KR20140132596A - A pixel circuit, method for driving a pixel circuit and an display panel apparatus using organic light emitting diode - Google Patents

Abstract

A driving circuit for applying a reference voltage, a data voltage or a power supply voltage to the first and second nodes of the capacitor in response to the first scan signal and the second scan signal; A driving transistor for outputting a driving current when an output voltage is inputted to the gate electrode, and an organic light emitting diode for emitting light with a luminance corresponding to the level of the output driving current.

Description

Technical Field [0001] The present invention relates to a pixel circuit, a method of driving a pixel circuit, and a display panel device using the same.

And more particularly, to a pixel circuit using an organic light emitting diode, a method of driving the pixel circuit, and a display panel device.

Flat panel display devices such as liquid crystal display (LCD), plasma display panel (PDP), and field emission display (FED) have been developed that overcome the disadvantages of cathode ray tube (CRT) displays. Among such display devices, an OLED display device using an organic light emitting diode (OLED) having excellent light emitting efficiency, luminance and viewing angle and a high response speed is receiving attention as a next generation display device.

Such an OLED display device displays an image on a display panel using an organic light emitting diode that generates light by recombination of electrons and holes. Such an OLED display device can be driven with low power consumption at the same time as it has a fast response speed, and the application fields thereof are increasingly used for smart phones, tablet devices, monitors, TVs and the like.

A pixel circuit using an organic light emitting diode, a driving method of a pixel circuit, and a display panel device. The technical problem to be solved by this embodiment is not limited to the above-described technical problems, and other technical problems may exist.

According to an aspect of the present invention, a pixel circuit using an organic light emitting diode applies a reference voltage and a data voltage to first and second nodes of a capacitor in response to a first scan signal, A driving controller for outputting a boosting voltage through the second node when a voltage is applied; A driving transistor for outputting a driving current based on a voltage difference between the power supply voltage and the boosting voltage when the boosting voltage is input to the gate electrode; And an organic light emitting diode that emits light at a luminance corresponding to the level of the output driving current.

In addition, the level of the output drive current is adjusted according to the level of the voltage difference between the reference voltage and the data voltage.

Also, the reference voltage and the power supply voltage are voltages at the same level.

When the power voltage is applied to the first node in response to the second scan signal, the boosting voltage is applied to the second node in order to maintain a voltage difference between the reference voltage charged in the capacitor and the data voltage. Lt; / RTI >

The first scan signal and the second scan signal are complementary signals.

In addition, the drive control unit includes a plurality of transistors for switching the application of the reference voltage, the data voltage, and the power supply voltage, respectively.

Also, the plurality of transistors are P-channel type transistors, the first scan signal has a low level during a programming period to charge the capacitor, and the organic light emitting diode is driven The second scan signal has a high level during the programming interval and a low level during the emitting interval.

The driving controller may further include: a capacitor connected between the first node and the second node to charge a charge corresponding to a voltage difference between voltages applied to the nodes; A first transistor coupled between the first node and a reference line providing the reference voltage; A second transistor coupled between the second node and a data line providing the data voltage; And a third transistor coupled between the first node and the power supply voltage, wherein the first transistor and the second transistor are commonly connected to a first scan line providing the first scan signal, A transistor is coupled to a second scan line providing the second scan signal.

The organic light emitting display further includes a fourth transistor, which is located between the power supply voltage and the driving transistor and is diode-connected to the gate electrode and the drain electrode.

According to another aspect, a pixel circuit using an organic light emitting diode includes: a capacitor connected between a first node and a second node; A first transistor coupled between the first node and a reference line for switching application of a reference voltage in response to a first scan signal; A second transistor coupled between the second node and a data line for switching application of a data voltage in response to the first scan signal; A third transistor coupled between the first node and a power supply voltage for switching application of the power supply voltage in response to a second scan signal; A driving transistor for outputting a driving current according to a voltage applied to a gate electrode connected to the second node; A fourth transistor connected between the power supply voltage and the driving transistor and diode-connected to the gate electrode and the drain electrode; And an organic light emitting diode that emits light at a luminance corresponding to the level of the output driving current, wherein the capacitor is responsive to the first scan signal for applying the reference voltage and the data voltage And outputs a boosting voltage through the second node when the power source voltage is applied to the first node in response to the second scan signal, And outputs the driving current based on the voltage difference between the voltage applied to the drain electrode of the fourth transistor and the boosting voltage when the voltage is input to the electrode.

In addition, the level of the output drive current is adjusted according to the level of the voltage difference between the reference voltage and the data voltage.

Also, the reference voltage and the power supply voltage are voltages at the same level.

