CN1567409A - Active organic light emitting display driving device and method - Google Patents

Abstract

An active organic light-emitting display driving device and method include the driving element proposed in the present invention, which includes a writing element, a zeroing element, a driving element, a switching element, and a storage element. This device uses an automatic zeroing mechanism to compensate for the variation of the critical voltage of each transistor element, thereby improving the uniformity of the image; the data is loaded by charging the storage element with a current source, and the size of the loaded voltage can be adjusted by controlling the size of the current source or the length of the charging time. This can save one capacitor compared to the related invention, thereby increasing the aperture ratio of the pixel, and at the same time, can reduce the complexity of the driving method.

Description

Active organic light emitting display driving device and method

technical field

The present invention relates to an active organic light emitting display driving device and method, in particular to a driving device and method for improving image unevenness of an organic light emitting display.

Background technique

Organic light emitting display (Organic Light Emitting Display; OLED) can be divided into passive type (Passive Matrix; PMOLED) and active type (Active Matrix; AMOLED) according to the driving method. The so-called active driving OLED (AMOLED) is to use thin film transistor (Thin Film Transistor; TFT) with a capacitor (Capacitor) to store signals to control the brightness grayscale performance of OLED.

Although the production cost and technical threshold of passive OLED are relatively low, the resolution cannot be improved due to the limitation of the driving method. Therefore, the size of the applied product is limited to about 5 inches, and the product will be limited to the low-resolution and small-size market. If you want to obtain high-definition and large-scale images, you need to use the active drive method as the main method. The so-called active drive 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, OLED does not need to be driven to a very high brightness, so the life of the product can be extended, and the requirement of high resolution can also be realized. The combination of OLED and TFT technology can realize active driving OLED, which can meet the increasingly higher requirements for the smoothness of screen playback and resolution in the current display market, and fully demonstrate the above-mentioned superior characteristics of OLED.

The technology of growing TFT on glass substrate can be amorphous silicon (a-Si) process and low temperature polysilicon (Low Temperature poly-silicon; LTPS) process. The biggest difference between LTPS TFT and a-Si TFT lies in its electrical properties The difference from the complex and simple process. LTPS TFT has a higher carrier mobility, which means that the TFT can provide more sufficient current, but its manufacturing process is more complicated; the opposite is true for a-SiTFT, although the carrier mobility of a-Si The efficiency is not as good as LTPS, but because of its relatively simple and mature manufacturing process, it has a good competitive advantage in cost.

In this way, due to the limitation of low-temperature polysilicon (LTPS) process capability, the threshold voltage (Threshold Voltage) and electron mobility (Mobility) of the manufactured thin-film transistor (TFT) elements will vary, so the characteristics of each TFT element will vary. different. When the system uses the conventional 2T1C (2 TFT transistors and 1 capacitor) drive circuit and uses analog voltage (Analog Voltage) modulation to express grayscale, because TFTs of different pixels have different characteristics, even different pixels Inputting the same data voltage (Data Voltage) signal may still produce output currents of different magnitudes, causing the organic light-emitting diode (OLED) to emit different magnitudes of brightness. Therefore, the performance of the image gray scale is easily affected by the characteristic variation of the TFT element, which destroys the uniformity of the image of the OLED panel (Image Uniformity).

Therefore, in order to solve the shortcomings of the uniformity of the above-mentioned panel images, US Patent No. 6,229,506 "Active Matrix Light Emitting Diode Pixel Structure And Concomitant Method (Active Matrix Light Emitting Diode Pixel Structure And Concomitant Method)", this patent has proposed a 4T2C ( 4 TFT transistors and 1 capacitor) pixel circuit, as shown in Figure 3. This circuit uses a mechanism called Auto-Zero to compensate for variations in the threshold voltage of TFT elements and improve image uniformity. Its action principle is described as follows:

The driving timing of the control signal of the driving line is divided into the zeroing phase (Auto-ZeroPhase) 410, the loading data phase (Load Data Phase) 420, and the lighting phase (Illuminate Phase) 430, please refer to Figure 4, which is Figure 3 Timing diagram of the control signal.

Before the zeroing stage 410, the transistor P3 and the transistor P4 are cut off (OFF), and the transistor P2 is turned on (ON). At this time, the current flowing through the organic light emitting diode (Organic LightEmitting Diode; OLED) 360 is the previous frame ( Frame) current is controlled by the Vsg (source-gate voltage difference, that is, the voltage difference stored at both ends of the storage element Cs′) of the transistor P1.

