TWI233077B - Driving circuit for active organic electro-luminescence display - Google Patents

Abstract

The present invention provides a driving circuit for active organic electro-luminescence display, wherein each pixel comprises four TFTs and two capacitors. The gate of scanning TFT is controlled by the scanning line of the row on which the pixel is located. The drain of scanning TFT is connected to the data line of the column on which the pixel is located. The reset TFT and the detection TFT are controlled by a threshold voltage latch line. A capacitor Cd is used to store the data voltage value (Vdata) representing the image signal. A capacitor Ct is used to store the threshold voltage vale (Vth) of the driving TFT. Thus, the total voltage stored at the capacitor Cd and the capacitor Ct will make the driving TFT outputting a corresponding amount of current to the organic electro-luminescence device.

Description

Special

j Case No. 92119606 Amendment V. Description of the invention (1) --- [Technical field to which the invention belongs] The present invention relates to a driving circuit for an active organic electroluminescent display, especially an improved organic light emitting diode Driving device and method for uneven panel image. [Previous technology] Organic electroluminescence display (0LED) technology can be divided into passive (Passive Matrix; PM0LED) and active (Active Matrix; AM0LED) according to the driving method. The so-called active driving LED (AMOLED) uses a thin film transistor (TFT) and a capacitor to store the signal, thereby controlling the grayscale performance of the 0LED. Although the production cost and technical threshold of passive 0LEDs are low, the resolution cannot be improved due to the driving method. Therefore, the size of the application product is limited to about 5 inches, and the product will be limited to the low-resolution small-size market. In order to obtain high-definition and large daylight, it is necessary to use active driving. The so-called active driving uses capacitors to store signals, so when scanning lines are scanned, the daylight can still maintain the original brightness. As for passive driving, Only the daylight selected by the scan line will be lit. Therefore, in the active driving mode, the 0LED does not need to be driven to a very high brightness, so it can achieve better life performance and also meet the requirements of high resolution. The technology of 0LED combined with TFT can actively drive 0LED, which can meet the requirements for the smoothness of the screen playback and the increasingly higher resolution in the current display market, fully displaying the above-mentioned superior characteristics of 0LED. The technology for growing TFTs on glass substrates can be amorphous silicon (

Page 5 No. 92119606 V. Description of the Invention Ή) amorphous silicon; a-Si) process and low temperature polycrystalline (LTPS) process, LTps 71 ^ and 81

The biggest difference between Si TFT lies in the difference between its electrical properties and the complicated process. ^ Tps TFT has a higher carrier mobility. A higher carrier mobility means that tft can know: for more damaging electricity, 'but its process is more complicated; while agi τ ρ τ is the opposite'. The carrier mobility of a-Si is not as good as ltps, but because of its simpler and more mature process, it has a good competitive advantage in terms of cost. If so, due to the limitation of the low temperature polycrystalline silicon (LTPS) process capability, the threshold voltage (Threshold Voltage) and electron mobility (MobUity) of the manufactured thin film transistor (TFT) device will vary. Therefore, each TFT device The characteristics will be different. When the drive system uses an analog voltage modulation method to represent gray levels, because the characteristics of j F τ of different books are different, even if the same data (Data) voltage signal is input, the organic light emitting diode (0LED) will be made. Different output currents are generated, resulting in different brightness of the organic light emitting diode (OLED) elements of different pixels on the display panel. This phenomenon will cause the organic light-emitting diode panel to display a poor grayscale image, which will seriously damage the uniformity of the panel image (I mage Uniformity). ○ At this stage, the most urgent problem for AM0LEDs is how to reduce the low-temperature polycrystalline silicon thin film. Adverse effects of non-uniform transistor characteristics. Since these adverse effects will be immediately noticeable from the image displayed on the panel, it is difficult to carry out the next development application without solving this problem. Therefore, in order to solve the above-mentioned shortcomings, US Patent 6,229,506 Active Matrix Light Emitting Diode Pixel

