KR20200125920A - Pixel and organic light emitting display device using the same - Google Patents

Abstract

The present invention relates to a pixel and an organic light emitting display device using the same. According to an embodiment of the present invention, the pixel includes: a pixel driver including a driving transistor which is activated according to a scan signal transmitted from a corresponding scan line and generates a driving current corresponding to a data voltage according to a data signal transmitted from a corresponding data line; an organic light emitting diode through which a first current flows among the driving currents; and a bypass transistor through which a second current other than the first current flows among the driving currents, wherein a light emission period in which the first current flows through the organic light emitting diode includes an off period in which the bypass transistor is in an off state. According to the present invention, a contrast ratio of a display image is improved by controlling a current flowing through an organic light emitting device under a black luminance condition.

Description

Pixel and organic light emitting display device using the same {PIXEL AND ORGANIC LIGHT EMITTING DISPLAY DEVICE USING THE SAME}

The present invention relates to a pixel and an organic light-emitting display device using the same, and more particularly, to a pixel structure for improving a contrast ratio in a high-resolution organic light-emitting display device and an organic light-emitting display device including the same.

In recent years, various flat panel display devices capable of reducing the weight and volume, which are the disadvantages of a cathode ray tube, have been developed. Flat panel devices include Liquid Crystal Display (LCD), Field Emission Display (FED), Plasma Display Panel (PDP), and Organic Light Emitting Diode Display. There is this.

Among flat panel displays, an organic light emitting diode displays an image using an organic light emitting diode such as an organic light emitting diode (OLED) that generates light by recombination of electrons and holes, and has a fast response speed. At the same time, it is driven by low power consumption and is attracting attention because it has excellent luminous efficiency, luminance and viewing angle.

In general, driving methods of an organic light emitting diode display are divided into an active (passive matrix) type and a passive (active matrix) type.

In the passive type, an anode and a cathode are alternately arranged in a matrix manner in a screen display area, and a pixel is formed at a portion where the anode and cathode cross each other.

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

The active type has advantages of less parasitic capacitance and less power consumption than the passive type, but has a disadvantage of non-uniform luminance.

In particular, there is a problem in that the current density for the high-resolution structure increases, and the material efficiency increases due to the material development of the organic light emitting device, so that the black current for displaying a black image is relatively increased. That is, when a black current, which is the minimum current for displaying a black image, is transmitted, a pixel including an organic light emitting device with improved efficiency is displayed as an image brighter than the black luminance corresponding to the black current. Accordingly, there is a problem that the contrast ratio in the entire display image of the panel including the pixels is lowered. Therefore, research on a pixel structure or a display device is required to maintain a high contrast ratio on the display screen by controlling the flow of the minimum driving current delivered to the organic light emitting device.

In order to solve the above problems, an object of the present invention is to provide a pixel circuit for improving a contrast ratio of a display image and maintaining an improved contrast ratio by controlling a current flowing to an organic light emitting device under a black luminance condition, and a display device using the same. .

In particular, a pixel circuit structure for changing and controlling the flow of driving current and a structure of an organic light emitting display device using the same in order to lower the luminance of an organic light emitting device emitting light with a minimum black current is proposed.

In addition, the present invention is a pixel structure capable of prolonging the life of the organic light-emitting device by preventing deterioration of the organic light-emitting device, which may be caused by applying a higher driving current than necessary to the organic light-emitting device emitting black luminance, and using the same. An object is to provide an organic light emitting display device.

The technical problems to be achieved by the present invention are not limited to the technical problems mentioned above, and other technical problems that are not mentioned will be clearly understood by those of ordinary skill in the art from the description of the present invention. .

In order to achieve the above object, the pixel according to an embodiment of the present invention is activated according to a scan signal transmitted from a corresponding scan line, and is driven to generate a driving current corresponding to a data voltage according to a data signal transmitted from a corresponding data line. A pixel driver including a transistor, an organic light emitting diode through which a first current among the driving currents flows, and a bypass transistor through which a second current other than the first current flows among the driving currents.

In this case, the light emission period in which the first current flows through the organic light emitting diode includes an off period in which the bypass transistor is in an off state.

The off period may be the same as the light emission period.

Meanwhile, the off period may be a period excluding at least a period in which the scan signal is transmitted at a gate-on voltage level in the light emission period.

In an embodiment, the gate electrode of the bypass transistor may be connected to a DC voltage supply source having a voltage value of a gate-off level of the bypass transistor.

In another embodiment, the gate electrode and the source electrode of the bypass transistor may be commonly connected between the driving transistor and the organic light emitting diode.

In another embodiment, the gate electrode of the bypass transistor is connected to a gate line connected to the corresponding scan line, and a gate signal transmitted from the gate line may be transmitted as a gate-off level voltage of the bypass transistor. have.

In addition, as an embodiment, the gate electrode of the bypass transistor is connected to the corresponding scan line, and the off period excludes a period in which at least a scan signal transmitted from the corresponding scan line is transmitted at a gate-on voltage level in the emission period. It can be a period.

In another embodiment, the gate electrode of the bypass transistor is connected to a previous scan line of the corresponding scan line, and in the off period, a scan signal transmitted from at least the previous scan line is transferred to a gate-on voltage level in the emission period. May be a period excluding period.

In the present invention, the drain electrode of the bypass transistor may be connected to a variable voltage supply source that finds an optimum DC voltage according to panel characteristics and applies the DC voltage level to supply a variable voltage with a set voltage value.

Meanwhile, the pixel driver may further include at least one light emission control transistor configured to allow the first current to flow through the organic light emitting diode according to a light emission control signal transmitted from a light emission control line connected to the corresponding scan line. .

In this case, the emission period is a period in which the emission control transistor is maintained in an on state, and the emission period is separated from a first period in which a first scan signal transmitted from the corresponding scan line is activated.

In addition, a gate electrode of the bypass transistor may be connected to the corresponding scan line.

In addition, the pixel driver further includes an initialization transistor for initializing a gate electrode voltage of the driving transistor by transmitting a first voltage to a gate electrode of the driving transistor according to a second scan signal transmitted from a previous scan line of the corresponding scan line. I can.

In this case, the light emission period is a period prior to the first period and the first period and is a period separated from the second period in which the second scan signal is activated.

In addition, a gate electrode of a bypass transistor may be connected to the previous scan line.

In the present invention, the current amount of the second current is not limited, but a voltage of the common contact point of the driving transistor to which the source electrode of the bypass transistor is connected and the organic light emitting diode, and a variable voltage supply source to which the drain electrode of the bypass transistor is connected It can be adjusted in response to the voltage difference between the variable voltages of.

In order to achieve the above object, an organic light emitting display device according to an embodiment of the present invention includes a scan driver that transmits a plurality of scan signals to a plurality of scan lines, a data driver that transmits a plurality of data signals to a plurality of data lines, and the plurality of A display unit including a plurality of pixels respectively connected to a corresponding scan line among the scan lines of and to a corresponding data line among the plurality of data lines, and each of the plurality of pixels emit light according to a corresponding data signal to display an image, and the plurality of A power supply unit that supplies a first power voltage, a second power voltage, and a variable voltage to each pixel, and the scan driver, data driver, and power supply unit are controlled, and the plurality of data signals are generated and supplied to the data driver. It includes a control unit.

Each of the plurality of pixels is a driving transistor that is activated according to a scan signal transmitted from a corresponding scan line to generate a driving current corresponding to a data voltage according to a data signal transmitted from a corresponding data line, and a first of the driving currents An organic light emitting diode through which a current flows, and a bypass transistor through which a second current other than the first current flows among the driving currents. In this case, the light emission period in which the first current flows through the organic light emitting diode may include an off period in which the bypass transistor is in an off state.

The power supply unit may find an optimum DC voltage according to panel characteristics and supply a variable voltage obtained by applying the DC voltage level to the voltage level of the variable voltage.

