KR20080054189A - Organic light emitting display - Google Patents

Abstract

An OLED(Organic Light Emitting Display) device is provided to improve the lifetime reduction of a display unit by preventing overcurrent flowing in the display unit. An OLED device includes a display unit(P), first and second source voltage supply units, and a feedback circuit(FB). The display unit includes plural sub-pixels at areas, which are defined by crossing signal lines having a first source voltage, a second source voltage, scan, and data lines. The first and second source voltage supply units supply a source voltage, which is required for driving the display unit, through the first and second source voltage lines. The feedback circuit, between the display unit and the first or second source supply unit, includes a transistor, an operational amplifier, and a resistor.

Description

Organic Light Emitting Display

1 is a schematic circuit diagram of an organic light emitting display device according to a first embodiment of the present invention.

FIG. 2 is a circuit diagram of a subpixel and a feedback circuit unit for explaining an organic light emitting display device according to a first embodiment of the present invention; FIG.

3 is a schematic circuit diagram of an organic light emitting display device according to a second embodiment of the present invention;

4 is a circuit diagram of a subpixel and a feedback circuit of an organic light emitting display device according to a second embodiment of the present invention.

<Explanation of symbols on main parts of the drawings>

TFT1: switching transistor TFT2: driving transistor

D: organic light emitting diode C: capacitor

OP: Op Amp R: Resistor

TFT3: Transistor SCAN: Scan Line

DATA: Data line VDD1: First power supply

VSS1: second power supply vdd: first power line

vss: second power line vref: third power line

The present invention relates to an organic light emitting display device.

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.

The organic light emitting display device (hereinafter referred to as OLED) includes a passive matrix method and an active matrix method using a thin film transistor (hereinafter referred to as a transistor).

The passive matrix method forms the anode and the cathode at right angles and selects and drives the line, whereas the active matrix method connects the transistor to each indium tin oxide (ITO) pixel electrode and applies the voltage maintained at a capacitor connected to the gate electrode of the transistor. Therefore, the organic light emitting diode emits light.

In the case of an active matrix scheme (hereinafter, AMOLED), it is generally composed of two or more transistors (eg, switching and driving transistors), a capacitor, and an organic light emitting diode (OLED).

In the conventional active matrix type organic light emitting display device, the amount of current flowing in the panel is increased due to various factors such as the temperature of the panel is increased by the current flowing in the panel during driving or the threshold voltage of the driving transistor is increased. Symptoms have occurred.

This increase in current causes a larger amount of current to flow than the desired current, causing uneven brightness, and this phenomenon lasts for a long time, causing a decrease in the life of the panel.

An object of the present invention for solving the above problems is to provide an organic light emitting display device that can improve the quality of the screen and increase the life.

In order to achieve the above object, the present invention provides a display device including a plurality of subpixels positioned in an area defined by an intersection of signal lines including a first power line, a second power line, a scan line, and a data line; First and second power supply units supplying power for driving to the display unit through a first power line and a second power line; And a feedback circuit unit positioned between the display unit and the first or second power supply unit and including a transistor, an operational amplifier, and a resistor.

In addition, the present invention, a first transistor for transmitting a data signal from the data line in response to the selection signal from the scan line, a capacitor for storing the data signal received through the first transistor, the data stored in the capacitor A subpixel including a second transistor for generating a driving current according to a signal and an organic light emitting diode for performing a light emitting operation according to the driving current, and receiving power through a first power line and a second power line; And

An organic light emitting display device is disposed between the first power line or the second power line and the sub pixel, and includes a feedback circuit unit including a transistor, an operational amplifier, and a resistor.

<First Embodiment>

1 is a schematic circuit diagram of an organic light emitting display device according to a first embodiment of the present invention.

Referring to FIG. 1, the organic light emitting display device according to the first exemplary embodiment of the present invention includes a display unit P including a plurality of sub pixels SP.

In addition, the display unit P is connected to the first and second power supply units VDD and VSS for supplying power for driving, and the first power supply unit VDD and the second power supply unit VSS are respectively connected to a first power line. Power is supplied to the display unit P via the vdd and the second power lines vss.

The feedback circuit unit FB is positioned between the display unit P and the second power supply unit VSS to adjust the amount of current flowing through the display unit P.

Here, the feedback circuit unit FB includes a transistor TFT3, an operational amplifier OP, and a resistor R, and further includes a third power supply line vref for supplying a reference voltage to the operational amplifier OP. The third power line vref is electrically connected to a third power supply unit (not shown).

Meanwhile, the first power supply unit VDD, the second power supply unit VSS, and the third power supply unit (not shown), which are schematically illustrated, are output from one power supply unit included in the driving device, and thus different output power values. See also that may have.

The feedback circuit unit FB may be located on a substrate on which a driving device (not shown) or a display unit P is provided to supply scan signals and data signals to scan lines and data lines.

