KR101726627B1 - Organic light emitting diode display device - Google Patents

Abstract

The present invention relates to an organic light emitting diode (OLED) display device capable of precisely sensing a threshold voltage of a driving switching element even in a high speed driving mode, and a driving method thereof. The OLED display device includes a first switching element ; A second switching element for supplying a first power supply voltage to a first node in response to a reset signal; A third switching element for supplying a reference voltage to a second node in response to a reset signal; A driving switching element for controlling the amount of current supplied to the organic light emitting diode according to the potential of the second node; A fourth switching device for supplying a reference voltage to the first node in response to the first emission signal; A fifth switching element for connecting the drain electrode of the driving switching element and the second node to each other in response to the sensing signal; And a sixth switching element for connecting the drain electrode of the driving switching element and the anode electrode of the organic light emitting diode to each other in response to the second emission signal; A second power supply voltage is supplied to the cathode electrode of the organic light emitting diode.

Description

TECHNICAL FIELD [0001] The present invention relates to an organic light emitting diode (OLED) display device,

The present invention relates to an organic light emitting diode (OLED) display device capable of precisely sensing a threshold voltage of a driving switching element even when driving at a high speed.

2. Description of the Related Art [0002] Organic light emitting diodes (OLED) display devices for displaying images by controlling the amount of light emitted from an organic light emitting layer have been spotlighted by a flat panel display capable of reducing weight and volume, which are disadvantages of a cathode ray tube (CRT) .

In an OLED display device, a plurality of pixels are arranged in a matrix form to display an image. Here, each pixel includes an OLED and a driving switching element that adjusts the amount of current flowing through the OLED to adjust the brightness of each pixel.

The luminance of each pixel is influenced by the data voltage, the difference voltage (Vgs) between the gate electrode and the source electrode of the driving switching element, and the threshold voltage of the driving switching element.

However, there has been a problem that the threshold voltage of the driving switching element, which affects the luminance, differs for each pixel and luminance is varied even when the same data voltage is applied. Accordingly, a technique of sensing and compensating the threshold voltage (Vth) of the drive switching device has been introduced.

On the other hand, the time required to drive each pixel is becoming shorter as the size of the display device is increased and the pixel is changed to a higher resolution, and a technology for driving each pixel in a shorter time is referred to as a high-speed driving technique. However, the time for sensing the threshold voltage of the driving switching element is shortened during high-speed driving, and the threshold voltage of the driving switching element can not be accurately sensed.

SUMMARY OF THE INVENTION It is an object of the present invention to provide an organic light emitting diode (OLED) display device capable of precisely sensing a threshold voltage of a driving switching element even at a high speed driving.

According to an aspect of the present invention, there is provided an organic light emitting diode display comprising: a first switching device for supplying a data voltage to a first node in response to a scan signal; A second switching element for supplying a first power supply voltage to a first node in response to a reset signal; A third switching element for supplying a reference voltage to a second node in response to a reset signal; A driving switching element for controlling the amount of current supplied to the organic light emitting diode according to the potential of the second node; A fourth switching device for supplying a reference voltage to the first node in response to the first light emitting signal; A fifth switching element for connecting the drain electrode of the driving switching element and the second node to each other in response to the sensing signal; A sixth switching element for connecting the drain electrode of the driving switching element and the anode electrode of the organic light emitting diode to each other in response to the second emission signal; A first capacitor connected between the first node and the second node; And a second capacitor connected between the first node and the source electrode of the drive switching element to which the first power supply voltage is supplied; And a pixel circuit to which a second power supply voltage is supplied to the cathode electrode of the organic light emitting diode.
The pixel circuit is driven in the order of the first initialization period, the second initialization period, the programming period, the sampling period, and the light emission period.
During the first initialization period, the first power supply voltage is supplied to the first node through the second switching element, and the reference voltage is supplied to the second node through the third switching element. ,
During the second initialization period, the data voltage is supplied to the first node through the first switching element, the second node is floated by the third switching element, and the potential of the first node is reduced from the first power supply voltage to the data voltage The potential of the second node is changed to the negative potential lower than the reference voltage by the first capacitor.
During the programming period, the data voltage is continuously supplied to the first node through the first switching element, and the potential of the second node through the driving of the fifth switching element and the driving switching element is varied to sense the threshold voltage of the driving switching element .
During the sampling period, the first node is floated by the first switching element, and the potential of the second node continuously changes through the driving of the fifth switching element and the driving switching element to sense the threshold voltage.
During the light emitting period, the reference voltage is supplied to the first node through the fourth switching element, and the driving switching element applies a current whose amount of current is controlled in accordance with the difference voltage between the data voltage and the reference voltage through the sixth switching element to the organic light emitting diode Supply.