In an embodiment, the gate electrode of the bypass transistor may be connected to a DC voltage supply source having a voltage value of a gate-off level of the bypass transistor.

In another embodiment, the gate electrode and the source electrode of the bypass transistor may be commonly connected between the driving transistor and the organic light emitting diode.

The organic light emitting display device of the present invention may further include a gate driver that transmits a plurality of gate signals to the plurality of gate lines. In addition, the controller generates and transmits a control signal for controlling the gate driver, a gate electrode of the bypass transistor is connected to a corresponding gate line among the plurality of gate lines, and a gate signal transmitted from the gate line is It is delivered as a gate-off level voltage of the bypass transistor.

In another embodiment, the gate electrode of the bypass transistor is connected to the corresponding scan line, and the off period is at least in the light emission period except for a period in which a scan signal transmitted from the corresponding scan line is transmitted at a gate-on voltage level. It can be a period.

In another embodiment, the gate electrode of the bypass transistor is connected to a previous scan line of the corresponding scan line, and the off period is a period in which at least a scan signal transmitted from the previous scan line is transferred to a gate-on voltage level in the emission period. May be a period excluding.

The organic light emitting display device of the present invention may further include an emission control driver that transmits a plurality of emission control signals to the plurality of emission control lines. In this case, the control unit generates and transmits a control signal for controlling the emission control driver, and each of the plurality of pixels includes the driving current according to a light emission control signal transmitted from a corresponding emission control line among the plurality of emission control lines. It may further include at least one light emission control transistor to flow through the organic light emitting diode.

The emission period is a period in which the emission control transistor is maintained in an on state, and the emission period is a period separated from a first period in which a first scan signal transmitted from the corresponding scan line is activated.

In addition, each of the plurality of pixels further includes an initialization transistor for initializing the gate electrode voltage of the driving transistor by transmitting a first voltage to the gate electrode of the driving transistor according to a second scan signal transmitted from a previous scan line of the corresponding scan line. Can include. In this case, the light emission period is a period prior to the first period and the first period and is a period separated from the second period in which the second scan signal is activated.

According to the present invention, a pixel structure that controls the flow of current transmitted to an organic light emitting device under conditions expressed by black luminance when displaying an image on an organic light emitting display device is provided, and by improving and maintaining the contrast ratio of the display image An organic light emitting display device can be provided.

In addition, deterioration of the organic light-emitting device can be prevented by controlling that a driving current that is higher than necessary is not applied to the organic light-emitting device to which the driving current corresponding to the black luminance is transmitted, thereby extending the life of the organic light-emitting device. A pixel and an organic light emitting display device using the same may be provided.

1 is a schematic diagram illustrating a pixel of an organic light emitting diode display according to an exemplary embodiment of the present invention.
2 is a block diagram of an organic light emitting diode display according to an embodiment of the present invention.
3 is a circuit diagram of the pixel shown in FIG. 2 according to the first embodiment.
4 is a circuit diagram of the pixel shown in FIG. 2 according to a second embodiment.
5 is a circuit diagram of the pixel shown in FIG. 2 according to a third exemplary embodiment.
6 is a block diagram of an organic light emitting diode display according to another exemplary embodiment of the present invention.
7 is a circuit diagram of the pixel shown in FIG. 6 according to the first embodiment.
8 is a block diagram of an organic light emitting diode display according to another exemplary embodiment of the present invention.
9 is a circuit diagram of the pixel shown in FIG. 8 according to the first embodiment.
10 is a circuit diagram of the pixel shown in FIG. 8 according to a second embodiment;
11 is a circuit diagram of the pixel shown in FIG. 8 according to a third exemplary embodiment.
11 is a circuit diagram of the pixel shown in FIG. 8 according to the fourth exemplary embodiment.
12 is a signal timing diagram for driving the pixels of FIGS. 9 to 11.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings so that those of ordinary skill in the art may easily implement the present invention. The present invention may be implemented in various different forms, and is not limited to the embodiments described herein.

In addition, in various embodiments, components having the same configuration are typically described in the first embodiment by using the same reference numerals, and in other embodiments, only configurations different from the first embodiment will be described.

In order to clearly describe the present invention, parts irrelevant to the description have been omitted, and the same reference numerals are assigned to the same or similar components throughout the specification.

Throughout the specification, when a part is said to be "connected" to another part, this includes not only "directly connected" but also "electrically connected" with another element interposed therebetween. . In addition, when a part "includes" a certain component, it means that other components may be further included rather than excluding other components unless specifically stated to the contrary.

1 is a schematic diagram illustrating a pixel 1 of an organic light emitting diode display according to an exemplary embodiment.

Referring to FIG. 1, a pixel 1 according to an embodiment of the present invention is located in an area where a corresponding scan line 4 and a corresponding data line 5 intersect.

In addition, the pixel 1 includes a pixel driver 2 connected to a supply line 6 of a first power voltage ELVDD, and a supply line 8 of a second power voltage ELVSS having a voltage lower than that of the first power voltage ELVDD. An organic light emitting diode (OLED) having a cathode electrode connected thereto, and a bypass unit 3 connected between the anode electrode of the organic light emitting diode OLED and the pixel driver 2. Specifically, the bypass unit 3 has one end connected to a junction node of the anode electrode of the organic light emitting diode OLED and the pixel driver 2, and the other end connected to the supply line 7 of the variable voltage Vvar.

The pixel driver 2 may be composed of a plurality of transistors and capacitors.

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* When the pixel driver 2 is activated in response to the scan signal scan supplied from the corresponding scan line 4, it receives the data signal DATA from the corresponding data line 5. The data signal DATA applied to the pixel driver 2 may be stored in the form of a voltage in a capacitor provided in the pixel driver 2. The data voltage according to the stored data signal DATA is generated as a corresponding predetermined driving current Idr and transmitted to the organic light emitting diode OLED, in response to the light emitting current Ioled transmitted to the organic light emitting diode OLED. It emits light to display an image.

At this time, the pixel driver 2 is connected to a supply line 6 that supplies a predetermined first power voltage ELVDD, and the pixel driver 2 is connected to the supply line 6 of the first power voltage ELVDD. Receive power required for generation.

The basic structure of the pixel driver 2 may be composed of two transistors and one capacitor (2TR1CAP structure), and circuit structures of various pixel driver 2 will be described in the following drawings.

When the material properties of the organic light-emitting diode (OLED) are developed and the material efficiency is improved, the pixel 1 according to an embodiment of the present invention is an organic light-emitting diode (OLED), since it can be displayed with a higher luminance than the black luminance even under a black luminance condition. It includes a bypass part 3 for bypassing some of the black current flowing to OLED). Here, the black current is applied to the transistor of the pixel 1 and is defined as a driving current required to emit light with the minimum luminance (black luminance) of the organic light emitting diode of the pixel.

In addition, bypassing some current of the black current may prevent unnecessarily high current from being transmitted to the organic light emitting diode OLED, thereby preventing deterioration of material properties of the organic light emitting diode OLED.

Specifically, as can be seen with reference to FIG. 1, in the pixel 1 according to an embodiment of the present invention, the driving current Idr generated by the pixel driver 2 is all converted to the emission current Ioled of the organic light emitting diode OLED. It is a structure including a bypass part 3 that diverges by bypassing a predetermined bypass current Ibcb without passing through ).

The bypass unit 3 is connected to a power supply line 7 that supplies a variable voltage Vvar, which is controlled to change the voltage level according to some sections of one frame in order to bypass the bypass current Ibcb.

According to an embodiment of the present invention, there is a problem that the actual display luminance of the black current increases as the material efficiency increases due to the material development of the organic light emitting diode (OLED), or the current density for the high-resolution structure increases. I can. Thus, there arises a problem that the contrast ratio is reduced, and it is impossible to lower the black current further below the threshold of the transistor off level to prevent this. Thus, as in the pixel structure of Fig. 1, a bypass part 3 is configured to allow a partial current to flow by bypassing the black current.

