KR20080060897A - Organic light emitting display and method for driving the same - Google Patents

Abstract

An OLED(Organic Light Emitting Display) device and a driving method thereof are provided to extend the lifetime thereof by adjusting the magnitude of voltages, which are supplied to a display unit. An OLED(Organic Light Emitting Display) device includes a display unit(210) and a power supply unit(250). The display unit includes signal lines having scan, data, and power lines, and plural pixel circuits, which are positioned at regions which are defined by the signal lines. The power supply unit supplies driving voltages having different magnitudes from one another to the display unit according to the luminance of images displayed in the display unit through the power lines.

Description

Organic Light Emitting Display and Method for Driving the Same

1 is a circuit diagram showing a conventional power supply.

2 is a block diagram illustrating an organic light emitting display device according to an embodiment of the present invention.

3 is a circuit diagram illustrating a pixel circuit of an organic light emitting display device according to an exemplary embodiment of the present invention.

4 is a circuit diagram illustrating a power supply unit according to an embodiment of the present invention.

5 is a block diagram illustrating a resistance selector according to an exemplary embodiment of the present invention.

FIG. 6 is a graph illustrating I-V characteristics and driving voltages of organic light emitting diodes according to gray levels when the organic light emitting display device is driven.

7 is a circuit diagram illustrating a power supply unit according to another embodiment of the present invention.

The present invention relates to an organic light emitting display device and a driving method thereof.

Recently, the importance of flat panel displays (FPDs) has increased with the development of multimedia. In response, a number of liquid crystal displays (LCDs), plasma display panels (PDPs), field emission displays (FEDs), organic light emitting devices (Organic Light Emitting Devices), etc. Branch-type flat panel displays have been put into practical use.

In particular, the organic light emitting display device has a high response time with a response speed of 1 ms or less, low power consumption, and self-emission. In addition, there is no problem in viewing angle, which is advantageous as a moving image display medium regardless of the size of the device. In addition, low-temperature manufacturing is possible, and the manufacturing process is simple based on the existing semiconductor process technology has attracted attention as a next-generation flat panel display device in the future.

In general, an organic light emitting display device is a display device that electrically excites fluorescent organic compounds and emits light, and performs voltage driving or current driving of N × M organic light emitting diodes (OLEDs) arranged in a matrix form. Programming to express an image. The organic light emitting display device may be driven by a passive matrix method and an active matrix method using a thin film transistor. The passive matrix method forms the anode and the cathode to be orthogonal and selects and drives the lines, whereas the active matrix method connects the thin film transistors to each pixel electrode and drives them according to the voltage maintained by the capacitor capacitance connected to the gate electrode of the thin film transistor. do.

1 is a circuit diagram illustrating a power supply unit of a conventional organic light emitting display device.

Referring to FIG. 1, the power supply unit 150 includes a DC-DC converter 151 and a resistor 152 to supply a voltage required for driving the display unit.

The resistor unit 152 includes a first fixed resistor R1 and a second fixed resistor R2 connected in series, and one end of the DC constant voltage supply unit 151 has a first fixed resistor R1 and a second fixed resistor ( It is connected to the node between R2), and the output terminal is connected to the first fixed resistor (R1).

Therefore, the voltage Vout output from the power supply unit 150 is determined by the ratio of the first fixed resistor R1 and the second fixed resistor R2 and can be expressed by the following equation.

As can be seen in the above equation, since the voltage output from the power supply unit 150 is determined by the resistor unit 152, the power supply unit 150 always outputs a constant voltage.

 When implementing a video image of an organic light emitting display device, a high display voltage is required to display a bright screen, but a high display voltage does not require a high driving voltage because most data signals have low gray levels. .

However, since the conventional power supply unit 150 always outputs a constant voltage regardless of the brightness of the image image, unnecessary power is wasted, and the lifespan of the organic light emitting display device is reduced as a high voltage is applied. There is.

Accordingly, an object of the present invention is to provide an organic light emitting display device and a driving method thereof, which can reduce power consumption and increase lifespan.

