Liquid crystal display device

• US 7,106,294 B2
• Filed: 03/25/2003
• Issued: 09/12/2006
• Est. Priority Date: 03/28/2002
• Status: Expired due to Fees

• Current Assignee: Matsushita Electric Industrial Company Limited (Panasonic Holdings Corporation)
• Original Assignee: Matsushita Electric Industrial Company Limited (Panasonic Holdings Corporation)
• Inventors: Kumamoto, Yasuhiro, Arimoto, Katsuyuki, Funamoto, Taro
• Primary Examiner(s): Hjerpe, Richard
• Assistant Examiner(s): Said, Mansour M.
• Application Number:
  US10/487,281
• Publication Number:
  US 20050007389A1
• Time in Patent Office: 1,267 Days
• Field of Search: 345 87- 88, 345/102, 345/204, 345208-214, 345 98- 99, 349/61, 349 69- 70
• US Class Current: 345/102
• CPC Class Codes: G09G 2310/061 for resetting or blanking
• CPC Class Codes: G09G 2320/0247 Flicker reduction other than flicker reduction circuits used for single beam cathode-ray tubes
• CPC Class Codes: G09G 2320/0606 Manual adjustment
• CPC Class Codes: G09G 2320/0626 for control of overall brightness
• CPC Class Codes: G09G 2320/064 by time modulation of the brightness of the illumination source
• CPC Class Codes: G09G 3/2018 by time modulation using two or more time intervals
• 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 doubler part doubles frequencies of video signals. A drive control circuit generates, in response to a synchronizing signal outputted from the doubler part, PWM dimming frequency information such that a PWM dimming frequency f and a black display ratio B satisfy the relationships f≧25B+250 and B>10, and provides such information to a PWM dimming signal generation circuit. In addition, the drive control circuit drives a gate driver and a source driver such that one frame period is divided into an image display period and a black display period. The PWM dimming signal generation circuit generates, in response to a synchronizing signal and the PWM dimming frequency information, a PWM dimming signal and provides the PWM dimming signal to a lighting circuit. The lighting circuit activates a backlight device with dimming, in response to the PWM dimming signal. This configuration reduces colored interference fringes in a liquid crystal display device resulting from the combination of a black insertion drive technique and a PWM dimming technique.

Claims

1. A liquid crystal display device for displaying images by irradiating a liquid crystal panel, which is driven in response to video signals, with light outputted from a backlight device, the liquid crystal display device comprising:

drive means for driving the liquid crystal panel in response to the video signals such that one frame period is divided into a black display period and an image display period;

a PWM dimming signal generation circuit for generating a PWM dimming signal for controlling the backlight device by a PWM dimming technique;

a lighting circuit for driving the backlight device in response to the PWM dimming signal; and

means for controlling a cycle and/or phase of the PWM dimming signal to prevent an occurrence of interference fringes in the liquid crystal panel, caused by the PWM dimming technique,

wherein a PWM dimming frequency f (Hz) in the PWM technique and a ratio B (%) of the black display period to one frame period satisfy the relationship f≧

25B+250.

2. The liquid crystal display device according to claim 1, wherein the drive means is operable to control the PWM dimming signal generation circuit such that the PWM dimming frequency f (Hz) and the ratio B (%) satisfy the relationship f≧

25B+250.

3. A liquid crystal display device for displaying images by irradiating a liquid crystal panel, which is driven in response to video signals, with light outputted from a backlight device, the liquid crystal display device comprising:

drive means for driving the liquid crystal panel in response to the video signals such that one frame period is divided into a black display period and an image display period;

a PWM dimming signal generation circuit for generating a PWM dimming signal for controlling the backlight device by a PWM dimming technique;

a lighting circuit for driving the backlight device in response to the PWM dimming signal; and

means for controlling a cycle and/or phase of the PWM dimming signal to prevent an occurrence of interference fringes in the liquid crystal panel, caused by the PWM dimming technique, wherein;

the backlight device is a direct-type backlight device having a structure in which a plurality of light sources are arranged in parallel and directly behind the liquid crystal panel; and

the PWM dimming signal generation circuit is operable to dim all light sources of an order i in response to a first PWM dimming signal and dim all light sources of an order j in response to a second PWM dimming signal, the order i satisfying the relationship (2n−