Therefore, some current passing through and bypassing the bypass unit 3, i.e., the bypass current Ibcb, has a current value at the level of the transistor off level, and thus has a large effect on the implementation of an image signal displaying black luminance. It has little effect on the implementation of an image signal displaying external high luminance (especially a white luminance image signal). Thus, the supply source of the variable voltage Vvar connected to the bypass unit 3 is a variable voltage whose voltage level is adjusted so that the bypass current Ibcb bypasses and flows during one frame period of the display image, especially during the period of the black luminance condition. (Vvar) can be supplied.

Specific configurations and structures of circuit elements of the pixel driver 2 and the bypass unit 3 will be described in various embodiments below corresponding to the structure of the organic light emitting display device according to an exemplary embodiment of the present invention.

2 is a block diagram of an organic light emitting diode display according to an exemplary embodiment.

Referring to FIG. 2, in an organic light emitting diode display according to an exemplary embodiment of the present invention, a display unit 10 including a plurality of pixels PX1 to PXn, a scan driver 20, a data driver 30, and a power supply unit ( 40), and a control unit 50.

Each of the plurality of pixels PX1 to PXn is connected to a corresponding one of the plurality of scan lines S1 to Sn connected to the display unit 10 and a corresponding one of the plurality of data lines D1 to Dm. Each is connected. In addition, although not directly shown on the display unit 10 of FIG. 2, each of the plurality of pixels PX1 to PXn is connected to a power supply line connected to the display unit 10 to provide a first power voltage ELVDD and a second power voltage ELVSS. ), a variable voltage (Vvar) is supplied.

The first power voltage ELVDD and the second power voltage ELVSS have a fixed voltage value during a plurality of frames in which an image is displayed, while the variable voltage Vvar is determined according to a predetermined period of one frame as described above. It may have a variable voltage value with a different voltage level.

For example, the first power voltage ELVDD may be a predetermined high level voltage, the second power voltage ELVSS may be a voltage lower than the first power voltage ELVDD or a ground voltage, and the variable voltage Vvar ) May be set to a voltage value equal to or lower than the second power voltage ELVSS according to a predetermined period.

The display unit 10 includes a plurality of pixels PX1 to PXn arranged in a substantially matrix form. Although not particularly limited, a plurality of scan lines S1 to Sn extend substantially in a row direction in the arrangement of the pixels and are substantially parallel to each other, and a plurality of data lines D1 to Dm extend substantially in a column direction. Almost parallel to each other

Each of the plurality of pixels PX1 to PXn emits light of a predetermined luminance by a driving current supplied to the organic light emitting diode according to a corresponding data signal transmitted through the plurality of data lines D1 to Dm.

The scan driver 20 generates and transmits a scan signal corresponding to each pixel through a plurality of scan lines S1 to Sn. That is, the scan driver 20 transmits a scan signal to each of a plurality of pixels included in each pixel line through a corresponding scan line.

The scan driver 20 receives the scan driving control signal SCS from the controller 50 to generate the plurality of scan signals, and sequentially supplies the scan signals to the plurality of scan lines S1 to Sn connected to each pixel line. do. Then, the pixel driver of each of the plurality of pixels included in each pixel line is activated.

The data driver 30 transmits a data signal to each pixel through a plurality of data lines D1 to Dm.

The data driver 30 receives a data driving control signal DCS from the controller 50 and supplies data signals corresponding to a plurality of data lines D1 to Dm connected to each of a plurality of pixels included in each pixel line. .

The controller 50 converts a plurality of image signals transmitted from the outside into a plurality of image data signals DATA, and transmits the converted image signals to the data driver 30. The controller 50 receives a vertical synchronization signal (Vsync), a horizontal synchronization signal (Hsync), and a clock signal (MCLK) (not shown) to control the driving of the scan driver 20 and the data driver 30 It generates a control signal for and delivers it to each. That is, the control unit 50 generates and transmits the scan driving control signal SCS for controlling the scan driving unit 20 and the data driving control signal DCS for controlling the data driving unit 30, respectively. In addition, the control unit 50 generates a power control signal PCS for controlling the driving of the power supply unit 40 and transmits it to the power supply unit 40.

The power supply unit 40 supplies a first power voltage ELVDD, a second power voltage ELVSS, and a variable voltage Vvar to each pixel of the display unit 10. The voltage values of the first power voltage ELVDD, the second power voltage ELVSS, and the variable voltage Vvar are not particularly limited, but the voltage values of the power control signal PCS transmitted from the controller 50 are controlled. Voltage values can be set or controlled.

In particular, according to an embodiment of the present invention, the power supply unit 40 transfers some of the black current in a predetermined pixel to a path other than the organic light emitting diode (OLED) side according to the control of the power control signal PCS. It is possible to supply by adjusting the voltage level of the variable voltage Vvar to flow in a bypass. At this time, the power supply unit 40 finds an optimal DC voltage according to the panel characteristics, and applies the DC voltage level to the variable voltage Vvar supplied to each panel.

3 to 5 are circuit diagrams of a pixel according to an exemplary embodiment of the present invention. In particular, FIGS. 3 to 5 show a pixel PXn 100 provided in a region defined by an n-th pixel row and an m-th pixel column among a plurality of pixels PX1 to PXn of the display unit 10 illustrated in FIG. 2. A circuit structure according to different embodiments of the present invention is shown.

First, the pixel 100-1 of FIG. 3 is a pixel driver 102-1 composed of two transistors M1 and M2 and one capacitor Cst, and a bypass part 103 composed of one transistor M3. It consists of -1). Since the pixel 100-1 of FIG. 3 is provided in an area defined by an n-th pixel row and an m-th pixel column among a plurality of pixels of the display, the n-th scan line Sn and the m-th data line Dm, and the It is connected to a power supply line that supplies the first power voltage ELVDD, the second power voltage ELVSS, and the variable voltage Vvar.

In a circuit diagram of a pixel to be described in the following drawings including FIG. 3, for convenience, a transistor, which is a circuit element, is illustrated as a PMOS transistor, and an operation accordingly will be described. However, it goes without saying that it is not necessarily limited to the structure and configuration of such a pixel.

Specifically, the pixel driver 102-1 includes a driving transistor M1, a switching transistor M2, and a storage capacitor Cst.

The driving transistor M1 includes a gate electrode connected to the first node N1, a source electrode connected to a supply line of the first power voltage ELVDD, and a drain electrode connected to the second node N2.

The switching transistor M2 includes a gate electrode connected to the n-th scan line Sn, a source electrode connected to the m-th data line Dm, and a drain electrode connected to the first node N1.

The storage capacitor Cst includes one electrode connected to the first node N1 and a second electrode connected to a contact node connected to a supply line of the first power voltage ELVDD and a source electrode of the driving transistor M1.

The switching transistor M2 is turned on or off in response to the scan signal S[n] through the corresponding n-th scan line Sn. When the switching transistor M2 receives the scan signal scan[n] of the gate-on voltage level, the data signal D corresponding to the first node N1 is transmitted through the m-th data line Dm connected to the source electrode. It transfers the data voltage according to [m]).

The storage capacitor Cst to which one electrode is connected to the first node N1 stores a voltage according to a voltage difference between both electrodes of the storage capacitor for a predetermined period. Accordingly, a voltage corresponding to a voltage difference between the data voltage transmitted to the first node N1 and the first power voltage ELVDD is stored.

Referring to FIG. 3, since both electrodes of the storage capacitor Cst are connected to the gate electrode and the source electrode of the driving transistor M1, respectively, a voltage corresponding to the voltage difference between both ends of the storage capacitor stored in the storage capacitor Cst Corresponds to the gate-source voltage Vgs of the driving transistor M1.

