乂1^-%11+¥(^+%_13), as shown in Fig. 7. The conduction condition of the drive switch Qi is VDD-VG &gt; Vth, that is, vDiHVDD_vth+vdata+vsweep) &gt; vth ' After finishing, the conduction condition of the drive switch a can be obtained, that is, the illumination condition of the mechanical light-emitting diode 〇LED is (vdata+vsweep)&lt; 0. It is worth noting that there is no gated voltage Vth in the last conditional inequality. This is caused by the clamping action of the bribe and the voltage of the gated voltage vth in the axis closing Ql. The influence of the threshold voltage vth drift. The above 5 brothers can know - (4) the conduction time of the electro-moisturizing body Qi, also, the illuminating time of the organic light-emitting diode 〇LED, which is the voltage of the material f as shown in Fig. 7 In this embodiment: 2:=data is straight' and the reference voltage u is fixed to the triangular wave of the waveform. When (Vdata+Vsweep)<G is satisfied, v is vDD-Vth, so τ〇η of FIG. 7 is organic light emission. 2 ^ illuminating time. In this embodiment, the moxibuster + bD ΛΛ „ person, / 芩 test voltage Vsweep waveform is solid Therefore, different Vdata will be sent according to different data, and the brightness of the organic light-emitting diode (LED) will be controlled by the hair-emitting diode (10)d. B on 'In the reverse stage, The thin film transistors Qf, Q and Q4 are turned off, so that the inter-electrode of the first-Q1 of the thin-film engraving A k η V5 ¥C C is connected to the bungee, and the younger brother who stores the electric connection is connected to the data line DL. The secret of organic light-emitting diode is connected to the finite electrode of the thin film transistor Q!, and the conduction state can be as shown in the solid line of u; the thin film; as shown in Fig. 11, the finder, the celestial moon, the Q3 V-pass, the drive switch Qi can be I2497?5J - the equivalent of -n and the implementation of the _ crane circuit can be equivalent to the circuit shown in Figure 12. This stage will send negative ς _vH from the data line DL, so that the gate voltage vG falls to VDD_Vth_VH, As shown in Figure 7, ^ ί ί Γ &lt;?! 5 Vh &gt; v〇D'Vth 5 W VG &lt; G 'This provides an organic light-emitting two-domain QLED bias to eliminate polarization. As shown in FIG. 7 'When the gate voltage % of the driving switch Q1 falls vDD-vth-vH, it will rise as the storage capacitor Cs is charged, and the drain voltage VG rises to 0V. The organic light-emitting diodes have a luminescence. In order to avoid this problem, the current implementation _ simple circuit must be in the clamp phase before the gate voltage VG returns to the GV, and then there are two before the clamp phase. She temporarily converted the steps. The first is to turn off the film transistor Q2, remove the negative voltage _Vh, the conduction state at this time is shown in the line of the line of the end of the line, and then the film transistor Q4 is turned on, at this time the second Figure 14 The solid line section is shown. At this time, the gate voltage Vg will rise to the high point indicated as VP in Figure 1, so that the drive switch Q ι will be turned off due to the reverse bias of the ink, and the organic light-emitting diode OLED will provide a discharge path to store the rain six.

Cs discharge. Although the organic light-emitting diode OLED will illuminate, because = too short will not affect the overall brightness. After the _-capacitor &amp; cross-voltage ^ VDD-Vth enables the drive switch to turn on, you can turn off the thin film Q5 and enter the clamp phase. The present invention also proposes a method for driving a halogen display of the organic light emitting display corresponding to the above embodiment. The main features of the method include: the thin film transistor before the thin film transistor a connected to the scan line SL is turned on. The gate of '12 I2497?5J-, the voltage Vth is stored in the storage power, the data voltage Vd and the reference power C vsweep jointly determine the on-time of the thin film transistor Qi, and the no-apple electric field period of the f-light emitting diode OLED Applying a reverse bias to the organic light emitting diode OLED. In the related art of the present invention, the general knowledge should be able to easily apply the driving method after referring to the driving circuit of the previous embodiment, and therefore will not be described.

