TWI252455B - Driving circuit for active matrix OLED - Google Patents

Abstract

A driving circuit for active matrix OLED has three thin film transistors and two capacitors in each pixel, wherein one of the scanning reset TFT gates is controlled by the scanning line of the row with the pixel, and the drain is connected to the data line of the column with the pixel. The detection of TFT is controlled by a threshold voltage. A storage capacitor is used to store the data voltage value (Vdata) representative of image signal. A compensation capacitor is used to store threshold voltage value (Vth) for driving TFT. Therefore, the summation of storage voltages in storage capacitor and compensation capacitor can drive TFT to output a current of corresponding magnitude to OLED component.

Description

1252455 V. INSTRUCTION DESCRIPTION (1) '*- [Technical Field of the Invention] The present invention relates to a driving circuit for an active organic electroluminescence diode display, and more particularly to an active organic light emitting diode display panel A drive circuit with uneven image. [Prior Art], organic electroluminescent display technology (OLED) can be divided into passive (Passive Matrix; PMOLED) and active (Active Matnx; AM0LED) depending on the driving method. The so-called active 〇LED (AM〇LED) uses a thin film transistor (TFT) with a capacitor to store the signal, thereby controlling the grayscale performance of the 〇LED. If the production is not restricted, it must be stored in the signal; as for the bright. Because the brightness needs to be consistent with the resolution, the more the drive mode is about 5 inches, the high-precision active drive can still maintain the selected picture without the need to reproduce, but also the active drive can be played smoothly. The above-mentioned superior dynamic OLED has no resolution, and the product will be thin and large. The brightness of the original brightness will be jogged to a very high level to achieve high resolution, 0LED, scalability, and solution characteristics. This and the technical gate are therefore applied to the low-resolution active drive side, so when the sweep is driven by the passive drive, it is active. 0LED junction The current display is higher

The lower the size, but the size of the product is limited to the small size market. If the pattern is dominant, the so-called trace line sweeps the picture ’ only in the scanning mode, the 0LED to the better life-matching TFT technology is available, and the market fully displays the 0LED for the picture

The technique of growing TFT on a glass substrate can be an amorphous germanium (am〇rph〇us S1 1 1C〇n; a — Si ) process and a low temperature polycrystalline germanium (Low Temperature).

Page 6 1252455 V. Description of the invention (2) Poly-silicon; LTPS) process, the biggest difference between LTPS TFT and a-Si TFT is the difference between its electrical and process complexity. LTPS TFTs have higher carrier mobility, and higher carrier mobility means that TFTs can provide more sufficient currents. However, the process is more complicated; while a_Si TFTs are the opposite, although the carrier mobility of a_Si is not as good. LTPS, but because of its simple and mature process, it has a good competitive advantage in terms of cost. In the current LTPS-TFT industry, since the mobility of low-temperature polycrystalline germanium film transistors (Mobi 1 ty) has reached 100~2〇〇cmVV -sec, TFT-(^LED driving ic and data ic can be gradually used The process of LTPS is realized, but due to the limitation of process technology, the characteristics of the TFT of the whole panel are not the same. Therefore, the most urgent problem to be solved by the active organic light-emitting diode display at this stage is how to reduce the transistor characteristics of the low-temperature polycrystalline germanium film. The adverse effects caused by unevenness. Because these adverse effects will immediately be noticeable from the image displayed on the panel, 'the organic light-emitting diode panel displays an image with poor gray scale, which seriously damages the uniformity of the panel image (Image Uni Form ity), therefore, it is difficult to carry out further development and application without solving this problem. Therefore, in order to solve the above disadvantages, US Patent No. 6,229, 5 0 "Active Matrix Light Emitting Diode Pixel Structure And Concomitant Method" In this patent, a 4T2C (4 TFT transistors and 2 capacitors) pixel circuits are proposed, as shown in Figure 1. The patent uses the auto-zero (Auto-Zero) mechanism, the threshold voltage compensation TFT element (Threshold Voltage; Vth) variations, to improve the uniformity of the image which is incorporated into the drive timing zero phase (.

