TW200811813A - Driving circuit of organic light emitting diodes and driving method therefor - Google Patents

Abstract

This invention relates to a driving circuit of organic light emitting diodes and a driving method therefor. The driving circuit has a switching transistor, a driving transistor, a storage capacitor, and an organic light emitting diode; a source/drain controlling transistor is connected to a source/drain driving transistor, and the controlling transistor is controlled by a scanning line. Within a frame time, the voltage source is at low level during the scanning and at high level otherwise. During the scanning, the voltage source may store the image data in the storage capacitor by the controlling transistor; when the voltage changes from a low level to a high level, a power impulse is fed into the parasitic capacitor of the driving transistor so as to compensate the time stability of the current supplied thereby and to prolong the durability of the display panel.

Description

200811813 IX. Description of the invention: [Technical field of invention] A technique for an organic electroluminescent display, in particular, a driving technique for an active unit halogen organic electroluminescent diode, which stably supplies current and extends the display panel The time of use. [Prior Art]

Organic Light-Emitting Diodes (OLEDs) can be classified into passive 〇LEDs (PM0LEDs) and active OLEDs (Active Matrix OLEDs; AMOLEDs) according to the driving method. QLED does not drive to very high brightness' to achieve better life performance and high resolution requirements. Therefore, 'OLED combined with thin film transistor (TFT) to achieve active drive OLED technology' can meet the requirements for the smoothness of the face-to-face playback in the market, and the increasingly high resolution requirements, fully demonstrate the superiority of 0LED above characteristic. Due to the continuous improvement of the luminescent efficiency of the OLED material, an amorphous = film transistor (a_Si TFT) device is used as a platform for driving the 〇 (4). In addition, the process of the a-Sl TFT is relatively close to the device, which can provide a lower manufacturing cost and greatly reduce the cost of the main. TFT W & TFT has the absolute advantage of low cost, but if you want to put a-Si on it, there are still technical problems to be overcome.

"There is a goal to be achieved: one is to improve a_siTF - 'two is to increase (4) the current drive of the component = 200811813 (Capability). The traditional drive circuit technology such as "the first unit of the unit's unit drive circuit sound HQ" = the traditional 2T1C (2 TFTs). The circuit structure of the mother's early position (heart 1) is the daily structure of the Japanese body. The switch and the electric body are all channels. N-Channel) a_Si TFTs, in which the driving transistor 12 is not connected to the $Ray ' ', one riding 3 is connected to the voltage source Vdd, and the source is connected to the organic light emitting body 14 Touch " Λ / 虿 machine t first pole 丨 4 cathode is coupled to the system s ~ say 'source access data signal vdata, the body u is not connected to the drive transistor η gate and reference The electric terminal, and the other end of the storage capacitor 13 is connected to the unit. The principle is as follows: after the scanning signal Vsean is used to control the switch crystal _vi/t, the data line representing the gray scale data of the data line is on the V data wheel. The gate of as + 12, one end of the storage capacitor 13 is used to control the driving transistor to be different and the driving transistor 12 is not Production will produce different gate at the gate voltage Vg, the source voltage Vgs (i.e., Vg -VS), the driving transistor size of the driving current 12 + 1D. In order to enable the driving transistor 12 to generate the driving voltage τα., D, the gate-source voltage Vgs of the driving transistor 12 must be 2; the threshold voltage value Vth of the transistor 12. When the unit _= and 4' unit pixel circuit is operated for a long time, there is a ": 9: the driving voltage VOLED of the egg body 14 will become larger with time, such as a decrease, and no. Therefore, it will cause The bias strip of the driving transistor 12 further reduces the output of the driving current ID, which indirectly causes a decrease in the amount of current flowing through the LED 118 having the 200811813, as shown in "Fig. 3". The relationship between the organic light-emitting diode 14 and the driving current Id can be expressed as iD^Kvgs-vth) 2 (1)

Ji^jkiVg- Vs - Vthf (7) L^KVg — V^-Vss-Vthf and VS = V0LED + WS (3) (4) where ' k is a characteristic constant of the thin film transistor, Vg=Vdata, and