The first scan signal and the second scan signal are complementary signals.

In addition, the transistors are P-channel type transistors, the first scan signal has a low level during a programming period to charge the capacitor, and the emitters for driving the organic light emitting diodes The first scan signal has a high level during an emission period and the second scan signal has a high level during the programming period and a low level during the emitting period.

According to another aspect of the present invention, a display panel device using an organic light emitting diode includes a scan driver for providing a first scan signal and a second scan signal to a first scan line and a second scan line; A data driver for providing a data voltage to a data line; A reference driver for providing a reference voltage as a reference line; And a plurality of pixel circuits disposed at positions where the first scan line, the second scan line, the data line, and the reference line cross each other, wherein each of the plurality of pixel circuits is responsive to a first scan signal A reference voltage and a data voltage are applied to the first and second nodes of the capacitor and a boosting voltage is output through the second node when a power supply voltage is applied to the first node in response to the second scan signal A drive control unit; A driving transistor for outputting a driving current based on a voltage difference between the power supply voltage and the boosting voltage when the boosting voltage is input to the gate electrode; And an organic light emitting diode that emits light at a luminance corresponding to the level of the output driving current.

In addition, the level of the output drive current is adjusted according to the level of the voltage difference between the reference voltage and the data voltage.

Also, the reference voltage and the power supply voltage are voltages at the same level.

The driving control unit may include a plurality of P-channel type transistors for switching application of the reference voltage, the data voltage, and the power source voltage, and the first scan signal may be a programming period for charging the capacitor And has a high level during an emission period for driving the organic light emitting diode and the second scan signal has a high level during the programming period, Lt; / RTI > has a low level.

The driving control unit may further include: a capacitor connected between the first node and the second node; A first transistor coupled between the first node and the reference line for switching application of the reference voltage in response to the first scan signal; A second transistor coupled between the second node and the data line for switching application of the data voltage in response to the first scan signal; And a third transistor connected between the first node and the power source voltage for switching application of the power source voltage in response to the second scan signal.

According to another aspect, a method of driving a pixel circuit using an organic light emitting diode includes applying a reference voltage and a data voltage to the first and second nodes of the capacitor in response to a first scan signal corresponding to a programming period step; Applying a power supply voltage to the first node in response to a second scan signal corresponding to an emitting period; Outputting a boosting voltage through the second node when a power supply voltage is applied to the first node; Outputting a driving current based on a voltage difference between the power supply voltage and the boosting voltage when the boosting voltage is input to the gate electrode of the driving transistor; And causing the organic light emitting diode to emit light at a luminance corresponding to the level of the output driving current.

According to the above, a display panel having higher image quality characteristics can be realized by using a pixel circuit having a fine current control and an IR-drop compensation function. Further, by producing a high-resolution large-screen OLED display device having such a display panel, for example, an AMOLED display device or the like, an image having sharp and accurate image quality characteristics can be displayed.

1 is a view for explaining the principle of light emission of an organic light emitting diode.
2A is a diagram illustrating an exemplary pixel circuit implemented with a P-channel type thin film transistor.
FIG. 2B is a diagram illustrating another type of exemplary pixel circuit implemented with a plurality of transistors.
3 is a block diagram showing the configuration of one pixel circuit 30 included in the display panel device according to an embodiment of the present invention.
4 is a circuit diagram showing the structure of one pixel circuit 40 provided in the display panel device according to the embodiment of the present invention.
5 is a diagram showing the driving timing of the pixel circuit 40 according to the embodiment of the present invention.
6 is a view showing a display panel device 60 according to an embodiment of the present invention.
7 is a diagram showing a simulation result of a current error between a pixel circuit according to an embodiment of the present invention and a conventional pixel circuit.
8 is a flowchart of a method of driving a pixel circuit using an organic light emitting diode according to an embodiment of the present invention.

Hereinafter, embodiments of the present invention will be described. The following description and accompanying drawings are for understanding the operation according to the present embodiment, and parts that can be easily implemented by those skilled in the art can be omitted.

Furthermore, the present specification and drawings are not provided for the purpose of limiting the present embodiment, and the scope of the present embodiment should be determined by the claims. It should be understood, however, that this invention is not intended to be limited to the particular forms disclosed, but is intended to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the invention.

In this embodiment, the terms first, second, and so on can be used to describe various components, but the components are not limited by the terms. The terms may be used for the purpose of distinguishing one component from another.

It is to be understood that when an element is referred to as being "connected" or "connected" to another element, it may be directly connected or connected to the other element, . Other expressions, such as "between" and the like, that describe the relationship between components should also be interpreted.