Page 6

92119606 V. Description of Invention (3) Years

"Structure And Concomitant Method", a patent proposed in this patent includes a 4T2C (4 TFT transistors and 2 capacitors) pixel circuit, as shown in "Figure 4", using Auto-Zero (Auto-Zero ) Mechanism to compensate for variations in the threshold voltage of the TFT element to improve the uniformity of the image. The driving timing of the control signal of the driving circuit is divided into an Auto-Zero Phase 510, a Load Data Phase 520, and an Illuminate Phase 530. 'Please refer to "Figure 5", It is the timing chart of the control signal of "Figure 4". Before the reset phase 510, transistor T3 and transistor T4 are OFF (transistor T2 is ON), and at this time, the current flowing through Organic Light Emitting Diode (OLED) 460 is The current of a frame is controlled by the transistor T1 2Vsg (the voltage difference between the source and the gate, which is stored in the capacitor. The voltage difference between the two ends). After entering the zeroing stage 51 °, the transistor T4 is turned on (ON) first, and then the transistor T3 is turned on (ON), so that the drain (1) of the transistor 11 is connected to the gate (11) with the gate 11). A diode connection is formed, and then the transistor T2 is turned off. At this time, the gate voltage of the transistor T1 will rise to a voltage value, which is equal to the high potential (Vdd) minus the transistor. The threshold voltage of n (m0ld V〇ltage; vth), which is stored in the capacitor c, and the voltage difference is the threshold voltage of transistor T1.

After the voltage at the threshold of the bottle 11 is turned off, the transistor T3 is turned off (p), and the threshold voltage (vth) of the transistor τι can be stored as the action of the zeroing stage 510. Emperor Tsai is on the electric valley Cs, and then enters the data loading stage 520. If the data line (Date Li

Page 7

Revise ψψ ^ 92119Rf) fi V. Description of the Invention (4) The voltage on 410 is Δν, and the transistor T4 and capacitor are used to reach the gate ((^ 4) of transistor 71, so it is stored in the capacitor. 3 The voltage difference between two & is Aγχ [cc / (cc + Cs)] plus Vth 'originally stored in the capacitor Cs, that is, the transistor T1 iVsg will include the transistor T1, which makes the output of the transistor τι The current is only related to the varying voltage (Δν) on the data line 410 ', and is not affected by the Vth of the transistor in each pixel. Finally, it enters the light-emitting stage 530, at which time the transistor T4 is turned off (0FF)' and When the electric body T2 is turned on, the transistor T1 will output the current of the current frame (Frame) to flow through the organic light emitting diode & 60, so that the organic light emitting diode 460 element is illuminated. The 4T2C day element circuit can compensate the variation of the threshold voltage (Vth) of the transistor element in each pixel, and improve the uniformity of the overall image of the display. However, the patent except for the data line 41 〇, the scan line 420, and the power supply line (vdd) Beyond 450, you need to have a zero-zero control line (Aut〇- Zero Line) 430 and The light control line (I 1 luminate Line) 440 and other control lines, through which the capacitor Cs is responsible for recording all critical voltages and some of the loaded data voltage, and the data loading is a more complicated way using capacitive coupling voltage, so The complexity of the driving method will increase, resulting in the need to use non-standard forms of data-driven ICs, which will increase the cost of manufacturing. Similarly, in order to solve the conventional problems, Philips also published a title entitled "A Comparison of Pixel Circuits for Active Matrix Polymer / 〇rganic LED Displays ”paper, this paper proposes a 4T2C daylight circuit, as shown in“ Figure 6. ”This circuit cleverly changes the above-mentioned US patent US 6,229,506 daylight circuit (No. 4

