KR100541829B1 - Current driving apparatus and method for active matrix oled - Google Patents

Abstract

The current driving device and method for an active matrix organic light emitting diode (AMOLED) according to the present invention includes two adjacent sub pixels (odd sub pixel and even sub pixel). The driving device of each sub pixel includes a recording element, a switching element, a driving element, a control element, a storage element and a light emitting element. The driving circuit includes an enabling odd line for odd sub pixels, an enabling even line for even sub pixels, a data line shared by the odd sub pixels and even sub pixels, a scan line, a supply line, and a common line. do. The present invention can improve the uniformity of the AMOLED panel and reduce the number of data lines required.

Description

Current driving device and method for an active matrix OLED {CURRENT DRIVING APPARATUS AND METHOD FOR ACTIVE MATRIX OLED}

1 is a wiring diagram of an apparatus according to the invention.

FIG. 2 is a drive wiring diagram of FIG. 1.

3 is a wiring diagram of a pixel circuit of US Pat. No. 6,229,506.

FIG. 4 is a wiring diagram of the drive wiring for FIG. 3. FIG.

The present invention relates to a current drive device and method for an active matrix organic light emitting diode display (AMOLED), and more particularly to a drive device and method for data current programming that improves the image uniformity of an AMOLED panel.

Methods for driving OLEDs can be divided into passive matrix OLEDs (PMOLED) and active matrix OLEDs (AMPLED). AMOLEDs use thin film transistors (TFTs) and capacitors to store signals for controlling the brightness and gray scale of the OLED. Although costs and technical thresholds for the manufacture of PMOLED have been lowered, PMOLED products are still limited to about 5 inches in size, and the resolution cannot be increased due to the limitations of the driving method. The products are therefore limited to the market of low resolution and small dimensions. In order to achieve higher resolutions and larger screens, an active driving method must be used. The active driving method uses a capacitor to store the signal so that the pixel can still maintain its original brightness even after scanning. In passive driving, only the pixels selected by the scan lines will glow. Thus, under the active driving method, the OLED does not need to be driven to very large luminance. As a result, the active driving method can achieve a higher resolution with a longer lifetime. Linking OLEDs with TFT technology enables active driving of OLEDs and meets the market demand for smoothness and much higher resolution of displays.

Techniques for growing a TFT on a glass substrate can be an amorphous silicon (a-Si) process and a low temperature poly-silicon (LTPS) process. The major difference between LTPS TFTs and a-Si TFTs lies in the electrical properties and manufacturing complexity. LTPS TFTs have higher carrier mobility, which means that the TFTs can supply sufficient current better, but the manufacturing process is more complicated. In contrast, a-Si TFTs have lower carrier mobility than LTPS, but their manufacturing process is simpler and advanced, so a-Si TFTs have a better competitiveness in terms of cost.

Because of the limitations in the manufacturing process of LTPS, the TFT devices to be manufactured have variations in threshold voltage and electron mobility. As a result, each TFT element has different characteristics. When the drive system adopts analog voltage adjustment to achieve gray level, even though the input data voltages are the same, the OLEDs produce different output currents, so that the OLEDs of different pixels on the display panel are different TFTs for different pixels. Due to the characteristics, different luminance is displayed. This phenomenon causes poor gray levels on the OLED display panel and seriously impairs the image uniformity of the panel.

In order to correct the aforementioned disadvantage, i.e., the image uniformity of the panel, U.S. Patent No. 6,229,506 named "Active Matrix Light Emitting Diode Pixel Structure and Concomitant Method" has a TFT threshold. A data current programming mechanism is proposed to compensate for voltage and electron mobility to improve image uniformity. 3 shows a schematic diagram of a pixel circuit used in US Pat. No. 6,229,506. The principle of operation of the circuit is described as follows.