After entering the zeroing stage 410, the transistor P4 is first turned on (ON), and then the transistor P3 is turned on (ON), so that the drain (Drain) of the transistor P1 is connected to the gate (Gate), forming a diode connection, and then Turn off (OFF) the transistor P2, at this time the gate (Gate) voltage of the transistor P1 will rise to a voltage value, which is equal to the high potential (Vdd) minus the threshold voltage (threshold voltage; Vth) of the transistor P1, that is The voltage difference stored at both ends of the storage element Cs' is the critical voltage of the transistor P1, and then the transistor P3 is turned off (OFF), so that the critical voltage (Vth) of the transistor P1 is stored on the storage element Cs', and the zeroing phase is completed Actions.

Then enter the data loading stage 420, if the voltage fluctuating on the data line (Date Line) 310 is ΔV, it is connected (Couple) to the gate (Gate) terminal of the transistor P1 through the transistor P4 and the storage element Cc', therefore, The voltage difference stored at both ends of the storage element Cs' is ΔV×[Cc'/(Cc'+Cs')] plus the Vth originally stored in Cs', that is, the Vsg of the transistor P1 will include the Vth of the transistor P1, which makes The current output by the transistor P1 is only related to the fluctuating voltage (ΔV) on the data line 310 and is not affected by the Vth of the transistor in each pixel.

Finally, it enters the light-emitting stage 430. At this time, the transistor P4 is cut off (OFF), and the transistor P2 is turned on (ON). The 360 elements are illuminated.

Although this 4T2C pixel 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, the components used include 4 transistors and 2 capacitors, because the capacitors will occupy the display pixels A large area leads to a significant reduction in the aperture ratio of the pixel. In addition to data lines 310, scan lines 320, and power supply lines (Vdd) 350, control lines such as an Auto-Zero Line (Auto-Zero Line) 330 and an Illuminate Control Line (Illuminate Line) 340 are required, so the driving method Therefore, the complexity of the device will increase, resulting in the need to use non-standard scan driver ICs and data driver ICs, increasing the manufacturing cost.

Contents of the invention

Therefore, the main purpose of the present invention is to solve the above-mentioned traditional defects and avoid the existence of defects. The present invention can be applied in the device of low-temperature polysilicon thin-film transistor (LTPS-TFT) active organic light-emitting diode display (AMOLED) to improve active organic light-emitting diode display (AMOLED). The shortcoming of the non-uniform image of the light-emitting diode panel; the complexity of the driving method of the present invention is low simultaneously, and the scan driver IC and the data driver IC of the traditional passive (Passive-Matrix) organic light-emitting diode display can be used, which can reduce the manufacturing cost.

In order to achieve the above-mentioned purpose, the driving element proposed by the present invention includes a writing element, a zeroing element, a driving element, a switching element, and a storage element. This device utilizes an automatic zeroing mechanism to compensate each transistor element The variation of the threshold voltage can improve the uniformity of the image. Compared with the 4T2C pixel circuit device, the present invention can save one capacitor and increase the aperture ratio of the pixel; at the same time, the complexity of the driving method can be reduced.

Description of drawings

Fig. 1 is a device schematic diagram of the present invention;

Fig. 2 is a control signal sequence diagram of Fig. 1;

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

FIG. 4 is a timing diagram of control signals in FIG. 3 .

Detailed ways

Relevant detailed content and technical specification of the present invention, now cooperate accompanying drawing to illustrate as follows:

Please refer to FIG. 1 , which is a schematic view of the device of the present invention. As shown in the picture: the device includes:

A data line 110, a scan line 120, a zero control line 130, a display control line 140, a power supply line 150;

A writing element T1, the drain of the writing element T1 is connected to the data line 110, and the gate (gate) is connected to the scanning line;

A zero return element T2, the gate of the zero return element T2 is connected to the zero return control line 130;

A driving element T3, the gate of the driving element T3 is connected to the source (source) of the above-mentioned writing element T1, its drain is connected to the source of the above-mentioned return-to-zero element T2, and its source is connected to the above-mentioned The power supply line 150 is connected;

A switching element T4, the gate of the switching element T4 is connected to the above-mentioned display control line 140, and its source is connected to the source of the zero-returning element T2 and the drain of the driving element T3;

A storage element Cs, the storage element Cs has two ends, one end is connected to the source of the above-mentioned driving element T3, the other end is connected to the source of the above-mentioned writing element T1, the drain of the reset element T2 is connected to the source of the driving element T3 The gate connection is connected;

A light-emitting element 160, one end of the light-emitting element 160 is a positive electrode connected to the drain of the switching element T4, the other end is a negative electrode, and the negative electrode is grounded (GND).

