WO2009082056A1 - Hybrid driving device and method of amoled panel using multi-analog gradation current - Google Patents

Hybrid driving device and method of amoled panel using multi-analog gradation current Download PDF

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Publication number
WO2009082056A1
WO2009082056A1 PCT/KR2008/001003 KR2008001003W WO2009082056A1 WO 2009082056 A1 WO2009082056 A1 WO 2009082056A1 KR 2008001003 W KR2008001003 W KR 2008001003W WO 2009082056 A1 WO2009082056 A1 WO 2009082056A1
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WO
WIPO (PCT)
Prior art keywords
gradation
gradation current
sub
current
frame
Prior art date
Application number
PCT/KR2008/001003
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French (fr)
Inventor
Ki Suk Sung
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Syncoam Co., Ltd
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Publication date
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Publication of WO2009082056A1 publication Critical patent/WO2009082056A1/en

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Classifications

    • G—PHYSICS
    • G09—EDUCATION; CRYPTOGRAPHY; DISPLAY; ADVERTISING; SEALS
    • G09G—ARRANGEMENTS OR CIRCUITS FOR CONTROL OF INDICATING DEVICES USING STATIC MEANS TO PRESENT VARIABLE INFORMATION
    • G09G3/00—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes
    • G09G3/20—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes for presentation of an assembly of a number of characters, e.g. a page, by composing the assembly by combination of individual elements arranged in a matrix no fixed position being assigned to or needed to be assigned to the individual characters or partial characters
    • G09G3/2007—Display of intermediate tones
    • G09G3/2018—Display of intermediate tones by time modulation using two or more time intervals
    • G09G3/2022—Display of intermediate tones by time modulation using two or more time intervals using sub-frames
    • G09G3/204—Display of intermediate tones by time modulation using two or more time intervals using sub-frames the sub-frames being organized in consecutive sub-frame groups
    • G—PHYSICS
    • G09—EDUCATION; CRYPTOGRAPHY; DISPLAY; ADVERTISING; SEALS
    • G09G—ARRANGEMENTS OR CIRCUITS FOR CONTROL OF INDICATING DEVICES USING STATIC MEANS TO PRESENT VARIABLE INFORMATION
    • G09G3/00—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes
    • G09G3/20—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes for presentation of an assembly of a number of characters, e.g. a page, by composing the assembly by combination of individual elements arranged in a matrix no fixed position being assigned to or needed to be assigned to the individual characters or partial characters
    • G09G3/2007—Display of intermediate tones
    • G09G3/2018—Display of intermediate tones by time modulation using two or more time intervals
    • G09G3/2022—Display of intermediate tones by time modulation using two or more time intervals using sub-frames
    • G09G3/2037—Display of intermediate tones by time modulation using two or more time intervals using sub-frames with specific control of sub-frames corresponding to the least significant bits
    • G—PHYSICS
    • G09—EDUCATION; CRYPTOGRAPHY; DISPLAY; ADVERTISING; SEALS
    • G09G—ARRANGEMENTS OR CIRCUITS FOR CONTROL OF INDICATING DEVICES USING STATIC MEANS TO PRESENT VARIABLE INFORMATION
    • G09G3/00—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes
    • G09G3/20—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes for presentation of an assembly of a number of characters, e.g. a page, by composing the assembly by combination of individual elements arranged in a matrix no fixed position being assigned to or needed to be assigned to the individual characters or partial characters
    • G09G3/2007—Display of intermediate tones
    • G09G3/2077—Display of intermediate tones by a combination of two or more gradation control methods
    • G09G3/2081—Display of intermediate tones by a combination of two or more gradation control methods with combination of amplitude modulation and time modulation
    • G—PHYSICS
    • G09—EDUCATION; CRYPTOGRAPHY; DISPLAY; ADVERTISING; SEALS
    • G09G—ARRANGEMENTS OR CIRCUITS FOR CONTROL OF INDICATING DEVICES USING STATIC MEANS TO PRESENT VARIABLE INFORMATION
    • G09G3/00—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes
    • G09G3/20—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes for presentation of an assembly of a number of characters, e.g. a page, by composing the assembly by combination of individual elements arranged in a matrix no fixed position being assigned to or needed to be assigned to the individual characters or partial characters
    • G09G3/22—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes for presentation of an assembly of a number of characters, e.g. a page, by composing the assembly by combination of individual elements arranged in a matrix no fixed position being assigned to or needed to be assigned to the individual characters or partial characters using controlled light sources
    • G09G3/30—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes for presentation of an assembly of a number of characters, e.g. a page, by composing the assembly by combination of individual elements arranged in a matrix no fixed position being assigned to or needed to be assigned to the individual characters or partial characters using controlled light sources using electroluminescent panels
    • G09G3/32—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes for presentation of an assembly of a number of characters, e.g. a page, by composing the assembly by combination of individual elements arranged in a matrix no fixed position being assigned to or needed to be assigned to the individual characters or partial characters using controlled light sources using electroluminescent panels semiconductive, e.g. using light-emitting diodes [LED]