The first power supply voltage has a potential relatively higher than the second power supply voltage, and the reference voltage has a potential between the first power supply voltage and the second power supply voltage.

The first power supply voltage, the data voltage, and the reference voltage are positive voltages and the second power supply voltage is a ground voltage.

During the programming period and the sampling period, the potential of the second node increases from the negative potential to the difference voltage between the first power supply voltage and the threshold voltage of the driving switching element.

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During the light emitting period, the current Ioled flowing through the organic light emitting diode is expressed by the following equation.

Here, "beta" represents a constant value determined by the mobility and parasitic capacitance of the drive switching element, "Vdata" represents the data voltage, and "Vref" represents the reference voltage.

The present invention senses the threshold voltage of the driving switching element over the programming and sampling periods. Therefore, the time for accurately sensing the threshold voltage of the driving switching element is secured even during high-speed driving, and the threshold voltage of the driving switching element can be more accurately sensed.

Further, by initializing the potential of the gate electrode of the driving switching element to negative (-) before sensing the threshold voltage of the driving switching element, the threshold voltage sensing of the driving switching element is faster and more accurate.

1 is a circuit diagram of a pixel of an OLED display according to an embodiment of the present invention.
2 is a driving waveform diagram of the pixel circuit diagram shown in Fig.
3A to 3E are circuit diagrams for explaining the driving method of the pixel driver step by step.
4 is a simulation in which the threshold voltage Vth of the driving TFT DT is sensed according to the present invention.

Hereinafter, an organic light emitting diode (OLED) display device and a driving method thereof according to an embodiment of the present invention will be described in detail with reference to the accompanying drawings.

1 is a circuit diagram of a pixel of an OLED display according to an embodiment of the present invention.

The pixel shown in FIG. 1 includes a pixel driver that independently drives the OLED and the OLED.

Specifically, the pixel driver includes first through sixth switching elements (hereinafter referred to as TFT) T1 through T6, a driving TFT DT, and first and second capacitors C1 and C2. The OLED is connected between the pixel driver and the second power source voltage (VSS) and is equivalently represented by a diode.

The pixel driving section is supplied with a data voltage Vdata, a reference voltage Vref and a first power supply voltage VDD and is supplied with a plurality of control signals IN, SCAN, EM1, EM2, SEN) are supplied.

The first power supply voltage VDD has a potential that is relatively higher than the second power supply voltage VSS. The second power supply voltage VSS is normally set to the ground voltage. The reference voltage Vref has a potential between the first power supply voltage VDD and the second power supply voltage VSS.

The scan signal SCAN, the first light emission signal EM1, the second light emission signal EM2, the sensing signal SEN, and the control signal IN, SCAN, EM1, EM2, And a description thereof will be given later.

Meanwhile, the first to sixth TFTs T1 to T6 and the driving TFT DT may be formed of N type or P type. Hereinafter, an example of the P type will be described.

The first TFT T1 is turned on or off according to the scan signal SCAN and supplies the turn-on data voltage Vdata to the first node N1.

Here, the first node N1 is a node to which the output terminals of the first, second, and fourth TFTs T1, T2, and T4 are commonly connected.

The second TFT T2 is turned on or off according to the reset signal IN and supplies the first power source voltage VDD to the first node N1 when turned on.

The third TFT T3 is turned on or off according to the reset signal IN and supplies the turn-on reference voltage Vref to the second node N2.