The terms used in this embodiment are used only to describe a specific embodiment, and should not be construed as limiting the present embodiment. The singular expressions include plural expressions unless the context clearly dictates otherwise. In the present embodiment, the terms "comprises ", or" having ", and the like, specify that the described features, integers, steps, operations, elements, or combinations thereof exist, , Steps, operations, elements, or combinations thereof, as a matter of convenience, without departing from the spirit and scope of the invention.

Unless otherwise defined, all terms used in this embodiment, including technical or scientific terms, have the same meaning as commonly understood by one of ordinary skill in the art. Terms such as those defined in commonly used dictionaries should be construed as meaning consistent with meaning in the context of the relevant art and are to be construed as ideal or overly formal in meaning unless explicitly defined in this embodiment Do not.

Hereinafter, the present embodiment will be described in more detail with reference to the accompanying drawings. The same reference numerals are used for the same constituent elements in the drawings, and redundant explanations for the same constituent elements are omitted.

2. Description of the Related Art Generally, an OLED display device is a display device for electrically exciting a fluorescent organic compound to emit light, and includes a display panel device capable of displaying images by driving a plurality of pixels arranged in a matrix form on the front surface. In particular, AMOLED (Active Matrix Organic Light Emitting Diodes) display devices have been applied from display devices provided in mobile devices such as smart phones and tablet devices due to their fast response speed, wide viewing angle, and ease of thinning, Is gradually expanding.

Each of the plurality of pixels provided in the display panel device of the OLED display device is provided with an organic light emitting element such as an organic light emitting diode (OLED). The organic light emitting diode emits light with a brightness corresponding to each pixel constituting the image, so that the whole image can be displayed. More specifically, the organic light emitting diode emits light with a luminance proportional to the level of the applied current. Therefore, in order to display an accurate and clear image in the OLED display device, it is important to accurately control the amount of current flowing through the organic light emitting diode provided in each pixel.

Recently, as the resolution of the display device is gradually changed to a high resolution, the area of the organic light emitting diode per pixel is gradually reduced, and the material efficiency of the organic light emitting diode is further improved. As a result, the amount of current flowing through the organic light emitting diode also decreases, and the driving current for controlling the luminance of the organic light emitting diode is also very small. Therefore, the range of the data voltage for determining the amount of current flowing in the organic light emitting diode has also narrowed. As a result, the voltage of the various gradations (for example, 256 gradations) is supplied to the pixel in the narrowed voltage range, so that the difference of the data voltages by gradation becomes finer. As a result, this complicates the design of the data driver for supplying the data voltage and causes problems such as an increase in the luminance error due to a variation in the process.

On the other hand, the power consumption of the panel is proportional to the area of the panel regardless of the resolution of the panel. Therefore, as the area of the panel increases, the current drop due to the IR-drop must be compensated, but more accurate and detailed image display is possible.

The pixel circuit according to the present embodiment to be described below can more precisely and finely control the minute current flowing through the organic light emitting diode and has a function of compensating the current drop due to the IR drop, It is possible to realize a display panel device which can display an image more precisely and precisely than the other.

1 is a view for explaining the principle of light emission of an organic light emitting diode.

The organic light emitting diode (OLED) has a structure in which an anode electrode layer made of ITO (indium tin oxide), an organic thin film, and a cathode electrode layer made of metal are stacked. The organic thin film includes an emitting layer (EML), an electron transport layer (ETL), and a hole transport layer (HTL) in order to enhance the balance between electrons and holes to improve luminous efficiency. In addition, the organic thin film may further include a hole injection layer (HIL) or an electron injection layer (EIL).

Such an organic light emitting diode may be formed by connecting a transistor such as a thin film transistor (TFT) or a metal oxide semiconductor field effect transistor (MOSFET) to an anode electrode of an organic light emitting diode and by maintaining a capacity of a capacitor connected to a gate electrode of the organic light emitting diode And can be driven according to the data voltage.

2A is a diagram illustrating an exemplary pixel circuit implemented with a P-channel type thin film transistor.

2A, when the scan signal SCAN supplied from the scan line is at a low level, the transistor M2 is turned on, and the data voltage DATA supplied from the data line, The potential difference of the voltage VDD is stored in the storage capacitor C1. Then, as the voltage corresponding to the potential difference stored in the storage capacitor C1 is inputted to the gate terminal of the driving transistor Ml, the driving transistor Ml outputs the driving current I _OLED . The driving current I _OLED flows to the organic light emitting diode OLED and the organic light emitting diode OLED emits light with the luminance corresponding to the driving current I _OLED . As a result, the organic light emitting diode OLED can emit light with a luminance corresponding to the voltage level of the data voltage DATA. Here, the driving current I _OLED flowing through the organic light emitting diode OLED can be calculated by the following equation (1).

