CN100365690C - Current driving device of active organic light emitting diode - Google Patents

Abstract

A current driving device of active organic light emitting diode (AMOLED) comprises a two adjacent Sub-pixels (odd Sub-Pixel and even Sub-Pixel); each sub-pixel comprises a writing element, a switching element, a driving element, a control element, a storage element and a light-emitting element, and the driving circuit comprises an odd-numbered enable line of the odd-numbered sub-pixel, an even-numbered enable line of the even-numbered sub-pixel, a data line shared by the odd-numbered sub-pixel and the even-numbered sub-pixel, a scanning line, a power supply line and a common cathode line; the method is used for improving the phenomenon of uneven images of the active organic light emitting diode panel and saving the number of data lines.

Description

Current-Driven Devices for Active Organic Light-Emitting Diodes

technical field

The present invention relates to a current driving device of an active organic light emitting diode display, in particular to a current programmed driving device capable of improving uneven images of an active organic light emitting diode panel.

Background technique

Organic light emitting displays can be divided into passive type and active type according to the driving method. The so-called active-driven organic light-emitting display uses thin film transistors and capacitors to store signals to control the brightness and gray-scale performance of the organic light-emitting display.

Although the production cost and technical threshold of passive organic light-emitting displays are low, they are limited by the driving method and the resolution cannot be increased. Therefore, the size of the applied products is limited to within about 5 inches, and the products will be limited to the market with low resolution and small size. If you want to obtain high-definition and large-scale images, you must use the active driving method. The so-called active driving uses capacitors to store signals, so when the scanning line is scanned, the pixels can still maintain the original brightness; Only the pixels selected by the scan line will be lit. Therefore, in the active driving mode, the organic light-emitting display does not need to be driven to a very high brightness, so it can achieve better life performance and high resolution requirements. Organic light-emitting displays combined with thin-film transistor technology can realize active driving of organic light-emitting displays, which can meet the current display market's requirements for smoother screen playback and higher and higher resolutions, fully reflecting the above-mentioned superior characteristics of organic light-emitting displays.

The technology of growing thin film transistors on glass substrates can be amorphous silicon (a-Si) process and low temperature polysilicon (Low Temperature poly-silicon; LTPS) process, the biggest difference between low temperature polysilicon thin film transistors and amorphous silicon thin film transistors , lies in the difference between its electrical properties and the complexity of the manufacturing process. Low-temperature polysilicon thin film transistors have higher carrier mobility, which means that thin film transistors can provide more sufficient current, but their manufacturing process is more cumbersome and complicated; amorphous silicon thin film transistors are the opposite, although non-crystalline The carrier mobility of crystalline silicon is not as good as that of low-temperature polysilicon, but because of its relatively simple and mature manufacturing process, it has a good competitive advantage in terms of cost.

Therefore, due to the limitation of low-temperature polysilicon process capability, the threshold voltage and electron mobility of manufactured thin film transistor elements will vary, so the characteristics of each thin film transistor element will be different. When the driving system uses analog voltage modulation to express grayscale, due to the different characteristics of thin film transistors in different pixels, even if the same data voltage signal is input, the organic light-emitting diodes will generate different output currents, resulting in the display panel. The OLED elements of different pixels emit different brightness. This phenomenon will cause the OLED panel to display an image with poor gray scale, which seriously damages the uniformity of the panel image.

Therefore, in order to solve the above-mentioned shortcomings of poor image uniformity of the panel, U.S. Patent No. 6,229,506 "Active Matrix Light Emitting Diode Pixel Structure And Concomitant Method" proposes a mechanism that uses data current writing to compensate the critical voltage and electron density of the thin film transistor element. Mobility variation to improve image uniformity. As shown in FIG. 3 , it is a schematic circuit diagram of a pixel in US Patent No. 6,229,506. The operating principle of the circuit is described as follows:

During scanning, the transistor P1 and the transistor P3 are turned on (ON), and the transistor N1 is turned off (OFF). At this time, the data current (I _data ) on the data line 31 will flow through the transistor P1. If the data current (I _data ) is not equal to the current (I _P2 ) flowing through the transistor P2, there will be a current (I _c ) to charge or discharge the storage element Cs, and the magnitude of the current is equal to the data current (I _data ) and the current flowing through the transistor P2 (I _P2 )Difference.

