KR101929790B1 - Measuring method of transistor characteristics of Organic light-emitting display device - Google Patents

Abstract

A method of measuring transistor characteristics of an organic light emitting diode display according to an embodiment includes: applying a precharge data voltage to a load capacitor through a data line of a pixel region; Discharging a precharge data voltage applied to the load capacitor to a transistor; Measuring a voltage value to be discharged; And calculating a characteristic of the transistor with the measured voltage value.

Description

[0001] The present invention relates to a method for measuring transistor characteristics of an organic light emitting display,

The embodiment relates to a method of measuring transistor characteristics of an organic light emitting display.

Display devices for displaying information are widely developed.

The display device includes a liquid crystal display device, an organic light emitting display device, an electrophoretic display device, a field emission display device, and a plasma display device.

Among them, the organic light emitting display device is lower in power consumption, wider in viewing angle, lighter in weight, and higher in brightness than the liquid crystal display device, and has attracted attention as a next generation display device.

The thin film transistor used in the organic light emitting diode display has increased the mobility by the semiconductor layer formed of polysilicon through the crystallization of amorphous silicon, thereby enabling high speed driving.

A laser scanning method is widely used for crystallization. In such a crystallization process, the threshold voltages of the thin film transistors formed on the scan lines, which means the scan passes, are different from each other due to the unstable power of the laser, resulting in a problem of uneven image quality in each pixel area.

In order to solve such a problem, a technique has been proposed in which a threshold voltage is detected in a pixel region to compensate a threshold voltage of the thin film transistor.

In order to achieve such a technique, a thin film transistor for detecting a threshold voltage needs to be added to the pixel region, and signal lines for controlling the thin film transistor have to be added, so that the pixel region is complicated and the aperture ratio is lowered.

Further, in order to measure the threshold voltage and the mobility in the I-V curve, different voltage values must be applied twice or more, thereby complicating the measuring method and complicating the circuit.

The embodiment provides a method for measuring the characteristics of a transistor in a short time with a simple circuit.

A method of measuring transistor characteristics of an organic light emitting diode display according to an embodiment includes: applying a precharge data voltage to a load capacitor through a data line of a pixel region; Discharging a precharge data voltage applied to the load capacitor to a transistor; Measuring a voltage value to be discharged; And calculating a characteristic of the transistor with the measured voltage value.

The embodiment can measure the mobility and the threshold voltage of the transistor by measuring the voltage during discharging and discharging after charging the load capacitor, and measure the transistor characteristics in a short time with a simple circuit.

1 is a block diagram illustrating an organic light emitting display according to an embodiment.
2 is a circuit diagram showing the organic luminescent panel of FIG.
3 is a view illustrating a pixel region and a data driver of the OLED display according to the embodiment.
4 is a diagram illustrating driving waveforms of an OLED display according to an embodiment of the present invention.
5 is a diagram illustrating the operation of each section of the pixel region according to the embodiment.
6 is a diagram illustrating a method for measuring a threshold voltage and a mobility by a waveform in a second section.

In describing an embodiment according to the invention, in the case of being described as being formed "above" or "below" each element, the upper (upper) or lower (lower) Directly contacted or formed such that one or more other components are disposed between the two components. Also, in the case of "upper (upper) or lower (lower)", it may include not only an upward direction but also a downward direction based on one component.

1 is a block diagram illustrating an organic light emitting display according to an embodiment.

Referring to FIG. 1, an organic light emitting display according to an exemplary embodiment of the present invention may include an OLED panel 10, a controller 30, a scan driver 40, and a data driver 50.

The scan driver 40 may supply the first and the first scan signals S1 and S2 to the organic light emitting panel 10.

The data driver 50 may supply the data voltage Vdata to the OLED panel 10.

2, the organic light emitting panel 10 includes a plurality of scan lines GL1 to GLn and GL'1 to GL'n, a plurality of data lines DL1 to DLm, Lines PL1 to PLm and a plurality of second power supply voltage lines PL'1 to PL'm.

Although not shown, the organic luminescent panel 10 may further include a plurality of signal lines as needed in addition to the above.

A plurality of pixel regions P can be defined by intersection of the scan lines GL1 to GLn and the data lines DL1 to DLm.

Each pixel region P includes first and second scan lines GL1 to GLn and GL'1 to GL'n and data lines DL1 to DLm and first and second power source voltage lines PL1 to PLm, PL'1 to PL'm).