Wherein, the writing element T1, the zeroing element T2, the driving element T3, and the switching element T4 are each a thin film transistor; the storage element Cs is a storage capacitor (Storage Capacitor); the light emitting element 160 is an organic light emitting diode .

Next, the action principle of the present invention is described as follows: Please cooperate with FIG. 2 , which is the timing diagram of control signals in FIG. 1 . The driving sequence of the present invention can be divided into three phases: Auto-Zero Phase 210, Scan Phase 220 and Display Phase 230.

Before entering the zeroing stage 210, the writing element T1 and the zeroing element T2 are turned off (OFF), the driving element T3 and the switching element T4 are turned on (ON), and the current flowing through the light emitting element 160 at this time is the same as that of the previous frame. The current of the frame is controlled by the Vsg (the source-gate voltage difference, that is, the voltage difference stored at both ends of the storage element Cs) of the driving element T3.

After entering the zeroing stage 210, the zeroing element T2 is first turned on (ON), so that the drain (Drain) of the driving element T3 is connected to the gate (Gate), forming a diode connection, and then the switching element T4 is turned off (OFF), which will cause the gate (Gate) voltage of the driving element T3 to rise to a voltage value, which is equal to the high potential (Vdd) minus the threshold voltage (Vth) of the transistor T3, which is stored in the storage element Cs The voltage difference between the two ends is the critical voltage of the driving element T3, and then the zeroing element T2 is turned off (OFF), so that the critical voltage (Vth) of the driving element T3 is stored on the storage element Cs, and the action of the zeroing stage 210 is completed .

Then enter the scanning phase 220. At this time, the writing element T1 is turned on (ON), and a certain current Ic is provided on the data line 110. The constant current (Ic) will charge the storage element Cs. If the constant current (Ic ) charging the storage element Cs is Tc, then the gate (Gate) voltage of the driving element T3 will become [Vdd-Vth-(Ic×Tc/C)] (C is the capacitance of the storage element Cs), also That is, the voltage difference stored at both ends of the storage element Cs is (Ic×Tc/C) plus the threshold voltage (Vth) of the driving element T3 originally stored in the storage element Cs, so the Vsg of the driving element T3 will include the threshold voltage (Vth) of the driving element T3 Voltage (Vth), which makes the current output by the driving element T3 only related to the magnitude of the constant current (Ic) on the data line 110, and the length of time (Tc) for the constant current Ic to charge the storage element Cs, and is not affected by the thin film transistor element. Effect of threshold voltage (Vth) variation.

Therefore, as far as the device and method of the present invention are concerned, as long as the magnitude of the constant current (Ic) on the data line 110 is properly adjusted, and the length of time (Tc) for the constant current (Ic) to charge the storage element Cs, the drive element can be adjusted. The magnitude of the current output by T3; however, the magnitude of the current output by the driving element T3 can be controlled, which controls the brightness emitted by the light emitting element 160, and realizes the gray scale performance of using the light emitting element 160 to display the overall image. Moreover, in the scanning phase 220, the writing operation of the scanning signal is performed from the first scanning line, and is performed sequentially to the last scanning line.

After the signal writing operation of each scanning line is completed, it finally enters the display stage 230. At this time, the switching element T4 is turned on (ON), so that the driving element T3 outputs the current of the current frame (Frame), and at the same time, the current flows through The light-emitting element 160 is used to make the light-emitting element 160 emit brightness corresponding to the gray scale of the image data.

The present invention uses an Auto-Zero mechanism to compensate the variation of the threshold voltage of each transistor element, so as to improve the uniformity of the image. At the same time, compared with the 4T2C pixel circuit proposed in U.S. Patent No. 6,229,506, the present invention has the following advantages: the present invention is a 4T1C pixel circuit device, and the capacitor occupies a very large area for a pixel, so the present invention is used because It saves 1 capacitor than the one usually used, so the aperture ratio of the pixel can be increased; in addition, the complexity of the driving method can also be reduced, and the known passive-matrix (Passive-Matrix) organic light-emitting diode display scan driver IC and A data-driven IC is enough, which will greatly reduce the manufacturing cost.

The above descriptions are only preferred embodiments of the present invention, and are not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and changes. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present invention shall be included within the scope of the claims of the present invention.