However, a generally known pixel circuit as shown in Fig. 1 has a limitation. More specifically, as described above, in the high resolution display, the current I _OLED of the organic light emitting diode _OLED becomes very small, and accordingly, the data voltage DATA becomes small. Actually, in a 4-inch 1000ppi high-resolution display, the maximum I _OLED at full white is only a few tens of nanometers, so the swing range of the data voltage (DATA) becomes very small. Therefore, it is difficult to fabricate a data driver for finely dividing a very small voltage to express gradations.

FIG. 2B is a diagram illustrating another type of exemplary pixel circuit implemented with a plurality of transistors.

Referring to FIG. 2B, a pixel circuit for controlling a fine current or for current scaling includes a driving transistor M1 and a transistor M2 corresponding to an active load .

Active load transistor (M2) is the gate of the connection between the power supply voltage (VDD) to the driving transistor (M1), the driving transistor (M1) - by lowering the source voltage (V _GS), the current flowing through the organic light emitting diode (OLED) . This pixel circuit allows fine current control by lowering the current I _OLED when the same data voltage DATA is applied, as compared with the pixel structure of 2T1C (2 transistor 1 capacitor) shown in FIG. 2A. However, since the pixel circuit of FIG. 2B has no IR-drop compensation function, it is difficult to apply the pixel circuit of FIG. 2B to a general display other than a micro-display.

On the other hand, when using a backplane material having a small V _T deviation according to the position of a pixel circuit on a display panel, such as crystallized silicon, there is no problem of current change due to V _T deviation, As the panel size increases, the IR-drop phenomenon may occur in which the brightness drops due to the power supply voltage drop due to the resistance existing in the power supply line and the current flowing in the power supply line. Therefore, a structure of a pixel circuit capable of compensating IR-drop in the pixel circuit is required.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. The following description and accompanying drawings are for understanding the operation according to the present embodiment, and parts that can be easily implemented by a person skilled in the art to which this embodiment belongs can be omitted.

3 is a block diagram showing the configuration of one pixel circuit 30 included in the display panel device according to an embodiment of the present invention.

3, the pixel circuit 30 includes a driving controlling unit 310, a driving transistor 320, and an organic light emitting diode 330. The pixel circuit 30 shown in Fig. 3 is shown in which each circuit component is divided into functional blocks. It will thus be appreciated by those skilled in the art that the circuit structure within each functional block may be implemented with various circuit components capable of performing the functions and operations of the pixel circuit 30, .

The drive control unit 310 includes a plurality of transistors and a capacitor. The driving control unit 310 applies the reference voltage V _REF to the first node of the capacitor in response to the first scan signal SCAN 1 and applies the data voltage DATA to the second node of the capacitor.

The driving control unit 310 applies the power supply voltage VDD to the first node of the capacitor in response to the second scan signal SCAN2. In this case, when the power supply voltage VDD is applied to the first node, the drive control unit 310 outputs a boosting voltage through the second node.

Here, when the power supply voltage VDD is applied to the first node in response to the second scan signal SCAN 2, the boosting voltage is a voltage difference between the reference voltage V _REF charged in the capacitor and the data voltage DATA Lt; / RTI > the voltage applied to the second node. In other words, the boosting voltage means the voltage changed at the second node due to the bootstrap action through the capacitor when the power supply voltage VDD is applied to the first node of the capacitor.

On the other hand, the reference voltage V _REF and the power source voltage VDD are voltages at the same level. As described below, the reference voltage V _REF is a voltage supplied separately to compensate for the IR-drop.

The first scan signal SCAN 1 and the second scan signal SCAN 2 are signals having complementary levels. That is, when the first scan signal SCAN 1 is at a low level, the second scan signal SCAN 2 has a high level, and vice versa.

The drive control unit 310 includes a plurality of transistors for switching the application of each of the reference voltage V _REF , the data voltage DATA and the power supply voltage VDD. According to the present embodiment, the plurality of transistors may correspond to P-channel type transistors, but are not limited thereto. When the transistors are of the P-channel type, the first scan signal SCAN 1 has a low level during a programming period to charge the capacitor, and emits light that drives the organic light emitting diode 330 Quot; high " level. The second scan signal SCAN 2 has a high level during a programming period and a low level during an emitting interval.

The driving transistor 320 outputs the driving current I _OLED based on the voltage difference between the power supply voltage VDD and the boosting voltage when the boosting voltage is input to the gate electrode.

Here, the level of the driving current is adjusted in accordance with the level of the voltage difference between the reference voltage V _REF and the data voltage DATA.