The vOLED is a driving voltage across the organic light emitting diode 14. It can be seen from the above formula (4) that when the driving voltage v0LED becomes larger as it is turned on for a long time, the driving current 1〇 flowing through the organic light-emitting diode 14 becomes smaller, thereby affecting the organic light-emitting diode 14 The illuminating condition, the brightness is reduced, which affects the display quality. In addition, if the driving method is applied to the driving circuit composed of the a_Si TFT, when the driving transistor 12 is turned on for a long time, the voltage greater than zero will be continuously established on the gate-source voltage Vgs of the driving transistor 12. That is, for the driving transistor 12, the gate-source voltage VgS is always maintained at a positive bias, which causes deterioration of the characteristics of the a_Si TFT element, and the threshold voltage value vth of the driving transistor 12 cannot be maintained. Maintaining the original value and increasing with time 'generates a positive offset and cannot maintain a long-term stable current output, as shown in Figure 4. When the threshold voltage value is increased, the drive current V 流 flowing through the organic light-emitting diode is reduced, so that the organic light-emitting diode 14 cannot maintain the original brightness and affect the display quality. . In order to solve the above-mentioned shortcomings of the conventional unit pixel drive circuit, a drive circuit for a unit element is disclosed in US Pat. No. 7, 200811813, US Pat. No. 6,677,713, the circuit structure of which is to utilize two switch transistors (first switch transistor 21, second switch) The transistor 22), and a combination of a driving transistor 23 and a storage capacitor 24, serve as a combination of the driving organic light-emitting diodes 25, as shown in Fig. 5. The gate of the first switching transistor 21 receives a first scanning clock VScanA, and the gate of the second switching transistor 22 receives a second scanning clock VscanB, and the second switching transistor The U pole receives a low voltage Vref2. Moreover, the second scan clock VscanB has the same frequency as the first scan clock VscanA, but the second scan clock VscanB has a delay time Δτ (in one frame time) for the scan clock VscanA. As shown in Figure 6. The patent mainly adds a switching transistor and performs a negative Bias Annealing operation by means of signal control, so that the variation of the critical voltage value Vth characteristic of the driving transistor 23 can be improved. However, in the patented technology, when the second switching transistor 22 is added to improve the characteristics of the driving transistor 23, it is necessary to add a scanning signal line (VscanB) and a low voltage line (Vref2) to control the single pixel. The increase in the number of traces causes a decrease in the aperture ratio of the halogen, which degrades the display quality. In addition, the patent does not take into account the influence of the variation of the driving voltage vOLED of the organic light-emitting diode 25, and when the display time increases, the driving voltage becomes larger with time, thereby causing the driving current to decrease, and the luminance of the light is decreased. . Another 'US Patent No. 6,680,580 also discloses a unit circuit driving circuit, as shown in Figure 7, the circuit structure except the traditional structure of 200811813 off transistor 3, _ transistor 33 and library capacitors , plus one ^ electricity (five) body 32. The source voltage of the control transistor 32 is connected to the anode clock of the organic light-emitting diode 35, vsaL. When the transistor 32 __ is controlled, the scanning level is received. The voltage Vcom includes a high voltage level and a low voltage=', as shown in the figure, alternately with the frequency, and the hill uses ^ The high level of IC〇m is larger than the low potential VSS of the system, and the low quasi-i is smaller than the first low potential Vss. When the switching transistor 31 and the control transistor 2 break the scanning clock v earn (four) control _ start, the data signal ^ta can turn people - image data „ and — close g voltage one. Although the sharing voltage Vcom When it is at a low level, it turns off the negative voltage input, and turns off the driving transistor 33 and the organic light emitting diode %. ^This patent mainly uses the addition of a control transistor 32 to apply the voltage of the mound to the VC0m signal. The source of the driving transistor 33 is applied, thereby avoiding (four) = the gate source extreme voltage across the electro-transistor 33 and the driving voltage VOLED characteristic of the organic light-emitting diode %. The image time is also performed using a frame time = In the display of the material, the driving transistor 33 on all the panels is subjected to negative pressure tempering by using the next frame time to effectively suppress the variation of the threshold voltage value vth characteristic of the driving transistor ^. Although the influence of the characteristic change of the driving voltage ¥01^0 on the reliability of the pixel circuit is improved, when the source voltage Vs of the control transistor 32 is driven to the transistor 33 is not completely equal to the voltage of the hill, the main cause is the control transistor 32. No _ source Impedance problem between

