Apparatus and method for driving lamp of liquid crystal display device

• US 8,243,005 B2
• Filed: 05/25/2005
• Issued: 08/14/2012
• Est. Priority Date: 05/27/2004
• Status: Active Grant

• Current Assignee: LG Philips LCD Company Limited (LG Display Co., Ltd.)
• Original Assignee: LG Display Co., Ltd.
• Inventors: Oh, Eui Yeol, Hong, Hee Jung, Park, Hee Jeong
• Primary Examiner(s): Nguyen, Chanh
• Assistant Examiner(s): MISTRY, RAM A
• Application Number:
  US11/137,631
• Publication Number:
  US 20050264516A1
• Time in Patent Office: 2,638 Days
• Field of Search: 345/102, 349 61- 70, 362/561
• US Class Current: 345/102
• CPC Class Codes: G09G 2320/0633 by amplitude modulation of the brightness of the illumination source
• CPC Class Codes: G09G 2320/064 by time modulation of the brightness of the illumination source
• CPC Class Codes: G09G 2360/16 Calculation or use of calculated indices related to luminance levels in display data
• CPC Class Codes: G09G 3/3406 Control of illumination source illumination devices structurally associated with liquid crystal cells G02F1/1336
• CPC Class Codes: H05B 41/2824 using control circuits for the switching element H05B41/2822 takes precedence

Abstract

A driving apparatus and method are presented to drive lamps that irradiate a liquid crystal display panel of a liquid crystal display device. A picture implementing period, during which a picture is implemented by the liquid crystal display device, and a shorter, scanning period before the picture implementing period are established. An output power supplied to the lamps to set a reference brightness is determined. A lamp driver changes a duty ratio and/or an amplitude of an AC signal supplied to the lamps to establish the reference brightness during the scanning period. The duty ratio/amplitude of the AC signal is adjusted dependent on the characteristics of the liquid crystal material in the liquid crystal display.

Claims

1. An apparatus for driving a lamp of a liquid crystal display device comprises:

a plurality of lamps to irradiate light to a liquid crystal display panel;

a lamp driver supplying a high voltage alternating current (AC) signal to, and controlling brightness of the plurality of lamps of the liquid crystal display panel, wherein the lamp driver comprises;

an inverter to receive;

an external direct current (DC) signal and a pulse generated from a Pulse Width Modulator controller, wherein the inverter converts the external direct current signal into the high voltage alternating current signal,

wherein the Pulse Width Modulator controller controls and adjusts based on a feedback signal, at least one of a duty cycle ratio and an amplitude of the high voltage alternating current signal to correspond to a specified reference brightness in accordance with a characteristic of the liquid crystal display panel during a scanning period, wherein the scanning period is prior to a picture implementing period; and

a timing controller to generate a brightness variation signal based on a brightness determination of input video signal, and supplies the brightness variation signal to the Pulse Width Modulator controller during the picture implementing period, wherein the brightness variation signal causes the Pulse Width Modulator controller to adjust the at least one of the duty cycle ratio and the amplitude of the high voltage alternating current signal based on a high and a low brightness of a picture implemented by the liquid crystal display panel;

wherein during the scanning period, the lamp driver allots a value corresponding to a specific reference brightness in accordance with the characteristic of the liquid crystal display panel, wherein the apparatus compensates for a delay time within the scanning period by supplying a voltage to a liquid crystal material to uniformly activate the liquid crystal display panel in advance,

wherein during the scanning period, if the on-time duty cycle ratio of the pulse generated from the Pulse Width Modulator controller is small or the on-time duty cycle ratio of the pulse is unchanged, increase the amplitude of the pulse to correspond to the specific reference brightness, and if the on-time duty cycle ratio of the pulse is large, decrease the amplitude of the pulse,

wherein the specific reference brightness is determined by an experimental result and a statistical result in accordance with the characteristic of the liquid crystal display panel, wherein the brightness of the lamp can be compensated to correspond to the specific reference brightness,

wherein during the scanning period, after determining a specific output power in accordance with the specific reference brightness, adjust the amplitude of the pulse of the Pulse Width Modulator controller to correspond to the determined specific output power, and

wherein during the scanning period, if the on-time duty cycle ratio of the pulse is unchanged, adjust the amplitude of the pulse to correspond to the determined specific output power.