    • G09G3/3208—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes for presentation of an assembly of a number of characters, e.g. a page, by composing the assembly by combination of individual elements arranged in a matrix no fixed position being assigned to or needed to be assigned to the individual characters or partial characters using controlled light sources using electroluminescent panels semiconductive, e.g. using light-emitting diodes [LED] organic, e.g. using organic light-emitting diodes [OLED]
    • G09G3/3275—Details of drivers for data electrodes
    • G09G3/3283—Details of drivers for data electrodes in which the data driver supplies a variable data current for setting the current through, or the voltage across, the light-emitting elements
    • G—PHYSICS
    • G09—EDUCATION; CRYPTOGRAPHY; DISPLAY; ADVERTISING; SEALS
    • G09G—ARRANGEMENTS OR CIRCUITS FOR CONTROL OF INDICATING DEVICES USING STATIC MEANS TO PRESENT VARIABLE INFORMATION
    • G09G2320/00—Control of display operating conditions
    • G09G2320/02—Improving the quality of display appearance
    • G09G2320/0266—Reduction of sub-frame artefacts

Definitions

  • the present invention relates to a hybrid driving device and method of an active- matrix organic light emitting diode (AMOLED) panel using a digital driving manner, and more particularly, to a hybrid driving device and method of an AMOLED panel using a multi-analog gradation current which includes a plurality of analog gradation current sources having a plurality of gradation values in an OLED panel and divides a frame into a sub-frame region implemented by a gradation current source having a low gradation value and a sub-frame region implemented by a gradation current source having a high gradation value to decrease a difference between a driving frequency for implementing a minimum gradation of a video signal and a driving frequency for implementing a maximum gradation thereof and prevent image quality degradation such as a false contour that may occur in the digital driving manner.
  • Background Art
  • An organic light emitting diode which has been used as a display device has good characteristics such as high-speed response and high luminance using organic materials emitting light.
  • the OLED does not require a backlight and can be manufactured to be thinner than a liquid crystal display (LCD).
  • LCD liquid crystal display
  • an electron injected from an electrode and a hole injected from the other electrode are combined at an emissive layer disposed between the two electrodes to generate an exciton, and the generated exciton emits energy to emit light.
  • the OLED is classified into an active-type and a passive-type according to a driving manner.
  • the active-matrix OLED (AMOLED) includes a thin film transistor (TFT) device per pixel to control the pixel.
  • the passive-matrix OLED (PMOLED) has a structure in that voltages are applied in horizontal and vertical directions to pixels where the directions intersect to supply power.
  • the PMOLED requires a high luminance at a unit pixel and has a short life-cycle and high power consumption, so that the PMOLED is generally applied to a low-cost product with a low resolution.
  • the AMOLED requires a very low luminance for a unit pixel by using the TFT and a memory function of a capacitor, so that the AMOLED is applied to a product such as a TV requiring a high resolution.
  • a luminance of a light emitting device of the AMOLED is controlled by a gradation current flowing across an OLED panel that is the light emitting device.
  • a frame time is divided into a plurality of sub-frames, light emitting times of the sub-frames are different from each other to differentiate weights of the sub-frames from each other, and the total amount of the current supplied to the OLED panel is differentiated, so that various gradations can be represented.
  • the video signal is represented by using only the gradation current having an analog gradation level. Therefore, a relatively high driving frequency is required.
  • the frame time is divided into 8 sub-frames including Hl to H8 by weights of the 256 gradations, and a time to supply the current to the OLED panel that is the light emitting device is controlled by dividing light emitted with a single light intensity (H) by time, so that luminances of the 256 gradations are represented.
  • the present invention provides a hybrid driving device and method of an active- matrix organic light emitting diode (AMOLED) using a multi-analog gradation current which uses a plurality of analog gradation current sources having a plurality of gradation values so as to enable a value of an intermediate gradation current for implementing a minimum gradation and a value of a maximum gradation current for implementing a maximum gradation to be different from each other, represents a desired gradation by increasing a frame on time of the intermediate gradation current which has a value smaller than the maximum gradation current, reduces a difference between driving frequencies of the maximum gradation and the minimum gradation, and significantly decreases a difference between frame on times, so as to prevent a false contour with a low driving frequency.
  • AMOLED active- matrix organic light emitting diode
  • the present invention also provides a hybrid driving device and method of an AMOLED panel using a multi-analog gradation current capable of reducing power consumption of a data driver which is a driving device by decreasing a driving frequency for representing the maximum gradation.