Therefore, the charging or discharging action of the storage element Cs will increase or decrease the current (I _P2 ) flowing through the transistor P2, and the charging or discharging action of the storage element Cs will continue until the current flowing through the transistor P2 (I P2 ) _P2 ) is equal to the data current (I _data ). When the current (I _P2 ) flowing through the transistor P2 is equal to the data current (I _data ), the voltage difference between the two ends of the storage element Cs can just provide the required current (I _P2 ) of the transistor P2 when it is equal to the data current (I _data ). Vsg (source, gate voltage difference). Afterwards, the transistor P1 and the transistor P3 are turned off to end the scanning and enter the display stage. After entering the display stage, the transistor N1 is turned on, and the S terminal (source terminal) of the transistor P2 is connected to the power supply line 33. Since the voltage difference between the two ends of the storage element Cs can just provide the current flowing through the transistor P2 (I _P2 ) equal to the data Current (I _data ) required Vsg (source, gate voltage difference), so the current flowing through the organic light emitting diode (OLED) 34 will be equal to the current size (I _P2 ) flowing through the transistor P2, that is, the data current (I _data ), so that the organic light emitting diode 34 emits brightness corresponding to the magnitude of the data current (I _data ).

The driving structure of the active organic light emitting diode display with the above-mentioned pixel circuit technology is shown in FIG. 4 . A picture frame 40 (1Frame=1/60sec) starts from the first scanning line to write the data current of the current picture frame 40 401, so that the voltage difference between the two ends of the storage element Cs in the pixel can just provide P2 flow The Vsg required when the current (I _P2 ) is equal to the data current (I _data ). After the first scanning line 32 completes the writing operation 401, the second scanning line 32 immediately performs the writing operation 401 of the data current of the current frame 40. At this time, the organic light emitting diode element 34 on the first scanning line 32 The organic light emitting diode element 34 on the first scanning line 32 is operated to display 402 the brightness of the current image by passing a current with the magnitude of the writing data current.

After the second scanning line 32 completes the writing operation 401, the third scanning line 32 performs the writing operation 401 of the data current of the current frame 40 in turn. At this time, the organic light emitting diode element 34 on the second scanning line The current of the same magnitude as the writing data current is passed through, so that the OLED element 34 on the second scan line 32 displays 402 the brightness of the current picture.

It is executed sequentially until the last scanning line 32 completes the writing operation 401 of the data current of the frame frame 40 , and then the first scanning line 32 performs the writing operation 401 of the data current of the next frame frame 40 again.

However, the above-mentioned patents must use P-type (P-Type) and N-type (N-Type) color low-temperature polysilicon thin-film transistor (C-TFT LTPS) process, the complexity of the process will be relatively increased, and the manufacturing cost will also be relatively increased.

Contents of the invention

Therefore, the main purpose of the present invention is to solve the above-mentioned traditional defects. In order to avoid the existence of this defect, the present invention can realize the driving method of data current writing, so as to compensate the variation of the critical voltage and electron mobility of the thin film transistor element, and achieve improvement. The image unevenness of the active organic light-emitting diode panel. At the same time, the number of data lines can be saved, only half of the number of data lines in the known design is needed, thus, the manufacturing cost can be saved.

In order to achieve the above object, the driving device proposed by the present invention is one or two adjacent sub-pixels (odd sub-pixels and even-numbered sub-pixels), and each sub-pixel driving device includes 4 thin film transistors and 1 capacitor; and each sub-pixel The pixel includes a writing element, a switching element, a driving element, a control element, a storage element, and a light-emitting element, and the driving circuit includes odd-numbered sub-pixels (Odd Line Enable), and even-numbered sub-pixels Even Line Enable, a data line shared by odd sub-pixels and even sub-pixels, a scanning line, a power supply line, and a common cathode line.

Description of drawings

Figure 1 is a schematic diagram of the device of the present invention.

Fig. 2 is a driving frame of the device shown in Fig. 1 .

Fig. 3 is a schematic diagram of a pixel circuit in US Patent No. 6,229,506.

FIG. 4 is a driving structure of the pixel circuit shown in FIG. 3 .

Detailed ways

Relevant detailed content and technical description of the present invention, now in conjunction with accompanying drawing, explain as follows:

Please refer to FIG. 1 , which is a schematic view of the device of the present invention. As shown in the figure: the driving device proposed by the present invention is one or two adjacent sub-pixels (odd sub-pixel 10 and even sub-pixel 20), and each sub-pixel driving device includes 4 thin film transistors and 1 capacitor; 10 and even-numbered sub-pixels 20 each include a writing element T1 and T1', a switching element T2 and T2', a driving element T3 and T3', a control element T4 and T4', a storage element C and C', a The light-emitting elements 11 and 21; and the driving circuit includes the odd enabling line 101 and a power supply line 52 of the odd sub-pixel 10, the even enabling line 201 and a power supply line 52' of the even sub-pixel 20, and an odd sub-pixel 10 and even sub-pixels 20 share a data line 50 , a scan line 51 , and a common cathode line 53 .

