KR20060093954A - Pixel circuit of organic light emitting display - Google Patents

Abstract

Disclosed is a pixel circuit for supplying a driving current to a current pixel region in which an organic light emitting display device is formed. The pixel circuit of the organic light emitting device has a first driving transistor in a current pixel region and a second driving transistor in a first adjacent pixel region adjacent to the current pixel region. The second driving transistor is connected in parallel with the first driving transistor. The organic light emitting diode formed in the current pixel region performs the light emission operation by the first driving current generated by the first driving transistor and the second driving current generated by the second driving transistor.

Description

Pixel Circuit of Organic Light Emitting Display

1 is a circuit diagram illustrating a pixel circuit disclosed in Korean Patent Laid-Open Publication No. 2004-0008684, which is cited in the prior art.

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

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

Explanation of symbols on the main parts of the drawings

200, 300: current pixel area 202, 302: first adjacent pixel area

204 and 304: second adjacent pixel region

The present invention relates to an organic electroluminescent device, and more particularly, to an organic electroluminescent device capable of minimizing luminance variation between adjacent pixels.

The organic light emitting display device is classified into a passive matrix type and an active matrix type according to a driving method. In the passive matrix method, the anode and the cathode are arranged in a matrix manner on the screen display area, and a pixel is formed at a portion where the anode and the cathode cross each other.

In contrast, in the active matrix method, a thin film transistor is disposed in each pixel and each pixel is controlled using the thin film transistor.

The biggest difference between the passive matrix type and the active matrix type is the emission time of the organic light emitting device. That is, in the case of the passive matrix system, the organic light emitting layer is instantaneously emitted at high luminance, while in the case of the active matrix system, the organic light emitting layer is continuously emitted at low luminance.

In the case of the passive matrix method, the instantaneous luminous brightness should be increased as the resolution is increased. In addition, since it emits light of high brightness, it has a great influence on the deterioration of the organic light emitting display device. On the other hand, in the case of the active matrix method, the device is driven using a thin film transistor and continuously emits light from the pixel for one frame, thereby driving at a low current. Therefore, the active matrix method has the advantages of less parasitic capacitance and less power consumption than the passive matrix method.

However, the active matrix method has the disadvantage of uneven brightness. Active matrix schemes often use low temperature poly silicon (LTPS) thin film transistors as active devices. The LTPS thin film transistor crystallizes amorphous silicon formed in a low temperature state using a laser. At this time, the characteristics of the transistor vary depending on the crystallization. That is, characteristic nonuniformity occurs in which the threshold voltage and the like of the transistor are not constant for each pixel. Therefore, each pixel shows the same brightness for the same screen signal, and when viewed as a whole, the pixels appear to be uneven in brightness. Various attempts have been made to solve the luminance non-uniformity problem.

In order to solve the luminance non-uniformity problem, a conventional method of compensating the threshold voltage of the driving transistor provided in each pixel has been taken. The method of compensating the threshold voltage of the driving transistor uses a method of storing the threshold voltage in a capacitor connected to the gate of the driving transistor and excluding the influence of the threshold voltage upon generation of the driving current.

The pixel circuit for compensating the threshold voltage of the driving transistor described above is disclosed in Korean Patent Laid-Open Publication No. 2004-0008684.

1 is a circuit diagram illustrating a pixel circuit disclosed in Korean Patent Laid-Open Publication No. 2004-0008684.

Referring to FIG. 1, the pixel circuit has five transistors M1, M2, M3, M4, M5, two capacitors C1, C2, and an organic light emitting diode OLED.

First, the first switching transistor M1 is turned off by the high level scan signal SCAN applied through the scan line 100. In addition, the second switching transistor M2, the third switching transistor M3, and the light emitting transistor M5 are turned on by the switching signals SW1, SW2, and SW3. Since DC current cannot flow through the capacitors C1 and C2, the voltage difference between the source and the drain of the second switching transistor M2 is substantially 0V (Volt). Therefore, VDD is applied to node A and node B. In addition, since a substantial current flowing through the source C and the source and the drain of the third switching transistor M3 is 0A (Ampere) and the third switching transistor M3 is turned on, the current between the source and the drain of the third switching transistor M3 is reduced. The voltage difference is substantially 0V.