During scanning, transistors P1 and P3 are turned on while transistor N1 is off. At this time, the data current I _data on the data line 31 passes through the transistor P1. If the data current I _data is not equal to the current I _p2 passing through the transistor P2, the current I _c will charge or discharge the storage element Cs. I _c is the difference between I _data and I _p2 . The charging (discharging) operation of the storage element Cs increases (decreases) the current I _p2 . The charging or discharging operation of the storage element Cs will continue until the current I _p2 becomes equal to the data current I _data . When the current I _p2 becomes equal to the data current I _data , the potential difference between the two ends of the storage element Cs is the required Vsg (source) for the transistor P2 to ensure that I _p2 is equal to I _data. Potential difference between the gate and the gate). Thus, transistors P1 and P3 are turned off to end the data current programming operation, and then the displaying step begins. In the display step, the S terminal (source terminal) of the transistor P2 is connected to the power supply line 33 due to the transistor N1 being turned on. Since the potential difference between the two ends of the storage element Cs is exactly the same as Vsg required for the transistor P2, I _p2 becomes equal to the data current I _data . Thus, the current flowing through the OLED 34 is equal to the current I _p2 , that is, the data current I _data , so that the luminance of the OLED 34 corresponds to the data current I _data .

A drive structure based on pixel circuit technology for an OLED display is shown in FIG. Frame 40 (1 frame = 1/60 seconds) is started from the first scan line of present frame 40 by write operation 401 for data current programming. The potential difference between the two ends of the storage element Cs of the pixel provides the Vsg necessary when the current through the transistor P2 is equal to the data current I _data . After the first scan line 32 completes the write operation 401, the second scan line 32 performs the write operation 401 for the current frame 40, during which the current Equal to the data current passing through the OLED element 34 on 32, causing the OLED element 34 of the first scan line 32 to perform the display operation 402.

After the second scan line 32 completes the write operation 401, the third scan line 32 in turn performs the write operation 401 of the data current for the current frame 40, during which the current It becomes equal to the data current passing through the OLED element 34 on the second scan line 32, causing the OLED element 34 of the second scan line 32 to perform the display operation 402.

The process proceeds in sequence until the last scan line 32 completes the write operation 401 for the existing frame 40. Then, the write operation 401 is repeated from the beginning, and the first scan line 32 performs the write operation 401 of the data current for the next frame 40.

However, the above-described patent invention must use P-type and N-type CMOS LTPS TFT fabrication processes. The process is relatively complex and the cost of production is higher.

Therefore, the main aim of the present invention is to solve the above-mentioned disadvantages of the prior art.

The present invention solves the problem of image non-uniformity of an AMOLED panel by providing a driving method for a data current programmed to compensate for variations in electron mobility and threshold voltage of a TFT device. Through the present invention, the number of data lines can be reduced to half of the conventional design. Thus production costs can also be reduced.

In order to achieve the above object, the driving apparatus of the present invention includes two adjacent sub pixels (odd sub pixel and even sub pixel). The driving device of each sub pixel includes four TFTs and one capacitor. In addition, each sub-pixel includes a recording element, a switching element, a driving element, a control element, a storage element and a light emitting element. The driving circuit includes an odd line for enabling odd sub pixels, an even line for enabling even sub pixels, a data line shared by the odd and even sub pixels, a scan line, a supply line, and a common line. .

Further objects as well as the foregoing features and advantages of the present invention will be readily apparent from the following description taken in conjunction with the accompanying drawings.

Referring to FIG. 1, FIG. 1 is a wiring diagram of an apparatus according to the invention. According to the drawing, the driving device proposed in the present invention includes two sub-pixels (odd sub-pixel 10 and even-numbered sub-pixel 20). The driving device of each sub pixel includes four TFTs and one capacitor. The odd subpixels 10 and the even subpixels 20 are the recording elements T1 and T1 ', the switching elements T2 and T2', the driving elements T3 and T3 ', and the control elements T4 and T4', respectively. , Storage elements C, C ′ and light emitting elements 11, 21. The driving circuit includes an enabling odd line 101 and an supply line 52 for the odd sub-pixels 10; Enabling even lines 201, supply lines 52 'for the even sub-pixels 20; Data lines 50 and scan lines 51 shared by odd sub-pixels 10 and even sub-pixels 20; And common line 53.

The sources of the recording elements T1 and T1 'are connected to the data line 50. The gates of the switching elements T2 and T2 'are connected to the gates of the recording elements T1 and T1', respectively, and the sources of the switching elements T2 and T2 'are also connected to the data line 50. Gates of the drive elements T3 and T3 'are connected corresponding to drains of the write elements T1 and T1', and sources of the drive elements T3 and T3 'are connected to the supply lines 52 and 52', respectively. . The gates of the control elements T4 and T4 'are connected to the scan line 51; The sources of the control elements T4 and T4 'are connected to the enabling odd line 101 and the enabling even line 201, respectively; The drains of the control elements T4 and T4 'are connected to the gates of the switching elements T2 and T2', respectively.