In order to achieve the above object, the present invention provides a display unit including scan lines, data lines, signal lines including power lines, and a plurality of pixel circuits positioned in regions defined by the signal lines. An organic light emitting display device includes a power supply unit supplying a driving voltage having a different size to a display unit according to luminance of an image image implemented in the display unit through lines.

In addition, the present invention, the organic light emitting display including a resistor unit including a first, second fixed resistor and a variable resistor unit and a power supply unit connected to the resistor unit and outputting a voltage having a different size according to the variable resistor of the resistor unit. A driving method of a display device, the method comprising: determining a reference gray level signal by receiving gray level signals from an external source, determining an optimal driving voltage corresponding to the determined gray level signal, and changing the variable voltage to supply the optimal driving voltage A method of driving an organic light emitting display device, the method comprising: setting a resistance value of a resistor unit and outputting a voltage.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings.

2 is a block diagram illustrating an organic light emitting display device according to an embodiment of the present invention, and FIG. 3 is a circuit diagram illustrating a pixel circuit of an organic light emitting display device according to an embodiment of the present invention.

Referring to FIG. 2, the organic light emitting display device includes a display unit 210, a scan driver 220, a data driver 230, a controller 240, and a power supply 250.

The display unit 210 includes data lines D1 -Dm arranged in a first direction and scan lines S1 -Sn and data lines (D1 -Dm) that cross the first direction and are arranged in a second direction. ) And pixel circuits P11 -Pnm positioned in an area where scan lines S1 -Sn intersect.

The control unit 240 outputs a control signal to the scan driver 220, the data driver 230, and the power supply unit 250, and the power supply unit 250 generates first power lines according to the control signal of the control unit 240. A voltage necessary for driving the display unit 210 is output through 260: L_VDD and the second power lines 270: L_VSS. Here, the first voltage VDD applied through the first power lines 260 is a power voltage generated by the DC constant voltage supply unit, and the second voltage applied through the second power lines 270 (L_VSS). VSS) may be a ground voltage. In addition, the magnitude of the first voltage VDD supplied through the first power lines 260 (L_VDD) may vary depending on the brightness of the display unit 210.

The scan driver 220 outputs a scan signal to scan lines S1 -Sn connected to the scan driver 220 according to a control signal of the controller 240. As a result, the pixel circuits P11 -Pnm positioned in the display unit 210 are selected in response to the scan signals S1 -Sn.

The data driver 230 may correspond to the data signals through the data lines D1 to Dm connected to the data driver 230 in synchronization with the scan signal output from the scan driver 220 according to the control signal of the controller 240. Applied to the pixel circuits 210. Therefore, the display unit 210 displays an image image by emitting light from the pixel circuits P1-Pnm in response to the data signals.

Referring to FIG. 3, each pixel circuit receives data through a switching transistor T1 and a switching transistor T2 that transfer a data signal from the data line Dm in response to a selection signal from the scan line Sn. A capacitor Cst for storing a signal, a driving transistor T2 for generating a driving current according to a data signal stored in the capacitor Cst, and a light emitting operation according to the driving current and connected to the first power line VDD. Organic light emitting diodes (OLED).

The gate electrode of the driving transistor T2 is connected to the drain electrode of the switching transistor T1 to receive a data signal, and the driving transistor T2 is the difference between the data signal and the second power line LVSS connected to the source electrode. A driving current corresponding to the driving current is generated and supplied to the organic light emitting diode OLED connected to the drain electrode. The anode of the organic light emitting diode OLED is connected to the first power line LVDD.

The amount of current flowing through the organic light emitting diode OLED can be expressed as follows.

Here, K is a constant, Vgs is the difference between the source-gate voltage of the driving transistor, and Vth is the threshold voltage of the driving transistor.

Therefore, the organic light emitting diode receives the first voltage VDD applied from the power supply 250 and generates a driving current corresponding to the difference between the data signal and the second voltage VSS, thereby emitting light.