9 200811813 Need to be considered. Since the current of the driving transistor 33 is now redirected to the control transistor 32, if the component size of the control transistor 32 is too small, the impedance problem becomes severe, that is, the source voltage Vs cannot be equal. The common voltage VC0ni. Moreover, the source voltage will vary when different currents flow through the control transistor 32. Although the component size of the control transistor 32 can be increased to solve the problem of the node Vs level, the aperture ratio of the pixel is lowered, and the luminance of the light is affected. Further, when this patent suppresses the variation of the threshold voltage value Vth of the driving transistor 33, it is necessary to perform negative pressure tempering using one frame time, and thus the brightness and quality of the display image are degraded. US 6,756,741 also uses a combination of three transistors and a storage capacitor to drive the organic light-emitting diode, as shown in Figure 9. The gate of the first switching transistor 41 and the second switching transistor 42 are simultaneously connected to the scanning signal Vscan; the first switching transistor 41 and the gate of the driving transistor 43 are connected to the voltage source vdd. The source of the first switching transistor 41 is connected to the gate of the driving transistor 43 and one end of the storage valley 44. The source of the second switching transistor 42 is connected to the data signal Vdata. The other end of the storage capacitor material is connected to the drain of the second switching transistor 42, the source of the driving transistor, and the anode terminal of the organic light emitting diode 45. The patent mainly passes through the first And the use of the second switching transistors 41, 42 to bias the Vgs bias voltage across the driving transistor 43 = Vdd - Vdata'. At this time, the driving transistor magic generates a driving current flowing through the organic light emitting diode. 45 illuminating the second. Thereby, the influence of the variation of the driving voltage v0LED characteristic of the 200811813 can be avoided. However, when the second switching transistor 42 is at the high level (High) of the scanning signal Vscan, the data signal Vdata is transmitted. The image data is connected to one end of the storage capacitor 44. At this time, the second switching transistor 42 and the organic light emitting diode 45 are both resistive loads, and when a quiescent current continues to pass through the first switching transistor 42, the actual operation is caused. Transfer of image data to End storage capacitor 44 has an error is present, so that input image data and Λ: Movies stored do not clump #

If there are different situations. Moreover, this patent has not changed. The problem of the critical voltage value vth variation of the forward crystal 43 causes that the driving electric crystal driving voltage value Vth cannot maintain the original value and increases with time, and the offset 'cannot maintain a stable current output for a long time. SUMMARY OF THE INVENTION [Invention] In order to solve the above-mentioned drawbacks, the present invention and the control method are suitable for use in a driving operation using a non-day-day film-filled transistor as a two-circuit circuit. Solving the increase of the driving voltage characteristic when the organic light emitting diode is illuminated by the Spark, the operating value between the driving voltages, and avoiding the amorphous silicon germanium transistor (a-Si TFT) based on a certain circuit When designing, the a-S i TF T component will work for a long time. The panel will maintain the stability of the a_Si TFT component for a long time, the special cost of the money and the improvement of the display quality. The extension panel The driving circuit of the unit of the invention comprises a switching source terminal and - the data line is connected, the secret body, the extreme and a storage capacitor drive the transistor &< The gate of the switch transistor and a control transistor I# t k 4 1 are connected to each other at the gate of the egg-making day. Axle motor 曰曰 = 200811813 汲 Extreme and hetero (4) crystal _ ^ extreme and an organic light-emitting diode of the steam /, the original 贩 extreme, control the source of the transistor _ the other end - Node, the cathode of the organic meal diode is terminated to a low potential of the driving circuit. The U frame of the present invention is a time unit. When the scanning signal is high-level, the switching transistor and the control transistor are simultaneously (4) activated. At this time, the poor signal line will input the human-image data to the storage capacitor. - the end, and the voltage source conveys - the low level to the end of the _ storage capacitor, the low level must avoid the illuminating malfunction of the organic light emitting diode during the data storage process; next, when the scanning signal is low level When the storage capacitor has turned the (fourth) signal of the grayscale value of the image, the amount of the grayscale value of the image (4) does not occur with the variation of the characteristic of the organic light emitting diode. After a period of time, the electric (four) rises from a low level to a high level, at which time the driving transistor begins to supply a current through the organic light emitting diode to cause the organic light emitting diode to emit light. When the voltage source is raised from the low level to the normal level, the power pulse feed-through is generated for the parasitic capacitance of the driving transistor, thereby compensating for the time for supplying the driving transistor. Stability, extending the use time of the display panel. [Embodiment] The detailed description and technical description of the present invention will now be described as follows: ° The present invention provides a design for driving an organic electroluminescent diode, which can be applied to an amorphous germanium film transistor (heart) Active driving organic electroluminescent display with Si TFT) and organic light emitting diode (OLED)