Wherein, the sources of the writing elements T1, T1' are connected to the data line 50; the gates of the switching elements T2, T2' are connected to the gates of the writing elements T1, T1', and their sources are connected to the data The gates of the driving elements T3, T3' are connected to the drains of the above-mentioned writing elements T1, T1', and their sources are connected to the above-mentioned power supply lines 52, 52'; the control elements T4, The gate of T4' is connected to the scanning line 51, the source is connected to the odd enabling line 101 (even enabling line 201), and the drain is connected to the gates of the switching elements T2 and T2'.

However, the storage elements C and C' have two ends, one end is connected to the source of the above-mentioned driving elements T3, T3', the other end is connected to the gate of the above-mentioned driving elements T3, T3' and the writing elements T2, T2' One end of the light-emitting elements 11, 21 is positive, connected to the drains of the driving elements T3, T3', and the other end is negative, connected to the common cathode line 53.

The driving frame of the present invention is as shown in Figure 2, is that the cycle (1Frame=1/60sec) of a picture frame 60 is divided into two periods, one is the writing period (Write Period) 601, and the other is the display period (Display Period) 602.

During the write-in period 601, the common cathode line 53 is raised to a high potential (Vdd), and all the light-emitting elements 11 and 21 on the panel will stop lighting the previous frame, and start the current frame 60 from the first scanning line 51. The writing operation of the data current makes the voltage difference _between the two ends of the storage elements (C and C') in the pixel just provide the Vsg (source, gate voltage difference) in sequence until the last scan line 51 completes the writing operation of the data current. After completing the writing period 601 of each scanning line 51, the common cathode line 53 is lowered to zero potential (GND) to enter the display period 602, and the light emitting elements 11 and 21 in each pixel on the panel will pass the same current as the writing data. Large and small currents make the light-emitting elements 11 and 21 of the display emit the brightness of the current picture.

The operating principle of the present invention is described as follows: during the writing period 601, since the common cathode line 53 rises to a high potential (Vdd), the light-emitting elements 11 and 21 cannot be illuminated because they are in reverse bias, and the light flowing through the light-emitting elements 11 and 21 current goes to zero.

Therefore, when the scanning line 51 sends out the scanning driving signal, the control element T4 of the odd-numbered sub-pixel 10 and the control element T4' of the even-numbered sub-pixel 20 are turned on; thus, the signal on the odd-numbered enable line 101 will pass through the control element T4 The conduction of the writing element T1 and the switching element T2 in the odd sub-pixel 10 is turned on, and the signal on the even enabling line 201 controls the conduction of the element T4' to make the writing element in the even sub-pixel 20 T1' and switching element T2' are turned off. At the same time, the data current (I _{data_odd} ) of the odd sub-pixels 10 is sent from the data line 50 .

Moreover, if the data current (I _{data_odd} ) on the data line 50 is not equal to the current (I _T3 ) flowing through the driving element T3 at this time, there will be a current (I _c ) to charge or discharge the storage element C. The magnitude of the current is equal to the difference between the data current (I _{data_odd} ) and the current (I _T3 ) flowing through the driving element T3. The charging or discharging action of the storage element C will increase or decrease the current (I _T3 ) flowing through the driving element T3, and the charging or discharging action of the storage element C will continue until the current flowing through the driving element T3 (I T3 ) _T3 ) is equal to the data current (I _{data_odd} ). However, when the current (I _T3 ) flowing through the driving element T3 is equal to the data current (I _{data_odd} ), the voltage difference between the two ends of the storage element C can just provide the driving element T3 with a flow current (I _T3 ) equal to the data current (I data_odd ). _{data_odd} ) required Vsg.

Next, the signal on the odd-numbered enabling line 101 will turn on the writing element T1 and the switching element T2 in the odd-numbered sub-pixel 10 through the conduction of the control element T4; and the signal on the even-numbered enabling line 201 will pass through the control element T4 ' is turned on so that the writing element T1' and the switching element T2' in the even sub-pixel 20 are turned on. At the same time, the data current (I _{data_even} ) of the even sub-pixels 20 is sent out from the data line 50 .