At this time, the voltage applied to the organic light emitting diode OLED is as follows. When a current flows in the organic light emitting diode OLED, the voltage applied to the output terminal of the power supply unit 250 is lowered.

4 is a circuit diagram illustrating a power supply unit according to an embodiment of the present invention.

Referring to FIG. 4, the power supply unit 250 according to an embodiment of the present invention may include a DC-DC converter 251, a resistor 252, a resistor selector 257, and a resistor 252. And a switch unit 257 connected between the resistor selection unit 256 and the resistor selection unit 256.

The DC constant voltage supply unit 251 converts a DC of low voltage into AC, boosts it, rectifies it, and rectifies the DC voltage of the higher voltage. The DC constant voltage supply unit 251 provides a constant feedback voltage Vfb. .

The resistor unit 252 includes a first resistor unit 253 and a second resistor unit 254 connected in series with each other, and one end of the DC constant voltage supply unit 251 has a first resistor unit 253 and a second resistor unit. The other end is connected to the node 254 and the other end is connected to the first resistor unit 253 to output a voltage. Therefore, the DC constant voltage supply unit 251 supplies the display unit 210 with a driving voltage determined according to the ratio of the first resistor unit 253 and the second resistor unit 254.

Here, the first resistor unit 253 includes a first fixed resistor (R1), the second resistor unit 254 is a second fixed resistor (R2) and a plurality of resistors (R) connected in parallel with each other. And a variable resistor portion 255 having Rn).

The second resistor unit 254 is connected to the resistor selector 256, and a switch unit 257 is positioned between the resistor selector 256 and the second resistor unit 254. The switch unit 257 includes transistors Sa ... Sn connected to the resistors Ra ... Rn of the variable resistor unit 255 and transistors S2 connected to the second fixed resistor R2, respectively. do.

Here, the gate electrodes of the transistors (Sa ... Sn, S2) are connected to the resistor selection unit 256, respectively, and one end of the transistors includes a plurality of resistors Ra .. One end of .Rn, R2 is connected to the other end, and the other end is commonly connected to the ground line. Thus, the transistors Sa ... Sn, S2 are turned on by the resistor selector 256, so that the variable resistor Rtotal is connected. To form

Here, the voltage output from the power supply 250 according to an embodiment of the present invention is as follows.

Here, Vout is a voltage output from the power supply unit 250, Vfb is a feedback voltage supplied from the DC constant voltage supply unit 251, and Rtotal is a variable resistor formed in the variable resistor unit 255.

Accordingly, as shown in Equation 4, the amount of the output voltage may vary according to the variable resistor. When the variable resistor Rtotoal is 0, the power supply unit 150 may output the maximum voltage. When all the transistors Sa ... Sn of the resistor unit 255 are turned on, the minimum voltage may be output.

5 is a block diagram illustrating a resistance selector according to an exemplary embodiment of the present invention.

Referring to FIG. 5, the resistance selector 256 includes a signal selector 256a and a signal processor 256b.

The signal selector 256a receives a gray level signal from the outside. Here, the gray level signal may be all gray level signals corresponding to one frame. The signal selector 256a determines a reference gradation signal among the received gradation signals, and then transmits the reference gradation signal to the signal processor 256b. The reference gray level signal may be the highest gray level signal.

The signal processor 256b may receive the highest gray level signal to determine an optimal driving voltage for expressing the highest gray level signal. The optimal driving voltage may be determined through calculation or by referring to a look-up table (LUT).

Hereinafter, a method of setting an optimal driving voltage stored in the look-up table LUT will be described with reference to FIG. 6.

FIG. 6 is a graph illustrating I-V characteristics and driving voltages of organic light emitting diodes according to gray levels when an organic light emitting display device is driven.

Referring to FIG. 6, graphs G1 to Gn are graphs showing IV characteristics according to gray levels, and referring to graphs G1 to Gn, organic light emitting display devices have saturated voltages (V1sat ... Vn.sat) of each gray level. In the above, it turns out that a fixed amount of electric current flows.

