KR20190066338A - Organic Light Emitting Display And Driving Method Thereof - Google Patents

Abstract

According to one embodiment of the present invention, an organic light emitting display comprises: a display panel having a plurality of pixels individually having light emitting devices; a timing controller time-dividing one frame into an image holding time during which image data is displayed and a black holding time during which a black data voltage is written and the light emitting devices are not emitted and varying the black data voltage in accordance with the black holding time; and a panel driving circuit writing an image data voltage corresponding to the image data and the black data voltage into the display panel.

Description

[0001] The present invention relates to an organic light emitting display,

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

The active matrix type organic light emitting display device includes an organic light emitting diode (OLED) which emits light by itself, has a high response speed, and has a high luminous efficiency, luminance, and viewing angle.

The OLED, which is a self-luminous element, includes an anode electrode, a cathode electrode, and an organic compound layer formed therebetween. The organic compound layer includes a hole injection layer (HIL), a hole transport layer (HTL), an emission layer (EML), an electron transport layer (ETL), and an electron injection layer EIL). When a power source voltage is applied to the anode electrode and the cathode electrode, holes passing through the HTL and electrons passing through the ETL are transferred to the EML to form excitons. As a result, the light emitting layer (EML) Thereby generating visible light.

The organic light emitting display device arranges the pixels each including the OLED in a matrix form and adjusts the brightness of the pixels according to the gradation of the video data. Each of the pixels includes a driving TFT (Thin Film Transistor) that controls a driving current flowing in the OLED according to the voltage applied between the gate electrode and the source electrode of the pixel, and the display gradation (luminance) of the OLED is proportional to the driving current. .

In such an organic light emitting display device, since the light emitting pixel and the non-light emitting pixel can be mixed in one screen according to the image reproduced on the display panel, the NBTiS (Negative Bias Temperature Illumination Stress) characteristic of the driving TFT may be a problem. Since the NBTiS characteristic of the driving TFT is affected by the ambient light, the NBTiS characteristic of the non-emitting pixel can be degraded by the light generated in the surrounding pixels. When the NBTiS characteristic deteriorates, the threshold voltage of the driving TFT can be excessively shifted in the negative (-) direction, so that the curve of the current characteristic of the driving TFT is distorted and a desired image becomes difficult to implement. In order to improve the NBTiS characteristics of the non-luminescent pixel, it is necessary to maximize the black data voltage written to the non-luminescent pixel.

Accordingly, the present invention provides an organic light emitting display device and a method of driving the same, which can improve NBTiS characteristics of a driving TFT by varying a black data voltage.

An organic light emitting display according to an embodiment of the present invention includes a display panel having a plurality of pixels each having a light emitting element; Dividing one frame into an image holding time at which the image data is displayed and a black holding time at which the black data voltage is written and the light emitting element is not emitting light and the black data voltage is varied according to the black holding time; And a panel driving circuit for writing the video data voltage corresponding to the video data and the black data voltage to the display panel.

The timing controller lowers the black data voltage as the black holding time becomes longer and increases the black data voltage as the black holding time becomes shorter.

The timing controller stores in advance the anode charge time of the light emitting element for each voltage based on the black hold time and selects the maximum voltage at which the light emitting element is not emitted during the black hold time as the black data voltage.

The timing controller detects motion of the image by analyzing the image data, and increases the black holding time in proportion to the motion of the image.

The timing controller increases the upward modulation width of the image data in proportion to the black holding time.

The panel driving circuit sequentially writes the image data voltages to the display panel by one horizontal pixel line, and sequentially writes the black data voltages to the display panel for a plurality of horizontal pixel lines.

According to another aspect of the present invention, there is provided an OLED display including: a display panel having a plurality of pixels each having a light emitting element; A timing controller for varying a black data voltage to be written to a non-light emitting pixel in units of a predetermined time; And a panel driving circuit for writing the black data voltage to the display panel.