12 200811813 • (ΑΜ_). Please refer to the "Picture 1", which is a circuit structure of a unit pixel of the present invention. The circuit structure includes: a switching transistor n〇, the source terminal of the switching transistor 110 and the data line 22 are secreted. The extreme is connected to the gate of the drive transistor 13G and the end of the storage capacitor 14〇. The gate terminal of the switching transistor no is connected to the gate of the scan line 21A and a control transistor 120. Moreover, the driving transistor 13A and the terminal are not connected to the voltage source Vdd, the source terminal of the driving transistor i3, and the anode terminal of an organic light emitting diode (2). The source terminal of the control transistor 12 is controlled, and the other end of the storage valley 140 is commonly coupled to a node. The cathode of the organic light emitting diode 15 is connected to a low potential of the driving circuit. The switching transistor 110, the control transistor 12A and the driving transistor 130 are N-type thin film transistors. For the driving method of the present invention, please refer to "Fig. 11", which is the timing relationship of the control signals according to the circuit of "10th drawing". Operation of the display • A frame is a time unit, and a corresponding scan line 210 is activated in a frame, and the scan line 210 cooperates with the size of the frame to provide a scan signal Vscan at a frequency. The scan signal Vscan is input to the gate of the switch transistor 110 and the control transistor 12 to control the opening of the 'body 11'. When the scan signal vscan is at a high level, the switch transistor 110 and the control transistor 12 are simultaneously turned on, and the data signal Vdata having the image with different gray scale values is transmitted through the data line 220, and the transistor is turned off. 110 is wheeled into one end of the storage capacitor 14 turns. On the other hand, the voltage source Vdd transmits a low voltage level through the control transistor 12 to

13 200811813 The other end of the storage capacitor 140 (that is, the control transistor ι2 〇, the source terminal of the driving transistor 130 and the anode terminal of the organic light emitting diode 15 )), the low voltage level of the turtle voltage source Vdd The stage is used to prevent the organic light-emitting diode 150 from performing illuminating malfunction during image data storage. Next, when the scan signal Vscan is at a low level, the switch transistor 11() and the control transistor 120 are both turned off. However, at this time, the storage capacitor 140 has maintained the data signal of the image grayscale value. ¥忪, so that the data signal Vdata of the grayscale value of the image does not have an error with the variation of the characteristic of the organic light emitting diode 15〇. After a period of time, the voltage source Vxian rises from a low voltage level to a high voltage level, and at this time, the driving transistor 130 starts to provide a current ID flowing through the organic light emitting diode 15〇 to make the organic light emitting diode The body 150 performs a light-emitting operation. Λ > wherein the high voltage level of the voltage source Vdd is higher than the low potential of the driving circuit, and the low voltage level of the voltage source Vdd is independent of the low potential of the driving circuit or lower than the low potential of the driving circuit low. With the "Fig. 12", the driving structure of the present invention is characterized in that the frame time is divided into two parts, that is, the exchange frequency of the low voltage level and the high power level of the voltage source Vdd is 1 frame- The period is changed to drive the non-emission/light-emitting state of the organic light-emitting diode to achieve the image. Lin low voltage level and high power (four) position 彳 _, disk: write and the screen display time ratio is equal. A picture: For the broom stage Ts' is used when the voltage source Vdd is low voltage and all the pixels on the board will be the data signal of the desired image Vdat^w storage capacitor UG '· the subsequent stage is - display stage Td, the ^ 14 200811813 When the original d is the voltage level, all the elements of the panel start to emit light.