 Graph A shows the driving voltages of the organic light emitting diodes required for expressing each gray level. As can be seen in Graph A, in the related art, VDD, a power supply voltage capable of satisfying the saturation voltage of the highest gray level, is uniformly applied in every frame so that all grays can be expressed when the organic light emitting display device is driven.

However, when displaying a video image, only low gray level digital signals are input in a dark screen, and a low driving voltage may be applied to express low gray level. For example, if the highest gray level signal is Gm in a screen having low luminance, the minimum driving voltage satisfying the saturation voltage Vm.sat of the gray level may be VDDm.

The optimum driving voltage can be expressed by the following equation.

The signal processor 256b according to an embodiment of the present invention may include a look-up table storing an optimum driving voltage according to the gray level signal as described above, and with reference thereto, the signal selector 256a may be determined. Select the optimum driving voltage according to the highest gradation signal. Then, to form an optimal driving voltage, a selection signal to be applied to the variable resistor unit 255 is formed. In this case, the transistors Sa, and Sn of the variable resistor unit 255 are selectively turned on according to the selection signal of the signal processor 256b, so that selection is made in consideration of each resistor Ra ... Rn. You can generate a signal.

Although not shown, a comparator may be further positioned between the signal selector 256a and the signal processor 256b, and the comparator may be the same or similar to the previous gray signal selected by the signal selector. The highest gray level signal may not be applied to the signal processor 256b.

In the exemplary embodiment of the present invention, the resistor selection unit 256 selects the highest gray level signal of each frame. However, the present invention is not limited thereto, and the mode or average value of each frame or a predetermined frame may be selected.

In addition, the resistance selector 256 may be formed in the control unit or separately from the control unit, or may be formed in the power supply unit 250.

Hereinafter, an operation of the organic light emitting display device having the above structure will be described with reference to FIGS. 2 to 5.

When the control unit 240 applies a control signal to the scan driver 220 and the data driver 230, the scan driver 220 applies a scan signal to each pixel circuit through the scan line.

The signal selector 256b of the resistance selector 256 receives a gray level signal corresponding to one frame from the outside, selects the highest digital gray level signal among these, and transmits it to the signal processor.

The signal processor 256b determines an optimal voltage corresponding to the highest digital gray level signal using a lookup table, generates a corresponding selection signal, and transmits the selected signal to the switch unit 257.

The switch unit 257 receives the selection signal to turn on the transistors, thereby forming a variable resistor Rtotal. In this case, when none of the transistors Sa ... Sn connected to the variable resistor unit 255 is selected, the signal processor 256b turns on the transistor S2 connected to the second fixed resistor R2. Let's do it. At this time, the maximum voltage is output from the power supply 250.

When the variable resistance value is determined, an output voltage is determined according to the ratio of the first resistor unit 253 and the second resistor unit 254, and the power supply unit 253 supplies a voltage required for driving to the first power line VDD1. Supply through.

The data driver 230 supplies a data signal to the pixel circuits P11 -Pnm selected by the scan signal, and the pixel circuits emit an image corresponding to the difference between the second power line VSS1 and the data signal. Can be displayed.

As described above, the organic light emitting display device according to the exemplary embodiment of the present invention may change the magnitude of the power voltage supplied according to the brightness of the video image implemented in the display unit. Therefore, there is an advantage that can prevent unnecessary power consumption, and by varying the magnitude of the voltage supplied to the display, there is an effect that can improve the life of the organic light emitting display device.

7 is a circuit diagram illustrating a power supply unit of an organic light emitting display device according to another embodiment of the present invention.

Referring to FIG. 7, a power supply unit 350 according to another embodiment of the present invention may include a DC-DC converter 351, a resistor 352, a resistor selector 357, and a resistor 352. And a switch unit 357 connected between the resistor selection unit 356 and the resistor selection unit 356.