The connection position of the two capacitors in the figure on page 8), to solve the above-mentioned patent document, the voltage loading method is too complicated to be implemented. Therefore, in addition to the data line 610, the scan line 6 20, and the power supply line (Vdd) 65 0, the day-to-day circuit mentioned in this paper also needs a zero-zero control line (Auto-Zero) as in the US patent US 6,229,506. Line) 630 and IUuminate Une 6 4 0 and other control lines. In addition, the driving timing of the control signal of the driving circuit in this paper is divided into the Uto-Zero Phase 510, the Load Data Phase 520, and the light emitting phase ( Illuminate Phase) 530, please refer to "Figure 5", which is also the timing chart of the control signal of "Figure 6". In the execution of the reset phase 510, the transistor T64 is turned off (0FF), and the transistor T63 is first turned on, so that the drain of the transistor T61 is connected to the gate to form a diode connection, and then Turn off transistor T62. At this time, the gate voltage of transistor T61 will rise to a high potential (Vdd) minus the threshold voltage (Vth) of transistor T61, which is the sum of the voltages stored in capacitor Cl and capacitor C2. After the threshold voltage (vth) of the transistor T6ι is turned off, the transistor T63 is turned off (0FF), and the operation of 5 1 0 in the return to zero phase is completed. The way to load the data voltage in this circuit is through the conduction of transistor T64. The data voltage will be stored in capacitor C1. At this time, the voltage across capacitor C2 will still maintain a certain percentage of V th voltage value stored before, which is equal to [c! / (Cl + C2)] x Vth. Therefore, the sum of the voltages of the capacitor ci and the capacitor C2 is (¥ (1 (1) (1 & 13 + [(: 1 / ((: 1 + € 2); ^ \ ^ 11), which is the transistor D 73 of 61 & V. Description of the invention (6) Including-part of the Vth voltage value of transistor T61, which can reduce the correlation between the m output current and the threshold voltage value of transistor T61, and to repair the transistor T61 due to the system Variation of the threshold voltage (hh) caused by factors The threshold voltage value of the driving transistor T63 in this paper is memorized by two solid capacitors (Cl, C2), and one of the threshold voltage values stored in one capacitor The information will be lost when the data voltage is loaded, so this method can only compensate part of the variation of the threshold voltage caused by process factors. [Summary of the Invention] 爰 Yes, the main purpose of the present invention is to solve the above-mentioned traditional defects and avoid Lack of existence 'The present invention is based on the current key components of AMOLED such as TFT-OLED Data 1C, so the technology of TFT-LCD Source 1C, which is currently developed and mature, is used to support the operation of TFT-10LED / but because of TFT- LCD Source 1C uses voltage regulation (v〇ltage

Modulation), so a voltage write type drive circuit must be designed. If so, the present invention proposes a voltage write-type active organic light emitting diode display driving circuit that can compensate for the variation of the threshold voltage of a thin film transistor ′ to improve image defects caused by unevenness of the threshold voltage characteristics of the thin film transistor. To achieve the above purpose, each pixel of the driving device provided by the present invention includes 4 TFTs and 2 capacitors, a scanning TFT, a resetting TFT, a detecting tft, a driving TFT, and two capacitors (Cd, Ct). And an organic electroluminescent element, wherein the gate of the scanning TFT is controlled by the scanning line in which the pixel is located, and the drain of the scanning TFT is connected to the book

92H9606 —Year 5th, the description of the invention⑺ ----—— The data line of the line where $ is reset; the reset m and the detection TFT are controlled by the = line; and the capacitor Cd is used to store the material voltage value ( Vdata), and the capacitor Ct is used as a voltage value (Vth) of t1, thereby the capacitor Cd and the capacitor. "::::: Makes the driving TFT output a current of a corresponding magnitude to the organic electro-excitation. [Embodiment] The detailed content and technical description of the present invention are described below in conjunction with the drawings: Please refer to" " "Shown in Figure 1" is a schematic diagram of the circuit of each day element of the present invention. As shown in the figure: the driving element of the day element 200 of the present invention includes 4 TFTs and 2 capacitors, and the connection relationship is as follows: a / TFT 210, the gate of the scanning TFT 210 and a scanning line 1 20 connection, its drain is connected to a data line 丨 丨; a reset TFT 220, the gate of the reset TFT 2 20 is connected to a threshold voltage lock line (ThreShold-L0Ck) 130, The source is connected to a power source for the twine 150, and the drain thereof is connected to the source of the above-mentioned scanning TFT 210;... A capacitor cd, which has two ends, is arranged on the above-mentioned scanning TFT 210. Between the source and the source of the reset TFT 220; a driving TFT 240 'the source of the driving TFT 2 40_the above power supply line 1 50 is connected;' a detecting TFT 230, the detecting TFT 2 30 The gate is connected to the above-mentioned threshold voltage lock line 130, and its drain is connected to the question of the driving TFT 240, and its source is connected to the above-mentioned driving TFT 240.