More specifically, the level of the driving current I _OLED in the conventional pixel circuit without IR-drop compensation function was adjusted according to the level of the voltage difference between the power supply voltage VDD and the data voltage DATA. However, as described above, when an active load transistor (M2 of FIG. 2B) is added for fine current control or current scaling in the past, an IR-drop occurs and the level of the power supply voltage VDD initially applied is maintained It is difficult to generate the driving current I _OLED .

Alternatively, instead of the power supply voltage VDD, the driving transistor 320 according to the present embodiment may be driven in accordance with the level of the voltage difference between the reference voltage V _REF and the data voltage DATA equal to the level of the power supply voltage VDD The driving current I _OLED can be adjusted so that the IR-drop of the power source voltage VDD can be compensated and the micro-current can be controlled.

Although not shown in FIG. 3, the pixel circuit 30 is an active load transistor for controlling a minute current, and is connected between the power source voltage VDD and the driving transistor 320 and has a gate electrode and a drain electrode And may further include a diode-connected transistor.

The organic light emitting diode 330 emits light at a luminance corresponding to the level of the driving current I _OLED output from the driving transistor 320.

4 is a circuit diagram showing the structure of one pixel circuit 40 included in the display panel device according to an embodiment of the present invention.

Referring to FIG. 4, the pixel circuit 40 includes the driving control unit 310, the driving transistor 320, and the organic light emitting diode 330 of the pixel circuit 30 shown in FIG. And can be applied to an example implemented by the present invention. However, as described above, it will be understood by those skilled in the art that the pixel circuit 30 of FIG. 3 is not limited to the structure of the pixel circuit 40 shown in FIG.

The pixel circuit 40 may be composed of five P-channel type transistors M1 to M5, one capacitor C1, and one organic light emitting diode OLED.

The capacitor C1 is connected between the first node A and the second node B and supplies the amount of charge corresponding to the voltage applied to the first node A and the voltage difference applied to the second node B Charge.

A first transistor (M1) is the application of the first node (A) and the reference voltage is connected between the reference line to provide (V _REF), a first scan signal (SCAN. 1) in response to the reference voltage (V _REF) in Lt; / RTI >

The second transistor M2 is connected between the second node B and the data line providing the data voltage DATA and switches the application of the data voltage DATA in response to the first scan signal SCAN1 .

The first transistor M1 and the second transistor M2 are commonly connected to a first scan line SCAN1 and provide a first scan signal SCAN1, And performs an operation.

The third transistor M3 is connected between the first node A and the power source voltage VDD and switches the application of the power source voltage VDD in response to the second scan signal SCAN2.

The driving transistor M5 outputs the driving current I _OLED according to the voltage applied to the gate electrode connected to the second node B. [

The fourth transistor M4 is connected between the power supply voltage VDD and the driving transistor M5 and is a diode-connected transistor having a gate electrode and a drain electrode.

The organic light emitting diode OLED emits light at a luminance corresponding to the level of the driving current I _OLED output from the driving transistor M5.

Hereinafter, the operation and function of the pixel circuit 40 will be described in more detail with reference to FIG. 5 relating to the driving timing of the pixel circuit 40. FIG.

5 is a diagram showing the driving timing of the pixel circuit 40 according to the embodiment of the present invention.

Referring to FIGS. 4 and 5, the pixel circuit 40 is driven over two stages, a programming period for charging the patters and an emitting period for driving the organic light emitting diodes.

The first scan signal SCAN 1 has a low level during a programming period and a high level during an emitting interval. The second scan signal SCAN 2 has a high level during a programming period and a low level during an emitting interval. That is, the first scan signal SCAN 1 and the second scan signal SCAN 2 are signals having a complementary level.

During the programming period, the first transistor M1 and the second transistor M2 are turned on by the first scan signal SCAN 1 having a low level. Thus, the reference voltage V _REF is applied to the first node A and the data voltage DATA is applied to the second node B. Here, the reference voltage V _REF is a direct current (DC) voltage having the same level as the power supply voltage VDD.

That is, during the programming period, voltages as shown in Equation 2 below are applied to both nodes A and B of the capacitor C1. The capacitor C1 charges the amount of charge corresponding to the voltage difference between the reference voltage V _REF applied to the first node A and the data voltage DATA applied to the second node B. [ In other words, the capacitor C1 stores the voltage corresponding to the voltage difference between the reference voltage V _REF and the data voltage DATA.

Meanwhile, during the programming period, the third transistor M3 is maintained in a turn-off state by the second scan signal SCAN 2 having a high level.