FIG. 2 is a circuit diagram illustrating a subpixel and a feedback circuit of an organic light emitting display device according to a first embodiment of the present invention. Referring to this, the organic light emitting display device according to the first embodiment of the present invention will be described in detail. do.

The subpixel SP of the organic light emitting display device according to the first embodiment of the present invention includes two or more transistors TFT1 and TFT2, a capacitor C, and an organic light emitting diode D. Two or more transistors TFT1 and TFT2 included in the subpixel are divided into a switching transistor TFT1 and a driving transistor TFT2.

Here, the switching transistor TFT1 has a gate connected to the scan line SCAN and a first electrode connected to the data line DATA. In addition, a gate of the driving transistor TFT2 is connected to the second electrode of the switching transistor TFT1. The capacitor C is connected between the gate of the driving transistor TFT2 and the second electrode. In addition, an anode of the organic light emitting diode D is connected to the first power line dvd and a cathode of the organic light emitting diode D is connected to the first electrode of the driving transistor TFT2.

The feedback circuit unit includes a third power supply line vref for supplying a reference voltage to the transistor TFT3, the operational amplifier OP, the resistor R, and the operational amplifier OP.

Here, in the transistor TFT3, the first electrode is connected to the second electrode of the driving transistor TFT2. The operational amplifier OP has a first end connected to a third power supply line vref, a second end connected to a second electrode of the transistor TFT3, and an output end connected to a gate of the transistor TFT3. The resistor R is connected at one end to a node Vx to which the second terminal of the operational amplifier OP and the second electrode of the transistor TFT3 are connected, and the other end thereof is connected to the second power line vss.

On the other hand, the first power line (vdd), the second power line (vss) and the third power line (vref) can be electrically connected to the first, second and third power supply, respectively, although not shown, they are driven Note that it can be output from one power supply included in the device.

When the structure of the transistors TFT1 and TFT2 included in the sub-pixel is schematically described, generally, a semiconductor layer, a first insulating film as a gate insulating film, a gate electrode, a second insulating film as an interlayer insulating film, a source electrode, and the like are formed on a substrate. And a drain electrode. Note that the transistors TFT1 and TFT2 may be formed of low temperature polysilicon or amorphous silicon. In addition, it is noted that any one of the source electrode and the drain electrode of the transistors TFT1 and TFT2 is electrically connected to the pixel electrode through the contact hole.

On the other hand, as described above, the transistors are divided into the switching transistor TFT1, the driving transistor TFT2, and the like. Generally, two or more transistors TFT1 and TFT2 and one capacitor C are referred to as “2T1C”. Note that pixels may be formed, but are not limited thereto.

Next, the structure of the organic light emitting diode (D) will be described schematically, which is an organic light emitting layer between common layers such as a hole injection layer (HIL), a hole transport layer (HTL), an electron transport layer (ETL) and an electron injection layer (EIL). (EML) is included. In general, the common film is selectively formed between the pixel electrode and the cathode electrode of the driving transistor TFT2 serving as the anode electrode.

On the other hand, one sub-pixel (Sub-Pixel) includes one organic light emitting diode (D). Each sub pixel emits red (R), green (G), and blue (B), and the sub pixels emitting red, green, and blue are defined as one pixel.

The operation of the organic light emitting display device according to the first embodiment of the present invention will be described below. (See Figures 1 and 2 together)

Each sub pixel SP formed in the display unit P receives a power supply voltage and a ground voltage through a first power supply line dvd and a second power supply line vss electrically connected to a driving device (not shown). The organic light emitting diode D emits light by receiving a scan signal and a data signal through the scan line SCAN and the data line DATA, thereby representing a desired image.

In this case, the feedback circuit part BP receives the reference voltage Vref through the third power line vref connected to the first end of the operational amplifier OP, and receives the reference voltage Vref1 and the node connected to the second end. Vx) voltages are compared and the transistor TFT3 is controlled according to the comparison result value.

Here, the transistor TFT3 is turned on when the reference voltage Vref1 at the first end of the operational amplifier OP is greater than or equal to the voltage of the node Vx at the second end. On the other hand, when the reference voltage Vref1 at the first end of the operational amplifier OP is greater than the voltage at the node Vx at the second end, the transistor TFT3 is turned on.

This is represented by the following equation, which is represented by Equation 1 below.

If Vref1≤ Vx, the TFT is TURN OFF,

If Vref1> Vx, TFT is TURN ON

Here, the reference voltage “Vref1” may be supplied from a power supply unit (not shown) included in the driving device (not shown), and the reference voltage value may be supplied by referring to a lookup table that is set in advance. Here, the node Vx voltage is (I _OLED ) x R.

When the organic light emitting display device according to the first embodiment of the present invention operates normally, since the positive amount of current flows through the light emitting diode D, the transistor TFT3 of the feedback circuit portion FB is turned on. Therefore, the current may continue to be connected to the second power supply unit VSS.

