Backlight driving apparatus for LCD

• US 20040145560A1
• Filed: 12/19/2003
• Published: 07/29/2004
• Est. Priority Date: 01/24/2003
• Status: Abandoned Application

• Current Assignee: Samsung Electronics Co. Ltd.
• Original Assignee: Samsung Electronics Co. Ltd.
• Inventors: Kim, Jae-Hyun
• Application Number:
  US10/739,308
• Publication Number:
  US 20040145560A1
• Time in Patent Office: Days
• US Class Current: 345/102
• 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 2310/08 Details of timing specific for flat panels, other than clock recovery
• CPC Class Codes: G09G 2320/064 by time modulation of the brightness of the illumination source
• CPC Class Codes: G09G 3/3406 Control of illumination source illumination devices structurally associated with liquid crystal cells G02F1/1336

Abstract

A backlight driving apparatus is provided which effectively suppresses noise by synchronizing a frequency of a pulse width modulation (PWM) signal to drive a backlight which projects rays on a liquid crystal panel with a scan frequency of the liquid crystal panel. The backlight driving apparatus is used for an liquid crystal display having a liquid crystal panel to display a picture signal and a backlight to project rays on the liquid crystal panel, and includes an NTSC/PAL detector, which detects a vertical frequency of the picture signal, and an inverter, which receives a predetermined constant voltage and generates the PWM signal to drive the backlight. The inverter controls the frequency of the PWM signal based on a decision result of the NTSC/PAL detector.

Claims

1. A backlight driving apparatus for a liquid crystal device having a liquid crystal panel displaying an output picture signal and a backlight projecting rays on the liquid crystal panel, comprising:

an NTSC/PAL detector, which detects a vertical frequency of an input picture signal; and

an inverter, which receives a predetermined constant voltage and generates a PWM signal to drive the backlight,

wherein the inverter controls a frequency of the PWM signal based on a decision result of the NTSC/PAL detector.

2. The apparatus of claim 1, wherein the NTSC/PAL detector detects whether the input picture signal applied to the liquid crystal device is an NTSC signal or a PAL signal.

3. The apparatus of claim 1, further comprising:

a frequency setter comprising;

two capacitors, which are switchably connectable to each other, in parallel; and

a switch to connect the two capacitors based on the decision result of the NTSC/PAL detector,

wherein the frequency of the pulse width modulation signal is proportional to a value obtained by multiplying a vertical frequency of the input picture signal by a number of vertical lines displayed on the liquid crystal panel.

4. The apparatus of claim 1, further comprising:

a frequency setter comprising;

a first capacitor; and

a series of a second capacitor and a switch, the series of the second capacitor and of the switch and the first capacitor being in parallel, the switch operating based on the decision result of the NTSC/PAL detector,

wherein the frequency of the pulse width modulation signal is proportional to a value obtained by multiplying a vertical frequency of the input picture signal by a number of vertical lines displayed on the liquid crystal panel.

5. An apparatus to drive a backlight for a liquid crystal device to display an output picture signal thereon, comprising:

an NTSC/PAL detector to detect a vertical frequency of an input picture signal; and

an inverter to generate a pulse width modulated signal to drive the backlight and to control a frequency of the pulse width modulated signal based on a decision result of the NTSC/PAL detector.

6. The apparatus of claim 5, wherein the NTSC/PAL detector detects whether the input picture signal applied to the liquid crystal device is an NTSC signal or a PAL signal.

7. The apparatus of claim 5, further comprising:

a frequency setter comprising;

a first capacitor; and

a series of a second capacitor and a switch, the series of the second capacitor and of the switch and the first capacitor being in parallel, the switch operating based on the decision result of the NTSC/PAL detector,

wherein the frequency of the pulse width modulation signal is proportional to a value obtained by multiplying a vertical frequency of the input picture signal by a number of vertical lines displayed on the liquid crystal device.

8. The apparatus of claim 5, further comprising:

a frequency setter comprising;

a switch operating based on the decision result of the NTSC/PAL detector; and

a variable capacitance selectively controlled by the switch such that the frequency of the pulse width modulation signal is proportional to a vertical frequency of the input picture signal.

