Liquid crystal display device, driving control circuit and driving method used in same device

• US 7,952,556 B2
• Filed: 07/09/2007
• Issued: 05/31/2011
• Est. Priority Date: 07/10/2006
• Status: Active Grant

• Current Assignee: NLT Technologies, Ltd.
• Original Assignee: NEC LCD Technologies Limited (Tianma Microelectronics Company Limited)
• Inventors: Honbo, Nobuaki
• Primary Examiner(s): Hjerpe; Richard
• Assistant Examiner(s): Parker; Jeffrey
• Application Number:
  US11/775,009
• Publication Number:
  US 20080007512A1
• Time in Patent Office: 1,422 Days
• Field of Search: 345/102, 345 87- 90, 345/94
• US Class Current: 345/102
• CPC Class Codes: G09G 2310/0245 Clearing or presetting the whole screen independently of waveforms, e.g. on power-on G09G2310/063 takes precedence
• CPC Class Codes: G09G 2320/0646 Modulation of illumination source brightness and image signal correlated to each other
• CPC Class Codes: G09G 3/3406 Control of illumination source illumination devices structurally associated with liquid crystal cells G02F1/1336
• CPC Class Codes: G09G 3/3648 using an active matrix G09G3/367 - G09G3/3696 take precedence

Abstract

A liquid crystal display device capable of improving quality of moving images is provided. Each LED (Light Emitting Diode) block is turned ON according to a response of a liquid crystal corresponding to a light emitting region and the brightest gray level is detected for each of red (R), green (G) and blue (B) of an input video signal in every frame period and an input video signal is converted into a value obtained by being multiplied by an upper limit gray level and then by being divided by the brightest gray level and a gray level voltage corresponding to the converted value is applied to each data electrode and, during a lighting period of LED blocks, each LED block is made to flash at a duty corresponding to a rate of the brightest gray level to the upper limit gray level.

Claims

1. A liquid crystal display device comprising:

a liquid crystal display panel;

a backlight; and

a driving control unit;

wherein said liquid crystal display panel displays images corresponding to an input video signal by a driving operation of each of scanning electrodes and each of data electrodes by which a specified gray level voltage is applied to a corresponding pixel region and a response of a liquid crystal is controlled in the pixel region according to the applied gray level voltage;

wherein said backlight illuminates the liquid crystal display panel from its rear side; and

wherein said driving control unit turns off said backlight during a frame period of said input video signal in which an upper limit gray level for each of red (R), green (G), and blue (B) is set until the liquid crystal shows a response to the application of said specified gray level voltage in said pixel region and turns on said backlight at a point of time when the liquid crystal has shown a response and detects a brightest gray level for each of the R, G, and B of said input video signal in every frame period and converts a gray level for each of the R, G, and B of said input video signal into a value which is given by a following equation, whereby the detected brightest gray level and the corresponding upper limit gray level become at a same level, and the gray level voltage corresponding to the converted value is applied to the corresponding pixel region and, during a lighting period of said backlight, makes said backlight flash at a duty corresponding to a rate of said brightest gray level to the corresponding upper limit gray level;

a value =[the gray level for each of R, G, and B of the input video signal]×

[the corresponding upper limit gray level]÷

[the detected brightest gray level] 

 

(equation).

2. The liquid crystal display device according to claim 1, wherein the data electrodes of said liquid crystal display panel are arranged in parallel to one another at specified intervals along a first direction and the scanning electrodes are arranged in parallel to one another at specified intervals along a second direction orthogonal to said first direction and wherein said backlight comprises a plurality of light source blocks whose light emitting region is divided into m (“

m”

is an integer being 1 or more) portions in said first direction of said liquid crystal display device and into k (“

k”

is an integer being 2 or more) portions in said second direction and wherein said driving control unit turns on the light source blocks during a specified period according to a response of the liquid crystal corresponding to the light emitting region of each of said light source blocks and detects a brightest gray level for each of the R, G, and B of said input video signal in each frame period in a manner to correspond to each of the light source blocks and converts a gray level of said input video signal so that the detected brightest gray level and said upper limit gray level become at a same level and, during a lighting period of said light source blocks, makes said backlight flash at a duty corresponding to a rate of said brightest gray level to said upper limit gray level.

3. The liquid crystal display device according to claim 1, wherein said backlight comprises LEDs (Light Emitting Diodes) of, each at least, the R, G, and B.

4. The liquid crystal display device according to claim 1, wherein said point of time when the liquid crystal has shown a response is set to be a first point of time when approximately up to 70% of the liquid crystals have shown a response or to be a second point of time after said first point.