Page 7 1252455 V. Description of invention (3)

Auto-Zero Phase 210, the data phase (L〇ad Data phase) 220 and the niuminate phase 23〇, please refer to the “Figure 2” for the control signal timing diagram.

Before the zeroing phase 210, the transistor 13 and the transistor are turned off (〇FF), and the transistor T2 is turned on (ON), and the current flowing through the organic light emitting diode (〇LED) 1 60 is the previous frame. (Frame) current, by the transistor η

Vsg (source and gate voltage difference, that is, the voltage difference stored across the capacitor ^) is controlled.

After entering the zeroing phase 2 1 〇, first turn on (qn) the transistor τ 4, then turn on (ON) the transistor T3, so that the transistor (^) is connected to the gate terminal ((〇) A diode connection, and then cut off (〇FF) transistor T2, the gate voltage of the transistor τι will rise to a voltage value equal to the high potential (Vdd) minus the threshold of the transistor T1 The voltage (vth), that is, the voltage difference stored across the capacitor Cs is the threshold voltage of the transistor, and then the transistor T3 is turned off (OFF), so that the threshold voltage (vth) of the transistor T1 is stored in the capacitor. On the Cs, the action of the zeroing phase 21 is completed.

Next, the loading data phase 220 is entered. If the voltage on the data line (Date Une) 110 is Δν, the transistor 4 and CoupU are transmitted through the transistor (4) to the extreme (6). Therefore, it is stored in electricity = (the difference between the two ends is MX [Cc / (Cc + Cs)] plus the Vsg originally stored in the capacitor "Vth", that is, the transistor T1 will contain the transistor T1 2Vth, which makes The current of the crystal=T1 output is only related to the voltage (Ay) of the data line 11〇 and the magnitude of the capacitance Cc and Cs, and is not affected by the transistor TkVth in each pixel.

1252455 V. INSTRUCTIONS (4) ---- Finally, enter the illuminating phase 230. At this time, the transistor T4 is turned off (〇FF), and the transistor T2 is turned on (0N), and the transistor T1 outputs the current frame. (

The current of the frame flows through the organic light-emitting diode 16 turns, causing the organic light-emitting diode 160 element to illuminate. Although the 4T2C pixel circuit can compensate for the variation of the threshold voltage (Vth) of the transistor components in each pixel, and improve the uniformity of the overall image of the display, the patent has the exception of the lean line 11 扫描, the scanning line 12 〇, the power supply. In addition to the supply line (Vdd) 150, a control line such as an Auto-Zero Line 130 and an I 1 luminate Line 140 is required, whereby the capacitor Cs is responsible for recording the entire threshold voltage (Vth). ) and the part 9 data voltage loaded, and the data voltage loading is capacitive coupling, which is complicated, so the complexity of the driving method will increase, resulting in the use of non-standard data driving ICs, increasing manufacturing. The cost. Similarly, in order to solve the conventional problem, PH I L I PS also published a title "A Comparison of Pixel Circuits for Active

A paper on Matrix Polymer/Organic LED Displays, in which a 4T 2 C pixel circuit is proposed, as shown in Figure 3. This circuit succinctly changes the connection position of the two capacitors in the above-mentioned U.S. Patent No. 6,229,506 in the pixel circuit (Fig. 1) to solve the problem that the voltage loading method of the prior patent is too complicated to implement. Therefore, in addition to the data line 310, the scan line 320, and the power supply line (Vdd) 350, the pixel circuit proposed in this paper requires a zero-control line (Auto-Zero Line) as in US Patent No. 6,229,506. 330 and control lines such as the Illuminate Line 340.

Page 9 1252455 V. Description of the invention (5) In addition, the control signals of the driving circuit in this paper are also divided into Auto-Zero Phase, L〇ad Data Phase and Luminous Phase ( I 1 1 uminate P hase ) three stages. When the zeroing phase is performed, the transistor 734 is turned off (〇FF), and the transistor T33 is turned on (ON), and the drain of the transistor T31 is connected to the gate to form a one-pole connection. The transistor T 3 2, at this time, the transistor τ 3 1 = the gate voltage rises to a high potential (Vdd) minus the critical electric f (vth) of the transistor T3 1 , that is, the voltage stored in both the capacitor and the capacitor C2 The sum is the threshold voltage (vth) of the transistor T31, and then the transistor T33 is turned off (OFF).