In the driving structure mode proposed by the present invention, the voltage source Vdd is at a low voltage level during the scanning period of the display panel, and the voltage source Vdd is from the low voltage level at the end of the scanning period. Becomes a high voltage level. During the voltage change of the voltage source Vdd, since the circuit components themselves can generate electricity (Cgdi, Cgd3, and C〇led), as shown in "Fig. 13". The driving transistor 130 is configured to provide a sufficiently large driving current for the organic light emitting body 150 to emit light, so that the size of the driving transistor 13 is designed to be large, resulting in the driving transistor 130. The parasitic capacitance value cgd3 also becomes larger, causing the gate terminal coupling potential of the driving transistor 13A to increase, so that the potential vn at which the driving transistor 13 is coupled to the storage valley 140 is increased by one. The value is "forward offset ΔvN". Therefore, in the original conventional circuit structure, the TFT element generates a forward voltage value Vth in the forward direction under long-term operation. In the present invention, the forward offset amount aVn generated by the voltage source Vdd is used as the threshold voltage value Vth. The amount of suppression to the offset further extends the life and display quality of the panel. The forward offset ΔνΝ is derived as follows:

Qcharge=Cgdl(VN_Vg110)+Cgd3 (VN-Vdd)+C14〇(VN_VP) Qdicharge^CgdUVN^VgllO^+Cg^^^Vdd^+CHO (VN^VP9) Qcharge- Qdicharge

•••CgdlVN-CgdlVg110+Cgd3VN_Cgd3vdd+C140VN_C140VP=CgdiVN'- CgdiVg110 +Cgd3VN'-Cgd3Vdd+Ci4〇VN'- Ci4〇Vp' ^ CgdiAVN.CgcnAVgno+Cg^AVN-CgdsAVdd+CHoAVN. 15 200811813 * Ci4〇AVp= 〇AVN-(CgdlAVg110+Cgd3AVdd+Cl4〇AVP)/(Cgdl+Cgd3+C140) where cg is „the parasitic capacitance of the switching transistor 110, Cgd3 is the parasitic capacitance of the read driving transistor 130, and Vn is the driving transistor 130 The potential of the gate terminal, VP is the potential of the source terminal of the driving transistor 130, and c!4〇 is the storage capacitor 140. Further, when the threshold voltage value offset ΔVth and the forward offset amount AVn are simultaneously considered, Substituting the drive current relationship (Equation (4)) 'can obtain h -^k (Vgs + AVn^(vth + AVih)). As the usage time increases, although the threshold voltage value Vth of the drive transistor 130 will follow It is raised, but as long as the voltage source Vdd is externally controlled, the voltage can be gradually increased with the panel use time to provide an increase of ΔVn, wherein the increase amount is approximated to the positive offset value of the threshold voltage value. △Vth, can be reduced due to the increase in the threshold voltage value Vth_ In the above, when the low-level signal of the voltage source Vdd is transmitted to the source terminal of the driving transistor 130, the driving transistor 130 does not generate static current, and therefore, the control is performed. The electric crystal 艨 120 does not have a source-to-source impedance problem, which does not cause the scale to be sent. The source of the electro-optical crystal 130 is at the extreme when there is a distortion, so the design of the control transistor 120 is not considered. The size of the component is such that, in comparison with the circuit proposed in the prior art, the third electro-crystallizer added by the present invention is minimized, and the impedance factor is not considered to maintain the aperture ratio of the element. 'This 16 200811813 invention in the a-SiTFT component threshold voltage value on the other is to use part of the frame time to do the sweeping action, the way to show the action, in the power supply line from the scanning crystal frame ~ between the high level of the highlight At the time of the driving, the driving body is raised to the brightening week to generate electricity Cgd3 'the original pulse wave reading (Power Pulse)

Feed-thr〇ugh), the potential forward offset value produced. The time stability of the current supplied by the driving transistor 13G can be compensated for, and the use time of the display panel can be prolonged.