Wherein the timing controller previously stores an anode charging time of the light emitting device for each voltage based on the predetermined time and selects a maximum voltage at which the light emitting device does not emit light for a predetermined period of time as a first black data voltage, 1 < / RTI > black data voltage is selected as the second black data voltage.

The timing controller assigns the first black data voltage to a first frame and the second black data voltage to a second frame following the first frame.

A method of driving an organic light emitting display in which a plurality of pixels each having a light emitting element is provided in a display panel according to an embodiment of the present invention is characterized in that an image holding time for displaying one frame of image data, Dividing the light emitting element into a black holding time at which the light emitting element is not lighted, and varying the black data voltage according to the black holding time; And writing the image data voltage corresponding to the image data and the black data voltage to the display panel.

According to another aspect of the present invention, there is provided a method of driving an organic light emitting display having a plurality of pixels each having a light emitting element in a display panel, the method comprising: varying a black data voltage to be written to a non-light emitting pixel in units of a predetermined time; And writing the black data voltage to the display panel.

The present invention can improve the NBTiS characteristics of the driving TFT by changing the black data voltage to be written in the non-light emitting pixel, and improve the display quality.

1 is a view illustrating an organic light emitting display according to an embodiment of the present invention.
2 is a view for explaining a black duty control technique according to an embodiment of the present invention.
3 is a diagram illustrating a pixel structure according to an embodiment of the present invention.
4 is a view showing a gate signal and a data signal for implementing a black duty control technique.
5 is a diagram illustrating an example in which the black duty is varied based on motion of image data.
6A to 6C are diagrams showing examples in which the black data voltage and the image data voltage are changed according to the black duty.
7A and 7B are views showing the OLED anode charging time per panel and gray scale.
FIG. 8 is a diagram illustrating a method of driving an organic light emitting display according to an embodiment of the present invention. Referring to FIG.
9 is a graph showing the relationship between the black holding time and the black data voltage.
10 is a diagram for explaining a black data voltage varying technique according to another embodiment of the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS The advantages and features of the present invention and the manner of achieving them will become apparent with reference to the embodiments described in detail below with reference to the accompanying drawings. It should be understood, however, that the invention is not limited to the disclosed embodiments, but is capable of many different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, To fully disclose the scope of the invention to those skilled in the art, and the invention is only defined by the scope of the claims.

The shapes, sizes, ratios, angles, numbers, and the like disclosed in the drawings for describing the embodiments of the present invention are illustrative, and thus the present invention is not limited thereto. Like reference numerals refer to like elements throughout the specification. In the following description, well-known functions or constructions are not described in detail since they would obscure the invention in unnecessary detail. Where the terms "comprises", "having", "done", and the like are used in this specification, other portions may be added unless "only" is used. Unless the context clearly dictates otherwise, including the plural unless the context clearly dictates otherwise.

In interpreting the constituent elements, it is construed to include the error range even if there is no separate description.

In the case of a description of the positional relationship, for example, if the positional relationship between two parts is described as 'on', 'on top', 'under', and 'next to' Or " direct " is not used, one or more other portions may be located between the two portions.

An element or layer is referred to as being another element or layer "on ", including both intervening layers or other elements directly on or in between.

Although the first, second, etc. are used to describe various components, these components are not limited by these terms. These terms are used only to distinguish one component from another. Therefore, the first component mentioned below may be the second component within the technical spirit of the present invention.

Like reference numerals refer to like elements throughout the specification.

The sizes and thicknesses of the individual components shown in the figures are shown for convenience of explanation and the present invention is not necessarily limited to the size and thickness of the components shown.

It is to be understood that each of the features of the various embodiments of the present invention may be combined or combined with each other partially or wholly and technically various interlocking and driving are possible and that the embodiments may be practiced independently of each other, It is possible.

Various embodiments of the present invention will now be described in detail with reference to the accompanying drawings.

1 and 2 show an organic light emitting display according to an embodiment of the present invention.

The organic light emitting display according to an embodiment of the present invention may employ a black duty control technique for adjusting the black duty in one frame in order to improve the moving image response characteristic and the low gradation display quality.