9. The apparatus of claim 6, wherein the NTSC/PAL detector is initialized to one of the NTSC signal and the PAL signal.

11. The apparatus of claim 9, wherein the detector detects whether the input picture signal applied to the liquid crystal device is an NTSC signal or a PAL signal.

10. An apparatus to drive a backlight for a liquid crystal device to display an output picture signal thereon, comprising:

a detector to detect a vertical frequency of an input picture signal; and

an inverter to generate a signal to drive the backlight and to control a frequency of the signal according to the detected vertical frequency of the input picture signal.

12. An apparatus to drive a backlight for a liquid crystal device to display an output picture signal thereon, comprising:

an NTSC/PAL detector to detect a number of vertical lines displayed on the liquid crystal device; and

an inverter to generate a pulse width modulated signal to drive the backlight and to control a frequency of the pulse width modulated signal based on a decision result of the NTSC/PAL detector.

13. An apparatus to drive a backlight for a liquid crystal device to display an output picture signal thereon, comprising:

a detector to detect a vertical frequency of an input picture signal and/or a number of vertical lines displayed on the liquid crystal device;

an inverter to generate a pulse width modulation signal to drive the backlight; and

a frequency setter to set a frequency of the pulse width modulation signal generated from the inverter according to a detected result of the detector.

14. The apparatus of claim 13, wherein the frequency setter comprises:

a switch such that a capacitance of the frequency setter varies according to an operating state of the switch.

15. A method of driving a backlight for a liquid crystal device to display an output picture signal thereon, comprising:

detecting a vertical frequency of an input picture signal;

generating a pulse width modulated signal to drive the backlight; and

controlling a frequency of the pulse width modulated signal based on the detecting.

16. The method of claim 15, wherein the detecting of the vertical frequency comprises:

detecting whether the input picture signal applied to the liquid crystal device is an NTSC signal or a PAL signal.

17. The method of claim 15, wherein the controlling of the frequency of the pulse width modulated signal comprises:

changing the frequency of the pulse width modulation signal proportional to a value obtained by multiplying a vertical frequency of the input picture signal by a number of vertical lines displayed on the liquid crystal device.

18. The method of claim 15, wherein the controlling of the frequency of the pulse width modulated signal comprises:

operating a switch based on a result of the detecting; and

selectively controlling the frequency of the pulse width modulation signal to be proportional to a vertical frequency of the input picture signal according to the operating.

19. The method of claim 15, wherein the controlling of the frequency of the pulse width modulated signal comprises:

initializing the frequency of the pulse width modulation signal to one of an NTSC input picture signal and a PAL input picture signal.

20. A method of driving a backlight for a liquid crystal device to display an output picture signal thereon, comprising:

detecting a number of vertical lines displayed on the liquid crystal device;

generating a pulse width modulated signal to drive the backlight; and

controlling a frequency of the pulse width modulated signal based on the detecting.

21. A method of driving a backlight for a liquid crystal device to display an output picture signal thereon, comprising:

detecting whether a picture signal input to the liquid crystal device is in a video standard;

converting a frequency of a pulse width modulated signal output from an inverter into a frequency corresponding to the video standard; and

driving the backlight using the frequency corresponding to the video standard.

22. The method of claim 21, further comprising:

initializing the frequency of the pulse width modulation signal to one of an NTSC video standard and a PAL video standard.

23. An apparatus to drive a backlight for a liquid crystal device to display an output picture signal thereon, comprising:

a detector to detect one or more attributes of a video standard of an input picture signal; and

an inverter to generate a pulse width modulated signal to drive the backlight such that a frequency of the pulse width modulated signal is based on a decision result of the detector.

24. The apparatus of claim 23, further comprising:

a frequency setter comprising;

a switch operating based on the decision result of the detector; and

a variable capacitance selectively controlled by the switch such that the frequency of the pulse width modulation signal is proportional to a vertical frequency of the input picture signal.