5. The liquid crystal display device according to claim 1, wherein said driving control unit performs an overdriving operation to said pixel region in every frame period.

6. The liquid crystal display device according to claim 1, wherein said driving control unit divides each frame of said input video signal input at a specified frame frequency into M (“

M”

is an integer being 2 or more) pieces of sub-frames having a sub-frame frequency M times higher than said frame frequency and performs an overdriving operation on the corresponding pixel region in the first sub-frame in every frame period and performs an ordinary driving operation in the second and thereafter sub-frames.

7. The liquid crystal display device according to claim 1, wherein said driving control unit turns on said backlight N (“

N”

is an integer being 2 or more) times at specified intervals in every frame period.

8. A liquid crystal display device comprising:

a liquid crystal display panel;

a backlight; and

a driving control unit;

wherein said liquid crystal display panel displays images corresponding to an input video signal by a driving operation of each of scanning electrodes and each of data electrodes by which a specified gray level voltage is applied to a corresponding pixel region and a response of a liquid crystal is controlled in the pixel region according to the applied gray level voltage;

wherein said backlight illuminates the liquid crystal display panel from its rear side; and

wherein said driving control unit turns off said backlight during a frame period of said input video signal in which an upper limit gray level for each of red (R), green (G), and blue (B) is set until the liquid crystal shows a response to the application of said specified gray level voltage in said pixel region and turns on said backlight at a point of time when the liquid crystal has shown a response and detects an average value of gray levels within a specified range including the brightest gray level for each of the R, G, and B of said input video signal in every frame period in a manner to correspond to each of the light source blocks and converts a gray level for each of the R, G, and B of said input video signal into a value which is given by a following equation, whereby the detected average value of gray levels and the corresponding upper limit gray level become at a same level, and the gray level voltage corresponding to the converted value is applied to the corresponding pixel region and, during a lighting period of said backlight, makes said backlight flash at a duty corresponding to a rate of said average value to the corresponding upper limit gray level;

a value =[the gray level for each of R, G, and B of the input video signal]×

[the corresponding upper limit gray level]±

[the detected brightest gray level] 

 

(equation).

9. The liquid crystal display device according to claim 8, wherein the data electrodes of said liquid crystal display panel are arranged in parallel to one another at specified intervals along a first direction and the scanning electrodes are arranged in parallel to one another at specified intervals along a second direction orthogonal to said first direction and wherein said backlight comprises a plurality of light source blocks whose light emitting region is divided into m (“

m”

is an integer being 1 or more) portions in said first direction of said liquid crystal display device and into k (“

k”

is an integer being 2 or more) portions in said second direction and wherein said driving control unit turns on the light source blocks during a specified period according to a response of the liquid crystal corresponding to a light emitting region of each of said light source blocks and detects an average value of gray levels within a specified range including a brightest gray level for each of the R, G, and B of said input video signal in every frame period in a manner to correspond to each of said light source blocks and converts a gray level of said input video signal so that the detected average value of gray levels and said upper limit gray levels become at a same level and, during a lighting period of said backlight, makes said backlight flash at a duty corresponding to a rate of said average value to said upper limit gray level.

10. The liquid crystal display device according to claim 8, wherein an average value of said gray levels is obtained by detecting gray levels corresponding to pixels within a specified range and by averaging values resulting from the detection, using a pixel having the brightest gray level in every frame period as a reference.

11. The liquid crystal display device according to claim 8, wherein said backlight comprises LEDs (Light Emitting Diodes) of, each at least, the R, G, and B.

12. The liquid crystal display device according to claim 8, wherein said point of time when the liquid crystal has shown a response is set to be a first point of time when approximately up to 70% of the liquid crystals have shown a response or to be a second point of time after said first point.

13. The liquid crystal display device according to claim 8, wherein said driving control unit performs an overdriving operation to said pixel region in every frame period.

14. The liquid crystal display device according to claim 8, wherein said driving control unit divides each frame of said input video signal input at a specified frame frequency into M (“

M”

is an integer being 2 or more) pieces of sub-frames having a sub-frame frequency M times higher than said frame frequency and performs an overdriving operation on the corresponding pixel region in the first sub-frame in every frame period and performs an ordinary driving operation in the second and thereafter sub-frames.

15. The liquid crystal display device according to claim 8, wherein said driving control unit turns on said backlight N (“

N”

is an integer being 2 or more) times at specified intervals in every frame period.