The black duty control technique divides one frame into an image holding time and a black holding time, and controls the black holding time according to the attribute of the image data. The image retention time is a time when the OLED (light emitting device) in the pixels emits light according to the image data voltage corresponding to the image data. The black hold time is the time when the black data voltage is written to the pixels and the OLED is not emitting light. The image duty within one frame is determined by the image holding time, and the black duty is determined by the black holding time.

In order to implement such a black duty control technique, an OLED display according to an embodiment of the present invention includes a display panel 10, a timing controller 11, a data driving circuit 12, and a gate driving circuit 13 can do. The data driving circuit 12 and the gate driving circuit 13 constitute a panel driving circuit.

A plurality of data lines 15 and reference lines 16 and a plurality of gate lines 17 and 18 are intersected with each other in the display panel 10. Pixels are arranged in a matrix form for each of the intersection areas, . The pixel array is provided with a plurality of horizontal pixel lines (HL1 to HLn). One horizontal pixel line includes a plurality of pixels arranged adjacent to each other along the horizontal direction.

The gate lines 17 and 18 may include first gate lines 17 to which a scan signal is applied and second gate lines 18 to which a sensing signal is applied. Each pixel is connected to one of the data lines 15, to one of the reference lines 16, to one of the first gate lines 17, and to one of the second gate lines 18 Lt; / RTI > Each pixel may include an OLED and a driving TFT.

These pixels can be supplied with a high potential driving voltage and a low potential driving voltage from the power supply block. The TFTs constituting the pixel may be implemented as a p-type, an n-type, or a hybrid type. Further, the semiconductor layer of the TFTs constituting the pixel may include amorphous silicon, polysilicon, or an oxide.

The data driving circuit 12 converts the input image data DATA into the image data voltage Vdata during the image holding time under the control of the timing controller 11 and outputs the image data voltage Vdata to the data lines 15, . The data driving circuit 12 generates the black data voltage Vblack during the black holding time under the control of the timing controller 11 and supplies the black data voltage Vblack to the data lines 15. The data driving circuit 12 can generate the reference voltage (Vref in FIG. 3) during the image holding time and the black holding time under the control of the timing controller 11 and supply the reference voltage to the reference lines 16. [

The gate drive circuit 13 can generate a scan signal (SCAN in FIG. 3) and a sensing signal (SEN in FIG. 3) twice in one frame under the control of the timing controller 11. FIG. The gate driver circuit 13 generates a first scan signal synchronized with the video data voltage and supplies the first scan signal to the first gate lines 17 and then generates a second scan signal synchronized with the black data voltage, (17). The gate driving circuit 13 generates a first sensing signal to be synchronized with the first scan signal and supplies the generated first sensing signal to the second gate lines 18 and then generates a second sensing signal synchronized with the second scan signal To the second gate lines (18). The gate drive circuit 13 may be embedded in the non-display area of the display panel 10 or may be bonded to the display panel 10 in the form of an IC.

The timing controller 11 receives input image data DATA from the host system 14 through an interface circuit and supplies the image data DATA to the data driving circuit 14 through various interface methods such as mini- (12).

The timing controller 11 receives timing signals such as a vertical synchronization signal Vsync, a horizontal synchronization signal Hsync, a data enable signal DE and a dot clock CLK from the host system 14, And generates control signals for controlling the operation timings of the drive circuit 12 and the gate drive circuit 13. [ These control signals include a gate timing control signal GDC for controlling the operation timing of the gate drive circuit 13 and a source timing control signal DDC for controlling the operation timing of the data drive circuit 12. [

The timing controller 11 can shorten the image holding time and increase the black holding time (black duty) by advancing the timing at which the black data voltage Vblack is written within one frame in the case where there is much movement of the image. However, when such a black duty control technique is employed, the NBTiS characteristic of the non-light emitting pixel may be degraded.