2. The apparatus according to claim 1, wherein the inverter alternately repeats an on-period and an off-period of the alternating current signal corresponding to the brightness of the variation signal generated from the timing controller.

3. The apparatus according to claim 2, wherein the brightness of each lamp is controlled to correspond to the high voltage alternating current signal.

4. A method of driving a lamp of a liquid crystal display device, the method comprising:

setting at least one of a duty cycle ratio and an amplitude of an alternating current (AC) signal supplied to the lamp in accordance with a reference brightness of a liquid crystal display panel during a scanning period before a picture implementing period of the liquid crystal display panel; and

adjusting based on a feedback signal, the at least one of the amplitude and the duty cycle ratio of the alternating current signal in accordance with the duty cycle ratio and the amplitude determined during the scanning period;

generating a brightness variation signal during the picture implementing period based on a high and a low brightness of a picture implemented by the liquid crystal display panel;

generating a control signal in accordance with the brightness variation signal,

generating an alternating current waveform corresponding to the control signal; and

generating light by supplying the alternating current waveform to the lamp to irradiate the light to the liquid crystal display panel,

wherein the generation of the brightness variation signal in accordance with the high and low brightness of the picture implemented by the liquid crystal display panel includes generating the brightness variation signal corresponding to video data input from external to the liquid crystal display panel,

wherein the generation of the control signal in accordance with the brightness variation signal includes at least one of adjusting a duty cycle ratio of the brightness variation signal and adjusting an amplitude of the brightness variation signal,

wherein the generation of the alternating current waveform corresponding to the control signal includes at least one of adjusting an on-time period of the alternating current waveform if the duty cycle ratio of the control signal is changed, and adjusting the amplitude of the alternating current waveform if the amplitude of the control signal is changed,

wherein during the scanning period, the lamp driver allots a value corresponding to a specific reference brightness in accordance with a characteristic of the liquid crystal display panel, wherein the apparatus compensates for a delay time within the scanning period by supplying a voltage to a liquid crystal material to uniformly activate the liquid crystal display panel in advance,

wherein during the scanning period, if the on-time duty cycle ratio of the pulse generated from the Pulse Width Modulator controller is small or the on-time duty cycle ratio of the pulse is unchanged, increase the amplitude of the pulse to correspond to the specific reference brightness, and if the on-time duty cycle ratio of the pulse is large, decrease the amplitude of the pulse,

wherein the specific reference brightness is determined by an experimental result and a statistical result in accordance with the characteristic of the liquid crystal display panel, wherein the brightness of the lamp can be compensated to correspond to the specific reference brightness,

wherein during the scanning period, after determining a specific output power in accordance with the specific reference brightness, adjust the amplitude of the pulse of the Pulse Width Modulator controller to correspond to the determined specific output power, and

wherein during the scanning period, if the on-time duty cycle ratio of the pulse is unchanged, adjust the amplitude of the pulse to correspond to the determined specific output power.

5. The method according to claim 4, wherein the setting of the at least one of the duty ratio and the amplitude of the AC signal supplied to the lamp in accordance with the reference brightness is determined in accordance with characteristics of liquid crystal material injected to the liquid crystal display panel.

6. The method according to claim 5, wherein the generation of light by supplying the alternating current waveform to the lamp to irradiate the light to the liquid crystal display panel includes:

supplying an adjusted tube current and an adjusted alternating current voltage to the lamp to generate light to achieve a particular brightness, wherein the adjusted tube current and the adjusted alternating current voltage correspond to at least one of the adjusted on-time period of the alternating current waveform and the adjusted amplitude of the alternating current waveform; and

generating light from the lamp in accordance with a brightness of video data input from external to the liquid crystal display panel to sequentially irradiate the light to the liquid crystal display panel during the picture implementing period.