Thus, the driving transistor M4 has substantially the same configuration as the diode connected transistor. If the threshold voltage of the driving transistor M4 is defined as Vth, the voltage of VDD-Vth is applied to the node C by the diode-connected driving transistor M4. Through the above process, it can be seen that the voltage of VDD is applied to the node A and the node B, and the voltage of VDD-Vth is applied to the node C. That is, capacitor C2 stores the voltage difference of Vth.

Subsequently, a scan signal SCAN having a low level is applied to the first switching transistor M1 through the scan line 100, and the first switching transistor M1 is turned on. In addition, the switching transistors M2 and M3 are turned off by the switching signals SW1 and SW2. The data signal DATA is applied from the data line 102 to the node B through the turned-on transistor M1. Therefore, the data signal DATA is applied to the node B, and the voltage of DATA-Vth is applied to the node C.

Therefore, the drive current generated by the drive transistor M4 is expressed by the following equation.

In Equation 1, I is a driving current, and K is a constant.

The above-described prior art mainly makes it possible to exclude the influence of the threshold voltage of the driving transistor for each pixel. However, for this purpose, a plurality of transistors must be provided in the pixel, and the plurality of transistors cause a decrease in the aperture ratio of the pixel.

An object of the present invention for solving the above problems is to provide a pixel circuit of the organic light emitting device that can minimize the luminance deviation between the pixels by using a transistor provided in the adjacent pixels.

The present invention for achieving the above object, in the organic light emitting device having a plurality of scan lines and a plurality of data lines are formed, a plurality of pixel areas formed in the region where the scan lines and the data lines intersect, A switching transistor for performing a switching operation according to a scan signal; A capacitor for storing a data signal received through the switching transistor; A first driving transistor for generating a first driving current according to the data signal stored in the capacitor; A second driving transistor formed in a first adjacent pixel region adjacent to the current pixel region in which the first driving transistor is formed, and generating a second driving current according to the data signal; And an organic light emitting display device for performing a light emitting operation according to the first driving current and the second driving current.

In addition, an object of the present invention is a switching transistor for performing a switching operation according to a scan signal; A capacitor for storing a data signal received through the switching transistor; A first driving transistor for generating a first driving current according to the data signal stored in the capacitor; A second driving transistor formed in a first adjacent pixel region adjacent to the current pixel region in which the first driving transistor is formed, and generating a second driving current according to the data signal; An organic light emitting display device for performing a light emitting operation according to the first driving current and the second driving current; And a light emitting transistor configured to perform an on / off operation according to a light emission control signal and to supply the first driving current and the second driving current to the organic light emitting diode. This can also be achieved.

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

Example

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

Referring to FIG. 2, the organic light emitting display device according to the present embodiment includes a plurality of scan lines, a plurality of data lines intersecting the plurality of scan lines, and a plurality of scan lines and regions formed in an area where the scan lines and data lines intersect. Has pixels.

For example, the scan signal SCAN [n] is transmitted to the nth scan line, and the scan signal SCAN [n + 1] is transmitted to the n + 1th scan line. In addition, the data signal VDATA [m] is transmitted through the m-th data line, and the data signal VDATA [m + 1] is transmitted through the m + 1th data line.

The current pixel circuit is formed in an area where the nth scan line and the mth data line cross each other. The current pixel circuit has a switching transistor T1, a first driving transistor T2, a second driving transistor T3, a capacitor C and an organic light emitting diode OLED.

In addition, the current pixel circuit is formed in the current pixel area 200 and the first adjacent pixel area 202. The switching transistor T1, the first driving transistor T2, the capacitor C and the organic light emitting diode OLED are formed in the current pixel region 200, and the second driving transistor T3 is formed in the first adjacent pixel region 202. The transistor T4 formed in the current pixel region 200 is a second driving transistor of the pixel circuit adjacent to the current pixel circuit.