The timing controller 11 can vary the black data voltage Vblack in accordance with the black holding time (black duty) in order to solve the NBTiS characteristic problem of the driving TFT which occurs when the black duty is controlled. In the present invention, the black data voltage Vblack means a voltage at which the driving TFT is turned on and the driving current is supplied to the driving TFT. However, the driving current according to the black data voltage Vblack is smaller than the driving current corresponding to the video data voltage Vdata. The larger the black data voltage Vblack is set, the more the driving current increases. When the driving current according to the black data voltage Vblack is applied to the OLED for a long time, the OLED may emit light. Therefore, the timing controller 11 considers the OLED anode charging time when the black data voltage Vblack is varied to improve the NBTiS characteristics do. This will be described in detail with reference to FIGS. 5 to 9. FIG.

FIG. 3 shows a pixel configuration for implementing a black duty control technique according to the present invention. In Fig. 3, the DAC represents a digital-analog converter in a data driving circuit that outputs a data voltage. Here, the data voltage is a video data voltage or a black data voltage.

Referring to FIG. 3, a pixel according to an embodiment of the present invention may include an OLED, a driving TFT DT, a storage capacitor Cst, a first switch TFT ST1, and a second switch TFT ST2 have.

The OLED includes an anode electrode connected to the source node Ns, a cathode electrode connected to the input terminal of the low potential driving voltage EVSS, and an organic compound layer positioned between the anode electrode and the cathode electrode.

The driving TFT DT controls the driving current flowing in the OLED according to the voltage difference between the gate node Ng and the source node Ns. The driving TFT DT has a gate electrode connected to the gate node Ng, a drain electrode connected to the input terminal of the high potential driving voltage EVDD, and a source electrode connected to the source node Ns. The storage capacitor Cst is connected between the gate node Ng and the source node Ns.

The first switch TFT ST1 switches the data voltage on the data line 15 to the gate node Ng by switching the current flow between the data line 15 and the gate node Ng in response to the scan signal SCAN. . The first switch TFT ST1 has a gate electrode connected to the first gate line 17, a drain electrode connected to the data line 15, and a source electrode connected to the gate node Ng.

The second switch TFT ST2 switches the reference voltage Vref on the reference line 16 to the node Ng (Ns) by switching the current flow between the reference line 16 and the source node Ns in response to the sensing signal SEN. . The second switch TFT ST2 has a gate electrode connected to the second gate line 18, a drain electrode connected to the reference line 16, and a source electrode connected to the source node Ns.

4 is a view showing a gate signal and a data signal for implementing a black duty control technique. FIG. 4 shows gate signals and data signals applied to the k-th horizontal pixel line HLk to the j-th horizontal pixel line HLj of FIG. In Fig. 4, the sensing signal SEN has been omitted for convenience of explanation.

The higher the panel resolution and the frame frequency, the shorter the data charging time allocated to one horizontal pixel line. If the black duty control technique is employed in this state, the data charging time becomes shorter, and therefore, a method of securing the charging time is required. The present invention can solve the insufficient charging time problem by simultaneously writing the black data voltage to the plurality of horizontal pixel lines as shown in FIG. That is, under the control of the timing controller 11, the panel drive circuit sequentially writes the image data voltage (Vdata) for one horizontal pixel line on the display panel, and supplies the black data voltage (Vblack) Can be sequentially written.

The data driving circuit 12 supplies the video data voltage Vdata to the data lines 15 within the image holding time and the gate driving circuit 13 supplies the first scan signals SCANk to SCANj, May be sequentially supplied to the first gate lines 17 of the k-th horizontal pixel line to the j-th horizontal pixel lines HLk to HLj in synchronization with the video data voltage Vdata. The data driving circuit 12 supplies the black data voltage Vblack to the data lines 15 within the black holding time and the gate driving circuit 13 supplies the second scanning signals SCANk to SCANj and Pa2 Can be simultaneously supplied to the first gate lines 17 of the k-th horizontal pixel line to the j-th horizontal pixel lines HLk to HLj in synchronization with the black data voltage Vblack.