Next, during the emitting period, the third transistor M3 is turned on by the second scan signal SCAN 2 having a low level. Therefore, the power supply voltage VDD is applied to the first node A in place of the reference voltage V _REF applied during the programming period.

As a result, the data voltage DATA applied to the second node B is changed to another voltage due to a bootstrap action through the capacitor C1. That is, when the power supply voltage VDD is applied to the first node A, the voltage difference between the reference voltage V _REF and the data voltage DATA charged in the capacitor C1 during the previous programming period is maintained The second node B is supplied with the boosting voltage VDD + DATA-V _REF .

Equation (3) below represents the voltage applied to the first node (A) and the second node (B) during the emitting interval.

Accordingly, during the emitting interval, the boosting voltage (VDD + DATA-V _REF ) is applied to the gate electrode of the driving transistor M5. Thus, the driving transistor M5 supplies the power supply voltage VDD and the boosting voltage VDD + and it outputs a voltage difference (V _REF -DATA) the driving current (I _OLED) based on the between _REF).

The driving current I _OLED output from the driving transistor M5 can be calculated by the following equation (4).

Referring to Equation 4, the driving current I _OLED according to the present embodiment can be expressed by the following expression, instead of "power supply voltage VDD - data voltage DATA" in Equation 1 relating to a conventional pixel circuit, (V _REF ) - data voltage (DATA) ". That is, the driving current I _OLED according to this embodiment is calculated by using the reference voltage V _REF instead of the power supply voltage VDD, and unlike the conventional pixel circuit, there is no problem of IR-drop. Further, in the driving current (I _OLED) is a "nV _T" instead of the expression (1) relates to the conventional pixel circuit, a bar, the same data voltage (DATA) is calculated using the "2nV _T" according to this embodiment Unlike a conventional pixel circuit, fine current control is possible.

The driving transistor M5 according to the present embodiment has a structure in which the voltage difference V _REF - DATA between the reference voltage V _REF and the data voltage DATA equal to the level of the power source voltage VDD is used instead of the power source voltage VDD. The driving current I _OLED can be adjusted according to the level, so that the IR-drop of the power source voltage VDD can be compensated and the micro-current can be controlled.

The organic light emitting diode OLED emits light with a luminance corresponding to the level of the driving current I _OLED output from the driving transistor M5.

6 is a view showing a display panel device 60 according to an embodiment of the present invention.

6, the display panel device 60 includes a scan driver 610, a data driver 620, a reference driver 630, and a plurality of pixels 640 arranged in an N × M matrix (N , And M is a natural number). Here, each of the plurality of pixels 640 corresponds to one pixel circuit 30 shown in FIG. 3 or one pixel circuit 40 shown in FIG.

The scan driver 610 generates a first scan signal SCAN N1 and a second scan signal SCAN N2 corresponding to the respective rows of the pixel matrix and outputs the first scan signal SCAN N1 and the second scan signal SCAN N2 to the first scan line and the second scan line, (SCAN N1) and the second scan signal (SCAN N2) to the plurality of pixels 640, respectively. Each first scan line providing the first scan signal SCAN N1 and each second scan line providing the second scan signal SCAN N2 may be coupled to a plurality of pixels 640 located in the same row have. The first scan signal SCAN N1 and the second scan signal SCAN N2 may be sequentially driven on a row-by-row basis.

The data driver 620 generates the data voltage DATA M from the RGB data of the video signal and outputs the data voltage DATA M to the plurality of pixels 640 through the data line. The data driver 620 can generate a data voltage (DATA M) from RGB data using a gamma filter, a digital-analog conversion circuit, or the like. The data voltage DATA M may be output to the plurality of pixels 640 located in the same row for one scan period, respectively. In addition, each of the data lines providing the data voltage DATA M may be connected to a plurality of pixels 640 located in the same column.

The reference driver 630 generates a reference voltage V _REF M having the same level as the power supply voltage VDD and outputs the reference voltage V _REF M to the plurality of pixels 640 as a reference line. The reference voltage V _REF M may be output to the plurality of pixels 640 located in the same row for one scan period, respectively. In addition, each of the reference lines providing the reference voltage V _REF M may be connected to a plurality of pixels 640 located in the same column.

Each of the plurality of pixels 640 arranged in the NxM matrix corresponds to one pixel circuit 30 shown in Fig. 3 or one pixel circuit 40 shown in Fig. 4 described above, Detailed explanation will be omitted.

On the other hand, the power supply voltage VDD may be applied to each of the plurality of pixels 640, and may be grounded.