Here, the second node N2 is a node connected to the gate electrode of the driving TFT DT.

The fourth TFT T4 is turned on or off according to the first emission signal EM1 and supplies the turn-on reference voltage Vref to the first node N1.

The fifth TFT T5 turns on or off according to the sensing signal SEN and connects the drain electrode of the driving TFT DT to the second node N2.

The sixth TFT T6 is turned on or off according to the second light emission signal EM2 to connect the drain electrode of the turn-on TFT DT and the anode electrode of the OLED to each other.

The first power supply voltage VDD is supplied to the source electrode of the driving TFT DT and the amount of light emitted from the OLED is controlled by controlling the amount of current supplied to the OLED according to the potential of the second node N2.

The first capacitor C1 is connected between the first node N1 and the second node N2.

The second capacitor C2 is connected between the first power supply voltage VDD supply line and the first node N1.

The OLED is composed of an anode electrode connected to the pixel driving unit, a cathode electrode to which the second power source voltage VSS is supplied, and an organic layer formed between the anode electrode and the cathode electrode.

The driving method of the pixel driver will be described in detail as follows.

FIG. 2 is a driving waveform diagram of the pixel circuit shown in FIG. 1, and FIGS. 3A to 3E are circuit diagrams for explaining the driving method of the pixel driving unit step by step.

In Fig. 2,? Represents the first initialization period,? Represents the second initialization period,? Represents the programming period,? Represents the sampling period, and? Represents the light emission period.

The first initializing period? Is a period for initializing the voltage of the first node N1 to the first power supply voltage VDD and the voltage of the second node N2 to the reference voltage Vref.

In the second initialization period (2), the voltage of the first node N1 is changed from the first power supply voltage VDD to the data voltage Vdata and the voltage of the second node N2 is changed to the negative voltage .

On the other hand, the first power supply voltage VDD, the data voltage Vdata, and the reference voltage Vref are positive (+) voltages.

The programming and sampling periods (3 and 4) are periods in which the gate electrode and the drain electrode of the driving TFT DT are connected to each other to sense the threshold voltage Vth of the driving TFT DT.

The emission period (5) is a period in which the OLED emits light in accordance with the gate voltage of the driving TFT DT including the threshold voltage of the driving TFT DT.

Referring to FIGS. 2 and 3A, a reset signal IN supplied to the pixel driver is supplied in a low logic state during a first initialization period (1), and a scan signal SCAN, first and second light emission signals EM1 , EM2, and the sensing signal SEN are supplied in a high logic state.

Accordingly, the second and third TFTs T2 and T3 are turned on in the first initialization period (1). The first, fourth, fifth, and sixth TFTs T1, T4, T5, and T6 are turned off.

The first power supply voltage VDD is supplied to the first node N1 through the second TFT T2 and the reference voltage Vref is supplied to the second node N2 through the third TFT T3. do.

2 and 3B, in a second initialization period (2), a scan signal SCAN supplied to the pixel driver is supplied in a low logic state, and a reset signal IN, first and second light emission signals EM1 , EM2, and the sensing signal SEN are supplied in a high logic state.

Thus, the first TFT T1 is turned on in the second initialization period (2). And the second to sixth TFTs T2 to T6 are turned off.

Then, the data voltage (Vdata) is supplied to the first node (N1) through the first TFT (T1). At this time, when the potential of the first node N1 is lowered from the first power supply voltage VDD to the data voltage Vdata, the potential of the second node N2 is also changed to the reference voltage Vdata by the coupling phenomenon of the first capacitor C1. Becomes lower than the voltage Vref.

At this time, the reference voltage Vref is a voltage that is relatively closer to the second power supply voltage VSS than the first power supply voltage VDD. Thus, the potential of the second node N2 is lowered at the reference voltage Vref, and finally changed to the negative (-) voltage.

As described above, when the potential of the second node N2 is changed to the negative (-) voltage in the second initialization period (2), the threshold voltage of the driving TFT DT (in the subsequent programming and sampling periods Vth) is faster and more accurate.