The resistor unit 352 includes a first resistor unit 353 and a second resistor unit 354 connected in series with each other, and one end of the DC constant voltage supply unit 351 has a first resistor unit 353 and a second resistor unit. It is connected to the node between the 354 and the other end is connected to the first resistor unit 353 to output a voltage. Therefore, the DC constant voltage supply unit 351 supplies the display unit 310 with a driving voltage determined according to the ratio of the first resistor unit 353 and the second resistor unit 354.

Here, the first resistor unit 353 includes a variable resistor unit 355 having a first fixed resistor R1 and a plurality of resistors Ra ... Rn connected in parallel with each other, and a second resistor unit 354 includes a second fixed resistor R2.

The first resistor 353 is connected to the resistor selector 356, and the switch 357 is positioned between the resistor selector 356 and the first resistor 353. The switch unit 357 includes transistors Sa ... Sn and S1 connected to the resistors Ra ... Rn and R1 of the first resistor unit 355, respectively.

Here, the gate electrodes of the transistors (Sa ... Sn, S1) are connected to the resistor selector 356, respectively, and one end of the transistors includes the plurality of resistors Ra .. One end of .Rn is connected to the other end, and the other end is commonly connected to the ground line. Thus, the transistors Sa ... Sn are turned on by the resistor selector 356 to form a variable resistor Rtotal. When none of the transistors of the variable resistor unit 355 is selected, the transistor connected to the first fixed resistor R1 is turned on, and the variable resistor value becomes zero.

Here, the voltage output from the power supply 350 according to an embodiment of the present invention is as follows.

Here, Vout is a voltage output from the power supply unit 350, Vfb is a feedback voltage supplied from the DC constant voltage supply unit 351, and Rtotal is a variable resistor formed in the variable resistor unit 355.

Therefore, according to the voltage driver 350 as described above, when all of the transistors Sa... Sn connected to the variable resistor unit 356 are turned on, the voltage Vout output from the power supply unit 350 is maximum. When all of the transistors Sa ... Sn connected to the variable resistor unit 356 are turned off, the transistor S1 connected to the first fixed resistor R1 is turned on so that the output voltage Vout ) Is the minimum.

 While the invention has been shown and described with reference to certain preferred embodiments, the invention is not so limited, and the invention is not limited to the scope and spirit of the invention as defined by the following claims. It will be readily apparent to one of ordinary skill in the art that various modifications and variations can be made.

The present invention has the effect of reducing power consumption and increasing the lifespan of the organic light emitting display device.

Claims (23)