Each storage element C, C 'has two ends. One end thereof is connected corresponding to the source of the driving elements T3 and T3 ', and the other end thereof is a connection portion of the "gate of the driving elements T3 and T3'" and "drain of the recording elements T2 and T2 '". Is connected to. The light emitting elements 11, 21 have one positive electrode connected to the drains of the driving elements T3, T3 '; The other end forms a negative electrode connected to the common line 53.

Referring to Fig. 2, Fig. 2 shows the drive structure of the present invention, wherein the period of a picture frame (1 frame = 1/60) is divided into two periods. One is a writing period 601 and the other is a display period 602.

During the writing period 601, the potential of the common line 53 is raised to the high potential Vdd, and all the light emitting elements 11 and 21 of the panel stop displaying the previous picture, and the data current programming operation is stopped. Starting from the first scan line 51 of the current picture frame 60, the potential difference between the two ends of the two storage elements C, C 'is equal to the data current when the drive elements T3, T3' are equal to the data current. It is the required Vsg (potential difference between source and gate) for T3 and T3 '. The process proceeds in this order until the last scan line 51 completes the write operation for data current programming. After all the scan lines 51 have completed the data current programming operation, the potential of the common line 53 returns to 0 (GND) to enter the display period 602. A current, such as a programmed data current, passes through the light emitting elements 11, 21 of each pixel on the panel, enabling the light emitting elements 11, 21, respectively, to display the brightness of the existing picture. Ring.

The operating principle of the present invention is as follows. During the writing period 601, the potential of the common line 53 rises to the high potential Vdd, and the light emitting elements 11 and 21 have a reverse bias such that the current of the light emitting elements 11 and 21 is zero. Due to (reverse vias) it becomes impossible to display.

Therefore, when the scan line 51 sends a scan driving signal, the control element T4 of the odd subpixel 10 and the control element T4 'of the even subpixel 20 are turned on. As a result, the signal of the odd enable-line 101 will turn on the recording element T1 and the switching element T2 of the odd sub-pixel 10 due to the control element T4 being turned on; The signal of the enabling even line 201 will turn off the recording element T1 'and the switching element T2' of the even sub-pixel 20 due to the control element T4 'turned on. In the meantime, the data line 50 sends the odd data current I _{data_odd} of the odd sub-pixel 10.

Furthermore, when the odd data current I _{data_odd} on the data line 50 is not equal to the current I _T3 flowing to the drive element T3, the current I _c may charge or discharge the storage element C. The current is equal to the difference between the odd data current I _{data_odd} and the current I _T3 flowing through the drive element T3. Discharge or charge of the storage element C results in an increase or decrease in the current I _T3 flowing through the drive element T3. The discharging or charging of the storage element C is continued until the current I _T3 flowing through the driving element _T3 becomes equal to the odd data current I _{data_odd} . When the current I _T3 flowing to the driving element T3 is equal to the odd data current I _{data_odd} , the potential difference between the two ends of the storage element C is such that the current flowing through the driving element T3 is the odd data current ( Vsg is required to drive element T3 to ensure the same as I _{data_odd} ).

Thus, the signal of the odd enable-line 101 will turn on the recording element T1 and the switching element T2 of the odd sub-pixel 10 due to the control element T4 being turned on, and enabling The signal of the even line 201 will turn on the recording element T1 'and the switching element T2' of the even sub-pixel 20 due to the control element T4 'turned on. In the meantime, the data line 50 sends the even data current I _{data_even} of the even sub-pixel 20.