As can be seen from the above embodiments, the present invention stores the threshold voltage of the driving switch in the storage capacitor and then cancels the self-phase in the on-state of the driving switch, thereby eliminating the uneven brightness caused by the threshold voltage drift. At the same time, the present invention also utilizes reverse bias to eliminate polarization, thereby increasing the material lifetime of the organic light-emitting body and increasing the mobility of the electron hole. In addition, the present invention can relax the time control of the thin film transistor because the clamping action of driving the threshold voltage of the switch is completed in advance without occupying the applied electric field period of the organic light emitting diode. It is to be understood that the present invention has been described above by way of a preferred embodiment, and is not intended to limit the scope of the present invention, and it may be possible to make some modifications and refinements without departing from the spirit of the invention. The instalment of the invention is to be determined by the scope defined in the appended claims. ^ [Simple Description of the Drawings] Figs. 1 and 2 are circuit diagrams of a prior art organic light emitting display. Figure 3 and Figure 4 are schematic diagrams showing the polarization phenomenon of an organic light-emitting diode. FIG. 5 is a prior art organic light emitting display pixel driving circuit @帝13 1249721 15897twfdoc/£ driving the organic light emitting display of the present invention - the organic light emitting display pixel of the present invention - the embodiment The drive switch gate voltage change diagram. A schematic diagram of the operation of the organic light-emitting display pixel of the present invention-embodiment. The organic light-emitting display of the invention-embodiment is driven by the organic light-emitting display of the invention-embodiment.示示哭二 Figure 14 is a schematic diagram of an organic light-emitting display according to an embodiment of the present invention.

Cref : Capacitor Cs : Storage Capacitor DL : Data Line E : Electric Field GND : Ground Line HD : ! Machine Light Emitting Dipole Ql~Q5 : Bound Film Transistor R: Reverse Electric Field SL : Scan Line I249H/g T1~T3 : Thin film transistor T〇n : on-time voltage signal

Vdata, Vh, Vp, Vsweep ·

Vdd · DC voltage source Vref : Voltage source Vth : Threshold voltage

15

Claims (1)

I249m 7twf.doc/g, the scope of application for patents: - an organic light-emitting display II halogen drive circuit, comprising: a germanium film transistor, the source is connected to a voltage source; a gate of the transistor is - a storage capacitor, The H terminal is connected to the same, and the organic light emitting diode has a cathode grounded; wherein the pole, in its stage, the gate of the (4) film transistor is connected to a second end of the storage capacitor of the No. 1 cloud; The said money capacity (four) two materials - data = several hair first - polar body - anode connected to the thin pole of the thin film transistor; the storage;;:, b segment 'the thin film transistor's pole connection bungee, Driving the int: the organic light-emitting display pixel receiving unit of the first item of the range 1 is disposed between the gate and the drain of the thin film transistor, and the signal of the line is drawn, and the second end of the open storage capacitor is The OLED switch device according to the second aspect of the present invention, wherein the light-emitting phase and the reverse phase turn on the first switch of the organic light-emitting _ 16 c/gc/g according to the first item of the driving range a device connected to the second end of the storage capacitor and 5. The OLED display driving circuit of claim 4, wherein the first switching device is turned on during the clamping phase. 6. The OLED display driving circuit of claim 5, further comprising: a second switching device that turns on or off the second end of the storage capacitor according to a signal received from a scan line. The data line. The OLED display circuit of the OLED display of claim 6, wherein the switching device is turned on when the illuminating phase and the reverse phase are performed. - the cylinder 8 of the organic light-emitting display as shown in claim 7, wherein when the reverse phase enters the clamping phase, the second switch is first turned off, and then the first is turned on - Switching device. Driving =12_The organic light-emitting display of the organic light-emitting display as described in item 1 = 2 of the organic light-emitting display according to the lion's illuminating device of the thin film transistor Turning off: the road 'in the light-emitting phase and the reverse phase, turning on the organic light-emitting display material according to claim 1 of the patent scope: factory: road: i in the light-emitting phase, by the data line Receive - Power [with 1 test voltage, which together determine the turn-on of the thin film transistor between 17 1249 721 5 97twf.doc / g. 12. The OLED display of the OLED display of claim 11, wherein the reference voltage is a triangular wave voltage. 13. The OLED display driving circuit of claim 1, wherein the data line receives the voltage during the reverse phase. ,, 'Bei The organic light-emitting display booklet % dynamic circuit of claim 1, wherein the clamping phase, the lighting phase, and the second phase are sequentially operated. &quot;&quot; I I5························································ Rail ^ If you want to use the organic light-emitting method described in Item 15, which uses the thin-film transistor to drive - organic light-emitting ς Su ΐ · · · · · · · · · 昼 昼 昼 昼 昼 昼 昼 昼 昼 昼 昼 昼 昼 昼The 苓 voltage determines the thin 暝 transistor 18· as in the patented method driving method, and further includes: the organic light emitting display described by the 昼, the organic light emitting diode + the organic light emitting diode. ..., 0 electric field, applying a reverse bias 18