The display panel device 60 provides the first scan signal SCAN N1 and the second scan signal SCAN N2 generated by the scan driver 610 to the pixel circuit 40 in accordance with the driving timing shown in FIG. And provides the data voltage DATA M and the reference voltage V _REF M generated by the data driver 620 and the reference driver 630 to the pixel circuit 40. This is also true for the entire pixels 640 including the pixel circuit 40. [

That is, the display panel device 60 supplies the brightness of the organic light emitting diode included in the pixel circuit 40 of each of the pixels 640 to the first scan signal SCAN N1, the second scan signal SCAN N2, (DATA M) and the reference voltage (V _REF M).

7 is a diagram showing a simulation result of a current error between a pixel circuit according to an embodiment of the present invention and a conventional pixel circuit.

Referring to FIG. 7, when VDD and VSS are simultaneously changed by 0.15 V, the conventional pixel circuit has a current error of about 70%, whereas in the pixel circuit according to the present embodiment Has a current error of only 1.7%. Therefore, unlike the conventional pixel circuit, the pixel circuit according to this embodiment can control the brightness of the organic light emitting diode by using the more precise driving current I _OLED due to the IR-drop compensation function .

It should be understood by those skilled in the art that the simulation results shown in FIG. 7 are merely examples obtained from experimental results, and that the present embodiment is not limited thereto.

8 is a flowchart of a method of driving a pixel circuit using an organic light emitting diode according to an embodiment of the present invention. Referring to Fig. 8, the driving method of the pixel circuit according to the present embodiment is composed of the steps of time-series processing in the pixel circuit 30 shown in Fig. 3 and the pixel circuit 40 shown in Fig. Therefore, the contents described above with reference to Figs. 3 and 4 are also applied to the driving method of the pixel circuit according to the present embodiment, even if omitted below.

In step 801, the driving control unit 310 generates a reference voltage Vg1 to the first node A and the second node B of the capacitor C1 in response to a first scan signal SCAN1 corresponding to a programming period, (V _REF ) and a data voltage (DATA).

In step 802, the driving controller 310 applies the power voltage VDD to the first node A in response to a second scan signal SCAN 2 corresponding to an emission period.

In step 803, the drive controller 310 outputs a boosting voltage (VDD + DATA-V _REF ) through the second node B when the power supply voltage VDD is applied to the first node A do.

In step 804, the driver transistor 320 is boosted voltage (VDD + DATA-V _REF), in this case the input to the gate electrode drive current based on the voltage difference between the supply voltage (VDD) and the boosting voltage (VDD + DATA-V _REF) (I _OLED ).

In step 805, the organic light emitting diode 330 emits light at a luminance corresponding to the level of the output driving current I _OLED .

The present invention has been described with reference to the preferred embodiments. It will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the appended claims. Therefore, the disclosed embodiments should be considered in an illustrative rather than a restrictive sense. The scope of the present invention is defined by the appended claims rather than by the foregoing description, and all differences within the scope of equivalents thereof should be construed as being included in the present invention.

30: pixel circuit 40: pixel circuit
310: drive control unit 320: drive transistor
330: organic light emitting diode

Claims (20)