  • a hybrid driving device of an AMOLED (active-matrix organic light emitting diode) using a multi- analog gradation current including a scan driver through which pixels of an OLED panel are sequentially selected and a data driver applied with a gradation current representing a gradation of a video signal
  • the data driver includes: a multi- gradation current unit selectively supplying analog gradation currents having various gradation values; a region determination unit determining a sub-frame region to be lit up according to an image of the video signal to be represented; a gradation current switch performing a switching operation to select an analog gradation current having a different gradation value for implementing a light intensity in the determined sub- frame in the multi-gradation current unit; and a pulse- width generation unit generating and supplying a pulse- width for implementing a light intensity of the video signal according to the analog gradation current supplied to the OLED panel.
  • a hybrid driving method of an AMOLED panel using a multi-analog gradation current in which pixels of an OLED panel are sequentially selected and a gradation current for representing a gradation of a video signal is applied to emit light and display the video signal, including: a region dividing step of dividing a frame of a video signal displayed by the OLED panel into a first sub-frame region implemented by an intermediate gradation current and a second sub-frame region implemented by a maximum gradation current; a sub-frame selecting step of selecting a sub-frame region for emitting light to represent a corresponding gradation from the first and second sub- frame regions according to a gradation of the video signal; a gradation current switching step of performing a switching operation at a terminal of a multi-gradation current unit to apply an analog gradation current having a different gradation value to the selected sub-frame region to emit light; and a driving pulse generating step of individually controlling a
  • FIG. 2 is a view illustrating an embodiment of the hybrid driving device of the
  • AMOLED panel using the multi-analog gradation current according to the present invention is a MOLED panel using the multi-analog gradation current according to the present invention.
  • a hybrid driving device of an active-matrix organic light emitting diode (AMOLED) panel using a multi-analog gradation current includes an OLED panel 100 including the matrix of pixels, a scan driver 10 for sequentially inputting selection signals to the OLED panel, and a data driver 20 for applying a gradation current to a pixel selected by the selection signal.
  • AMOLED active-matrix organic light emitting diode
  • the data driver 20 includes a multi-gradation current unit 200 for selectively supplying analog gradation currents having various gradation values, a region determination unit 300 for determining a sub-frame region to be lit up according to an image of a video signal to be represented, a gradation current switch 400 for performing a switching operation on the gradation current to be transmitted to the determined sub-frame in the multi-gradation current unit 200, and a pulse- width generation unit 500 for generating and supplying a pulse- width of the gradation current supplied to the OLED panel.
  • a multi-gradation current unit 200 for selectively supplying analog gradation currents having various gradation values
  • a region determination unit 300 for determining a sub-frame region to be lit up according to an image of a video signal to be represented
  • a gradation current switch 400 for performing a switching operation on the gradation current to be transmitted to the determined sub-frame in the multi-gradation current unit 200
  • a pulse- width generation unit 500 for generating and supplying
  • a video signal having predetermined bits is divided into most significant bit (MSB) data and least significant bit (LSB) data, and a frame on time that is a time for which a frame is in an ON state is controlled by a ratio of weights of the datas, so that a gradation to be represented can be controlled by frame modulation for representing the gradation.
  • MSB most significant bit
  • LSB least significant bit
  • a video signal having 8 bits is implemented by using only a single intermediate gradation current M having a value that is half of the maximum gradation current H for frame modulation.
  • a number of intermediate gradation currents having various values may be included.
  • the hybrid driving method includes a region dividing step SlO of dividing regions of a sub-frame according to the total light intensity represented by the OLED panel, a sub-frame selecting step S20 of selecting a region of the sub-frame applied with a gradation current which is different according to a gradation of a video signal to be represented by the OLED panel, a gradation current switching step S30 of performing a switching operation to apply an analog gradation current which has a different gradation value according to the regions, a driving pulse generating step S40 of controlling a driving pulse so that the total light intensity implemented by each of the analog gradation currents is proper for the gradation of the video signal, and a pixel light emitting step S50 of displaying the video signal by a pixel which emits light for an applied time of the driving pulse.
  • a frame for representing a video signal is divided into the first sub-frame region LSB implemented by the intermediate gradation current M due to the low total light intensity and the second sub-frame region MSB implemented by the maximum gradation current H due to the high total light intensity.
  • the in- termediate gradation current may have current values obtained by decreasing the maximum gradation current by predetermined ratios.
  • the region determining unit 300 receives the video signal to be represented by the OLED panel from the input unit and selects one for representing a corresponding gradation from the first and second sub-frame regions LSB and MSB according to a gradation of the video signal.
  • the region determination unit 300 selects one from the sub-frame regions so that the video signal representing a low gradation is represented by the first sub-frame region LSB and the video signal representing a high gradation is represented by the second sub-frame region MSB.
  • both of the first and second sub-frame regions LSB and MSB may be selected so that light is emitted for a predetermined time by the driving pulses for controlling the analog gradation currents applied to the both sub-frames to represent the gradation.