, complete the action of the zeroing phase. Under, the circuit loads the data voltage by the conduction of the transistor 34. The data f is stored in the capacitor C1. At this time, the voltage across the capacitor C2 will still maintain a certain proportion of the vth voltage stored before. The value is equal to [c丨/ (c + C2)]X Vth. Therefore, the sum of the voltages of both the capacitor C1 and the capacitor C2 is (

Vdd Vdata+[C1/(C1+C2)]X Vth ), that is, the transistor T31. It will contain a part of the Vth voltage value of the transistor T31, which can reduce the correlation between the output current of the transistor tji and the threshold voltage of the transistor T31, and compensate for the critical voltage caused by the process factor of the resistor T31. variation.

In this paper, the threshold voltage value of the driving transistor T31 is shared by two electrodes, and one of the capacitors is stored in a critical state, and the threshold is lost when the data voltage is loaded. Therefore, the method can only The damage of the threshold voltage (Vth) caused by the process factor is compensated. SUMMARY OF THE INVENTION The present invention proposes a compensation for the critical voltage of a thin film transistor.

1252455 V. INSTRUCTIONS (6) Variant voltage-writing active organic ~ To improve the criticality of the thin film transistor 'X,> one-pole driving circuit, image defects. i) The non-uniformity is caused by the above-mentioned purpose. The present invention proposes three TFTs and two capacitors, including _ _ >& Le Ling, the mother-single package-driving TFT, "FT", a detecting TFT, an electroluminescent element; wherein the scanning/setting CTdF; the complementary capacitance C" and the - organic pixel are arranged by the scan line of the gate terminal (^) is the voltage Locking the line to control; and storing = f FT is the data voltage value (Vdata) of the critical number, and the compensation capacitor 〃 stores the threshold voltage value (Vth) representing the TFT of the image signal, thereby storing, /总 used to store the sum of the storage voltages of both drives, which will drive the output of the m, the second and the additional Ct to the organic electroluminescent element. The current of the corresponding size [Embodiment] As follows: π谷和技术呪明, now with the schema said = read "Figures 4 and 5" is a schematic diagram of the connection and control of each of the solar panels on the present invention. Fig. _ = Inverted display panel 40 0 Each scan line 42〇 intersects with each of the feed lines 41〇 to form a pixel 50 0 drive power π 7 : The circuit includes 3 cuts, 2 capacitors and erguang = ^,:i*〇T^5i:,:r:A7i5i〇iM^(G) ^^ ( D ) is connected to a data line 4 1 0

Page 11 1252455 V. Inventive Description (7); a storage capacitor Cd having two ends disposed at a source terminal (S) of the scan reset TFT 510 and a power supply line (Vdci) 451 between. A driving TFT 530' is connected to the power supply line (Vdd) 450 as described above. A gate TFT 520' is connected to the threshold voltage lock line (Threshold-Lock) 430, and the gate terminal (D) and the gate terminal (G) of the above-mentioned driver TFT 530 are connected. Connected, the source terminal (S) is connected to the 汲 terminal (D) of the driving TFT 530; a compensation capacitor Ct, which has two ends, is set at the source terminal of the above scanning reset 5 1 〇 (S) is between the detection terminal 520 and the extreme (D) of the TFT 520. ", an organic electroluminescent device 540, the one end is an anode, connected to the 汲 terminal (D) of the driving TFT 530, and the other end is a cathode, the cathode is connected to a common cathode line (Common Line) 440. 5, wherein the intersection of scan line 420 (si, S2, S3 ... Sn = data line 410 (D1, D2, D3 . . Dm) is where the parent pixel 500 is located. See also "4th, 5, wherein the main control relationship of the u-nuclear 500 is as follows, and the scan resets the gate of τρτ: ί it) The hawthorn is controlled by the scanning line 420 of the column of the pixel 5〇0. Also:, then) is connected to the data line 410 where the pixel 50 is located. The electric six cd system is controlled by the threshold voltage lock line 430. The storage voltage value (Vdata) of the image signal is stored, and the voltage Ct is used to store the threshold voltage of the driving TFT 53〇. In this case, the storage capacitor Cd and the compensation capacitor CW store the voltage. General meeting