When a data voltage according to a data signal is applied to the driving transistor M1 through the switching transistor M2 activated by the scan signal S[n], the gate-source voltage Vgs stored in response to the data voltage A driving current Idr according to) is generated and transferred to the organic light emitting diode OLED.

At this time, under the black luminance condition where the applied data signal is a black image signal, when the black current is transmitted as the driving current Idr, the organic light emitting diode (OLED) emits light with a luminance higher than the expected luminance of the black luminance, thereby reducing the contrast ratio within the screen It can drop and cause picture quality deterioration. Therefore, in order to improve this, it is necessary to reliably lower the light emission current Ioled applied to the organic light emitting diode OLED under the black luminance condition. However, since it is impossible to lower the black current below the limit of the off-level voltage of the transistor, the pixel according to an embodiment of the present invention further includes a bypass unit 103-1 as shown in FIG. 3 to provide a partial current of the black current. Bypass That is, the bypass part 103-1 of FIG. 3 transfers a part of the black current to the organic light emitting diode OLED so that the driving current Idr, which is a black current corresponding to the black image data signal, is not transmitted to the organic light emitting diode OLED. Ibcb). Then, the light emission current Ioled applied to the organic light emitting diode OLED becomes a lower current value than the black current applied as the driving current, so that light can be reliably emitted with black luminance. Thereby, the contrast ratio can be improved.

Referring to FIG. 3, the bypass unit 103-1 includes a gate electrode and a source electrode connected together with a second node N2 to which the drain electrode of the driving transistor M1 and the anode electrode of the organic light emitting diode OLED are connected. , And a bypass transistor M3 including a drain electrode connected to a power supply line of a variable voltage Vvar.

At this time, the variable voltage Vvar is connected to the drain electrode of the bypass transistor M3 to adjust the voltage difference Vds between the source electrode voltage and the drain electrode voltage of the bypass transistor M3. Thus, the bypass current Ibcb can be controlled.

Since the gate electrode and the source electrode of the bypass transistor M3 are commonly connected to one second node N2, the voltage difference between the gate and source is 0V, and the bypass transistor M3 is always in an off state. do. In addition, since the variable voltage Vvar supply line is connected to the drain electrode of the bypass transistor M3, a predetermined bypass from the black current through the bypass transistor M3 by the set voltage value of the variable voltage Vvar in the off state. The pass current Ibcb flows. At this time, the set voltage value of the variable voltage Vvar is not particularly limited, and for example, may be equal to or less than the second power voltage ELVSS, which is the voltage value of the cathode electrode of the organic light emitting diode OLED. When the bypass transistor M3 is always off, the set voltage value of the variable voltage Vvar becomes a variable that adjusts the amount of current of the bypass current Ibcb.

The bypass part 103-1 of the pixel according to the exemplary embodiment of FIG. 3 can always be kept in an off state due to the structure of the bypass transistor M3, so it includes not only the black current but also the maximum driving current representing white luminance. Even when an image driving current according to an image data signal having a general luminance is transmitted to the organic light emitting diode, the bypass current can be bypassed. In the pixel structure of FIG. 3, the path bypass effect of the bypass current when the black current is transmitted is large, but there is little effect of the path bypass of the bypass current when the driving current for implementing other luminance images is transmitted. I can. This is because the corresponding bypass current magnitude is very small. Accordingly, the pixel according to the exemplary embodiment of FIG. 3 and the display device including the same can accurately express a target luminance value when an image is expressed in a low luminance step without affecting the image display quality in the general luminance step. It can be improved.

4 is a circuit diagram illustrating a circuit structure of the pixel (PXn) 100 illustrated in FIG. 2 according to an exemplary embodiment different from that of FIG. 3.

Since the pixel driver 102-2 included in the pixel 100-2 according to the embodiment of FIG. 4 is the same as that of FIG. 3, a description of the structure and operation thereof will be omitted, and the structure of the bypass unit 103-2 will be focused. It will be described as.

The bypass portion 103-2 of the pixel 100-2 of FIG. 4 is constituted by a bypass transistor M30. The bypass transistor M30 is a node connected to the gate electrode connected to the n-th scan line Sn to which the gate electrode of the switching transistor M20 is connected, the drain electrode of the driving transistor M10 and the anode electrode of the organic light emitting diode (OLED). And a source electrode connected to N20 and a drain electrode connected to a power supply line of a variable voltage Vvar.

Unlike FIG. 3, the bypass transistor M30 of FIG. 4 is not always turned off, but is turned on or off in response to a scan signal S[n] transmitted to the gate electrode through the n-th scan line Sn. Can be. Accordingly, the bypass transistor M30 is also turned on during the scan period in which the scan signal S[n] is transmitted at the gate-on voltage level to activate the pixel driver 102-2 in the image driving frame. Then, the bypass current Ibcb may bypass and flow toward the bypass transistor M30 according to the voltage level of the variable voltage Vvar. In this case, the current amount of the bypass current Ibcb may increase, and the amount of the actual light emission current Ioled of the organic light emitting diode OLED that emits light with a corresponding luminance image according to the image data signal may be significantly reduced. Since this has a great adverse effect on the realization of image quality, in the case of the embodiment having the pixel structure of FIG. 4, the variable voltage Vvar is the second voltage, which is the cathode electrode voltage of the organic light emitting diode OLED, so that the bypass current Ibcb does not flow. It may be set higher than the power voltage ELVSS.

Meanwhile, in the embodiment of FIG. 4, while the scan signal S[n] is transferred to a high level voltage, which is the gate-off voltage level of the transistor, and the bypass transistor M30 is turned off, the bypass transistor M30 is The bypass current Ibcb may be bypassed and flow according to the set voltage value of the variable voltage Vvar connected to the drain electrode. In other words, to prevent light emission by passing a minute leakage current even during a period in which the emission current Ioed is not transmitted to the organic light emitting diode (OLED) because the driving transistor M10 does not operate, and to prevent deterioration of the organic light emitting diode. The bypass current Ibcb, which is a minute current, may be bypassed through the bypass transistor M30 in the turn-off state. In this case, the set voltage of the variable voltage Vvar may be a predetermined low voltage and is not particularly limited, but may be, for example, a voltage equal to or lower than the second power voltage ELVSS.

5 is a circuit diagram illustrating a circuit structure of the pixel (PXn) 100 shown in FIG. 2 according to an exemplary embodiment different from that of FIGS. 3 and 4.

Since the pixel driver 102-3 included in the pixel 100-3 according to the exemplary embodiment of FIG. 5 is the same as in FIGS. 3 and 4, a description of its structure and operation is omitted, and the bypass unit 103-3 is Let's focus on the structure.

The bypass unit 103-3 of FIG. 5 includes a bypass transistor M300, wherein the bypass transistor M300 includes a source electrode connected to the second node ND200, a drain electrode connected to a variable voltage supply source, and And a gate electrode connected to a DC voltage source.

The DC voltage supply source supplies a DC voltage of a predetermined level to the gate electrode of the bypass transistor M300 so that the bypass transistor M300 is always turned off. Since the bypass transistor M300 of FIG. 5 is a PMOS transistor, the DC voltage may be a predetermined high-level voltage capable of always turning off the bypass transistor M300. For example, the voltage applied to the gate electrode of the bypass transistor M300 may be a DC voltage having the same level as or higher than the first power voltage ELVDD.

6 is a block diagram of an organic light emitting diode display according to another exemplary embodiment of the present invention.

Since the organic light emitting display device according to the exemplary embodiment of FIG. 6 is not different from that of FIG. 2, an additional component will be described.

Unlike the OLED display of FIG. 2, the OLED display of FIG. 6 includes a display unit 10 including a plurality of pixels PX1 to PXn, a scan driver 20, a data driver 30, and a power supply unit 40. , And a gate driver 60 in addition to the control unit 50.