  • the gradation current switch 400 connected to the terminal of the multi-gradation current unit 200 performs a switching operation so that an analog gradation current having a different gradation value is applied to the sub-frame region selected by the region determination unit 300.
  • the intermediate gradation current M is applied
  • the maximum gradation current H is applied.
  • both of the intermediate gradation current M and the maximum gradation current H are applied.
  • the pulse- width generation unit 500 since the gradation value of the analog gradation current supplied from the multi-gradation current unit 200 is different, the pulse- width generation unit 500 generates and supplies a width of a pulse for controlling a time to supply the gradation current to the gradation current switch 400 so that a light intensity that can represent the gradation of the video signal is displayed according to the value of the gradation current applied to the sub-frame region. Accordingly, after supplying the gradation current corresponding to the pulse- width, the gradation current switch 400 performs a switching operation to represent a gradation of a next frame.
  • the analog gradation current is supplied for a time corresponding to the pulse- width generated by the pulse- width generation unit 500, a pixel emits light for a supply time of the gradation current to display the video signal, and the gradation current switch 400 performs the switching operation to represent a gradation of a next frame.
  • an intermediate gradation current having a low gradation value and a maximum gradation current having a high gradation value are provided.
  • a frame for implementing a video signal is divided into a sub-frame region for emitting light by the intermediate gradation current and a sub-frame region for emitting light by the maximum gradation current, so as to emit light by using the different gradation values. Therefore, a driving frequency for representing a maximum gradation is decreased, and a difference between driving frequencies for implementing the minimum gradation and the maximum gradation can be significantly reduced, so that a false contour that may occur in a digital driving manner can be prevented and image quality can be significantly improved.

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  • Engineering & Computer Science (AREA)
  • Physics & Mathematics (AREA)
  • Computer Hardware Design (AREA)
  • General Physics & Mathematics (AREA)
  • Theoretical Computer Science (AREA)
  • Electroluminescent Light Sources (AREA)
  • Control Of El Displays (AREA)
  • Control Of Indicators Other Than Cathode Ray Tubes (AREA)

Abstract

Provided is a hybrid driving device and method of an active-matrix organic light emitting diode (AMOLED) panel using a digital driving manner, and more particularly, a hybrid driving device and method of an AMOLED panel using a multi-analog gradation current which includes a plurality of analog gradation current sources having a plurality of gradation values in an OLED panel and divides a frame into a sub-frame region implemented by a gradation current source having a low gradation value and a sub-frame region implemented by a gradation current source having a high gradation value to decrease a difference between a driving frequency for implementing a minimum gradation of a video signal and a driving frequency for implementing a maximum gradation thereof and prevent image quality degradation such as a false contour that may occur in the digital driving manner.

Description

Description
HYBRID DRIVING DEVICE AND METHOD OF AMOLED PANEL USING MULTI-ANALOG GRADATION CURRENT
Technical Field
[1] The present invention relates to a hybrid driving device and method of an active- matrix organic light emitting diode (AMOLED) panel using a digital driving manner, and more particularly, to a hybrid driving device and method of an AMOLED panel using a multi-analog gradation current which includes a plurality of analog gradation current sources having a plurality of gradation values in an OLED panel and divides a frame into a sub-frame region implemented by a gradation current source having a low gradation value and a sub-frame region implemented by a gradation current source having a high gradation value to decrease a difference between a driving frequency for implementing a minimum gradation of a video signal and a driving frequency for implementing a maximum gradation thereof and prevent image quality degradation such as a false contour that may occur in the digital driving manner. Background Art
[2] An organic light emitting diode (OLED) which has been used as a display device has good characteristics such as high-speed response and high luminance using organic materials emitting light. In addition, the OLED does not require a backlight and can be manufactured to be thinner than a liquid crystal display (LCD). In the OLED, an electron injected from an electrode and a hole injected from the other electrode are combined at an emissive layer disposed between the two electrodes to generate an exciton, and the generated exciton emits energy to emit light.
[3] As a voltage applied to both terminals of the OLED increases to be higher than a threshold voltage, a current flowing across the OLED increases, and an intensity of light emitted from the OLED is in proportion to the current.
[4] The OLED is classified into an active-type and a passive-type according to a driving manner. The active-matrix OLED (AMOLED) includes a thin film transistor (TFT) device per pixel to control the pixel. The passive-matrix OLED (PMOLED) has a structure in that voltages are applied in horizontal and vertical directions to pixels where the directions intersect to supply power.
