Liquid crystal display

• US 20060208998A1
• Filed: 12/16/2002
• Published: 09/21/2006
• Est. Priority Date: 12/16/2002
• Status: Active Grant

• Current Assignee: Panasonic Liquid Crystal Display Company Limited (Panasonic Holdings Corporation)
• Original Assignee: Panasonic Liquid Crystal Display Company Limited (Panasonic Holdings Corporation)
• Inventors: Komatsu, Masaaki, Aono, Yoshinori, Okishiro, Kenji, Shiiki, Masatoshi
• Granted Patent: US 7,916,115 B2
• Time in Patent Office: Days
• US Class Current: 345/102
• CPC Class Codes: G02F 1/133601 for spatial active dimming
• CPC Class Codes: G02F 1/133622 Colour sequential illumination
• CPC Class Codes: G09G 2310/0221 with use of split matrices G09G3/3644 and G09G3/3666 take precedence
• CPC Class Codes: G09G 2310/0237 Switching ON and OFF the backlight within one frame
• CPC Class Codes: G09G 2310/024 Scrolling of light from the illumination source over the display in combination with the scanning of the display screen
• CPC Class Codes: G09G 2310/0251 Precharge or discharge of pixel before applying new pixel voltage
• CPC Class Codes: G09G 2310/066 Waveforms comprising a gently increasing or decreasing portion, e.g. ramp
• CPC Class Codes: G09G 2310/08 Details of timing specific for flat panels, other than clock recovery
• CPC Class Codes: G09G 2320/0242 Compensation of deficiencies in the appearance of colours
• CPC Class Codes: G09G 2320/0261 in the context of movement of objects on the screen or movement of the observer relative to the screen
• CPC Class Codes: G09G 3/2011 by amplitude modulation
• 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
• CPC Class Codes: G09G 3/3666 with the matrix divided into sections

Abstract

A liquid crystal display including a blink backlight system light source and a liquid crystal panel for adjusting the amount of light transmitted from the light source. The light source is made of a plurality of light emitting tubes each having one or more kinds of phosphors, and having a turned-on state and a turned-off state within one frame. A luminance factor area of light from each of the phosphors is substantially equal to that of light from any other phosphor in at least one of a luminance rise time when the light source changes from the turned-off state to the turned-on state and a luminance fall time when the light source changes from the turned-on state to the turned-off state.

Claims

1. A liquid crystal display comprising:

a light source made of a plurality of light emitting tubes each having one or more kinds of phosphors, and having a turned-on state and a turned-off state within one frame; and

a liquid crystal panel for adjusting the amount of light transmitted from said light source;

wherein a luminance factor area of light from each of said phosphors or a change in luminance factor per time of said light is substantially equal to that of light from any other phosphor in at least one of a luminance rise time when said light source changes from said turned-off state to said turned-on state and a luminance fall time when said light source changes from said turned-on state to said turned-off state.

2. A liquid crystal display according to claim 1, wherein said light source is made of light emitting tubes of one kind, and each of said light emitting tubes is a multicolor light emitting tube having three or more kinds of phosphors.

3. A liquid crystal display according to claim 1, wherein luminance of said phosphors is controlled by a current value of a current applied to each of said light emitting tubes.

4. A liquid crystal display according to claim 3, wherein at the beginning of said luminance rise time, said current value of said current applied to said light emitting tube is a current value I₂ not smaller than a current value I₁ necessary for said phosphors to emit light with predetermined luminance in one frame.

5. A liquid crystal display according to claim 4, wherein a time Δ

t_OD when said current value I₂ not smaller than said current value I₁ necessary for said phosphors to emit light with said predetermined luminance is applied to said light emitting tube, a ratio N of said current value I₂ to said current value I₁, and a rise response time τ

_on of a fastest luminance response phosphor of said phosphors belonging to said light emitting tube, satisfy a relationship of Expression 1;

Δ

t_OD≦

{−

τ

_on/ln 10}×

(1−

1/N) 

 

(Expression

     1)

where N=I₂/I₁.

6. A liquid crystal display according to claim 5, wherein said ratio N of said current value I₂ to said current value I₁ is larger than 1 and smaller than 6.5.

7. A liquid crystal display according to claim 2, wherein a current value of a current applied to each of said light emitting tubes is increased stepwise in said luminance rise time.

8. A liquid crystal display according to claim 7, wherein a step time width Δ

t_step of said current whose current value is increased stepwise is set to be shorter than a luminance rise response time of a slow luminance response phosphor of said phosphors and to be longer than a luminance rise response time of a fast luminance response phosphor of said phosphors.