The electric valley Ct, a Hai electric valley Ct has two ends, which are arranged between the drain of the reset tft 220 and the gate of the driving TFT 24o; the mountain, an organic electric excitation light element 2 5o, the organic electric One end of the excitation light element 2500 is an anode, which is connected to the drain of the driving TFT 24b, and the other end is a cathode. The negative electrode is connected to a common cathode line 140. Please cooperate with "Figure 2" again, which is a schematic diagram of the connection and control of the daylight circuit on the substrate of the present invention. As shown in the figure, where the father of the scanning line 12 (S1, S2, s3, ..., Sn) and the data line 11 (D1, D2, D3, ..., Dm) is 200 times per day. Where. Now refer to "Figures 1 and 2" at the same time. Among them, the main control relationship of the diurnal 200 is as follows. The gate of scanning 71 to 210 is the scanning line listed by the diurnal 200. 12 ′ is controlled and the scanning electrode drai η is connected to the data line 11 of the row where the dioxin 20 is located. Reset again! ^^ 22〇 and detection TFT 23〇 are controlled by the threshold voltage lock line 1 30. The capacitor Cd is used to store the data voltage value (Vdata) representing the image signal, and the capacitor Ct is used to store the threshold voltage value (Vth) of the driving TFT 240. Thus, the capacitor Cd and the capacitor Ct store the total voltage The driving TFT 240 is caused to output a current of a corresponding magnitude to the organic electroluminescent light element 250.

That is, the reset TFT in the circuit of each day element 200 on the display panel 100

220 and detection TFT 230 are controlled by the same threshold voltage lock line 1 30, and the cathode of the organic electro-optical light element 250 in each pixel 20 0 is connected to a common cathode line 1 40, and a common cathode line 1 40 will be connected to the ground terminal of the system through an external switching element 170. The switching element 170 is controlled by a display signal line 160. Drive τ F T in the circuit of each day element 2 0 0

; y man

El 矣 Mongolia No. 92119606 Amended V. Description of the Invention (9) The source of 24 0 is connected to a power supply line (Vdd) 1 50. The circuit operation of the present invention is described as follows: Please refer to "Figure 3", which is a timing chart of the control signal of the present invention. As shown in the figure, the driving signal cycle of the present invention can be divided into three phases. First, the threshold voltage lock phase (Threshold-Lock Phase) 310: the signal of the threshold voltage lock line (Threshold-Lock) 130 will cause each The reset TFT 220 and the detection TFT 230 in the daylight driving circuit are turned on. When the reset TFT 220 is turned on, the capacitor Cd that originally stored the image data voltage value is discharged (Discharge). After that, the display signal line 160 will control the switching element 170 outside the display panel 100 to turn it off. If so, the common cathode line 140 and the system ground terminal will be in an open circuit state. At this time, the original The current flowing through the driving TFT 240 of the organic electro-excitation light element 250 no longer passes through the organic electro-excitation light element 250, but instead flows to the detection TFT 230 which is in an on state at this time, so that the driving TFT 240 detects the Action of critical voltage. Because the current driving TFt 240 will pass through the way of detecting TFT 230, capacitor Ct, and resetting TFT 22 0 to force the storage voltage on valley Ct to become smaller and smaller, this will cause the driving TFT 2 40 current to increase. As it gets smaller, this phenomenon will continue until the drive τ ρ τ 240 current becomes zero. Finally, the capacitor Cd will not store any charge (that is, the voltage across the capacitor is 0), and the voltage difference across the capacitor Ct will be equal to the threshold voltage (Vth) of the driving TFT 24o, that is, the valley Cd will be reset and the capacitor will be discharged. Remember the threshold voltage. (Please refer to "Figure 1" for pixel 200 circuit). In summary, the driving TFT 24 in each pixel 200 circuit after the critical voltage lock-in phase 310 has passed.