[5] The PMOLED requires a high luminance at a unit pixel and has a short life-cycle and high power consumption, so that the PMOLED is generally applied to a low-cost product with a low resolution. On the other hand, the AMOLED requires a very low luminance for a unit pixel by using the TFT and a memory function of a capacitor, so that the AMOLED is applied to a product such as a TV requiring a high resolution. [6] A luminance of a light emitting device of the AMOLED is controlled by a gradation current flowing across an OLED panel that is the light emitting device. In order to control various luminances of a video signal using the gradation current, a frame time is divided into a plurality of sub-frames, light emitting times of the sub-frames are different from each other to differentiate weights of the sub-frames from each other, and the total amount of the current supplied to the OLED panel is differentiated, so that various gradations can be represented.
[7] As described above, in a conventional digital driving manner of representing various gradations by controlling a supply time of the gradation current, the video signal is represented by using only the gradation current having an analog gradation level. Therefore, a relatively high driving frequency is required. Specifically, as illustrated in FIG. 5, the frame time is divided into 8 sub-frames including Hl to H8 by weights of the 256 gradations, and a time to supply the current to the OLED panel that is the light emitting device is controlled by dividing light emitted with a single light intensity (H) by time, so that luminances of the 256 gradations are represented.
[8] Accordingly, in the sub-frame Hl representing a low luminance, light is emitted for a time calculated by dividing the total time by 255, and in the sub-frame H8 representing a high luminance, light is emitted for 128 times the time of the sub-frame Hl. As described above, a difference between the times to emit light in the sub-frames Hl and H8 is very large. Therefore, in order to smoothly represent the total gradations, a high driving frequency is required.
[9] Moreover, as a screen is enlarged and the number of gradations to be represented increases, the conventional digital driving manner using the single analog gradation current has a problem in that the driving frequency is increased exponentially.
[10] In addition, for frame modulation, since a difference between a frame on time of a minimum gradation and a frame on time of a maximum gradation is large, when a video is reproduced, a boundary of an original video signal cannot be generated and a false contour occurs in a portion where gradations are smoothly changed, so that there is a problem in that image quality is degraded. The false contour occurs when the driving frequency cannot deliver the changes in which signals having a high gradation and a low gradation are continuously changed.
[11] Accordingly, conventionally, in order to solve the aforementioned problem, as disclosed in Korean Patent Application Publication No. 10-2007-0077068, the frame on time of the maximum gradation at which the sub-frame is lit up in order to represent the maximum gradation is divided into several ones so that gradations having weights at intermediate levels are inserted into the frame on time of the maximum gradation to reduce a ratio of the maximum gradation to the minimum gradation. However, in this case, the number of sub-frames increases, and the driving frequency of the OLED panel is increased, so that there is a problem in that false contour prevention effects are not evident.
Disclosure of Invention
Technical Problem
[12] The present invention provides a hybrid driving device and method of an active- matrix organic light emitting diode (AMOLED) using a multi-analog gradation current which uses a plurality of analog gradation current sources having a plurality of gradation values so as to enable a value of an intermediate gradation current for implementing a minimum gradation and a value of a maximum gradation current for implementing a maximum gradation to be different from each other, represents a desired gradation by increasing a frame on time of the intermediate gradation current which has a value smaller than the maximum gradation current, reduces a difference between driving frequencies of the maximum gradation and the minimum gradation, and significantly decreases a difference between frame on times, so as to prevent a false contour with a low driving frequency.
[13] In addition, the present invention also provides a hybrid driving device and method of an AMOLED panel using a multi-analog gradation current capable of reducing power consumption of a data driver which is a driving device by decreasing a driving frequency for representing the maximum gradation. Technical Solution
[14] According to an aspect of the present invention, there is provided a hybrid driving device of an AMOLED (active-matrix organic light emitting diode) using a multi- analog gradation current, including a scan driver through which pixels of an OLED panel are sequentially selected and a data driver applied with a gradation current representing a gradation of a video signal, wherein the data driver includes: a multi- gradation current unit selectively supplying analog gradation currents having various gradation values; a region determination unit determining a sub-frame region to be lit up according to an image of the video signal to be represented; a gradation current switch performing a switching operation to select an analog gradation current having a different gradation value for implementing a light intensity in the determined sub- frame in the multi-gradation current unit; and a pulse- width generation unit generating and supplying a pulse- width for implementing a light intensity of the video signal according to the analog gradation current supplied to the OLED panel.
[15] In the above aspect of the present invention, the multi-gradation current unit may include a maximum gradation current source for representing a light intensity of the maximum gradation, an intermediate gradation current source for representing a light intensity lower than the maximum gradation, and a plurality of analog current sources having various analog gradation values.
[16] In addition, the sub-frame determined by the region determination unit may include a first sub-frame region in which a light intensity is implemented by the intermediate gradation current having a low gradation value corresponding to the light intensity that is half of the maximum gradation current and a second sub-frame region in which a light intensity is implemented by the maximum gradation current having the high gradation value, and the first sub-frame region for implementing the minimum gradation and the second sub-frame region for implementing the maximum gradation may be implemented by the analog gradation currents having different gradation current values from each other to decrease the maximum driving frequency for implementing the maximum gradation.