At this time, the display unit 10 including the plurality of pixels PX1 to PXn arranged in a substantially matrix form is connected to the gate driving unit 60 to substantially face the pixels in a row direction, so that the plurality of pixels extend substantially parallel to each other. The gate lines G1 to Gn are connected.

The gate driver 60 generates and transmits a gate signal corresponding to each pixel through a plurality of gate lines G1 to Gn. The gate driver 60 transmits a gate signal to each of a plurality of pixels included in each pixel line through a corresponding gate line. At this time, since the plurality of gate signals transmitted to each pixel through the plurality of gate lines G1 to Gn are applied to keep the bypass transistor included in each pixel in the turned-off state, the gate turns off the transistor during one frame. It can be delivered simultaneously to the off voltage level.

Then, due to the control of the plurality of gate signals, the operation state of the bypass transistor of each pixel is reliably maintained in an off state, and the bypass current can be bypassed through the bypass transistor. In this case, the variable voltage Vvar supply source connected to the drain electrodes of the bypass transistors may be adjusted to bypass the bypass current by setting the variable voltage Vvar to a low voltage.

In the embodiment of FIG. 6, the variable voltage Vvar supply source will be the power supply unit 40, and the power supply unit 40 provides a first power supply voltage ELVDD, a second power supply voltage ELVSS, and a variable voltage Vvar. It is supplied to each pixel of the display unit 10. In particular, the power supply unit 40 may set the voltage value of the variable voltage Vvar to be a low voltage according to the control of the power control signal PCS transmitted from the controller 50. For example, the voltage value of the variable voltage Vvar may be equal to or lower than the second power voltage ELVSS.

In addition, the gate driver 60 receives the gate driving control signal GCS from the controller 50 to generate the plurality of gate signals, and supplies the gate signals to the plurality of gate lines G1 to Gn connected to each pixel line. do. Thus, the bypass transistor of each of the plurality of pixels included in each pixel line is controlled to maintain the turned off state.

7 is a circuit diagram of the pixel 200 shown in FIG. 6 according to the first embodiment.

The pixel 200 illustrated in FIG. 7 also has a structure including three transistors and one capacitor, like the pixel according to the embodiments of FIGS. 3 to 5.

The pixel driver 202 including the driving transistor A1, the switching transistor A2, and the storage capacitor Cst is the same as in FIGS. 3 to 5, so the structure and operation description thereof will be omitted, and the bypass unit 203 Let's focus on the structure of

The bypass portion 203 of the pixel 200 of FIG. 7 is formed of a bypass transistor A3. The bypass transistor A3 includes a gate electrode connected to the n-th gate line Gn, a source electrode connected to a node Q2 to which the drain electrode of the driving transistor A1 and the anode electrode of the organic light emitting diode OLED are connected, and And a drain electrode connected to a power supply line of a variable voltage Vvar.

As described in FIG. 4, the gate signal G[n] applied to the gate electrode of the bypass transistor A3 through the n-th gate line Gn is high, which is the off voltage level of the transistor during one frame period. It can be delivered as a level voltage. Thus, the bypass transistor A3 can be turned off during one frame period. Then, the variable voltage Vvar applied to the drain electrode of the bypass transistor A3 may be set to a voltage lower than the second power voltage ELVSS to which the cathode electrode of the organic light emitting diode OLED is connected, and thus bypass The bypass current Ibcb from the node Q2 through the transistor A3 may bypass and flow toward the variable voltage supply source.

8 is a block diagram of an organic light emitting diode display according to another exemplary embodiment of the present invention.

The organic light-emitting display device of FIG. 8 is not significantly different from the organic light-emitting display device of FIG. 2, and thus additional components will be described.

In particular, unlike the organic light emitting display device of FIG. 2, the organic light emitting display according to the exemplary embodiment of FIG. 8 includes a display unit 10 including a plurality of pixels PX1 to PXn, a scan driver 20, a data driver 30, In addition to the power supply unit 40 and the control unit 50, a light emission control driving unit 70 is further included.

The emission control driver 70 is connected to a plurality of emission control lines EM1 to EMn connected to the display unit 10 including a plurality of pixels PX1 to PXn arranged in a matrix form. That is, a plurality of light emission control lines EM1 to EMn extending substantially parallel to each other while facing each of the plurality of pixels in a substantially row direction connects each of the plurality of pixels to the emission control driver 70.

The emission control driver 70 generates and transmits the emission control signal corresponding to each pixel through the plurality of emission control lines EM1 to EMn. Each pixel receiving the emission control signal is controlled to emit an image according to the image data signal in response to the control of the emission control signal. That is, the operation of the emission control transistor included in each pixel is controlled in response to the emission control signal transmitted through the corresponding emission control line, and accordingly, the organic light emitting diode connected to the emission control transistor is applied to the driving current corresponding to the data signal. It may or may not emit light with a corresponding luminance.

The control unit 50 of FIG. 8 transmits a light emission driving control signal ECS for controlling the operation of the emission control driving unit to the emission control driving unit 70. The emission control driver 70 receives the emission driving control signal ECS from the controller 50 and generates the plurality of emission control signals.

Meanwhile, referring to FIG. 8, each of the plurality of pixels PX1 to PXn of the display unit 10 is connected to two corresponding scan lines. That is, a scan line corresponding to a pixel row including a corresponding pixel is connected before a scan corresponding to a previous pixel row of the pixel row. Each of the plurality of pixels included in the first pixel row may be connected to the first scan line S1 and the dummy scan line S0. In addition, each of the plurality of pixels included in the n-th pixel row has an n-th scan line Sn corresponding to the n-th pixel row, which is the corresponding pixel row, and the n-1th scan line Sn corresponding to the n-1th pixel row, which is the previous pixel row. Connected to -1).

The organic light-emitting display device of the present invention according to the exemplary embodiment of FIG. 8 receives a scanning signal corresponding to a corresponding pixel row and a scanning signal corresponding to a previous pixel row through two scanning lines connected to each pixel, and emits organic light in each pixel. Adjusts to bypass some current of the luminous current delivered to the diode.

9 to 12 are examples of circuit diagrams of a plurality of pixels PX1 to PXn included in the organic light emitting display device of FIG. 8, and illustrate a structure of a pixel that may be included in the organic light emitting display device of FIG. 8. In addition, FIG. 13 is a signal timing diagram for driving the pixels of FIGS. 9 to 12, and by looking at them together, an operation process of the pixel circuit diagram according to the exemplary embodiment of FIGS. 9 to 12 may be described.

9 to 12 illustrate a pixel PXn 300 provided in a region defined by an n-th pixel row and an m-th pixel column among a plurality of pixels PX1 to PXn of the display unit 10 illustrated in FIG. 8. A circuit structure according to different embodiments is shown. In addition, the pixels of FIGS. 9 to 12 are each composed of a pixel driver composed of six transistors and two transistors, and a bypass part composed of one transistor. In these embodiments, each transistor is assumed to be a PMOS transistor for convenience of description.

First, the pixel 300-1 illustrated in FIG. 9 includes a pixel driver 302-1, an organic light emitting diode (OLED), and a bypass part 303-1 connected therebetween.

The pixel driver 302-1 includes a driving transistor T1, a switching transistor T2, a threshold voltage compensation transistor T3, light emission control transistors T4 and T5, an initialization transistor T6, and a storage capacitor Cst. And a first capacitor C1. Further, the bypass unit 303-1 is constituted by a bypass transistor T7.

The driving transistor T1 is connected to the gate electrode connected to the first node ND1, the source electrode connected to the third node ND3 to which the drain electrode of the first emission control transistor T4 is connected, and the second node ND2. It includes a connected drain electrode. The driving transistor T1 is based on the corresponding data signal D[m] applied to the third node ND3 to which the source electrode of the driving transistor is connected through the m-th data line Dm and the switching transistor T2. The driving current Idr of the data voltage is generated and transmitted to the organic light emitting diode OLED through the drain electrode. The driving current Idr is a current corresponding to a voltage difference between the source electrode and the gate electrode of the driving transistor T1, and the driving current Idr varies in response to a data voltage according to a data signal applied to the source electrode. .