1252455 V. DESCRIPTION OF THE INVENTION (8) A drive current T F T 5 3 0 is outputted to a current of a corresponding magnitude to the organic electroluminescence element 54 0 . That is, the detecting TFTs 5 20 in each of the pixels 5 显示 on the display panel 40 0 are controlled by the same threshold voltage locking line 43 0 , and the source terminals (S ) of the driving TFTs 5 30 are connected to The same power supply line (vd d4 5 〇. and the cathode of the organic electroluminescent element 540 in each quinone 500 is connected to a common cathode line 4 4 0 'the common cathode line 4 4 0 will pass through an external The switching element 4 7 〇 is connected to the ground terminal of the system, and the switching element 47 0 is controlled by a display signal line (Display L ine ) 460. The circuit driving method of the present invention is described as follows: Please refer to "Fig. 6" The control signal timing diagram of the present invention is shown in the figure. As shown in the figure, the driving signal period of the present invention can be divided into three stages, first of all, 'Threshold-Lock Phase 610: Scanning Line 4 2 0 and the threshold voltage lock the signal of the line 4 3 ,, the scan reset TFT 510 and the detecting TFT 52 0 in each pixel driving circuit are turned ON, and the data line 410 is reset. It is the same as the voltage level of the power supply line (vdd) 45〇, when the scan is reset ^ 51〇 When the pass (〇N), the original image data storage capacitor would present voltage value stored Cd reset TFT 5 1 via the scan and data lines 410 square discharge (Discharge). After the display signal line 460 signal line

The switching element 47 of the display panel 40 0 is controlled to be turned off (〇FF), and if so, the common cathode line 440 and the ground end of the system are in a state of "open circuit". At this time, the organic electroluminescent element is originally flowed. The current of the driving TFT 530 of 54〇 is no longer passed through the organic electroluminescent element 54〇, but is changed to the detecting TFT 52〇 which is in an ON state at this time, so that the driving TFT is driven.

Page 13 1252455 V. Description of the invention (9) 53 0 The action of detecting the threshold voltage is performed. Because the current of the driving transistor 520, the compensation capacitor ct, and the scanning reset TFT 51 0 force the storage voltage on the compensation capacitor Ct to become smaller and smaller, which will cause the driving TFT 5 30 current to also be Therefore, it will become smaller and smaller, and this phenomenon will be until the driving TFT 530 current becomes zero. Finally, the storage capacitor Cd does not store any charge (ie, the voltage at both ends is 〇), and the voltage difference across the compensation capacitor Ct is equal to the threshold voltage value (Vth) of the driving TFT 530. That is, the storage capacitor Cd is discharged and reset, and the compensation is performed. The capacitance ct will memorize the threshold voltage value (vth) of the driving TFT 530. (Please refer to Figure 4 for the 昼素500 circuit). In summary, the threshold voltage value (vth) of the driving TFT 530 in each pixel 500 circuit after the threshold voltage locking phase 6 is stored in the compensation capacitor ct in the circuit of the pixel 50. Next, the scan line 420 and the threshold voltage lock line 430 are nicknames, so that the scan reset TFT 510 and the detection TFT 52 0 in each pixel 500 drive circuit are turned off (OFF), and then enter. The second stage, Write Phase 620: In the write phase 620, each scan line 4 20 (SI, S2 · · .Sn) will sequentially send a scan signal (Scan), when the scan signal (scan) When shifting to the scan line 420, the scan reset TFT 510 of all the pixel circuits of the pixel 4 of the scan line 420 is turned on (ON), and the ON (ON) of the TFT 510 is reset due to the scan. The cutoff (OFF) of the TFT 520 is detected. Therefore, the data voltage (Vdata) on the data line 410 can be stored in the storage capacitor Cd through the turn-on (0 N ) of the scan reset TFT 510. The compensation capacitor C t is due to <贞 τ FT FT 5 2 0 cutoff (〇 FF ) and always maintain the threshold value of the previous recall (