 For example, the first and second scan lines GL1 to GLn and GL'1 to GL'n are electrically connected to a plurality of pixel regions P arranged in the horizontal direction, and the data lines DL1 to DLm May be electrically connected to a plurality of pixel regions P arranged in the vertical direction.

First and second scan signals S1 and S2, a precharge data voltage Vpre, a data voltage, first and second power supply voltages VDD and VSS may be supplied to the pixel region P. That is, the first and second scan signals S1 and S2 are supplied to the pixel region P through the first and second scan lines GL1 to GLn and GL'1 to GL'n, The charge data voltage Vpre and the data voltage are supplied to the pixel region P through the data lines DL1 to DLm and the first and second power supply voltages VDD and VSS are supplied to the pixel regions P, And may be supplied to the pixel region P through the two power supply voltage lines PL1 to PLm, PL'1 to PL'm.

A sensing voltage Vs for a specific node of the pixel region P from the pixel region P may be provided to the data driver 50 of FIG. 1 through the data lines DL1 to DLm.

3 is a view illustrating a pixel region and a data driver of the OLED display according to the embodiment.

Referring to FIG. 3, the pixel region of the OLED display according to the exemplary embodiment includes first through third transistors T1 through T3, a storage capacitor Cst, a load capacitor Cload, and an organic light emitting diode OLED But is not limited to this. That is, the number of transistors formed in each pixel region P and the connection structure therebetween can be variously modified by the designer, and the embodiment can be applied to the circuit structure of all the pixel regions P that can be deformed by the designer .

The first and second transistors T1 and T2 may be switching transistors for transmitting a signal and the third transistor T3 may be a driving transistor for generating a driving current for driving the organic light emitting diode OLED. Transistor.

The storage capacitor Cst may maintain the data voltage Vdata for one frame.

The load capacitor Cload may charge the precharge data voltage Vpre provided from the outside and may provide the precharge data voltage Vpre to the organic light emitting diode OLED.

The organic light emitting diode (OLED) is a member for generating light, and light having different brightness may be generated depending on the intensity of the driving current.

The organic light emitting diode OLED may include a red organic light emitting diode OLED for generating red light, a green organic light emitting diode OLED for generating green light, and a blue organic light emitting diode OLED for generating blue light. have.

The first to third transistors T1 to T3 may be PMOS type thin film transistors, but the present invention is not limited thereto. The first to third transistors T1 to T3 may be turned on by a low level signal and may be turned off by a high level signal.

Here, the high level may be a ground voltage or a voltage close thereto, and the low level may be a voltage lower than the ground voltage.

The first power supply voltage VDD may be a high level signal and the second power supply voltage VSS may be a low level signal.

The first and second power supply voltages VDD and VSS may be a DC voltage having a constant level.

3, the first and second scan lines GL1 to GLn and GL'1 to GL'n are started, and the first and second scan lines GL1 to GLn and GL'1 to GL'n And the first and second scan signals S1 and S2 are separately supplied.

However, since the first and second scan signals S1 and S2 have substantially the same waveform, the same scan signal can be supplied to the first and second transistors T1 and T2. Accordingly, the first and second scan lines GL1 to GLn and GL'1 to GL'n are formed as one scan line

And a single scan signal may be supplied to the one scan line.

The load capacitor Cload may be connected to the data lines DL1 to DLm. Therefore, the load capacitor Cload may be charged with the precharge data voltage Vpre or the data voltage supplied to the data lines DL1 to DLm.

The gate electrode of the first transistor T1 is connected to the first scan lines GL1 to GLn to which the first scan signal S1 is supplied and the source electrode thereof is connected to the data lines DL1 to DLm, The electrode may be connected to the first node forming the source voltage of the third transistor T3.

The first transistor T1 is turned on by the first scan signal S1 of a low level supplied to the first scan lines GL1 to GLn and supplies a precharge data voltage Vdd to the data lines DL1 to DLm Vpre) or a data voltage for image display may be charged to the first node.

The first node may be commonly connected to the drain electrode of the first transistor T1, the storage capacitor Cst, the source electrode of the third transistor T3, and the first power supply voltage lines PL1 to PLm .

The gate electrode of the second transistor T2 is connected to the second scan lines GL'1 to GL'n to which the second scan signal S2 is supplied and the source electrode thereof is connected to the reference voltage Vref Voltage line, and the drain electrode may be connected to the second node.