When the black data voltage is simultaneously written to the plurality of horizontal pixel lines, the data transition frequency of the data driving circuit 12 can be lowered and the power consumption can be reduced.

5 is a diagram illustrating an example in which the black duty is varied based on motion of image data. 6A to 6C are diagrams showing examples in which the black data voltage and the image data voltage are changed according to the black duty. 7A and 7B are views showing the OLED anode charging time by panel and by gray level.

Referring to FIG. 5, the timing controller 11 may analyze input image data on a frame-by-frame basis to detect motion of an input image and to control black duty in proportion to motion of the input image.

The timing controller 11 can detect the motion of the input image in various ways. For example, the timing controller 11 may calculate a motion of an object included in an input image to obtain a motion vector (MV) corresponding to a change in motion. Various algorithms such as Pel-recusive algorithm, phase correlation algorithm, and block matching method are known to calculate motion, but block matching algorithm (BMA) is commonly used because of its convenience in implementation . The motion compensation frame rate up conversion MC-FRUC using the block matching algorithm BMA searches for a motion vector MV for a block in a previous frame on the basis of a block in the current frame do.

The timing controller 11 improves the moving image response characteristic and the low gradation display quality by increasing the black holding time in proportion to the motion of the image. Since the luminance is lowered when the black holding time is relatively increased within one frame, the timing controller 11 can prevent the luminance from lowering by increasing the upward modulation width of the video data in proportion to the black holding time. For example, as shown in Figs. 6A to 6C, the magnitude of the image data voltage Vdata increases in proportion to the black duty. Therefore, even if the black duty is controlled on a frame-by-frame basis in accordance with the attribute of the image data, there is an advantage that the perceived luminance is not changed.

The timing controller 11 can vary the black data voltage Vblack in accordance with the black holding time (black duty) in order to solve the NBTiS characteristic problem of the driving TFT which occurs when the black duty is controlled. Since the NBTiS characteristic of the driving TFT is improved as the voltage applied to the gate electrode of the driving TFT is increased, the timing controller 11 can increase the black data voltage Vblack as much as possible without emitting the OLED. 6A to 6C, the timing controller 11 lowers the black data voltage Vblack as the black holding time becomes longer and decreases the black data voltage Vblack as the black holding time becomes shorter, It is possible to improve the NBTiS characteristics of the driving TFT.

Since the pixel driving current required for each model and the specification differs depending on the model and the specification, even if the same gradation is expressed as shown in FIGS. 7A and 7B, the corresponding video data voltages are different for each panel and gradation, Charging time is also different for each panel and gradation. For example, FIG. 7A shows the anode charging time of the panels A and B at the 32th gradation, and FIG. 7B shows the anode charging time of the panels A and B at the 64th gradation.

In consideration of this, the timing controller 11 stores the anode charging time of the OLED according to the voltage on the basis of the black holding time in advance in the lookup table, and sets the maximum voltage at which the OLED is not emitted during the black holding time to the black data voltage Vblack By selecting this, the NBTiS characteristics of the driving TFT can be improved.

FIG. 8 is a diagram illustrating a method of driving an organic light emitting display according to an embodiment of the present invention. Referring to FIG. 9 is a graph showing the relationship between the black holding time and the black data voltage.

Referring to FIG. 8, the present invention calculates black duty by analyzing input image data, and calculates black sustain time corresponding to black duty in one frame (S1, S2, S3).

The present invention refers to the OLED anode charging time for each voltage stored in advance on the basis of the black holding time in the lookup table and selects and applies the maximum voltage for causing the OLED to emit no light during the black holding time as the black data voltage Vblack S4, S5, S6).

Therefore, the black data voltage Vblack has an inverse relationship with the black duty (black holding time) as shown in FIG. That is, the lower the black holding time is, the lower the black data voltage Vblack is applied, and the higher the black holding time, the higher the black data voltage Vblack is applied.

10 is a diagram for explaining a black data voltage varying technique according to another embodiment of the present invention.