Page 14 1252455 V. Description of invention (10)

Vth). So, the voltage difference between the storage capacitor Cd will be equal to the power supply voltage (Vdd) minus the data voltage (Vdata), that is, the voltage across the storage capacitor Cd is (Vdd - Vdata), if both the storage capacitor cd and the compensation capacitor ct are stored. The sum of the voltages will be equal to (Vdd - Vdata + Vth); however, the sum of the voltages (Vdd - Vdata + Vth) will cause the driving TFT 530 to output a current of a corresponding magnitude in the next stage (display phase 63 〇). The electromechanical excitation element 54〇, so the current (I) size can be expressed in the following mathematical formula: I = (1/2) χ βχ (Vsg - Vth) 2 I = (l / 2) x β χ (Vdd - Vdata + Vth —Vth)2 I = (l/2)x )5 x (Vdd -Vdata)2 From the above mathematical formula (where cold is the conductivity coefficient of the driving TFT 53〇 (

Transconductance Parameter)), the output current (I) of the driving TFT 530 is independent of its own threshold voltage value (Vth), and is only related to the size of the written data voltage (V data), so it can compensate for the thin film transistor (TFT). The variation of the threshold voltage (Vth) due to process factors. After the last scan line 42 0 (Sn) also completes the writing of the data voltage (vdata) signal, next, the display signal line 460 controls the switching element 470 to turn it on (ON), connecting the common cathode line 440 to The ground terminal of the system enters the third stage, Display Phase 630: In this display phase 630, the drive TFT 53 0 in each pixel 500 drive circuit can output and write the data voltage (Vdata The current (I) is applied to the organic electroluminescent device 504 to cause the organic electroluminescent device to emit appropriate brightness, and the output current (I) and the threshold voltage of the driving TFT 530 (Vth) ) Nothing.

Page 15 1252455 V. INSTRUCTIONS (11) In combination with the above description, the present invention is only one more reset before the data voltage is loaded compared to the conventional US patent US 6,2 2 9,5 0 6 ' The Reset action "to complete the so-called threshold voltage lock phase 61" action to avoid complex data voltage (Vdata) loading. In addition, compared with the well-known PHILIPS paper "A Comparison of Pixel Circuits for Active Matrix P〇1 ymer/Organic LED Displays", the technology of this case records all the critical voltage values in a supplemental valley Ct (critical voltage storage capacitor). To compensate for the effects of critical voltage variations. The present invention uses two capacitors (storage capacitor Cd, compensation capacitor Ct) to separately handle two different things. The compensation capacitor ct is responsible for recording all threshold voltage values (Vth), and the other storage capacitor Cd is responsible for all data. Record of the voltage value (Vdata). Different from the US patent us 6, 22 9 5 〇6, the electricity voltage Cs must be recorded in the whole threshold voltage (Vth) and the part of the data voltage (Vdata) loaded; also different from the paper of pHILips, Capacitor C1 and capacitor C2 jointly record the threshold voltage, so the capacitor C2 port has two partial threshold voltages. The partial threshold voltage recorded in the capacitor C1 is the most = that is, the active organic electric excitation of the present invention The light display crying circuit can have the following advantages: °. Heart drive 1·The critical electric value (Vth) can be recorded in one c t , so the effect deer can be completely compensated for the critical voltage variation. Capacitor 2· The data voltage (Vdat a ) loading method only needs one more (Reset), and the town avoids complex circuit actions as is conventional. action

Page 16 1252455 V. INSTRUCTION DESCRIPTION (12) 3. This technique places the transistor switching element 470, which controls the OLED current, outside the halogen 500 to increase the aperture ratio of the pixel 500. 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.