16. A driving control circuit to be used in a liquid crystal display device comprising a liquid crystal display panel to display images corresponding to an input video signal by a driving operation of each of scanning electrodes and each of data electrodes by which a specified gray level voltage is applied to a corresponding pixel region and a response of a liquid crystal is controlled in the pixel region according to the applied gray level voltage and a backlight to illuminate the liquid crystal display panel from its rear side, said driving control circuit comprising:

components to turn off said backlight during a frame period of said input video signal in which an upper limit gray level for each of red (R), green (G), and blue (B) is set until the liquid crystal shows a response to the application of said specified gray level voltage in said pixel region and to turn on said backlight at a point of time when the liquid crystal has shown a response and to detect a brightest gray level for each of the R, G, and B of said input video signal in the frame period and to convert a gray level for each of the R, G, and B of said input video signal into a value which is given by a following equation, whereby the detected brightest gray level and the corresponding upper limit gray level become at a same level, and to apply the gray level voltage corresponding to the converted value to the corresponding pixel region and, during a lighting period of said backlight, to make said backlight flash at a duty corresponding to a rate of said brightest gray level to the corresponding upper limit gray level;

a value =[the gray level for each of R, G, and B of the input video signal]×

[the corresponding upper limit gray level]×

[the detected brightest gray level] 

 

(equation).

17. The driving control circuit according to claim 16, wherein the data electrodes of said liquid crystal display panel are arranged in parallel to one another at specified intervals along a first direction and the scanning electrodes are arranged in parallel to one another at specified intervals along a second direction orthogonal to said first direction and wherein said backlight comprises a plurality of light source blocks whose light emitting region is divided into m (“

m”

is an integer being 1 or more) portions in said first direction of said liquid crystal display device and into k (“

k”

is an integer being 2 or more) portions in said second direction and wherein said components further turns on the light source blocks during a specified period according to a response of the liquid crystal corresponding to a light emitting region of each of said light source blocks and detects a brightest gray level for each of the R, G, and B of said input video signal in every frame period in a manner to correspond to each of said light source blocks and converts a gray level of said input video signal so that the detected brightest gray level and said upper limit gray level become at a same level and, during a lighting period of said light source blocks, makes said backlight flash at a duty corresponding to a rate of said brightest gray level to said upper limit gray level.

18. The driving control circuit according to claim 16, wherein said driving control circuit comprises one integrated circuit.

19. A driving control circuit to be used in a liquid crystal display device comprising a liquid crystal display panel to display images corresponding to an input video signal by a driving operation of each of scanning electrodes and each of data electrodes by which a specified gray level voltage is applied to a corresponding pixel region and a response of a liquid crystal is controlled in the pixel region according to the applied gray level voltage and a backlight to illuminate the liquid crystal display panel from its rear side, said driving control circuit comprising:

components to turn off said backlight during a frame period of said input video signal in which an upper limit gray level for each of red (R), green (G), and blue (B) is set until the liquid crystal shows a response to the application of said specified gray level voltage in said pixel region and to turn on said backlight at a point of time when the liquid crystal has shown a response and to detect an average value of gray levels within a specified range including a brightest gray level for each of the R, G, and B of said input video signal in each frame period in a manner to correspond to each of said light source blocks and to convert a gray level for each of the R, G and B of said input video signal into a value which is given by a following equation, whereby the detected average value of gray levels and the corresponding upper limit gray levels become at a same level, and to apply the gray level voltage corresponding to the converted value to the corresponding pixel region and, during a lighting period of said backlight, to make said backlight flash at a duty corresponding to a rate of said average value to the corresponding upper limit gray level;

a value =[the gray level for each of R, G, and B of the input video signal]×

[the corresponding upper limit gray level]÷

[the detected brightest gray level] 

 

(equation).

20. The driving control circuit according to claim 19, wherein the data electrodes of said liquid crystal display panel are arranged in parallel to one another at specified intervals along a first direction and the scanning electrodes are arranged in parallel to one another at specified intervals along a second direction orthogonal to said first direction and wherein said backlight comprises a plurality of light source blocks whose light emitting region is divided into m (“

m”

is an integer being 1 or more) portions in said first direction of said liquid crystal display device and into k (“

k”

is an integer being 2 or more) portions in said second direction and wherein said components turn on the light source blocks during a specified period according to a response of the liquid crystal corresponding to a light emitting region of each of said light source blocks and detect an average value of gray levels within a specified range including a brightest gray level for each of the R, G, and B of said input video signal in every frame period in a manner to correspond to each of said light source blocks and convert a gray level of said input video signal so that the detected average value of gray levels and said upper limit gray levels become at a same level and, during a lighting period of said backlight, make said backlight flash at a duty corresponding to a rate of said average value to said upper limit gray level.

21. The driving control circuit according to claim 19, wherein said driving control circuit comprises one integrated circuit.