[17] According to another aspect of the present invention, there is provided a hybrid driving method of an AMOLED panel using a multi-analog gradation current in which pixels of an OLED panel are sequentially selected and a gradation current for representing a gradation of a video signal is applied to emit light and display the video signal, including: a region dividing step of dividing a frame of a video signal displayed by the OLED panel into a first sub-frame region implemented by an intermediate gradation current and a second sub-frame region implemented by a maximum gradation current; a sub-frame selecting step of selecting a sub-frame region for emitting light to represent a corresponding gradation from the first and second sub- frame regions according to a gradation of the video signal; a gradation current switching step of performing a switching operation at a terminal of a multi-gradation current unit to apply an analog gradation current having a different gradation value to the selected sub-frame region to emit light; and a driving pulse generating step of individually controlling a supply time of the analog gradation current by controlling a width of a driving pulse to represent the grade corresponding to the video signal. Brief Description of the Drawings
[18] FIG. 1 is a block diagram illustrating a hybrid driving device of an active-matrix organic light emitting diode (AMOLED) panel using a multi-analog gradation current according to the present invention.
[19] FIG. 2 is a view illustrating an embodiment of the hybrid driving device of the
AMOLED panel using the multi-analog gradation current according to the present invention.
[20] FIG. 3 is a flowchart of a hybrid driving method used in the AMOLED panel using the multi-analog gradation current according to the present invention.
[21] FIG. 4 is a view illustrating frames used in the driving method using the multi-analog gradation current according to the present invention. [22] FIG. 5 is a view illustrating frames used in a conventional driving method using a single analog gradation current. Best Mode for Carrying Out the Invention
[23] Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the attached drawings.
[24] A hybrid driving device of an active-matrix organic light emitting diode (AMOLED) panel using a multi-analog gradation current according to an embodiment of the present invention includes an OLED panel 100 including the matrix of pixels, a scan driver 10 for sequentially inputting selection signals to the OLED panel, and a data driver 20 for applying a gradation current to a pixel selected by the selection signal. The data driver 20 includes a multi-gradation current unit 200 for selectively supplying analog gradation currents having various gradation values, a region determination unit 300 for determining a sub-frame region to be lit up according to an image of a video signal to be represented, a gradation current switch 400 for performing a switching operation on the gradation current to be transmitted to the determined sub-frame in the multi-gradation current unit 200, and a pulse- width generation unit 500 for generating and supplying a pulse- width of the gradation current supplied to the OLED panel.
[25] Here, the driving device of the AMOLED panel does not control a light intensity of the AMOLED panel to enable a human to feel the light intensity. Instead, the driving device has a light intensity having the maximum gradation value and supplies a maximum gradation current by dividing a time for the OLED panel to emit light by a predetermined number in a digital driving manner so as to enable a viewer to feel dark or bright.
[26] In addition, in the digital driving method, a video signal having predetermined bits is divided into most significant bit (MSB) data and least significant bit (LSB) data, and a frame on time that is a time for which a frame is in an ON state is controlled by a ratio of weights of the datas, so that a gradation to be represented can be controlled by frame modulation for representing the gradation.
[27] The multi-gradation current unit 200 includes a plurality of analog current supply sources 201, 202, and 203 having various analog current values. Here, as illustrated in FIG. 2, the analog gradation current includes a maximum gradation current source H for representing a light intensity of the maximum gradation and one or more intermediate gradation current sources M for emitting light having an intensity lower than the maximum gradation current.
[28] Here, when a gradation current is reduced, a light emitting time is increased to achieve a light intensity represented by the maximum gradation current H. Therefore, the intermediate gradation current M may have a value obtained by dividing the maximum gradation current H by a predetermined ratio.
[29] According to the embodiment, as illustrated in FIG. 4, in order to represent 256 gradations, a video signal having 8 bits is implemented by using only a single intermediate gradation current M having a value that is half of the maximum gradation current H for frame modulation. However, when the number of gradations to be represented is increased or the OLED panel is enlarged, a number of intermediate gradation currents having various values may be included. As described above, when a number of the intermediate gradation currents are included, values of the intermediate gradation currents may be obtained by decreasing the maximum gradation current by predetermined ratios of 1/2, 1/4, 1/6, and the like so that the light intensity represented by the maximum gradation current can be easily achieved by increasing light emitting times two times, four times, six times, and the like.
[30] The region determination unit 300 is connected to a video signal input unit 600 to determine a region on a sub-frame for emitting light by using image information on a video signal to be represented. Here, according to the embodiment, the sub-frame is divided into a first sub-frame region (referred to as LSB 4bit) in which a light intensity is implemented by using the intermediate gradation current M having a low gradation value corresponding to the half of the light intensity of the maximum gradation current and a second sub-frame region (referred to as MSB 4bit) in which a light intensity is implemented by the maximum gradation current H having a high gradation value, and a region is determined by perceiving a gradation value of the video signal applied to the video signal input unit 600.