Page 17 1252455

Brief description of the drawing [Simplified description of the drawing] Fig. 1 is a schematic diagram of a halogen circuit of the US patent US 6, 2 2 9, 5 0 6 . Figure 2 is a timing diagram of the control signals of U.S. Patent No. 6, 2 2 9, 5 06. Figure 3 is a schematic diagram of the pixel circuit of the paper by PHIL IPS. Figure 4 is a schematic diagram of the circuit within each pixel of the present invention. Fig. 5 is a diagram showing the connection and control of the pixel circuit on the display panel of the present invention. Fig. 6 is a timing chart of the control signal of the present invention. [Description of the figure] Transistor ΤΙ, T2, T3, T4, T31, T32, T33, T34 Capacitance Cc, Cs, Cl, C2 Storage capacitor Cd Compensation capacitor Ct Data line 1 1 0, 3 1 0 Scan line 1 2 0, 3 2 0 Return to zero control line 1 3 0, 3 3 0 Illumination control line 1 4 0, 3 4 0 Power supply line 1 5 0, 3 5 0 Organic light-emitting diode 1 6 0, 3 6 0 Zero phase 2 1 0 Loading data phase 2 2 0 Lighting phase 2 3 0 Display panel 4 0 0 Data line 4 1 0

Page 18 1252455 Schematic description of the scan line 4 2 0 Threshold voltage lock line 4 3 0 Common cathode line 4 4 0 Power supply line 4 5 0 Display signal line 4 6 0 Switching element 4 7 0 Pixel 500 Scan reset TFT 510 Detecting TFT 520 Driving TFT 530 Organic Electroluminescent Element 5 4 0 Threshold Voltage Locking Phase 6 1 0 Write Phase 6 2 0 Display Phase 6 3 0

Page 19

Claims (1)

!252455 VI. The patent application scope of the turtle ^ A main ί-type organic electro-excitation diode drive circuit 4 t display panel on the mother-strip scan line and each record ί The invention is driven by 3 channels, each of which The driving circuit of the prime includes, and is configured to, a scan reset TF Τ, the broadcast y tongue τ ρ τ is drawn, and the end (D) is “connected to — the end of the pole line (G) and the Sweep reset mWA' the storage capacitor has two ends 'set in the upper pass 浐 reset m source extreme (s) and _ power supply for the upper scan-drive tft 'the source of the drive TFT s ( :d) m The line (Vdd) is connected; ), the above power supply supplies a detecting TFT, and the detecting TFT is connected to the gate terminal 〇))), and the source terminal (S) and the driving m are 汲 'extreme (G)-compensated Capacitor, the compensation capacitor has two ends, the system is connected with (); the source terminal (s) of the reset TFT and the detection TFT ^_ ^ ^ scan line; the cathode is a cathode, and the cathode is connected to a common cathode and the display panel has a switch Component, the above common cathode line and grounding terminal. ΜSwitching element is used to connect the pole body 2 drive: the active active organic power supply is Same-bar critical electricity::::= Na in each pixel - Pole body 3 drive π mm: The active organic electroluminescence light is described in the second way. Its hhai display is not driven by each pixel on the substrate. Page 20, 1252455 VI. The patent source range source (s) is connected to the same power supply line. Polar body 4 = active organic electroluminescence two-way as described in item 1 of the patent scope, where each of the display substrates The cathode of the organic electro-acoustic yoke in the individual elements is connected to the common cathode line. The active organic electroluminescence two-body corpse circuit of the first embodiment of the polar body 5 drive range, wherein the switching element is - A thin-film transistor. The active-type organic electric power according to the first aspect of the invention, wherein the switching element is controlled by a display signal line, and is controlled by a display signal line. The polar body drive circuit, Α Φ dynamic organic electric excitation light dichotomy - Pro circuit method will drive the signal cycle human phase U ^ Ph lock order / MThreSh〇ld ~ L〇Ck Phase), - write a stage PhaS〇 and a display phase (Display Phase) and other triodes 8 drive m. The voltage level of the active organic electroluminescence two-wire line described in item 7 # # ^ ^ & locks the ^ segment at the beginning, the pressure level 4 is the same as the power supply line is reset (Reset) Udd) electrode body 9 drive nm" in the active organic electroluminescent diode drive according to the seventh item, the active organic electroluminescence light described in the seventh item of the iW item 7th τ δ hai writing stage voltage ( Vdata) will pass Page 21 1252455 VI. Application for Patent Range Scanning resets the ON (ON) of the TFT and stores it in the storage capacitor. The compensation capacitor always maintains the previously stored threshold voltage due to the OFF of the detection TFT. Vth). Page 22