However, when the display unit P continuously displays an image, when the panel temperature rises and the amount of current I _OLED flowing through the panel increases, the voltage of the node Vx increases, so that the feedback circuit unit FB The transistor TFT3 is turned off and cannot receive power from the second power supply VSS.

As described above, the organic light emitting display device according to the first exemplary embodiment of the present invention can prevent a problem in which an overcurrent flows in the display unit, thereby improving the lifespan of the display unit and a problem of increasing luminance over time.

In the first embodiment of the present invention, the feedback circuit unit FB is connected between the second power supply unit VSS and the display unit P to adjust the amount of current flowing through the entire panel, but the present invention is not limited thereto. The feedback circuit unit FB may exist every time.

In the first embodiment of the present invention, the structure of the subpixel is illustrated as including two transistors, one capacitor, and a light emitting diode, but the present invention is not limited thereto, and may include a larger number of transistors and capacitors.

Second Embodiment

3 is a schematic circuit diagram of an organic light emitting display device according to a second embodiment of the present invention.

The display unit P shown in FIG. 3 includes a plurality of sub pixels SP.

In addition, the display unit P is connected to the first and second power supply units VDD1 and VSS1 for supplying power for driving, and the first power supply unit VDD1 and the second power supply unit VSS1 are respectively connected to a first power line. Power is supplied to the display unit P through the vdd and the second power line vss.

The feedback circuit unit FB is positioned between the display unit P and the first power supply unit VDD1 to adjust the amount of current flowing through the display unit P.

The feedback circuit unit FBP includes a transistor TFT3, an operational amplifier OP, and a resistor R, and supplies a third power supply line vref for supplying a reference voltage Vref1 to the operational amplifier OP. It includes more. The third power line vref is electrically connected to a third power supply unit (not shown).

Meanwhile, the first power supply unit VDD, the second power supply unit VSS, and the third power supply unit (not shown), which are schematically illustrated, are output from one power supply unit included in the driving device, and thus different output power values. See also that may have.

The feedback circuit unit FB may be located on a substrate on which a driving device (not shown) or a display unit P is provided to supply scan signals and data signals to scan lines and data lines.

4 is a circuit diagram illustrating a subpixel and a feedback circuit unit of an organic light emitting display device according to a second embodiment of the present invention.

The subpixel includes two or more transistors TFT1 and TFT2, a capacitor C, and an organic light emitting diode D. Two or more transistors TFT1 and TFT2 included in the subpixel are divided into a switching transistor TFT1 and a driving transistor TFT2.

Here, the switching transistor TFT1 has a gate connected to the scan line SCAN and a first electrode connected to the data line DATA. In addition, a gate of the driving transistor TFT2 is connected to the second electrode of the switching transistor TFT1. The capacitor C is connected between the gate of the driving transistor TFT2 and the first electrode. The organic light emitting diode D has an anode connected to the second electrode of the driving transistor TFT2 and a cathode connected to the second power line VSS.

Referring to the circuit configuration of the feedback circuit unit FB, it includes a third power supply line (vref) for supplying a reference voltage to the transistor TFT3, the operational amplifier (OP), the resistor (R) and the operational amplifier (OP). .

Here, one end of the resistor (R) is connected to the first power line (vdd). The operational amplifier OP has a first end connected to a node Vx connected to a first electrode of the transistor TFT3 and the other end of the resistor R, and a second end connected to a third power line vref. An output terminal is connected to the gate of the transistor TFT3. In the transistor TFT3, a second electrode is connected to the first electrode of the driving transistor TFT2.

On the other hand, the first power line (vdd), the second power line (vss) and the third power line (vref) are not shown, but may be electrically connected to the first, second and third power supply, respectively, these drive devices Note that it can be output from one power supply included therein.

The operation of the organic light emitting display device according to the second embodiment of the present invention will be described below. (See Figures 3 and 4 together)

Each sub-pixel formed in the display unit receives a power supply voltage and a ground voltage through a first power supply line dvd and a second power supply line vss electrically connected to a driving device (not shown). The organic light emitting diode D emits light by receiving a scan signal and a data signal through the data line DATA, thereby representing a desired image.

The feedback circuit unit compares the reference voltage Vref supplied through the third power line vref connected to the second end of the operational amplifier OP with the node Vx voltage applied to the first end, and according to the comparison result value. The transistor TFT3 is controlled. Here, the transistor TFT3 is turned on when the reference voltage Vref1 at the second end of the operational amplifier OP is less than or equal to the voltage of the node Vx at the first end. On the other hand, when the reference voltage Vref1 at the second end of the operational amplifier OP is greater than the voltage at the node Vx at the first end, the transistor TFT3 is turned off.