22. A driving method to be used to be used in a liquid crystal display device comprising a liquid crystal display panel to display images corresponding to an input video signal by a driving operation of each of scanning electrodes and each of data electrodes by which a specified gray level voltage is applied to a corresponding pixel region and a response of a liquid crystal is controlled in the pixel region according to the applied gray level voltage and a backlight to illuminate the liquid crystal display panel from its rear side, said driving method comprising:

turning off said backlight during a frame period of said input video signal in which an upper limit gray level for each of red (R), green (G), and blue (B) is set until the liquid crystal shows a response to the application of said specified gray level voltage in said pixel region, turning on said backlight at a point of time when the liquid crystal has shown a response, detecting a brightest gray level for each of the R, G, and B of said input video signal in the frame period, converting a gray level for each of the R, G, and B of said input video signal into a value which is given by a following equation, whereby the detected brightest gray level and the corresponding upper limit gray level become at a same level, applying the gray level voltage corresponding to the converted value to the corresponding pixel region and, during a lighting period of said backlight, making said backlight flash at a duty corresponding to a rate of said brightest gray level to the corresponding upper limit gray level;

a value =[the gray level for each of R, G, and B of the input video signals]×

[the corresponding upper limit gray level]÷

[the detected brightest gray level] 

 

(equation).

23. The driving method according to claim 22, wherein the data electrodes of said liquid crystal display panel are arranged in parallel to one another at specified intervals along a first direction and the scanning electrodes are arranged in parallel to one another at specified intervals along a second direction orthogonal to said first direction and wherein said backlight comprises a plurality of light source blocks whose light emitting region is divided into m (“

m”

is an integer being 1 or more) portions in said first direction of said liquid crystal display device and into k (“

k”

is an integer being 2 or more) portions in said second direction and wherein said driving method further comprises steps of turning on the light source blocks during a specified period according to a response of the liquid crystal corresponding to a light emitting region of each of said light source blocks, of detecting a brightest gray level for each of the R, G, and B of said input video signal in each frame period in a manner to correspond to each of said light source blocks, of converting a gray level of said input video signal so that the detected brightest gray level and said upper limit gray level become at a same level and, during a lighting period of said light source blocks, and of making said backlight flash at a duty corresponding to a rate of said brightest gray level to said upper limit gray level.

24. A driving method to be used in a liquid crystal display device comprising a liquid crystal display panel to display images corresponding to an input video signal by a driving operation of each of scanning electrodes and each of data electrodes by which a specified gray level voltage is applied to a corresponding pixel region and a response of a liquid crystal is controlled in the pixel region according to the applied gray level voltage and a backlight to illuminate the liquid crystal display panel from its rear side, said driving method comprising:

turning off said backlight during a frame period of said input video signal in which an upper limit gray level for each of red (R), green (G), and blue (B) is set until the liquid crystal shows a response to the application of said specified gray level voltage in said pixel region, turning on said backlight at a point of time when the liquid crystal has shown a response, detecting an average value of gray levels within a specified range including a brightest gray level for each of the R, G, and B of said input video signal in every frame period in a manner to correspond to each of said light source blocks, converting a gray level for each of the R, G, and B of said input video signal into a value which is given by a following equation, whereby the detected average value of gray levels and the corresponding upper limit gray levels become at a same level, applying the gray level voltage corresponding to the converted value to the corresponding pixel region and, during a lighting period of said backlight, and making said backlight flash at a duty corresponding to a rate of said average value to the corresponding upper limit gray level;

a value =[the gray level for each of R, G, and B of the input video signal]×

[the corresponding upper limit gray level]÷

[the detected brightest gray level] 

 

(equation).

25. The driving method according to claim 24, wherein the data electrodes of said liquid crystal display panel are arranged in parallel to one another at specified intervals along a first direction and the scanning electrodes are arranged in parallel to one another at specified intervals along a second direction orthogonal to said first direction and wherein said backlight comprises a plurality of light source blocks whose light emitting region is divided into m (“

m”

is an integer being 1 or more) portions in said first direction of said liquid crystal display device and into k (“

k”

is an integer being 2 or more) portions in said second direction and wherein said driving method comprises steps of turning on the light source blocks during a specified period according to a response of the liquid crystal corresponding to a light emitting region of each of said light source blocks, of detecting an average value of gray levels within a specified range including a brightest gray level for each of the R, G, and B of said input video signal in every frame period in a manner to correspond to each of said light source blocks, of converting a gray level of said input video signal so that the detected average value of gray levels and said upper limit gray levels become at a same level and, during a lighting period of said backlight, and of making said backlight flash at a duty corresponding to a rate of said average value to said upper limit gray level.