Page 13

The critical voltage value (Vth) will be stored in the capacitor Ct in the circuit of the daytime 200. The signal of the threshold voltage lock line 丨 30 will make each daytime 200 drive the reset tft 220 and detect TFT 230 cut off (OFF)

'Re-enter the second phase' Write phase 320: During the writing phase 3 20, each scanning line 12o (SI, S2 · · .Sn) will send the scanning signal in sequence. When the scanning signal is shifted to When the scanning line is 20, the scanning of the driving circuit in all the celestial elements on the scanning line 120 will turn on 210, because the scanning TFT 210 is turned on and resets the TFT 220 and the detection Measure the cut-off (FF) of the TFT 230, so the data voltage (Vdata) on the data line 110 can be stored in the capacitor Cd by scanning the ON of the TFT 210, and the capacitor Ct is reset by the TFT 220 and detected The TFT 230 is turned off and always maintains the threshold voltage value (vth) previously memorized. In the end, the voltage difference between the capacitor Cd will be equal to the power supply voltage (Vdd) minus the data voltage (Vdata), that is, the voltage across the capacitor Cd will be (Vdd-Vdata)

If the storage voltage of the capacitor Cd and the capacitor Ct is equal to (vdd-Vdata + Vth); and this voltage (vdd-Vdata + Vth) will drive the TFT 240 in the next stage (display stage 330) A current of a corresponding magnitude can be output to the organic electroluminescent light element 2 50, so the magnitude of this current (I) can be expressed by the following mathematical formula: 1 = (1/2) X ^ X (Vsg-Vth) 2 I = ( l / 2) x y3x (Vdd-Vdata + Vth-Vth) 2 1 = (1/2) x ^ x (Vdd-Vdata) 2 According to the above mathematical formula (where / 3 is the conductivity coefficient of the driving TFT 240 (

Page 14

Year Month Fj t No. 92119606_Year Month _Revision _ ΪΤ 发 日 (11)

Transconductance Parameter) learned that the magnitude of the output current (I) of the driving TFT 240 has nothing to do with its own threshold voltage value (Vth), and it is only related to the size of the written data voltage (Vdata). Variation of the threshold voltage (vth) caused by process factors. After the writing of the data voltage (Vdata) signal is also completed in the last scanning line 120 (Sn), the display signal line 160 will control the switching element 170 to be turned on, so that the common cathode line 140 is connected to the system. The ground terminal enters the third phase, the display phase (Display Phase) 33〇 «In this display phase 330, the driving TFT 240 in the driving circuit of each day element 200 can output the data voltage (Vdata) The current (I) is applied to the organic electroluminescent device 250, so that the organic electroluminescent device 250 emits appropriate brightness, and the magnitude of the output current (I) is independent of the threshold voltage of the driving TFT 240). Based on the above description, compared with the conventional U.S. patent US 6,2 2,9,506, the present invention can implement the voltage loading method of the technical data in this case, which can use the TFT-LCD Source IC (Voltage Mode), which is generally common today. Complex actions. Also ’compared to the acquainted PHILIPS paper" A Comparison of

Pixel Circuits for Active Matrix Po1ymer / Organic LED Displays ”, the technology of this case records all the threshold voltage values in a capacitor (threshold voltage storage capacitor) to compensate the effect of the threshold voltage variation.

Page 15

The title of the month was 92119606. _ ^ V. Description of the invention (12) Furthermore, the supply of key components for the AMOLED industry is still immature, such as TFT-OLED Data 1C. If the currently mature tft-LCD Source 1C can be used The technology to support TFT-OLED applications will solve many problems driving 1C development. The TFT-LCD Source 1C adopts the Voltage Modulation method, so it is necessary to design the driving circuit of the voltage writing type according to the present invention. The present invention uses two capacitors (Cd, Ct) to deal with two different things respectively. One capacitor Ct is specifically responsible for recording of all critical voltage values (Vth). The other capacitor Cd is specifically responsible for all data voltage values (Vdata). recording. Different from the US patent US 6,229, 506, the capacitor cs is responsible for all the critical voltages (V t h) and some of the data voltages loaded, 0 (13 7 8); also different? In the paper of 1111 ^ 1? 3, the critical voltage is recorded by capacitor (] 1 and capacitor [2), so capacitor C2 only records part of the critical voltage, and part of the critical voltage recorded in capacitor C1 will eventually be lost. 'The driving circuit of the active organic electroluminescent display proposed by the present invention can have the following advantages: 1. The critical voltage value (vth) can be recorded in a capacitor ct (critical voltage storage capacitor), so it can be completely Compensate the effect of the threshold voltage variation. '2. The data voltage (Vdata) loading method can be implemented using the TFT_LCD Source IC Uoltage Mc3de, which is commonly used today, to avoid complicated circuit actions as is known. However, the above are only preferred embodiments of the present invention and are not intended to limit the scope of implementation of the present invention. That is, everything done in accordance with the scope of the patent application of the present invention