And applying a reference voltage and a data voltage to the first and second nodes of the capacitor in response to the first scan signal and, when a power supply voltage is applied to the first node in response to the second scan signal, a driving control unit for outputting a boosting voltage;
A driving transistor for outputting a driving current based on a voltage difference between the power supply voltage and the boosting voltage when the boosting voltage is input to the gate electrode; And
And an organic light emitting diode that emits light at a luminance corresponding to the level of the output driving current.
The method according to claim 1,
The level of the output drive current is
And is adjusted in accordance with a level of a voltage difference between the reference voltage and the data voltage.
The method according to claim 1,
The reference voltage and the power supply voltage
The pixel circuit being a voltage of the same level.
The method according to claim 1,
The boosting voltage
Wherein the second voltage is a voltage applied to the second node to maintain a voltage difference between the reference voltage and the data voltage charged in the capacitor when the power supply voltage is applied to the first node in response to the second scan signal, Pixel circuit.
The method according to claim 1,
The first scan signal and the second scan signal are
A pixel circuit, the signal having a complementary level.
The method according to claim 1,
The drive control unit
And a plurality of transistors for switching the application of each of the reference voltage, the data voltage, and the power supply voltage.
6. The method of claim 5,
The plurality of transistors
P-channel type transistors,
The first scan signal
A low level during a programming period for charging the capacitor and a high level during an emission period for driving the organic light emitting diode,
The second scan signal
Wherein the pixel circuit has a high level during the programming period and a low level during the emitting period.
The method according to claim 1,
The drive control unit
The capacitor connected between the first node and the second node to charge a charge corresponding to a voltage difference between the voltages applied to the nodes;
A first transistor coupled between the first node and a reference line providing the reference voltage;
A second transistor coupled between the second node and a data line providing the data voltage; And
And a third transistor coupled between the first node and the power supply voltage,
The first transistor and the second transistor
And a second scan line connected to the first scan line for providing the first scan signal,
The third transistor
And to a second scan line providing the second scan signal.
The method according to claim 1,
And a fourth transistor, which is located between the power supply voltage and the driving transistor and is diode-connected to the gate electrode and the drain electrode.
A capacitor coupled between the first node and the second node;
A first transistor coupled between the first node and a reference line for switching application of a reference voltage in response to a first scan signal;
A second transistor coupled between the second node and a data line for switching application of a data voltage in response to the first scan signal;
A third transistor coupled between the first node and a power supply voltage for switching application of the power supply voltage in response to a second scan signal;
A driving transistor for outputting a driving current according to a voltage applied to a gate electrode connected to the second node;
A fourth transistor connected between the power supply voltage and the driving transistor and diode-connected to the gate electrode and the drain electrode; And
And an organic light emitting diode which emits light with a luminance corresponding to the level of the output driving current,
The capacitor
Wherein when the reference voltage and the data voltage are applied to the first node and the second node in response to the first scan signal and the power supply voltage is applied to the first node in response to the second scan signal, Outputting a boosting voltage through a second node,
The driving transistor includes:
And outputs the driving current based on a voltage difference between a voltage applied to the drain electrode of the fourth transistor and the boosting voltage when the boosting voltage is input to the gate electrode.
11. The method of claim 10,
The level of the output drive current is
And is adjusted in accordance with a level of a voltage difference between the reference voltage and the data voltage.
11. The method of claim 10,
The reference voltage and the power supply voltage
The pixel circuit being a voltage of the same level.
11. The method of claim 10,
The first scan signal and the second scan signal are
A pixel circuit, the signal having a complementary level.
11. The method of claim 10,
The transistors
P-channel type transistors,
The first scan signal
A low level during a programming period for charging the capacitor and a high level during an emission period for driving the organic light emitting diode,
The second scan signal
Wherein the pixel circuit has a high level during the programming period and a low level during the emitting period.
A scan driver for providing a first scan signal and a second scan signal to the first scan line and the second scan line;
A data driver for providing a data voltage to a data line;
A reference driver for providing a reference voltage as a reference line; And
And a plurality of pixel circuits arranged at positions where the first scan line, the second scan line, the data line, and the reference line cross each other,
Each of the plurality of pixel circuits comprising:
And applying a reference voltage and a data voltage to the first and second nodes of the capacitor in response to the first scan signal and, when a power supply voltage is applied to the first node in response to the second scan signal, a driving control unit for outputting a boosting voltage;
A driving transistor for outputting a driving current based on a voltage difference between the power supply voltage and the boosting voltage when the boosting voltage is input to the gate electrode; And
And an organic light emitting diode that emits light at a luminance corresponding to the level of the output driving current.
16. The method of claim 15,
The level of the output drive current is
The reference voltage and the data voltage are adjusted in accordance with a level of a voltage difference between the reference voltage and the data voltage.
16. The method of claim 15,
The reference voltage and the power supply voltage
And a voltage of the same level.
16. The method of claim 15,
The drive control unit
A plurality of transistors of a P-channel type for switching application of each of the reference voltage, the data voltage, and the power supply voltage,
The first scan signal
A low level during a programming period for charging the capacitor and a high level during an emission period for driving the organic light emitting diode,
The second scan signal
And has a high level during the programming period and a low level during the emitting period.
16. The method of claim 15,
The drive control unit
A capacitor coupled between the first node and the second node;
A first transistor coupled between the first node and the reference line for switching application of the reference voltage in response to the first scan signal;
A second transistor coupled between the second node and the data line for switching application of the data voltage in response to the first scan signal; And
And a third transistor connected between the first node and the power source voltage, for switching the application of the power source voltage in response to the second scan signal.
A method of driving a pixel circuit using an organic light emitting diode,
Applying a reference voltage and a data voltage to the first and second nodes of the capacitor in response to a first scan signal corresponding to a programming period;
Applying a power supply voltage to the first node in response to a second scan signal corresponding to an emitting period;
Outputting a boosting voltage through the second node when a power supply voltage is applied to the first node;
Outputting a driving current based on a voltage difference between the power supply voltage and the boosting voltage when the boosting voltage is input to the gate electrode of the driving transistor; And
And causing the organic light emitting diode to emit light at a luminance corresponding to the level of the output driving current.

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