2 and 3C, the scan signal SCAN and the sensing signal SEN are supplied in the low logic state during the programming period (3), and the reset signal IN, the first and second emission signals EM1, EM2 are supplied in the high logic state.

Thus, during the programming period (3), the first and fifth TFTs T1 and T5 are turned on, and the second to fourth TFTs T2 to T4 and the sixth TFT T6 are turned off.

Then, the potential of the first node N1 is maintained at the data voltage Vdata, and the potential of the second node N2 converges to "VDD-Vth " at the negative (-) voltage.

Referring to FIG. 2 and FIG. 3D, in the sampling period (4), the sensing signal SEN is supplied in a low logic state, and the reset signal IN, the scan signal SCAN, EM2 are supplied in the high logic state.

Accordingly, in the sampling period (4), the fifth TFT (T5) is turned on, and the first to fourth TFTs (T1 to T4) and the sixth TFT (T6) are turned off.

Then, the potential of the first node N1 maintains the data voltage Vdata in a floating state. At this time, the second capacitor C2 allows the data voltage Vdata of the first node N1 to be stably maintained.

And the potential of the second node N2 subsequently converges to "VDD-Vth" from the negative (-) voltage.

Thus, the present invention senses the threshold voltage Vth of the driving TFT DT over the programming and sampling periods (3, 4). Therefore, a time for accurately sensing the threshold voltage (Vth) of the driving TFT (DT) can be ensured even during high-speed driving, and the threshold voltage (Vth) of the driving TFT (DT) can be more accurately sensed.

Further, by initializing the potential of the second node N2 to negative (-) before sensing the threshold voltage (Vth) of the driving TFT (DT), the threshold voltage (Vth) sensing of the driving TFT There is an effect of correcting.

2 and 3E, the first and second emission signals EM1 and EM2 are supplied in the low logic state during the light emission period (⑤), and the reset signal IN, the scan signal SCAN, SEN) is supplied in a high logic state.

Thus, during the light emission period (5), the fourth and sixth TFTs T4 and T6 are turned on, and the first to third TFTs T1 to T3 and the fifth TFT T5 are turned off.

Then, the reference voltage Vref is supplied to the first node N1 through the fourth TFT T4. At this time, when the potential of the first node N1 changes from the data voltage Vdata to the reference voltage Vref, the potential of the second node N2 becomes "VDD- Vth "to" VDD-Vth + Vref-Vdata ". At the same time, since the sixth TFT T6 is turned on, a drive current is supplied to the OLED to emit light.

On the other hand, the driving current supplied to the OLED is expressed by Equation (1). "Vsg" represents a voltage difference between the gate electrode and the source electrode of the driving TFT DT, "Vth" represents the threshold voltage of the driving TFT DT, and " And a constant value determined by the mobility and the parasitic capacitance.

Therefore, the OLED driving current is summarized in Equation (2) in the light emission period (5).

Referring to Equation 2, it can be seen that the OLED driving current is not affected by the threshold voltage Vth of the driving TFT DT and the first power supply voltage VDD.

Therefore, it is possible to compensate the change of the threshold voltage Vth of the driving TFT DT due to the deterioration that may be generated in the manufacturing process or the image display and the change of the first power supply voltage VDD to provide uniform brightness, Quality can be improved.

4 is a simulation in which the threshold voltage Vth of the driving TFT DT is sensed according to the present invention.

Specifically, FIG. 4 shows two graphs showing the potential of the gate electrode of the driving TFT DT. One of the two graphs shown in Fig. 4 is a graph when the threshold voltage Vth of the driving TFT DT is x and the other is a graph when the threshold voltage Vth of the driving TFT DT is x + 1 .

That is, the two graphs are set so that the threshold voltage Vth of the driving TFT DT is different by 1 V, and the potential of the gate electrode of the driving TFT DT from the first initializing period (1) to the light emitting period .

Therefore, after sensing the threshold voltage Vth of the driving TFT DT, the threshold voltage Vth of the driving TFT DT is accurately sensed as the potential difference of the two graphs approaches 1V.