Page 16

Page 17 T: 1; By Μ 92119606

Λ_E 修-Simple illustration of the drawing [Simplified illustration of the drawing is a schematic diagram of the circuit of each day in the invention. It is a schematic diagram of the connection and control of the day circuit on the substrate of the present invention. It is a timing chart of the control signal of the present invention. It is a schematic diagram of the diurnal circuit of the US patent US 6, 229, 506. It is a timing diagram of the control signal of the U.S. patent US 6,229,506. It is a schematic diagram of the pixel circuit of the Philips paper. [Explanation of reference numerals of the figure] Display panel 1 0 0 1st figure 2nd figure. Figure 3 Figure 4 Figure 5 Figure 6 Scan line 1 2 0 Common cathode line 140 Display signal line 1 6 0 Pixel 200 Reset TFT 220 Drive TFT 240 Capacitors Cd, Ct, Cc, Cs, critical voltage lock-in phase 3 1 0 Display stage 330 Transistor Ti, T2, T3, T4 Data line 41 0, 6 1 0 Zeroing control line 4 3 0, 6 3 0 Power supply line 4 5 0, 6 5 0 Zeroing phase 51 0 Data Line 11 0 Critical voltage lock line 1 3 0 Power supply line 1 5 0 Switching element 1 7 0 Scan TFT 210 Detect TFT 230 Organic electro-optical light element 2 5 0 Cl, C2 Writing stage 320, T61, T62, T63 , T64 Scan line 420, 620 Luminance control line 440, 640 Organic light emitting diode 460 Load data phase 520

Page 18

Schematic description of light-emitting stage 5 3 0

Hill Page 19

Claims (1)

6. Scope of patent application 1. A driving circuit for an active organic electroluminescent display. The elements in the driving circuit of each display element on the display panel of the present invention include:-a scanning TFT, the gate of the scanning TFT and a scanning line Connected, its drain is connected to a data line; 'a reset TFT, the gate of the reset TFT is connected to a critical voltage lock line, its source is connected to a power supply line, its anode is connected to the above-mentioned scan T The sources of ρ τ are connected; a capacitor (Cd) 'the capacitor (Cd) has two ends, which are arranged between the source of the scanning TFT and the source of the reset TFT; a driving TFT' the driving TFT The source is connected to the power supply line; a detection TFT, the gate of the detection TFT is connected to the threshold voltage lock line, the drain is connected to the gate of the driving TFT, and the source is connected to the drive The drain of the TFT is connected; a capacitor (Ct), which has two ends, is disposed between the drain of the reset TFT and the gate of the driving TFT; an organic electro-optic light element, the one end Is the anode, which is in phase with the drain of the above driving TFT Then, the other end of the cathode, the anode connected to the cathode lines total, while the display panel has a switching element, the switching element for connecting the common cathode line and the ground line. 2. The driving circuit of the active organic electroluminescent display as described in item 1 of the scope of patent application, wherein the reset TFT and the detection TFT in each day element on the display panel are locked by the same threshold voltage Stay online to control. Deposit-month name | case number 92119606_year month name revision_ VI. Patent application scope 3, as described in the patent application scope item 1, the driving circuit of the active organic electroluminescent display, wherein each of the display panel The cathode of the organic electroluminescent element in daylight is connected in common to the common cathode line. 4. The driving circuit of the active organic electroluminescent display as described in item 1 of the scope of patent application, wherein the switching element is a thin film transistor. 5. The active type as described in item 1 of the scope of patent application The driving circuit of the electromechanical excitation light display, wherein the switching element is controlled by a display signal line. Page 21