2)M+1≦

i≦

(2n−

1)M and the order j satisfying the relationship (2n−

1)M+1≦

j≦

2nM, wherein i and j (i, j=1, 2, 3, . . .) are natural numbers that represent the order of the light sources from one end of the backlight device, n (n=1, 2, 3, . . .) is an arbitrary natural number, and M (M=1, 2, 3, . . .) is an arbitrary natural number, the first and second PWM dimming signals being similar signals having phases that are shifted by about (PWM dimming cycle/2) relative to each other.

4. The liquid crystal display device according to claim 3, further comprising a delay circuit for controlling the first and second PWM dimming signals such that the phases of the first and second PWM dimming signals are shifted by about (PWM dimming cycle/2) relative to each other.

5. The liquid crystal display device according to claim 3, further comprising a control signal generation circuit for controlling the PWM dimming signal generation circuit such that the first and second PWM dimming signals synchronize to a synchronizing signal of an image.

6. The liquid crystal display device according to claim 3, wherein the natural number M satisfies the relationship M=1.

7. The liquid crystal display device according to claim 3, wherein the light sources arranged directly behind the liquid crystal panel are fluorescent lamps.

8. A liquid crystal display device for displaying images by irradiating a liquid crystal panel, which is driven in response to video signals, with light outputted from a backlight device, the liquid crystal display device comprising:

drive means for driving the liquid crystal panel in response to the video signals such that one frame period is divided into a black display period and an image display period;

a PWM dimming signal generation circuit for generating a PWM dimming signal for controlling the backlight device by a PWM dimming technique;

a lighting circuit for driving the backlight device in response to the PWM dimming signal; and

means for controlling a cycle and/or phase of the PWM dimming signal to prevent an occurrence of interference fringes in the liquid crystal panel, caused by the PWM dimming technique, wherein;

the backlight device is a direct-type backlight device having a structure in which a plurality of light sources are arranged in parallel and directly behind the liquid crystal panel; and

the PWM dimming signal generation circuit is operable to dim all light sources of an order i′

in response to a first PWM dimming signal, dim all light sources of an order j′

in response to a second PWM dimming signal, and dim all light sources of an order k′

in response to a third PWM dimming signal, the order i′

satisfying the relationship (3n′

−

3)M′

+1≦

i′

≦

(3n′

−

2)M′

,the order j′

satisfying the relationship (3n′

−

2) M′

+1≦

J′

≦

2(3n′

−

1)M′

, and the order k′

satisfying the relationship (3n′

−

1)M′

+1≦

k′

≦

3n′

M′

, wherein i′

, j′

, and k′

(i′

, j′

, k′

=1, 2, 3, . . .) are natural numbers that represent the order of the light sources from one end of the backlight device, n′

(n′

+1, 2, 3, . . .) is an arbitrary natural number, and M′

(M′

=1, 2, 3,...) is an arbitrary natural number, the first, second, and third PWM dimming signals being similar signals in which phases of the first and second PWM dimming signals are shifted by about (PWM dimming cycle/3) relative to each other and the phase of the second PWM dimming signal and a phase of the third PWM dimming signal are shifted by about (PWM dimming cycle/3) relative to each other.

9. The liquid crystal display device according to claim 8, further comprising a delay circuit for controlling the first, second, and third PWM dimming signals such that the phases of the first and second PWM dimming signals are shifted by about (PWM dimming cycle/3) relative to each other and the phases of the second and third PWM dimming signals are shifted by about (PWM dimming cycle/3) relative to each other.

10. The liquid crystal display device according to claim 8, further comprising a control signal generation circuit for controlling the PWM dimming signal generation circuit such that the first, second, and third PWM dimming signals synchronize to a synchronizing signal of an image.

11. The liquid crystal display device according to claim 8, wherein the natural number M′

is 1.

12. The liquid crystal display device according to claim 8, wherein the light sources arranged directly behind the liquid crystal panel are fluorescent lamps.