The second transistor T2 is turned on by the second scan signal S2 of a low level supplied to the second scan lines GL'1 to GL'n so that the second node is turned to the reference voltage Vref Can be discharged

The second node may be commonly connected to the drain electrode of the second transistor T2 and the gate electrode of the third transistor T3.

The storage capacitor Cst may be coupled between the first and second nodes.

A gate electrode of the third transistor T3 may be connected to a second node, and a source electrode of the third transistor T3 may be coupled to a first node and a first power supply voltage line PL1 to PLm.

The third transistor T3 may generate a driving current according to the voltage of the second node and supply the driving current to the organic light emitting diode OLED.

The organic light emitting diode OLED may emit light by the driving current of the third transistor T3.

Although not shown in FIG. 3, a transistor that is controlled to be switched by an emission signal may be disposed between the first power source voltage lines PL1 to PLm and the third transistor T3.

The data lines DL1 to DLn may be connected to a data driver, and the data driver may include a DAC, an ADC, and a selection means 51. [

The DAC may generate a precharge data voltage Vre and a data voltage. The DAC can convert a precharge data voltage Vpre and a data voltage, which are analog signals, in response to a precharge data signal Dpre, which is a digital signal.

The ADC can convert the sensing voltage Vs, which is an analog voltage sensed in the pixel region P, into a sensing signal (Sensing), which is a digital signal.

The selection means 51 may electrically connect the data lines DL1 to DLm of the pixel region P to the DAC or the ADC.

The selection means 51 can be switched and controlled by the selection signal Sel. For example, in response to the low level selection signal Sel, the selection means 51 controls the switching of the data lines DL1 to DLm to be electrically connected to the DAC, and in response to the selection signal Sel of high level, DL1 to DLm are electrically connected to the ADC.

4 is a diagram illustrating driving waveforms of an OLED display according to an embodiment of the present invention.

As shown in Fig. 4, the circuit structure of the pixel region P can be driven by two individual sections.

The first period P1 is a period for charging the load capacitor Cload with the precharge data voltage Vpre and the second period P2 is a period for sensing a change in the sensing voltage Vs.

5 is a diagram illustrating the operation of each section of the pixel region according to the embodiment.

FIG. 5A is a diagram illustrating an operation of a first section of a pixel region according to an embodiment, and FIG. 5B is a diagram illustrating an operation of a second section of a pixel region according to an embodiment.

The first and second scan signals S1 and S2 at the high level are applied to the first and second scan lines GL1 to GLn and GL'1 to GL'n at the first section P1 as shown in FIG. And the data lines DL1 to DLm may be connected to the DAC.

The first and second scan signals S1 and S2 may be applied at a high level so that the first and second transistors T1 and T2 may be turned off. When the first and second transistors T1 and T2 are turned off, the source and drain of the first and second transistors T1 and T2 are electrically opened and the precharged data voltage Vpre is applied to the load capacitor Cload.

The first and second scan signals S1 and S2 of the low level are applied to the first and second scan lines GL1 to GLn and GL'1 to GL'n in the second period P2 as shown in FIG. And the data line may be coupled to the ADC.

The first and second scan signals S1 and S2 may be applied at a low level so that the first and second transistors T1 and T2 may be turned on. The source and the drain of the first and second transistors T1 and T2 are electrically short-circuited by turning on the first and second transistors T1 and T2, The charge data voltage Vpre may be charged to the first node via the first transistor T1 and the reference voltage Vref may be charged to the second node via the second transistor T2. Accordingly, the driving current of the third transistor T3 can be supplied to the organic light emitting diode OLED.

During the second period, the first node may be discharged to the threshold voltage of the third transistor T3. In this case, the voltage of the first node is the sensing voltage Vs to be measured. During the second period, the ADC senses the sensing voltage Vs of the first node, converts the sensed voltage Vs to a digital value, and transmits the digital value to the controller.

The ADC internally has a high resistance and can extract the voltage of the first node, convert it into a digital value, and transmit it to the controller. Even if the first node is discharged in the second period, there is no load effect of the ADC.

6 is a diagram illustrating a method for measuring a threshold voltage and a mobility by a waveform in a second section.