This is represented by the following equation, which is represented by Equation 2 below.

If Vref1≤ Vx, the TFT is TURN ON,

If Vref1> Vx, TFT is TURN OFF

Here, the reference voltage "Vref1" may be supplied from a driving device (not shown), and the reference voltage value may be supplied by referring to a lookup table that is set in advance, and the node Vx voltage may be a first power line. Reference is made to the amount of current I _OLED flowing between vdd and the second power supply line vss. Here, the node Vx voltage is VDD− (I _OLED ) × R.

When the organic light emitting display device according to the second embodiment of the present invention normally operates, since the positive amount of current flows through the light emitting diode D, the transistor TFT3 of the feedback circuit unit FB is turned on. Therefore, the current may be continuously connected to the first power supply unit VDD1.

However, as the display unit P continuously displays an image, when the temperature of the panel increases and the amount of current I _OLED flowing through the panel increases, the voltage of the node Vx decreases, so that the feedback circuit unit FB The transistor TFT3 is turned off and cannot receive power from the first power supply unit VDD1.

As described above, the organic light emitting display device according to the second embodiment of the present invention can prevent the problem of overcurrent flowing in the display unit, thereby improving the lifespan of the display unit and the problem of increasing luminance over time.

In the second embodiment of the present invention, although the feedback circuit unit FB is connected between the first power supply unit VDD1 and the display unit P to adjust the amount of current flowing through the entire panel, the present invention is not limited thereto. The feedback circuit unit FB may exist every time.

In the second embodiment of the present invention, the structure of the subpixel is illustrated as including two transistors, one capacitor, and a light emitting diode, but the present invention is not limited thereto, and may include a larger number of transistors and capacitors.

Although the embodiments of the present invention have been described above with reference to the accompanying drawings, the technical configuration of the present invention described above may be modified in other specific forms by those skilled in the art to which the present invention pertains without changing its technical spirit or essential features. It will be appreciated that it may be practiced. Therefore, the embodiments described above are to be understood as illustrative and not restrictive in all aspects. In addition, the scope of the present invention is shown by the claims below, rather than the above detailed description. Also, it is to be construed that all changes or modifications derived from the meaning and scope of the claims and their equivalent concepts are included in the scope of the present invention.

As described above, the present invention has the effect of improving the lifespan of the organic light emitting display device and solving the problem of uneven light point.

Claims (9)

A display unit including a plurality of subpixels positioned in an area defined by an intersection of signal lines including a first power line, a second power line, a scan line, and a data line; First and second power supply units supplying power for driving to the display unit through a first power line and a second power line; And An organic light emitting display device positioned between the display unit and the first or second power supply unit and including a feedback circuit unit including a transistor, an operational amplifier, and a resistor. The method of claim 1, A third power supply for supplying a reference voltage to the operational amplifier further comprises, And the operational amplifier receives the reference voltage through a third power supply line. The method of claim 2, In the transistor of the feedback circuit unit, a first electrode is connected to the display unit, The operational amplifier has a first end connected to the third power line, a second end connected to a second electrode of the transistor, and an output end connected to a gate of the transistor, And one end of the resistor is connected to a node to which the second end of the operational amplifier and the second electrode of the transistor are connected, and the other end of the resistor is connected to the first or second power line. The method of claim 3, wherein the operational amplifier, And the transistor is controlled according to the reference voltage across the first stage and the node voltage across the second stage. The method of claim 1, The subpixel may include a first transistor configured to transfer a data signal from the data line in response to a selection signal from the scan line; A capacitor for storing a data signal received through the first transistor, A second transistor for generating a driving current according to the data signal stored in the capacitor; An organic light emitting display device comprising an organic light emitting diode for performing a light emitting operation according to the driving current. A first transistor that transfers the data signal from the data line in response to the selection signal from the scan line, a capacitor for storing the data signal received through the first transistor, and a driving current generated according to the data signal stored in the capacitor A subpixel including a second transistor for performing light emission and an organic light emitting diode for performing light emission according to the driving current, and receiving power through a first power line and a second power line; And And a feedback circuit unit positioned between the first power line or the second power line and the sub pixel, the feedback circuit unit including a transistor, an operational amplifier, and a resistor. The method of claim 6, The operational amplifier of the feedback circuit unit, And a third power line for supplying a reference voltage for supplying a reference voltage to the operational amplifier. The method of claim 7, wherein In the transistor of the feedback circuit unit, a first electrode is connected to a sub pixel, The operational amplifier has a first end connected to the third power line, a second end connected to a second electrode of the transistor, and an output end connected to a gate of the transistor, And one end of which is connected to a node to which the second end of the operational amplifier and the second electrode of the transistor are connected, and the other end of which is connected to the first or second power line. The method of claim 8, The operational amplifier, And the transistor is controlled according to the reference voltage across the second stage and the node voltage across the first stage.

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