Claims (8)

1. active organic light-emitting display drive unit, the component arrangement of each pixel that described drive unit is display frame is characterized in that described device comprises:

One data line (110), one scan line (120), the control line (130) that makes zero, one shows control line (140), a power supply line (150);

One write element (T1), the drain electrode of said write element (T1) is connected with data line (110), and grid is connected with sweep trace (120);

One RZ element (T2), the grid of described RZ element (T2) is connected with the control line that makes zero (130);

One driving element (T3), the grid of described driving element (T3) is connected with the source electrode of above-mentioned write element (T1), and its drain electrode is connected with the source electrode of above-mentioned RZ element (T2), and its source electrode is connected with above-mentioned power supply line (150);

One switches element (T4), and the grid of described switching device (T4) is connected with above-mentioned demonstration control line (140), and its source electrode is connected with the source electrode of RZ element (T2) and the drain electrode of driving element (T3);

One storage unit (Cs), described storage unit (Cs) has two ends, one end is connected with above-mentioned driving element (T3) source electrode, and the grid junction of the source electrode of the other end and above-mentioned write element (T1), the drain electrode of RZ element (T2) and driving element (T3) is connected; And

One light-emitting component (160), described light-emitting component (160) one ends are anodal, are connected with the drain electrode of above-mentioned switching device (T4), and the other end is a negative pole, described minus earth (GND).

2. active organic light-emitting display drive unit according to claim 1 is characterized in that said write element (T1) is a thin film transistor (TFT).

3. active organic light-emitting display drive unit according to claim 1 is characterized in that described RZ element (T2) is a thin film transistor (TFT).

4. active organic light-emitting display drive unit according to claim 1 is characterized in that described driving element (T3) is a thin film transistor (TFT).

5. active organic light-emitting display drive unit according to claim 1 is characterized in that described switching device (T4) is a thin film transistor (TFT).

6. active organic light-emitting display drive unit according to claim 1 is characterized in that described storage unit (Cs) is a storage capacitors.

7. active organic light-emitting display drive unit according to claim 1 is characterized in that described light-emitting component (160) is an Organic Light Emitting Diode.

8. active organic light-emitting display driving method is characterized in that described driving method comprises:

Sequential be will drive and the stage of making zero (210), sweep phase (220) and demonstration stage (230) three phases will be divided into;

Enter the stage of making zero (210) before, write element (T1) and RZ element (T2) are for ending (OFF), driving element (T3) and switching device (T4) are conducting (ON), the electric current that flow through light-emitting component (160) this moment is the electric current of previous menu frame (Frame), and described electric current is controlled by the Vsg of driving element (T3) (source electrode, grid voltage poor);

Enter the stage of making zero (210) afterwards, elder generation's conducting (ON) RZ element (T2), the drain electrode of driving element (T3) is connected with grid, form the connection of a diode, then again switching device (T4) T4 is ended, this can make grid (Gate) voltage of driving element (T3) T3 rise to a magnitude of voltage, this magnitude of voltage equals the critical voltage (Vth) that noble potential (Vdd) deducts driving element (T3), that is the voltage difference that is stored in storage unit (Cs) two ends is the critical voltage of driving element (T3), again RZ element (T2) is ended (OFF) afterwards, the critical voltage (Vth) of driving element (T3) is stored on the storage unit (Cs), finishes the stage of making zero the action of (210);

Next enter sweep phase (220), write element this moment (T1) is conducting (ON), provide certain electric current (Ic) on the data line (110) again, this decides electric current (Ic) can be to storage unit (Cs) action of charging, if deciding electric current (Ic) is Tc to the time that storage unit (Cs) charges, then grid (Gate) voltage of driving element (T3) T3 can become (Vdd-Vth-(Ic * Tc/C)), wherein C is the electric capacity of storage unit (Cs), that is the voltage difference that is stored in storage unit (Cs) two ends is (Ic * Tc/C) add that script is stored in the critical voltage (Vth) of the driving element (T3) of storage unit (Cs), so, the Vsg of driving element (T3) can comprise the critical voltage (Vth) of driving element (T3), this make driving element (T3) output electric current only with data line (110) on decide electric current (Ic) size, and it is relevant to storage unit (Cs) duration of charging (Tc) length to decide electric current I c;

Whereby, suitably modulation data line (110) is gone up the size of deciding electric current (Ic), is reached and decide the length of electric current (Ic) to storage unit (Cs) Cs duration of charging (Tc), can adjust the size of current of change driving element (T3) output, also control the brightness that light-emitting component (160) sends.

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