In FIG. 6, t0 represents a time point from a first period to a second period, t1 represents an arbitrary time during the discharge of the third transistor, and t3 represents a time when the discharge is completed. Also, Vs0 represents the magnitude of the sensing voltage at t0, Vs1 represents the magnitude of the sensing voltage at t1, and Vs2 represents the magnitude of the sensing voltage at t2.

Equations (1) and (2) relate to the current flowing in the third transistor. The above equations (1) and (2) are summarized

When the above equation (3) is integrated with respect to time

By calculating and summarizing Equation (4) above,

In Equation (5), Vg = Vref. Where V _PRE is the precharge data voltage applied to the data line, C is the amount of charge, and T is the detection time. C and T can be derived from the current detection equation.

(6) is finally derived.

In FIG. 6, the sensing voltage at t1 is Vt1, the sensing voltage at t0 is Vpre, and the sensing voltage at t2 is the sum of Vref and Vth, thus satisfying Vth = Vs2-Vref.

Substituting the above values into Equation (6)

(7), and the threshold voltage (Vth) can be measured through the sensing voltage (Vs2) and the reference voltage (Vref) at the time t2.

From Equation (7), K 'and C correspond to the device values, so that the mobility (μ) can be obtained by knowing the sensing voltage (Vs1) at t1 and the sensing voltage (Vs2) at t2.

The threshold voltage Vth and the mobility can be measured by the above-described method, the circuit structure of the pixel region is simplified, the measuring method is simplified, and the measuring time is shortened, It is possible to compensate the mobility μ, thereby ensuring a uniform luminance and improving the image quality.

In other words, it is possible to measure the threshold voltage (Vth) and the mobility (μ) by one voltage application and discharge, thereby improving the image quality.

10: organic light emitting panel 30:
40: scan driver 50: data driver
51: selection means VDD, VSS: power supply voltage
S1, S2: scan signal Vpre: precharge data voltage
Dpre: precharge data signal T1 to T3: transistor
OLED: organic light emitting element Vref: reference voltage
Vs: sensing voltage Vth: threshold voltage μ: mobility Vsync: vertical synchronization signal
Hsync: Horizontal sync signal Enable: Enable signal
RGB: first video signal R'G'B ': second video signal
SCS: scan control signal DCS: data control signal
Sel: Selection signal Sensing: Sensing signal
P1 to P3: time interval

Claims (11)

Charging a precharge voltage to the load capacitor by supplying a precharge voltage through the data line to a load capacitor connected between the data line and the ground in a parallel structure with the data line in the pixel region;
Discharging the precharge data voltage charged in the load capacitor to the first node through which the driving transistor is connected through the data line and the switching transistor;
Measuring a voltage value of the first node to be discharged to a threshold voltage of the driving transistor;
Calculating a characteristic of the driving transistor with the measured voltage value; And
And charging and discharging a data voltage supplied to the first node by a storage capacitor connected to the first node. The method according to claim 1,
The data line is connected to a data driver,
The data driver includes:
A DAC for applying the precharge data voltage;
An ADC for sensing a voltage value to be discharged; And
And selection means for switching the data line to be selectively connected to the DAC or the ADC. The method according to claim 1,
Wherein the characteristics of the driving transistor to be calculated are the threshold voltage and the mobility. The method according to claim 1,
And calculating the threshold voltage with a voltage value sensed after discharging to the driving transistor. The method according to claim 1,
Wherein the mobility is calculated through two sensing operations in the discharging step. 6. The method of claim 5,
Wherein the sensing in the discharging step is voltage value sensing at an arbitrary point in time during discharge and voltage value sensing after discharging. 5. The method of claim 4,
Wherein the threshold voltage is measured by a difference between a voltage after discharge and a reference voltage. The method according to claim 6,
The mobility

,

Where V _PRE is a precharge data voltage applied to a data line, C is a charge amount, T is a detection time, and V is a precharge voltage applied to the data line.
Method of measuring transistor characteristics of an organic light emitting display. 3. The method of claim 2,
The DAC generates a precharge data voltage from the precharge data signal,
Wherein the ADC generates a sensing signal by sensing a voltage to be discharged. 10. The method of claim 9,
And a control unit electrically connected to the DAC and the ADC to output the precharge data signal through the DAC and receive a sensing signal through the ADC. 11. The method of claim 10,
Wherein the controller calculates a threshold voltage and a mobility from the sensed value.

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