9. A liquid crystal display according to claim 2, wherein a current value of a current applied to each of said light emitting tubes is attenuated stepwise in said luminance fall time.

10. A liquid crystal display according to claim 9, wherein a step time width Δ

t_step of said current whose current value is attenuated stepwise is set to be shorter than a luminance fall response time of a slow luminance response phosphor of said phosphors and to be longer than a luminance fall response time of a fast luminance response phosphor of said phosphors.

11. A liquid crystal display according to claim 1, wherein said light source is made of light emitting tubes of at least two kinds, and each of said light emitting tubes is a multicolor light emitting tube having at least two kinds of phosphors.

12. A liquid crystal display according to claim 1, wherein said light source is made of light emitting tubes of at least two kinds, and at least one of said light emitting tubes is a unicolor light emitting tube having only one kind of phosphor.

13. A liquid crystal display according to claim 1, wherein said light source is made of light emitting tubes of at least three kinds, and each of said light emitting tubes is a unicolor light emitting tube having only one kind of phosphor.

14. A liquid crystal display according to claim 11, wherein at least two kinds of phosphors belonging to one and the same tube of said multicolor light emitting tubes have a substantially equal luminance rise response time and a substantially equal luminance fall response time.

15. A liquid crystal display according to claim 12, wherein at least two kinds of phosphors belonging to one and the same tube of said multicolor light emitting tubes have a substantially equal luminance rise response time and a substantially equal luminance fall response time.

16. A liquid crystal display according to claim 1, wherein luminance of said phosphors is controlled by a current value of a current applied to each of said light emitting tubes.

17. A liquid crystal display according to claim 16, wherein a current value of a current applied to each light emitting tube having a fast luminance response phosphor is increased gradually in said luminance rise time.

18. A liquid crystal display according to claim 16, wherein at the beginning of said luminance rise time, said current value of said current applied to each light emitting tube having a fast luminance response phosphor is a current value I₂ not smaller than a current value I₁ necessary for said phosphors to emit light with predetermined luminance in one frame.

19. A liquid crystal display according to claim 16, wherein said current value of said current applied to each light emitting tube having a fast luminance response phosphor is attenuated gradually in said luminance fall time.

20. A liquid crystal display according to claim 16, wherein in said luminance rise time and a lighting period, a current value of a current applied to each light emitting tube is changed like a rectangular shape so as to drive said light emitting tube.

21. A liquid crystal display according to claim 20, wherein in said current having a current value changed like a rectangular shape, a time width of said rectangular current value immediately after start of application of said current is longer than a time width of said rectangular current value immediately before termination of application of said current.

22. A liquid crystal display according to claim 20, wherein a time width of said rectangular current value is not longer than 3.3 msec.

23. A liquid crystal display according to claim 16, wherein in said luminance rise time, time of start of application of a current to each light emitting tube having a fast luminance response phosphor is controlled to be delayed by a predetermined time Δ

t_i with respect to time of start of application of a current to each light emitting tube having a slow luminance response phosphor, so that a luminance factor area of said fast luminance response phosphor is substantially equal to a luminance factor area of said slow luminance response phosphor.

24. A liquid crystal display according to claim 16, wherein in said luminance fall time, time of termination of application of a current to each light emitting tube having a slow luminance response phosphor is controlled to be delayed by a predetermined time Δ

t_f with respect to time of termination of application of a current to each light emitting tube having a fast luminance response phosphor, so that a luminance factor area of said fast luminance response phosphor is substantially equal to a luminance factor area of said slow luminance response phosphor.

25. A liquid crystal display according to claim 24, wherein said luminance rise time and said luminance fall time are not longer than 3.3 msec.

26. A liquid crystal display according to claim 16, wherein a luminance rise response time and a luminance fall response time of a slow luminance response phosphor of said phosphors are not longer than 3.3 msec.

27. A liquid crystal display according to any one of claims 22 through 25, wherein said delay times Δ

t_i and Δ

t_f are almost half as long as a luminance rise response time and a luminance fall response time of a slow response phosphor of said phosphors respectively.

28. A liquid crystal display according to any one of claims 22 through 26, wherein said delay times Δ

t_i and Δ

t_f are not longer than 1.7 msec.

29. A liquid crystal display according to claim 1, wherein said phosphors are fluorescent materials to be excited by ultraviolet rays to thereby emit visible light.

30. A liquid crystal display according to claim 1, wherein said light emitting tubes are cold cathode tubes.