At this time, when the even data current I _{data_even} on the data line 50 is not equal to the current I _{T3 '} flowing to the driving element T3', the current I _{c '} is the storage element C'. _Will charge or discharge, and the current will be equal to the difference between the even data current I _{data_even} and the current I _{T3 '} flowing through the driving element T3'. Discharge or charging of the storage element C 'results in an increase or decrease in the current I _T3' flowing through the drive element T3 '. The discharge or charge of the storage element C 'continues until the current I _T3' flowing through the driving element _{T3 '} becomes equal to the even data current I _{data_even} . When the current I _{T3 '} flowing to the driving element T3' is equal to the even data current I _{data_even} , the potential difference between the two ends of the storage element C 'is equal to the current flowing through the driving element T3'. The Vsg 'required for the driving element T3' is provided to ensure that it is equal to the even data current I _{data_even} .

After all the scan lines 51 have completed the data current programming operation, the potential of the common line 53 returns to 0 (GND) to enter the display period 602 and the display period 602 begins. The light emitting elements 11 and 21 emit light due to forward vias. A current, such as a programmed data current, passes through the light emitting elements 11, 21 of each pixel on the panel, enabling the light emitting elements 11, 21, respectively, to display the brightness of the current picture. The driving device when the same as the storage element (Cs, Cs ') potential difference between two ends of a driving device (T3, T3') current is hole number of data current (I _{data_odd)} and the even data current (I _{data_even)} passing through the ( Provide Vsg and Vsg ', respectively, for T3.

In summary, the current driving device for the AMOLED of the present invention has the following advantages.

1. The present invention realizes a driving method for a data current programmed to compensate for variations in electron mobility and threshold voltage of a TFT element in order to solve the problem of image non-uniformity of an AMOLED panel.

2. The technique provided by the present invention can reduce the number of data lines 50 required to half the number required by the prior art. As a result, the cost of the circuit and the manufacturing cost for combining the modular system can be reduced, while at the same time increasing the durability of the modular system connection.

3. The present invention does not require the use of P-type and N-type CTFT LTPS manufacturing processes, so that manufacturing costs can be reduced.

4. The present invention allows the OLED device to be reverse biased for a period of time during the data current programming operation. This mode of operation can extend the life of OLED devices.

Claims (7)

A current driving device for an active matrix organic light emitting diode (AMOLED) using two adjacent sub-pixels (odd sub-pixel and even sub-pixel), wherein the driving device of each sub-pixel is: Enabling odd line enable for the odd sub-pixels; Enabling even line enable for the even sub-pixels; A data line shared by the odd subpixels and the even subpixels; Scan line; Supply line; Common line; A writing element having a source connect to the data line; A switching element having a gate connection to the gate of the recording element and a source connection to the data line; A driving element having a gate connection to the drain of the recording element and a source connection to the supply line; A control element having a gate connection to the scan line, a source connection to the enabling odd line (an enabling even line), and a drain connection to the gate of the switching element; A storage element having two ends, one end of which is connected to a source of the drive element and the other end of which is connected to a connection of a gate of the drive element and a drain of the recording element; And 2. An active matrix organic light emitting diode (AMOLED) comprising a light emitting element having two ends, one end being a positive electrode connected to the drive element and the other end being a negative electrode connected to the common line. Current driving device. The method of claim 1, The recording element is a current driving device for an active matrix organic light emitting diode (AMOLED) which is a thin film transistor. The method of claim 1, The switching device is a current driving device for an active matrix organic light emitting diode (AMOLED) is a thin film transistor. The method of claim 1, The driving device is a current driving device for an active matrix organic light emitting diode (AMOLED) is a thin film transistor. The method of claim 1, The control element is a current driving device for an active matrix organic light emitting diode (AMOLED) is a thin film transistor. The method of claim 1, The storage element is a current driving device for an active matrix organic light emitting diode (AMOLED) which is a storage capacitor. A current driving method for an active matrix organic light emitting diode, Dividing a picture frame into two periods during a drive, a write period and a display period; The potential of the common line is changed to prevent light emitting elements of the panel from displaying a previous picture frame and to proceed with a data current programmed operation from a first scan line of the existing picture frame. Raising the potential to a high potential in the writing period, wherein the potential difference between the two ends of the storage element is equal to the Vsg (between the source and the gate) required for the drive element when the current passing through the drive element is equal to the data current; A potential difference); And The common line to enter the display period after each scan line completes the writing period, and to make the current through the light emitting elements of each pixel on the panel equal to the programmed data current Returning the potential of to zero (GND), whereby the light emitting elements display at the brightness required for the picture.

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