1 to 9, the black data voltage varying method is based on a black duty control technique for controlling black duty according to an image. On the other hand, the black data voltage varying method described in FIG. 10 is not limited to the black duty control technique. The technique of FIG. 10 is directed to the organic light emitting display of FIG.

The technique of FIG. 10 is also intended to improve the NBTiS characteristics of the driving TFT by varying the black data voltage to be written to the non-emitting pixel. Referring to FIG. 10, the organic light emitting diode display according to another embodiment of the present invention includes a display panel having a plurality of pixels each having a light emitting element, and black data voltages Vblack1 and Vblack2 to be written to non- A timing controller for varying a predetermined time unit, and a panel driving circuit for writing black data voltages Vblack1 and Vblack2 to the display panel.

The timing controller stores the anode charge time of the OLED according to the voltage in advance in the lookup table and selects the maximum voltage REF at which the OLED is not emitted for a predetermined time as the first black data voltage Vblack1, A voltage lower than the one black data voltage Vblack1 can be selected as the second black data voltage Vblack2.

The timing controller assigns the first black data voltage Vblack1 to the first frame (e.g., the odd frame) and the second black data voltage Vblack2 to the second frame (e.g., the excellent frame) can do.

It will be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the spirit or scope of the invention. Therefore, the technical scope of the present invention should not be limited to the contents described in the detailed description of the specification, but should be defined by the claims.

10: Display panel 11: Timing controller
12: data driving circuit 13: gate driving circuit

Claims (11)

A display panel having a plurality of pixels each having a light emitting element;
Dividing one frame into an image holding time at which the image data is displayed and a black holding time at which the black data voltage is written and the light emitting element is not emitting light and the black data voltage is varied according to the black holding time; And
And a panel driving circuit for writing the video data voltage corresponding to the video data and the black data voltage into the display panel. The method according to claim 1,
The timing controller includes:
Wherein the black data voltage is lowered as the black holding time is longer and the black data voltage is higher as the black holding time is shorter. 3. The method of claim 2,
The timing controller includes:
Storing the anode charging time of the light emitting device in advance according to the voltage based on the black holding time and selecting the maximum voltage at which the light emitting device is not emitted during the black holding time as the black data voltage. The method according to claim 1,
The timing controller includes:
And detects the motion of the image by analyzing the image data to increase the black holding time in proportion to the motion of the image. 5. The method of claim 4,
The timing controller includes:
And increases the upward modulation width of the image data in proportion to the black holding time. The method according to claim 1,
In the panel driving circuit,
And sequentially writing the image data voltages to the display panel by one horizontal pixel line and sequentially writing the black data voltages to the display panel for a plurality of horizontal pixel lines. A display panel having a plurality of pixels each having a light emitting element;
A timing controller for varying a black data voltage to be written to a non-light emitting pixel in units of a predetermined time; And
And a panel driving circuit for writing the black data voltage to the display panel. 8. The method of claim 7,
The timing controller includes:
The method comprising: storing an anode charge time of the light emitting device for each voltage in advance based on the predetermined time; selecting a maximum voltage at which the light emitting device is not emitted for a predetermined time as a first black data voltage; And selects a low voltage as the second black data voltage. 9. The method of claim 8,
The timing controller includes:
The first black data voltage is assigned to a first frame, and the second black data voltage is assigned to a second frame following the first frame. A method of driving an organic light emitting display in which a plurality of pixels each having a light emitting element are provided in a display panel,
Dividing one frame into an image holding time at which the image data is displayed and a black holding time at which the black data voltage is written and the non-emitting light of the light emitting element is written, and varying the black data voltage according to the black holding time; And
And writing the image data voltage corresponding to the image data and the black data voltage to the display panel. A method of driving an organic light emitting display in which a plurality of pixels each having a light emitting element are provided in a display panel,
Varying a black data voltage to be written to a non-light emitting pixel in units of a predetermined time; And
And writing the black data voltage to the display panel.

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