The switching transistor T1 formed in the current pixel region 200 performs an on / off operation under the control of the scan signal SCAN [n] and transmits the data signal VDATA [m] to the node N1. The driving transistor T2 is connected between the node N2 and the ELVDD line, and forms a first driving current required for light emission of the organic light emitting diode OLED. The capacitor C stores the data signal VDATA [m] transmitted through the switching transistor T1. The second driving transistor T3 is formed in the first adjacent pixel region 202 and supplies a second driving current to the organic light emitting diode OLED currently formed in the pixel region 200.

In addition, a second driving transistor T3 formed in the first adjacent pixel region 202 is connected to the nodes N1 and N2 of the current pixel circuit. That is, the second driving transistor T3 is connected in parallel with the first driving transistor T2 and supplies a second driving current to the organic light emitting diode OLED.

First, when the scan signal SCAN [n] is activated, the switching transistor T1 is turned on. The data signal VDATA [m] is transmitted to the node N1 by turning on the switching transistor T1. The data signal VDATA [m] delivered to the node N1 is stored in the capacitor C. Therefore, the voltage difference across the capacitor C becomes ELVDD-VDATA [m].

The first driving current I1 formed in the first driving transistor T2 by the data signal VDATA [m] applied to the node N1 is as follows.

In Equation 2, the constant K1 is determined by the mobility of the charge carriers of the first driving transistor T2, the capacitance between the gate and the body, and the length and width of the channel. Vth1 is a threshold voltage of the first driving transistor T2. The threshold voltage Vth1 is determined according to the impurity concentration of the gate insulating layer and the gate electrode of the first driving transistor T2. Thus, the constant K1 and the threshold voltage Vth1 depend on the structure and properties of the first driving transistor T2.

In addition, the second driving current I2 formed in the second driving transistor T3 by the data signal VDATA [m] applied to the node N1 is expressed by the following equation (3).

In Equation 3, the constant K2 is determined by the mobility of the charge carriers of the second driving transistor T3, the capacitance between the gate and the body, and the length and width of the channel. Vth2 is a threshold voltage of the second driving transistor T3. The threshold voltage Vth2 is determined according to the impurity concentration of the gate insulating layer and the gate electrode of the second driving transistor T3. Thus, the constant K2 and the threshold voltage Vth2 depend on the structure and properties of the second driving transistor T3.

The first driving current I1 of the first driving transistor T2 and the second driving current I2 of the second driving transistor T3 flow to the organic light emitting diode OLED, and the organic light emitting diode has a luminance corresponding to the driving current I1 + I2. Light emission operation. That is, the driving current required for the light emission operation of the organic light emitting diode is the first driving current of the first driving transistor T2 formed in the current pixel region 200 and the first adjacent pixel region 202 adjacent to the current pixel region 200. ) Is the sum of the second driving currents of the second driving transistors T3.

In addition, the transistor T4 provided in the current pixel region 200 supplies a driving current to the organic light emitting diode formed in the second adjacent pixel region 204 adjacent to the current pixel region 200. The second adjacent pixel area 204 may be formed at a position facing the first adjacent pixel area 204 with respect to the current pixel area 200.

According to the manufacturing process of the thin film transistor, a transistor formed in each pixel region has a characteristic difference for each pixel. For example, the driving transistors formed in each pixel region should have the same characteristics, but have a variation in characteristics in actual manufacturing. In order to reduce such variations in characteristics, at least one driving transistor may be formed in an adjacent pixel region, thereby reducing variations in characteristics between pixels.

In addition, although FIG. 2 illustrates that the second driving transistor T3 for supplying a second driving current to the organic light emitting diode is formed in the first pixel region 202 located above the pixel region 200, The two driving transistors may be positioned in pixels adjacent to the top, bottom, left, and right sides of the current pixel area 200.

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

Referring to FIG. 3, the current pixel circuit of the organic light emitting device has a switching transistor T1, a first driving transistor T2, a second driving transistor T3, a light emitting transistor T5, a capacitor C, and an organic light emitting diode OLED.

The current pixel circuit is formed over the current pixel region 300 and the first adjacent pixel region 302. In the current pixel region 300, a switching transistor T1, a first driving transistor T2, a transistor T4, a light emitting transistor T5, a capacitor C, and an organic light emitting diode OLED are formed. In addition, a second driving transistor T3 is formed in the first adjacent pixel region 302.