If the data current (I _{data_even} ) on the data line 50 is not equal to the current (I _T3 ') flowing through the driving element T3', there will be a current (I _c ') to charge or discharge the storage element C' , the magnitude of the current is equal to the difference between the data current (I _{data_even} ) and the current (I _T3 ′) flowing through the driving element T3 ′. The action of charging or discharging the storage element C' will increase or decrease the current (I _T3 ') flowing through T3', while the action of charging or discharging the storage element Cs' will continue until the current flowing through the driving element T3' When the size (I _T3 ') is equal to the data current (I _{data_even} ). When the current (I _T3 ') flowing through the driving element T3' is equal to the data current (I _{data_even} ), the voltage difference between the two ends of the storage element C' can just provide the current (I _T3 ') of the driving element T3' equal to Vsg' required for data current (I _{data_even} ).

After the writing of each scanning line 51 is completed, the common cathode line 53 is lowered to zero potential to enter the display period 602, so that the light-emitting elements 11 and 21 are in the forward bias and turn on and light up, because the two storage elements Cs and Cs' The voltage difference between the terminals can just provide the Vsg and Vsg' required when the current flowing through the drive elements T3 and T3' is equal to the data current, so the light-emitting elements 11 and 21 in each pixel on the panel will pass a current equal to the current for writing data , so that the light-emitting elements 11 and 21 of the display emit the brightness required by the current picture.

Based on the above description, the current driving device for active organic light emitting diodes has the following advantages:

(1) The present invention can realize the driving method of data current writing, so as to compensate the variation of the threshold voltage and electron mobility of the thin film transistor element, and achieve the improvement of the image unevenness of the active organic light emitting diode panel.

(2) The present invention can save the number of data lines 50, and only needs half the number of data lines 50 of the known design, thus, it can save circuit cost, reduce the cost of pressing and manufacturing the module system, increase the robustness of the connection of the module system, etc.

(3) The present invention does not need to use P-type (P-Type) and N-type (N-Type) colored low-temperature polysilicon thin-film transistor (C-TFT LTPS) manufacturing process, and the manufacturing cost can be reduced.

(4) The technology of the present invention will cause the OLED element to be under reverse bias voltage for a period of time during operation. In this operating mode, the service life of the OLED element can be increased.

Obviously, those skilled in the art can make various modifications and changes to the present invention without departing from the spirit and scope of the present invention. Therefore, various modifications and changes of the present invention are covered by the appended claims and their equivalents.

Claims (6)

1. the current driving device of an active organic light-emitting diode, described drive unit comprises one or two adjacent sub-pixel, i.e. odd number sub-pixel (10) and even sub-pixel (20);

It is characterized in that: each described odd number sub-pixel (10) comprises odd number enable line (101), and each described even sub-pixel (20) comprises even number enable line (201), and the drive unit of each described sub-pixel also comprises:

The data line (50) that one described odd number sub-pixel (10) and described even sub-pixel (20) are shared;

One scan line (51);

One power supply line (52,52 ');

Have cathode line (53) altogether;

One write element (T1, T1 '), the source electrode of said write element (T1, T1 ') is connected with described data line (50);

One switches element (T2, T2 '), and the grid of described switching device (T2, T2 ') is connected with the grid of said write element (T1, T1 '), and its source electrode is connected with described data line (50);

One driving element (T3, T3 '), the grid of described driving element (T3, T3 ') is connected with the drain electrode of said write element (T1, T1 '), and its source electrode is connected with described power supply line (52,52 ');

One control element (T4, T4 '), the grid of described control element (T4, T4 ') is connected with described sweep trace (51), its source electrode is connected with described odd number enable line (101) or described even number enable line (201), and its drain electrode is connected with the grid of described switching device (T2, T2 ');

One storage unit (C, C '), described storage unit (C, C ') has two ends, one end is connected with the source electrode of described driving element (T3, T3 '), and the grid of the other end and described driving element (T3, T3 ') is connected with the junction of the drain electrode of said write element (T1, T1 ');

One light-emitting component (11,21), an end of described light-emitting component (11,21) are anodal, are connected with the drain electrode of described driving element (T3, T3 '), and the other end is a negative pole, is connected with described common cathode line (53).

2. the current driving device of active organic light-emitting diode according to claim 1 is characterized in that, said write element (T1, T1 ') is a thin film transistor (TFT).

3. the current driving device of active organic light-emitting diode according to claim 1 is characterized in that, described switching device (T2, T2 ') is a thin film transistor (TFT).

4. the current driving device of active organic light-emitting diode according to claim 1 is characterized in that, described driving element (T3, T3 ') is a thin film transistor (TFT).

5. the current driving device of active organic light-emitting diode according to claim 1 is characterized in that described control element (T4, T4 ') is a thin film transistor (TFT).

6. the current driving device of active organic light-emitting diode according to claim 1 is characterized in that, described storage unit (C, C ') is a storage capacitors.

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