A display unit including scan lines, data lines, signal lines including power lines, and a plurality of pixel circuits positioned in an area defined by the signal lines; And And a power supply unit supplying a driving voltage having a different size to the display unit according to the brightness of a video image implemented in the display unit through the power lines. The method of claim 1, The power supply unit includes a DC constant voltage supply unit and a resistor connected to the DC constant voltage supply unit. The method of claim 1, The resistor unit includes a first resistor unit and a second resistor unit connected in series, one end of the DC constant voltage supply unit is connected to a node between the first resistor unit and the second resistor unit, and an output terminal of the DC constant voltage supply unit is An organic light emitting display device connected to one end of a first resistor unit. The method of claim 3, The first or second resistor unit includes a variable resistor unit including a fixed resistor and a plurality of resistors connected in parallel. The method of claim 4, wherein And the variable resistor unit is connected to a switch unit including transistors connected to the resistors of the first and second resistor units, respectively. The method of claim 4, wherein And the switch unit is connected to a resistance selecting unit for setting a resistance value of the variable resistor unit. The method of claim 5,  The gate electrode of the transistors of the switch unit is connected to a resistor selection unit, one end of the transistors are respectively connected to the resistors of the first or second resistor unit, and the other end of the transistors are commonly connected to a ground line. . The method of claim 7, wherein And when the transistors connected to the variable resistor part are all turned off, the transistor connected to the fixed resistor of the first resistor part or the second resistor part is turned on. The method of claim 5, The resistance selector includes a signal selector and a signal processor, and the signal selector receives a gray level signal from an external device to determine a highest gray level signal, and the signal processor determines an optimal driving voltage corresponding to the highest gray level signal. An organic light emitting display device generating a selection signal corresponding thereto. The method of claim 9, The signal processor includes a look-up table, and the look-up table stores a selection signal corresponding to an optimal driving voltage of each gray level signal. The method of claim 9 or 10, The optimal driving voltage is a voltage greater than a saturation voltage of the highest gray level signal plus a voltage applied to the organic light emitting diode when the highest gray level signal is applied. The method of claim 9, The resistance selector further includes a comparator coupled between the signal selector and the signal processor, wherein the comparator compares a previous highest grayscale signal with a current highest grayscale signal and applies the current highest grayscale signal to the signal processor according to a comparison result. , Organic light emitting display device not applied. The method of claim 1, The pixel circuit may include a switching transistor that transfers a data signal from the data line according to a scan signal from the scan line, a capacitor that receives the data signal from the switching transistor and stores the data signal, and according to the data signal stored in the capacitor. An organic light emitting display device comprising: a driving transistor generating a driving current; and a light emitting diode receiving the driving current to perform a light emitting operation. A driving method of an organic light emitting display device comprising: a resistor unit including first and second fixed resistors and a variable resistor unit; and a power supply unit connected to the resistor unit and outputting a voltage having a different magnitude depending on the variable resistor of the resistor unit. In Determining a reference gray level signal by receiving gray level signals from the outside; Determining an optimal driving voltage corresponding to the determined gray level signal; And setting a resistance value of the variable resistor unit so as to supply the optimum driving voltage, and outputting a voltage. The method of claim 14, The variable resistor unit includes a plurality of resistors connected in parallel, and the variable resistor unit and the first fixed resistor or the second fixed resistor are connected to a switch unit to set the variable resistor according to a selection signal applied to the switch unit. A method of driving an organic light emitting display device. The method of claim 15, The switch unit is connected to a resistor selection unit for applying the selection signal, a gate electrode of transistors of the switch unit is connected to the resistor selection unit, and one end of the transistors is connected to the variable resistor unit and the first or second fixing unit. A method of driving an organic light emitting display device connected to a resistor, the other end of which is connected to a ground line in common. The method of claim 16, And when all the transistors connected to the variable resistor are turned off, the transistor connected to the first or second fixed resistor is turned on. The method of claim 16, The resistance selector includes a signal selector and a signal processor, and the signal selector receives a gray level signal from an external device to determine a highest gray level signal, and the signal processor determines an optimal driving voltage corresponding to the highest gray level signal. A method of driving an organic light emitting display device generating a selection signal corresponding thereto. The method of claim 18, The signal processor includes a look-up table, wherein the look-up table stores a selection signal corresponding to an optimal driving voltage of each gray level signal. The method of claim 18 or 19, The optimal driving voltage is a voltage greater than a saturation voltage of the highest gray level signal plus a voltage applied to the organic light emitting diode when the highest gray level signal is applied. The method of claim 18, The resistance selector further includes a comparator coupled between the signal selector and the signal processor, wherein the comparator compares a previous highest grayscale signal with a current highest grayscale signal and applies the current highest grayscale signal to the signal processor according to a comparison result. And a method of driving an organic light emitting display device which is not applied. The method of claim 14, The resistor unit includes a first resistor unit including the first fixed resistor and a second resistor unit including the second fixed resistor and the variable resistor unit, The first resistor unit and the second resistor unit are connected in series, and one end of the DC constant voltage supply unit is connected to a node between the first resistor unit and the second resistor unit, and an output terminal of the DC constant voltage supply unit is connected to the first resistor unit. A method of driving an organic light emitting display device connected to one end. The method of claim 14, The resistor unit includes a first resistor unit including the first fixed resistor and the variable resistor unit and a second resistor unit including the second fixed resistor, The first resistor unit and the second resistor unit are connected in series, and one end of the DC constant voltage supply unit is connected to a node between the first resistor unit and the second resistor unit, and an output terminal of the DC constant voltage supply unit is connected to the first resistor unit. A method of driving an organic light emitting display device connected to one end.

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