The switching transistor T1 performs an on / off operation under the control of the scan signal SCAN [n] and transfers the data signal VDATA [m] to the node N1. The driving transistor T2 is connected between the node N2 and the ELVDD line, and forms a first driving current required for light emission of the organic light emitting diode OLED. The capacitor C stores the data signal VDATA [m] transmitted through the switching transistor T1.

In addition, the transistor T4 currently formed in the pixel region 300 supplies a driving current to the organic light emitting diode formed in the second adjacent pixel region 304.

In addition, a second driving transistor T3 formed in the first adjacent pixel region 302 is connected to the nodes N1 and N2 of the current pixel circuit. That is, the second driving transistor T3 is connected in parallel with the first driving transistor T2 and is formed in the first adjacent pixel region 302 adjacent to the current pixel region 300 in which the first driving transistor T2 is formed.

The light emitting transistor T5 is connected between the organic light emitting diode OLED and the node N2, and supplies driving current generated in the first driving transistor T2 and the second driving transistor T3 to the organic light emitting diode OLED through an on / off operation. .

First, when the scan signal SCAN [n] is activated, the switching transistor T1 is turned on. The data signal VDATA [m] is transmitted to the node N1 by turning on the switching transistor T1. The data signal VDATA [m] delivered to the node N1 is stored in the capacitor C. Therefore, the voltage difference across the capacitor C becomes ELVDD-VDATA [m].

Subsequently, the light emitting transistor T5 is turned on by the light emission control signal EMI [n]. By the turn-on of the light emitting transistor T5, a driving current corresponding to the voltage stored in the capacitor C flows into the organic light emitting diode OLED, and the organic light emitting diode OLED starts emitting light.

The first driving current I1 formed in the first driving transistor T2 by the data signal VDATA [m] applied to the node N1 is as follows.

In Equation 4, the constant K1 is determined by the mobility of the charge carriers of the first driving transistor T2 currently formed in the pixel region 300, the capacitance between the gate and the body, and the length and width of the channel. Vth1 is a threshold voltage of the first driving transistor T2. The threshold voltage Vth1 is determined according to the impurity concentration of the gate insulating layer and the gate electrode of the first driving transistor T2. Thus, the constant K1 and the threshold voltage Vth1 depend on the structure and properties of the first driving transistor T2.

In addition, the second driving current I2 formed in the second driving transistor T3 by the data signal VDATA applied to the node N1 is expressed by the following expression (5).

In Equation 5, the constant K2 is determined by the mobility of the charge carriers of the second driving transistor T3 formed in the first adjacent pixel region 302, the capacitance between the gate and the body, and the length and width of the channel. Vth2 is a threshold voltage of the second driving transistor T3. The threshold voltage Vth2 is determined according to the impurity concentration of the gate insulating layer and the gate electrode of the second driving transistor T3. Thus, the constant K2 and the threshold voltage Vth2 depend on the structure and properties of the second driving transistor T3.

The first driving current I1 of the first driving transistor T2 and the second driving current I2 of the second driving transistor T3 flow to the organic light emitting diode OLED, and the organic light emitting diode OLED corresponds to the luminance corresponding to the driving current I1 + I2. Perform the light emission operation with. That is, the driving current required for the light emission operation of the organic light emitting diode OLED is the first driving current of the first driving transistor T2 formed in the current pixel region 300 and the first adjacent pixel region adjacent to the current pixel region 300 ( The sum of the second driving currents of the second driving transistors T3 formed in 302 is obtained.

In addition, the transistor T4 provided in the current pixel region 300 supplies a driving current to the organic light emitting diode formed in the second adjacent pixel region 304 adjacent to the current pixel region 300. The second adjacent pixel area 304 is preferably formed at a position facing the first adjacent pixel area 302 with respect to the current pixel area 300.