The switching transistor T2 includes a gate electrode connected to the n-th scan line Sn, a source electrode connected to the m-th data line Dm, and a source electrode of the driving transistor T1 and a drain electrode of the first emission control transistor T4. And a drain electrode connected to the third node ND3 connected in common. The switching transistor T2 activates driving of the pixel in response to a corresponding scan signal S[n] transmitted through the n-th scan line Sn. That is, the switching transistor T2 applies the data voltage according to the data signal D[m] transmitted through the m-th data line Dm to the third node ND3 in response to the scan signal S[n]. Deliver.

The threshold voltage transistor T3 includes a gate electrode connected to the n-th scan line Sn, and both end electrodes connected to the gate electrode and the drain electrode of the driving transistor T1, respectively. The threshold voltage transistor T3 operates in response to a corresponding scan signal S[n] transmitted through the n-th scan line Sn. By connecting the gate electrode and the drain electrode of the driving transistor T1, the driving transistor ( By diode-connecting T1), the threshold voltage of the driving transistor is compensated.

That is, when the driving transistor T1 is diode-connected, the voltage Vdata-Vth lowered by the threshold voltage of the driving transistor T1 from the data voltage applied to the source electrode of the driving transistor T1 is applied to the driving transistor T1. Applied to the gate electrode. Since the gate electrode of the driving transistor T1 is connected to one electrode of the storage capacitor Cst, the voltage Vdata-Vth is maintained by the storage capacitor Cst. Since the voltage Vdata-Vth reflecting the threshold voltage Vth of the driving transistor T1 is applied to the gate electrode and maintained, the driving current Idr flowing through the driving transistor T1 is applied to the threshold voltage of the driving transistor T1. Is not affected by it.

The first emission control transistor T4 includes a gate electrode connected to the n-th emission control line EMn, a source electrode connected to the supply line of the first power voltage ELVDD, and a drain electrode connected to the third node ND3. .

The second emission control transistor T5 includes a gate electrode connected to the n-th emission control line EMn, a source electrode connected to the second node ND2, and a fourth node ND4 connected to the anode electrode of the organic light emitting diode OLED. It includes a drain electrode connected to ).

The first emission control transistor T4 and the second emission control transistor T5 operate in response to an n-th emission control signal EM[n] transmitted through an n-th emission control line EMn. That is, when the first emission control transistor T4 and the second emission control transistor T5 are turned on in response to the n-th emission control signal EM[n], the organic light emitting diode from the first power supply voltage ELVDD A current path is formed so that the driving current Idr can flow in the direction of (OLED), so the organic light emitting diode emits light according to the emission current Ioled corresponding to the driving current Idr to display the image of the data signal. Make it possible.

The initialization transistor T6 includes a gate electrode connected to the n-1th scan line Sn-1, a source electrode connected to the variable voltage Vvar supply line, and the gate electrode of the driving transistor T1 and the threshold voltage compensation transistor T3. And a drain electrode connected to the first node ND1 to which one electrode is commonly connected. The initialization transistor T6 is a variable voltage applied through the variable voltage Vvar supply line in response to the n-1th scan signal S[n-1] transmitted through the n-1th scan line Sn-1. Vvar) is transferred to the first node ND1. The initialization transistor T6 is an n-1th scan signal S[n-1] that is previously transmitted to an n-1th scan line corresponding to a previous pixel row of the nth pixel row including the corresponding pixel 300-1. In response to, before the pixel driver 302-1 is activated, the variable voltage Vvar may be used as an initialization voltage and may be transmitted to the first node ND1. At this time, the voltage value of the variable voltage Vvar is not limited, but may be set to have a low level voltage value so that the gate electrode voltage of the driving transistor T1 is sufficiently lowered to be initialized. That is, during a period in which the n-1th scan signal S[n-1] is transmitted to the gate electrode of the initialization transistor T6 at the gate-on voltage level, the gate electrode of the driving transistor T1 is initialized to the initialization voltage.

The storage capacitor Cst includes one electrode connected to the first node ND1 and the other electrode connected to a supply line of the first power voltage ELVDD. Since the storage capacitor Cst is connected between the gate electrode of the driving transistor T1 and the supply line of the first power voltage ELVDD as described above, the voltage applied to the gate electrode of the driving transistor T1 can be maintained. .

The first capacitor C1 includes one electrode connected to the first node ND1 and the other electrode connected to the gate electrode of the switching transistor T2. The first capacitor C1 stores and maintains a voltage corresponding to a difference between a variable voltage Vvar applied as an initialization voltage to one electrode and a gate electrode voltage of the switching transistor T2 to which the other electrode is connected.

In addition, the bypass transistor T7 includes a gate electrode and a source electrode connected together with a fourth node ND4 to which the drain electrode of the second emission control transistor T5 and the anode electrode of the organic light emitting diode OLED are connected, and a variable voltage. It includes a drain electrode connected to the power supply line of (Vvar). Referring to FIG. 8, since the gate electrode and the source electrode of the bypass transistor T7 are commonly connected to the fourth node ND4, the voltage difference between the gate and source is 0V, and the bypass transistor T7 is It is always off. And since the variable voltage (Vvar) supply line is connected to the drain electrode of the bypass transistor (T7), the bypass transistor (T7) through the bypass transistor (T7) by the set voltage value of the variable voltage (Vvar) when the bypass transistor (T7) is off. The bypass current Ibcb flows. At this time, the set voltage value of the variable voltage Vvar is not particularly limited, and for example, may be equal to or less than the second power voltage ELVSS, which is the voltage value of the cathode electrode of the organic light emitting diode OLED. Even when the minimum current of the transistor displaying the black image flows as the driving current, if the organic light emitting diode (OLED) emits light, the black image is not displayed properly, so the minimum current of the transistor is also the bypass current (Ibcb), It can be distributed to a current path other than the current path on the diode side. Here, the minimum current of the transistor means the current under the condition that the transistor is turned off because the gate-source voltage Vgs of the transistor is less than the threshold voltage Vth. In this way, the minimum driving current (for example, a current of 10 pA or less) under the condition of turning off the transistor is transmitted to the organic light emitting diode and is expressed as an image with black luminance.

When the minimum driving current for displaying a black image flows, the bypass current Ibcb has a large effect, whereas when a large driving current for displaying an image such as a normal or white image flows, the bypass current Ibcb ) Has little effect. Therefore, when the driving current displaying the black image flows, the emission current Ioled of the organic light emitting diode reduced by the current amount of the bypass current Ibcb that has escaped from the driving current Idr through the path of the bypass unit is the black image It has the minimum amount of current at a level that can be expressed reliably.

When the driving operation according to the timing diagram of FIG. 13 is described based on the circuit diagram of the pixel 300-1 of FIG. 9, a driving process in which the pixels emit light in time series and display an image can be seen.

At time t1, the scan signal S[n-1] transmitted through the n-1th scan line changes to a low level and maintains the low level for a period from time t1 to time t2. At this time, the scan signal S[n] transmitted through the n-th scan line is maintained at a high level. In addition, at this time, the emission control signal EM[n] transmitted through the n-th emission control line is maintained at a high level voltage.

Accordingly, the initialization transistor T6 receiving the scan signal S[n-1] from the pixel 300-1 of FIG. 9 is turned on. In addition, the switching transistor T2 and the threshold voltage compensation transistor T3 through which the scan signal S[n] is transmitted are turned off, and the first emission control transistor T4 through which the emission control signal EM[n] is transmitted. ) And the second emission control transistor T5 are also turned off. Since the gate and the source are connected to the same contact point, the bypass transistor T7 is always turned off because there is no voltage difference between the gate and source.