Referring to FIG. 4, the potential difference of the two graphs is obtained when the threshold voltage Vth of the driving TFT DT is almost accurately sensed at 1.0017 V in the light emission period (5) after the programming and sampling periods (3, .

As described above, the present invention senses the threshold voltage (Vth) of the driving TFT (DT) over the programming and sampling periods (3, 4). Therefore, the time for accurately sensing the threshold voltage (Vth) of the driving TFT (DT) is secured even during high-speed driving, and the threshold voltage (Vth) of the driving TFT (DT) can be accurately sensed.

The threshold voltage (Vth) sensing of the driving TFT (DT) is performed by initializing the potential of the gate electrode of the driving TFT (DT) to negative (-) before sensing the threshold voltage It is faster and more accurate.

It will be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the spirit or scope of the general inventive concept as defined by the appended claims and their equivalents. Will be clear to those who have knowledge of.

IN: Reset signal SCAN: Scan signal
EM1: first emission signal EM2: second emission signal
SEN: sensing signal DT: drive switching element

Claims (11)

A first switching element for supplying a data voltage to a first node in response to a scan signal;
A second switching element for supplying a first power supply voltage to the first node in response to a reset signal;
A third switching element for supplying a reference voltage to the second node in response to the reset signal;
A driving switching element for controlling an amount of current supplied to the organic light emitting diode according to a potential of the second node;
A fourth switching device for supplying the reference voltage to the first node in response to the first light emitting signal;
A fifth switching element for connecting the drain electrode of the driving switching element and the second node to each other in response to a sensing signal;
A sixth switching device for connecting the drain electrode of the driving switching device and the anode electrode of the organic light emitting diode to each other in response to the second emission signal;
A first capacitor connected between the first node and the second node;
And a second capacitor connected between the first node and a source electrode of the drive switching element to which the first power supply voltage is supplied;
And a pixel circuit to which a second power supply voltage is supplied to the cathode electrode of the organic light emitting diode,
The pixel circuit is driven in the order of a first initialization period, a second initialization period, a programming period, a sampling period, and a light emission period,
During the first initialization period, the first power supply voltage is supplied to the first node through the second switching element, the reference voltage is supplied to the second node through the third switching element,
Wherein during the second initialization period, the data voltage is supplied to the first node through the first switching element, and the second node is floated by the third switching element, The potential of the second node is changed to a negative potential lower than the reference voltage by the first capacitor by a decrease from the first power supply voltage to the data voltage,
Wherein during the programming period, the data voltage is continuously supplied to the first node through the first switching element, and the potential of the second node through the driving of the fifth switching element and the driving switching element becomes the negative potential Lt; / RTI > gradually increases,
Wherein during the sampling period, the first node is floated by the first switching element, and the potential of the second node continues to increase through driving of the fifth switching element and the driving switching element so that the threshold of the driving switching element Variable until the voltage is sensed,
Wherein the reference voltage is supplied to the first node through the fourth switching element during the light emission period and the drive switching element supplies a current whose amount of current is controlled according to the difference voltage between the data voltage and the reference voltage, 6 switching element to the organic light emitting diode. The method according to claim 1,
Wherein the first power supply voltage has a relatively higher potential than the second power supply voltage,
Wherein the reference voltage has a potential between the first power supply voltage and the second power supply voltage. 3. The method of claim 2,
Wherein the first power supply voltage, the data voltage, and the reference voltage are positive voltages and the second power supply voltage is a ground voltage. delete delete delete delete delete The method according to claim 1,
Wherein the potential of the second node is increased from the negative potential to a voltage difference between the first power supply voltage and the threshold voltage of the drive switching element during the programming period and the sampling period. delete The method according to claim 1,
During the light emission period, the current Ioled flowing through the organic light emitting diode is expressed by the following equation.

Here, "beta" represents a constant value determined by the mobility and parasitic capacitance of the drive switching element, "Vdata" represents the data voltage, and "Vref" represents the reference voltage.

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