[31] A terminal of the gradation current switch 400 is connected to the region determination unit 300 and another terminal thereof is connected to each of a number of the current sources included in the multi-gradation current unit 200 to perform the switching operation so that the gradation current switch 400 easily selects a gradation current to be transmitted to the first or second sub-frame region according to a result of the determination of the region determination unit 300.
[32] Accordingly, the gradation current switch 400 turns the intermediate gradation current source M on when the video signal has a gradation to be implemented by the first sub-frame region according to the result of the determination of the region determination unit 300 and turns the maximum gradation current source H on when the video signal has a gradation to be implemented by the second sub-frame region, so as to supply different analog currents to the regions.
[33] The pulse- width generation unit 500 generates and supplies pulses having different pulse- widths for controlling supply times of the gradation currents transmitted to the sub-frame regions in order to accurately implement the light intensity of the video signal in the OLED panel. [34] Here, since the first sub-frame region LSB emits light by using the intermediate gradation current source having the low gradation value, the first sub-frame region has to be constructed to have a pulse-width capable of increasing a supply time so that the total intensity of the emitted light achieves a desired light intensity.
[35] Accordingly, in the first sub-frame region LSB, relatively lower gradations Ml, M2,
M3, and M4 are implemented by the intermediate gradation currents M, and in the second sub-frame region MSB, higher gradations Hl, H2, H3, and H4 are implemented by changing the supplied analog current.
[36] As described above, the first sub-frame region LSB representing low gradations and the second sub-frame region MSB representing high gradations are implemented by different analog current sources, and a width of a pulse applied to the intermediate gradation current M having the low gradation current value is increased, so that a difference between driving frequencies consumed to implement the minimum gradation and the maximum gradation can be decreased.
[37] According to the embodiment, a time difference between the minimum gradation and the maximum gradation is 8 times while a time difference between the minimum gradation and the maximum gradation is 128 times when the conventional analog gradation current having a single value is used. Accordingly, without adding sub- frames or increasing the driving frequency, image quality degradation such as a false contour can be solved.
[38] Next, a hybrid driving method used in the AMOLED using the multi-analog gradation current configured as described above according to the present invention will be described in detail with reference to FIG. 3.
[39] The hybrid driving method includes a region dividing step SlO of dividing regions of a sub-frame according to the total light intensity represented by the OLED panel, a sub-frame selecting step S20 of selecting a region of the sub-frame applied with a gradation current which is different according to a gradation of a video signal to be represented by the OLED panel, a gradation current switching step S30 of performing a switching operation to apply an analog gradation current which has a different gradation value according to the regions, a driving pulse generating step S40 of controlling a driving pulse so that the total light intensity implemented by each of the analog gradation currents is proper for the gradation of the video signal, and a pixel light emitting step S50 of displaying the video signal by a pixel which emits light for an applied time of the driving pulse.
[40] In the region dividing step SlO, a frame for representing a video signal is divided into the first sub-frame region LSB implemented by the intermediate gradation current M due to the low total light intensity and the second sub-frame region MSB implemented by the maximum gradation current H due to the high total light intensity. Here, the in- termediate gradation current may have current values obtained by decreasing the maximum gradation current by predetermined ratios.
[41] In the sub-frame selecting step S20, the region determining unit 300 receives the video signal to be represented by the OLED panel from the input unit and selects one for representing a corresponding gradation from the first and second sub-frame regions LSB and MSB according to a gradation of the video signal. Here, the region determination unit 300 selects one from the sub-frame regions so that the video signal representing a low gradation is represented by the first sub-frame region LSB and the video signal representing a high gradation is represented by the second sub-frame region MSB.
[42] In addition, according to the gradation of the video signal to be represented, both of the first and second sub-frame regions LSB and MSB may be selected so that light is emitted for a predetermined time by the driving pulses for controlling the analog gradation currents applied to the both sub-frames to represent the gradation.
[43] In the gradation current switching step S30, the gradation current switch 400 connected to the terminal of the multi-gradation current unit 200 performs a switching operation so that an analog gradation current having a different gradation value is applied to the sub-frame region selected by the region determination unit 300. Specifically, for a video signal having a gradation to be implemented by the first sub- frame region LSB, the intermediate gradation current M is applied, and for a video signal having a gradation to be implemented by the second sub-frame region MSB, the maximum gradation current H is applied. For a video having a grade to be implemented by both of the first and second sub-frame regions LSB and MSB, both of the intermediate gradation current M and the maximum gradation current H are applied.