Then, a variable voltage Vvar is applied as an initialization voltage through the initialization transistor T6 to the first node ND1 to which the gate electrode of the driving transistor T1 is connected during the time period t1 to time t2. In this case, the variable voltage Vvar may be set to a voltage sufficient to initialize the gate electrode voltage of the driving transistor T1.

During the period t1 to t2, one electrode of the storage capacitor Cst is connected to the first node ND1, so that a variable voltage Vvar is applied to the one electrode as an initialization voltage, and the storage capacitor Cst Since the high-level first power voltage ELVDD is applied to the other electrode, a voltage value corresponding to ELVDD-Vvar is stored during the period from the time point t1 to the time point t2.

Thereafter, the scanning signal S[n-1] transitions to the high level at the time point t2, and the scanning signal S[n] transmitted through the n-th scan line changes to the low level at the time t3, and the time t3 to the time point Maintains the low level during the period t4. Even at this time, the light emission control signal EM[n] is still maintained at a high level voltage.

During the time period t3 to time t4, the initialization transistor T6 is turned off, and the switching transistor T2 and the threshold voltage compensating transistor T3 receiving the scan signal S[n] are turned on. Then, the data voltage Vdata according to the data signal D[m] is transmitted to the source electrode of the driving transistor T1 through the switching transistor T2, and the driving transistor T1 is transferred to the threshold voltage compensation transistor T3. Connected by a diode. The voltage maintained at the first node ND1 connected to one electrode of the storage capacitor Cst is a voltage Vgs corresponding to the voltage difference between the gate-source electrode of the driving transistor T1, and is driven at the data voltage Vdata. This is the voltage value Vdata-Vth lowered by the threshold voltage Vth of the transistor T1. The storage capacitor Cst stores and maintains a voltage corresponding to a difference in voltage across both electrodes.

And when the scan signal S[n] transitions to the high level at time t4, the switching transistor T2 and the threshold voltage compensation transistor T3 are turned off, and the voltage of the first node ND1 is floated again. do.

At time t5, the emission control signal EM[n] transmitted through the n-th emission control line changes to a low level.

Then, the first emission control transistor T4 and the second emission control transistor T5 of the pixel 300-1 to which the emission control signal EM[n] is transmitted are turned on, and scans of the time t3 to the time t4 And the driving current Idr of the data voltage according to the data signal stored in the storage capacitor Cst during the data writing period is transferred to the organic light emitting diode OLED to emit light.

Specifically, the corresponding voltage for calculating the driving current Idr becomes ELVDD-Vdata in which the influence of the threshold voltage Vth of the driving transistor T1 is excluded.

If the driving current Idr is transmitted as a minimum current for displaying a black luminance image, a small amount of bypass current Ibcb is transmitted through the bypass transistor T7, which is always off, to accurately display a black luminance image. ) May flow in a bypass. Accordingly, the remaining current Idr-Ibcb, which is subtracted by the bypass current Ibcb from the driving current Idr, may be emitted as light of black luminance from the organic light emitting diode OLED as the emission current Ioled. The process of bypassing the path of some currents through the bypass transistor T7 is the same for not only black luminance images but also image signals displayed with various luminances, but driving current Idr for displaying images of various luminances including white luminance ) Has a large amount of current, so the effect of the bypass current Ibcb is not large as in the black luminance image.

Meanwhile, the structure of the pixel 300-2 that may be included in the organic light emitting display device of FIG. 8 shown in FIG. 10 is also not much different from the embodiment of FIG. 9.

The pixel 300-2 of FIG. 10 includes a pixel driver 302-2 and an organic light emitting diode (OLED) having the same circuit elements and circuit structures as the pixel driver of FIG. 9, and a bypass unit 303-2. Only the connection of the bypass transistor T17 of) is different from the bypass part of FIG. 9.

That is, the gate electrode of the bypass transistor T17 is connected to the n-1th scan line Sn-1 together with the gate electrode of the initialization transistor T16.

The source electrode of the bypass transistor T17 is connected to the fourth node ND14 to which the drain electrode of the second emission control transistor T15 and the anode electrode of the organic light emitting diode OLED are commonly connected. In addition, the drain electrode of the bypass transistor T17 is connected to a power supply line of the variable voltage Vvar.

In the case of the pixel having the structure as shown in FIG. 10, an operation process is described with reference to FIG. 13. During the initialization period of the time point t1 to the time point t2, the n-1th scan signal transmitted through the n-1th scan line Sn-1 ( The bypass transistor T17 is turned on together with the initialization transistor T16 due to the low level voltage of S[n-1]). Therefore, the variable voltage Vvar adjusted to a voltage level capable of initializing the gate electrode voltage of the driving transistor T11 through the initialization transistor T16 is transferred to the first node ND11.

On the other hand, since the n-1th scan signal S[n-1] is changed to and maintained at a high level voltage during the rest of the periods excluding the periods of the times t1 to t2, the bypass transistor T17 is turned off. And while the corresponding pixel 300-2 is activated to receive a voltage according to the data signal to emit light, a bypass current Ibcb having a minute amount of current is bypassed and flows through the turned-off bypass transistor T17, When a pixel displays a black image, a clear black luminance can be realized.

The pixel 300-3 according to the embodiment of FIG. 11 has the same structure as the pixel 300-2 of FIG. 10, but the difference in which the gate electrode of the bypass transistor T27 is connected to the n-th scan line Sn. There is.

Accordingly, when the driving process of the pixel 300-3 of FIG. 11 is described with reference to FIG. 13, there is no significant difference from the driving of the pixel of FIG. 10, but the scan signal S[n] transmitted through the n-th scan line Sn In response to ), the bypass transistor T27 is opened and closed. Therefore, after the initialization process of the driving transistor T21 is finished, when the scan signal S[n] is transmitted as a low-level voltage during the period from time t3 to time t4, the bypass transistor T27 together with the switching transistor T22 is It turns on.

According to the embodiment of FIG. 11, during this period, the data voltage according to the data signal is transmitted to the source electrode of the driving transistor T21 through the switching transistor T22, and the driving current Idr corresponding to the driving transistor T21 Is generated and transmitted to the organic light emitting diode. At this time, when the bypass current Ibcb flows in the bypass path through the turned-on bypass transistor T27, the loss of the light emission current Ioled increases and the image quality is greatly degraded. Accordingly, the variable voltage Vvar connected to the drain electrode of the bypass transistor T27 during the period from time t3 to time t4 should be set to be higher than a predetermined voltage level so that the bypass current Ibcb does not flow. For example, at least the cathode electrode of the organic light emitting diode OLED is set higher than the connected second power voltage ELVSS so that the bypass current Ibcb does not move toward the variable voltage Vvar.

In addition, in a period other than the time period t3 to time t4, since the scan signal S[n] transmitted to the gate electrode of the bypass transistor T27 is transmitted as a high level voltage, the bypass transistor T27 is turned off. . During the period in which the bypass transistor T27 is turned off, the light emission control signal EM[n] is transmitted to the low level in the period after the time point t5, and the driving current from the driving transistor T21 toward the organic light emitting diode OELD ( Idr) is formed. Then, in response to the voltage difference (Vds) between the variable voltage (Vvar) connected to the drain electrode of the bypass transistor (T27) and the source electrode voltage (Vds), some bypass current (Ibcb) from the driving current (Idr) is a variable voltage (Vvar) supply source. It will be able to bypass and flow to the side.

When the driving current Idr corresponds to the current value for displaying a black luminance image, the minute current amount of the bypass current Ibcb bypasses and exits, so the luminance of light directly emitted from the organic light emitting diode (OLED) Corresponds to the light emission current Ioled having a current value of Idr-Ibcb. Therefore, even with an organic light-emitting diode having a high-efficiency organic light-emitting material, a black luminance image can be clearly realized according to the emission current Ioled.