In this case, it is only necessary to modulate the timing variation of the voltage source Vdd, so as to avoid the influence of the variation of the characteristics of the organic light-emitting diode and avoid the display brightness to the shirt. Moreover, in the aspect of compensating for the positive bias voltage Vth of the a_Si TFT, there is no need to add an additional control signal line, so the present invention does not have the A-line occupying an additional light-emitting area, which affects the aperture ratio of the display area. The above are only the preferred embodiments of the present invention and are not intended to limit the scope of the present invention. That is, the equivalent changes and modifications made by the scope of the patent application of the present invention are covered by the scope of the invention.

17 200811813 • [Simple description of the diagram], 1 diagram, is a schematic diagram of the unit pixel drive circuit of the conventional display panel. Fig. 2 is a graph showing the variation of the driving voltage with the use time in Fig. 1. Figure 3 is a graph showing the change in drive current with time of use in Figure 1. Brother 4 shows the change of the threshold voltage of the driving transistor with the use time. Figure 5 is a diagram of the driving circuit in the unit of the US patent 1 ^ 6,677,713 units. φ Fig. 6 is the timing relationship of the scanning clock of Fig. 5. Figure 7 is a diagram of the driving circuit in the U.S. patent 1186, 68 〇, 58 〇 unit pixel. ^Fig. 7 is a timing sequence control relationship with the input voltage. Figure 9 is a diagram showing the driving circuit of the unit US 6,756,74G unit. 10 is a driving circuit diagram of the unit pixel of the present invention. The πth diagram is a timing diagram of the corresponding control signals of the present invention. Figure 12 is a schematic view of the driving structure of the present invention. ~ Figure 13, is a schematic diagram of the parasitic capacitance of the circuit components of the present invention. [Explanation of main component symbols] "(Practical) 11, 31: Switching transistors 12, 23, 33, 43: Driving transistors 13, 24, 34, 44 · · Storage capacitors 14, 25, 35, 45: Organic light Diode 21, 41: first switching transistor 22, 42 · second switching transistor 200811813 • 32: control transistor • (invention) 110: switching transistor 120: control transistor 130: driving transistor 140 ··Storage Capacitor 15Ό: Organic Light Emitting Diode 210: Scanning Line ▲ 220: Data Line

Claims (1)

200811813 X. Application for Patent Park: ' 1. A driving circuit for an organic electroluminescent diode, the driving circuit comprising: a switching transistor having a gate coupled to a scan line and a source coupled to a a control circuit, having a gate coupled to the scan line, a drain coupled to a voltage source; a drive transistor having a gate and the switch transistor a pole connected to the voltage source and a source; a storage capacitor having one end coupled to the drain of the switching transistor and the gate of the driving transistor, and the other end coupled Connected to the source of the driving transistor; an organic light emitting diode having an anode coupled to the source of the driving transistor, and a cathode coupled to the low potential of the driving circuit. 2. The driving circuit according to claim 1, wherein the switching transistor, the control transistor and the driving transistor system are each an N-conducting thin film transistor. 3. A method for driving an organic electroluminescence diode, the driving circuit method comprising: a voltage source having a low power level and a high voltage level, and the level is alternately changed by a frequency; When the voltage source is at a low voltage level, a switching transistor and a control transistor are simultaneously controlled by a scanning signal to enable a data signal to be stored to one end of the storage capacitor, and the other end of the storage capacitor is the same 20 200811813 The low voltage level of the two voltage sources makes the organic light emitting diode not emit light; when the voltage source is at the high voltage level, the high voltage level drives the organic light emitting body to emit light. 4. The driving method according to claim 3, wherein the exchange frequency of the low voltage level and the high voltage level of the voltage source is changed by a frame to change a period to drive the organic light emitting diode The non-illuminating/illuminating state of the body reaches a frame inversion operation. 5. The driving method according to claim 4, wherein the ratio of the low voltage level of the voltage source to the high voltage level is equal to the ratio of the data writing to the display time. 6. The driving method of claim 3, wherein a high voltage level of the voltage source is higher than a low potential of the driving circuit, and a low voltage level of the voltage source is equal to a low potential of the driving circuit. . 7. The driving method of claim 3, wherein a high voltage level of the voltage source is higher than a low potential of the driving circuit, and a low voltage level of the voltage source is lower than a low of the driving circuit. Potential. twenty one