[44] In the driving pulse generation step S40, since the gradation value of the analog gradation current supplied from the multi-gradation current unit 200 is different, the pulse- width generation unit 500 generates and supplies a width of a pulse for controlling a time to supply the gradation current to the gradation current switch 400 so that a light intensity that can represent the gradation of the video signal is displayed according to the value of the gradation current applied to the sub-frame region. Accordingly, after supplying the gradation current corresponding to the pulse- width, the gradation current switch 400 performs a switching operation to represent a gradation of a next frame.
[45] In the pixel light emitting step S50, the analog gradation current is supplied for a time corresponding to the pulse- width generated by the pulse- width generation unit 500, a pixel emits light for a supply time of the gradation current to display the video signal, and the gradation current switch 400 performs the switching operation to represent a gradation of a next frame.
[46] While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the present invention as defined by the appended claims. Industrial Applicability
[47] According to the present invention, an intermediate gradation current having a low gradation value and a maximum gradation current having a high gradation value are provided. A frame for implementing a video signal is divided into a sub-frame region for emitting light by the intermediate gradation current and a sub-frame region for emitting light by the maximum gradation current, so as to emit light by using the different gradation values. Therefore, a driving frequency for representing a maximum gradation is decreased, and a difference between driving frequencies for implementing the minimum gradation and the maximum gradation can be significantly reduced, so that a false contour that may occur in a digital driving manner can be prevented and image quality can be significantly improved.
[48] In addition, by decreasing the driving frequency for representing the maximum gradation, power consumption of a data driver can be reduced. In addition, by decreasing a ratio of frame on times of the maximum gradation to the minimum gradation, image quality can be improved.

Claims

Claims
[1] A hybrid driving device of an AMOLED (active-matrix organic light emitting diode) using a multi-analog gradation current, including a scan driver through which pixels of an OLED panel are sequentially selected and a data driver applied with a gradation current representing a gradation of a video signal, wherein the data driver includes: a multi-gradation current unit selectively supplying analog gradation currents having various gradation values; a region determination unit determining a sub-frame region to be lit up according to an image of the video signal to be represented; a gradation current switch performing a switching operation to select an analog gradation current having a different gradation value for implementing a light intensity in the determined sub-frame in the multi-gradation current unit; and a pulse-width generation unit generating and supplying a pulse- width for implementing a light intensity of the video signal according to the analog gradation current supplied to the OLED panel.
[2] The hybrid driving device of claim 1, wherein the multi-gradation current unit includes a maximum gradation current source for representing a light intensity of the maximum gradation, an intermediate gradation current source for representing a light intensity lower than the maximum gradation, and a plurality of analog current sources having various analog gradation values.
[3] The hybrid driving device of claim 2, wherein an intermediate gradation current supplied from the intermediate gradation current source has a value obtained by decreasing the maximum gradation current supplied from the maximum gradation current source by a predetermined ratio.
[4] The hybrid driving device of claim 3, wherein the sub-frame determined by the region determination unit includes a first sub-frame region in which a light intensity is implemented by the intermediate gradation current having a low gradation value corresponding to the light intensity that is half of the maximum gradation current and a second sub- frame region in which a light intensity is implemented by the maximum gradation current having the high gradation value, and wherein the first sub-frame region for implementing the minimum gradation and the second sub-frame region for implementing the maximum gradation are implemented by the analog gradation currents having different gradation current values from each other to decrease the maximum driving frequency for implementing the maximum gradation.
[5] A hybrid driving method of an AMOLED panel using a multi-analog gradation current in which pixels of an OLED panel are sequentially selected and a gradation current for representing a gradation of a video signal is applied to emit light and display the video signal, including: a region dividing step of dividing a frame of a video signal displayed by the OLED panel into a first sub-frame region implemented by an intermediate gradation current and a second sub-frame region implemented by a maximum gradation current; a sub-frame selecting step of selecting a sub-frame region for emitting light to represent a corresponding gradation from the first and second sub-frame regions according to a gradation of the video signal; a gradation current switching step of performing a switching operation at a terminal of a multi-gradation current unit to apply an analog gradation current having a different gradation value to the selected sub-frame region to emit light; and a driving pulse generating step of individually controlling a supply time of the analog gradation current by controlling a width of a driving pulse to represent the grade corresponding to the video signal.
[6] The hybrid driving method of claim 5, wherein in the gradation current switching step, a gradation current is applied from an intermediate gradation current source when the video signal has a gradation to be implemented at the first sub-frame region, a gradation current is applied from a maximum gradation current source when the video signal has a gradation to be implemented at the second sub-frame region, and gradation currents are applied from the intermediate gradation current source and the maximum gradation current source when the video signal has a grade to be implemented at both of the first and second sub-frame regions.
PCT/KR2008/001003 2007-12-24 2008-02-21 Hybrid driving device and method of amoled panel using multi-analog gradation current WO2009082056A1 (en)

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