Meanwhile, the pixel 300-4 according to the exemplary embodiment of FIG. 12 has the same structure as the pixel 300-3 of FIG. 11, but the difference in which the gate electrode of the bypass transistor T37 is connected to the DC voltage supply source. have.

That is, the bypass part 303-4 of FIG. 12 is composed of a bypass transistor T37, wherein the bypass transistor T37 includes a source electrode connected to the fourth node ND34 and a drain electrode connected to the variable voltage supply source. And a gate electrode connected to a DC voltage source. Accordingly, a predetermined DC voltage is always received from the DC voltage source regardless of the operation of elements of the pixel according to the driving timing diagram of FIG. 13. In this case, the DC voltage is a predetermined level voltage capable of always turning off the bypass transistor T37. In the example of FIG. 12, since the pixel is composed of a PMOS transistor, the DC voltage may be a predetermined high level voltage.

Thus, by receiving the DC voltage of the transistor off level to the gate electrode, the bypass transistor T37 is always turned off, and in the off state, the bypass current Ibcb is passed from the driving current Idr to the bypass path. .

The organic light emitting display device including the pixels 300-1, 300-2, 300-3 and 300-4 according to the embodiments shown in FIGS. 9 to 12 is a bypass unit that controls to implement an accurate black luminance image. Therefore, the contrast ratio is improved to have excellent image quality characteristics.

The present invention has been described above in connection with the specific embodiments of the present invention, but this is only an example and the present invention is not limited thereto. Those skilled in the art may change or modify the described embodiments without departing from the scope of the present invention, and such changes or modifications also belong to the scope of the present invention. In addition, the material of each component described in the specification can be easily selected and replaced by a person skilled in the art from various known materials. In addition, those skilled in the art may omit some of the components described in the present specification without deteriorating performance, or add components to improve performance. In addition, those skilled in the art may change the order of the method steps described herein according to the process environment or equipment. Accordingly, the scope of the present invention should be determined not by the described embodiments, but by the claims and their equivalents.

10: display unit 20: scan driving unit
30: data driver 40: power supply
50: control unit 60: gate driver
70: light emission control driver
100,200,300: pixels

Claims (21)

Organic light emitting diode (OLED),
A first transistor including a gate connected to a first node and connected between a first voltage line and an anode of the organic light emitting diode,
A second transistor including a gate connected to a scan line and connected between a data line and the first node, and
A third transistor including a gate connected to a gate line and connected between the anode and a second voltage line
Including,
In a black luminance condition in which light of the minimum luminance is emitted from the organic light emitting diode, current is transmitted through the first transistor while the organic light emitting diode emits light, and is controlled to flow to the third transistor,
Pixels. The method of claim 1,
The cathode of the organic light emitting diode is connected to a third voltage line,
The voltage applied to the second voltage line is less than or equal to the voltage applied to the third voltage line,
Pixels. The method of claim 1,
The first period in which the gate signal for turning off the third transistor while the organic light emitting diode emits light is applied to the gate line is a voltage level for transferring the data voltage transferred from the data line, and a scan signal from the scan line Excluding the period in which it is delivered,
Pixels. The method of claim 3,
During the first period, current is transmitted through the first transistor to flow to the organic light emitting diode and the third transistor,
Pixels. The method of claim 4,
During the first period, a voltage applied to the second voltage line is controlled so that some of the current flows to the third transistor,
Pixels. The method of claim 1, wherein a variable voltage is applied to the second voltage line,
Pixels. A scan driver for transmitting a plurality of scan signals to a plurality of scan lines,
A gate driver that transmits a plurality of gate signals to a plurality of gate lines,
A data driver that transmits a plurality of data signals to a plurality of data lines,
A display unit including a plurality of pixels connected to a corresponding scan line, a corresponding gate line, and a corresponding data line, and displaying an image by emitting light according to the plurality of data signals
A power supply unit supplying a first voltage, a second voltage, and a third voltage to the pixels, respectively, and
A control unit that controls the scan driver, the gate driver, the data driver, and a power supply unit
Including,
Each of the plurality of pixels,
Organic light emitting diode (OLED),
A first transistor including a gate connected to a first node and connected between a first voltage line and an anode of the organic light emitting diode,
A second transistor including a gate connected to a scan line and connected between a data line and the first node, and
A third transistor including a gate connected to a gate line and connected between the anode and a second voltage line,
In a black luminance condition in which light of the minimum luminance is emitted from the organic light emitting diode, current is transmitted through the first transistor while the organic light emitting diode emits light, and is controlled to flow to the third transistor,
Organic light emitting display device. The method of claim 7,
The cathode of the organic light emitting diode is connected to a third voltage line,
The voltage applied to the second voltage line is less than or equal to the voltage applied to the third voltage line,
Organic light emitting display device. The method of claim 7,
The first period in which the gate signal for turning off the third transistor while the organic light emitting diode emits light is applied to the gate line is a voltage level for transferring the data voltage transferred from the data line, and a scan signal from the scan line Excluding the period in which it is delivered,
Organic light emitting display device. The method of claim 9,
During the first period, current is transmitted through the first transistor to flow to the organic light emitting diode and the third transistor,
Organic light emitting display device. The method of claim 10,
During the first period, a voltage applied to the second voltage line is controlled so that some of the current flows to the third transistor,
Organic light emitting display device. The method of claim 7,
A variable voltage is applied to the second voltage line,
Organic light emitting display device. A first voltage line connected to the first voltage source,
An organic light emitting diode (OLED) comprising an anode and a cathode electrically connected to a second voltage source,
A third voltage line connected to a third voltage source,
A first transistor electrically connected to the organic light emitting diode and transmitting a driving current to the organic light emitting diode,
A second transistor having a gate connected to a scan line and electrically connected between a data line and one electrode of the first transistor,
A third transistor electrically connected between the other electrode of the first transistor and the third voltage line,
A fourth transistor electrically connected between one electrode of the first transistor and the first voltage line,
A fifth transistor electrically connected between the other electrode of the first transistor and the anode,
A sixth transistor electrically connected between one electrode of the third transistor and the third voltage line and controlled by a first signal, and
A seventh transistor that includes one end electrically connected to the anode and the other electrode of the fifth transistor, and the other end electrically connected to the third voltage line, and is controlled by a second signal
Including,
In the black luminance condition in which light of the minimum luminance is emitted from the organic light emitting diode, some of the driving current transmitted through the first transistor while the organic light emitting diode emits light flows through the turned-off seventh transistor. Controlled,
Pixels. The method of claim 13,
While the fourth and fifth transistors are maintained in a turned-on state, some of the driving current flows through the turned-off seventh transistor,
Pixels. The method of claim 13,
Both the gate and the source of the seventh transistor are connected to a node between the fifth transistor and the anode,
Pixels. The method of claim 13,
A gate of the seventh transistor is connected to a DC voltage source having a voltage value for turning off the seventh transistor,
Pixels. The method of claim 13,
A gate of the seventh transistor is connected to the scan line,
While the scan signal transferred from the scan line is transferred to a voltage level for turning off the seventh transistor, some of the driving current flows through the turned-off seventh transistor,
Pixels. The method of claim 13,
The gate of the seventh transistor is connected to a previous scan line,
While the second signal transferred from the previous scan line is transferred to a voltage level for turning off the seventh transistor, some of the driving current flows through the turned-off seventh transistor,
Pixels. The method of claim 13,
The third voltage source applies a variable voltage based on the level of the DC voltage based on the characteristics of the panel,
Pixels. The method of claim 13,
Some of the driving current is controlled according to a voltage difference between the voltage of the anode and the voltage of the third voltage source,
Pixels. The method of claim 13,
In a black luminance condition in which light having a minimum luminance is emitted from the organic light emitting diode, the third voltage source is controlled so that a part of the driving current flows through the turned-off seventh transistor,
Pixels.

Images