According to the manufacturing process of the thin film transistor, a transistor formed in each pixel region has a characteristic difference for each pixel. For example, the driving transistors formed in each pixel region should have the same characteristics, but have a variation in characteristics in actual manufacturing. In order to reduce such variations in characteristics, at least one driving transistor may be formed in an adjacent pixel region, thereby reducing variations in characteristics between pixels.

In addition, although FIG. 3 illustrates that the second driving transistor T3 for supplying a second driving current to the organic light emitting diode is formed in the first pixel region 302 located above the pixel region 300, the second driving transistor T3 is formed in the first pixel region 302. The two driving transistors may be positioned in pixels adjacent to the top, bottom, left, and right sides of the current pixel area 300. In addition, driving currents generated in the plurality of driving transistors may be used in the organic light emitting diode by connecting the driving transistors formed in the pixels disposed on the upper, lower, left, and right sides adjacent to the current pixel region 300 by wiring.

According to the embodiment of the present invention described above, a driving current required for the light emitting operation of the organic light emitting display device of the current pixel circuit is formed in the current pixel area where the organic light emitting device is formed and the adjacent pixel area adjacent to the current pixel area. . This can reduce the characteristic variation of the thin film transistor which plays the same role in each pixel area in the manufacturing process of the organic light emitting device, and can form driving transistors having uniform characteristics.

According to the present invention as described above, the driving current of the pixel circuit is formed by two driving transistors. One driving transistor of the two driving transistors is formed in the current pixel region in which the organic light emitting diode is formed, and the other driving transistor is formed in the adjacent pixel region adjacent to the current pixel region. Therefore, it is possible to compensate the characteristics of the driving transistor having a deviation according to the manufacturing process, it is possible to supply a driving current having a uniform characteristic to the organic light emitting device.

Although the above has been described with reference to the preferred embodiment of the present invention, those skilled in the art will be variously modified and modified within the scope of the present invention without departing from the spirit and scope of the present invention described in the claims below. It will be appreciated that it can be changed.

Claims (10)

In an organic light emitting display device, in which a plurality of scan lines and a plurality of data lines are formed, and have a plurality of pixel regions formed in a region where the scan lines and data lines intersect. A switching transistor for performing a switching operation according to a scan signal; A capacitor for storing a data signal received through the switching transistor; A first driving transistor for generating a first driving current according to the data signal stored in the capacitor; A second driving transistor formed in a first adjacent pixel region adjacent to the current pixel region in which the first driving transistor is formed, and generating a second driving current according to the data signal; And And an organic light emitting display device for performing a light emitting operation according to the first driving current and the second driving current. The pixel circuit of claim 1, wherein the first adjacent pixel area is formed at a predetermined position among upper, lower, left, and right sides of the current pixel area. The pixel circuit of claim 2, wherein the second driving transistor is connected in parallel with the first driving transistor. 4. The pixel circuit according to claim 3, wherein the current pixel region has a transistor for supplying a driving current to an organic light emitting element of a second adjacent pixel region adjacent to the current pixel region. The pixel circuit of claim 4, wherein the second adjacent pixel area faces the first adjacent pixel area about the current pixel area. A switching transistor for performing a switching operation according to a scan signal; A capacitor for storing a data signal received through the switching transistor; A first driving transistor for generating a first driving current according to the data signal stored in the capacitor; A second driving transistor formed in a first adjacent pixel region adjacent to the current pixel region in which the first driving transistor is formed, and generating a second driving current according to the data signal; An organic light emitting display device for performing a light emitting operation according to the first driving current and the second driving current; And And a light emitting transistor configured to perform an on / off operation according to a light emission control signal and to supply the first driving current and the second driving current to the organic light emitting diode. 7. The pixel circuit of claim 6, wherein the first adjacent pixel area is formed at a predetermined position among upper, lower, left, and right sides of the current pixel area. The pixel circuit of claim 7, wherein the second driving transistor is connected in parallel with the first driving transistor. 10. The pixel circuit according to claim 8, wherein the current pixel region has a transistor for supplying a driving current to an organic light emitting element of a second adjacent pixel region adjacent to the current pixel region. 10. The pixel circuit of claim 9, wherein the second adjacent pixel area faces the first adjacent pixel area about the current pixel area.

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