7. The method according to claim 4, wherein the liquid crystal display panel comprises a plurality of lamps, and the method further comprising adjusting at least one of an amplitude and a duty cycle ratio of an alternating current signal supplied to each of the lamps in accordance with a duty cycle ratio and an amplitude determined during the scanning period.

8. The method according to claim 7, further comprising determining the reference brightness experimentally based on characteristics of the liquid crystal material in the liquid crystal display panel.

9. The method according to claim 7, comprising setting the scanning period to be longer than a delay time of the liquid crystal material in the liquid crystal display to activate the liquid crystal material to transmit light.

10. The method according to claim 7, comprising setting the scanning period to be less than an amount of time in which a viewer of the liquid crystal display can distinguish a change in brightness of the liquid crystal display.

11. The method according to claim 7, comprising, during the picture implementing period for each lamp:

generating a brightness variation signal in accordance with a high and a low brightness of the picture;

generating a control signal in accordance with the brightness variation signal;

generating an alternating current waveform corresponding to the control signal; and

supplying the alternating current waveform to the lamp to generate light.

12. The method according to claim 11, wherein the generation of the control signal in accordance with the brightness variation signal includes at least one of:

adjusting a duty cycle ratio of the brightness variation signal; and

adjusting an amplitude of the brightness variation signal.

13. The method according to claim 12, wherein the generation of the alternating current waveform corresponding to the control signal includes at least one of:

adjusting an on-time period of the alternating current waveform if the duty cycle ratio of the control signal is changed; and

adjusting the amplitude of the alternating current waveform if the amplitude of the control signal is changed.

14. A method of driving a plurality of lamps in a liquid crystal display device, the method comprising performing within each lamp:

establishing a picture implementing period in which a picture is implemented by the liquid crystal display device and a scanning period before the picture implementing period, the scanning period being substantially less than the picture implementing period;

determining an amount of power to be supplied to the lamp to establish a reference brightness;

adjusting based on a feedback signal, at least one of an amplitude and a duty cycle ratio of an alternating current (AC) signal supplied to the lamp to establish the reference brightness during the scanning period,

generating a brightness variation signal during the picture implementing period based on a high and a low brightness of a picture implemented by the liquid crystal display panel;

generating a control signal in accordance with the brightness variation signal,

generating an alternating current waveform corresponding to the control signal; and

generating light by supplying the alternating current waveform to the lamp to irradiate the light to the liquid crystal display panel,

wherein the generation of the brightness variation signal in accordance with the high and low brightness of the picture implemented by the liquid crystal display panel includes generating a brightness variation signal corresponding to video data input from external to the liquid crystal display panel,

wherein the generation of the control signal in accordance with the brightness variation signal includes at least one of adjusting a duty cycle ratio of the brightness variation signal and adjusting an amplitude of the brightness variation signal,

wherein the generation of the alternating current waveform corresponding to the control signal includes at least one of adjusting an on-time period of the alternating current waveform if the duty cycle ratio of the control signal is changed and adjusting the amplitude of the alternating current waveform if the amplitude of the control signal is changed,

wherein during the period before a picture implementing period, the lamp driver allots a value corresponding to a specific reference brightness in accordance with the characteristic of the liquid crystal display panel,

wherein during the scanning period, the lamp driver allots a value corresponding to a specific reference brightness in accordance with the high and the low brightness characteristic of the liquid crystal display panel, wherein the apparatus compensates for a delay time within the scanning period by supplying a voltage to a liquid crystal material to uniformly activate the liquid crystal display panel in advance,

wherein during the scanning period, if the on-time duty cycle ratio of the pulse generated from the Pulse Width Modulator controller is small or the on-time duty cycle ratio of the pulse is unchanged, increase the amplitude of the pulse to correspond to the specific reference brightness, and if the on-time duty cycle ratio of the pulse is large, decrease the amplitude of the pulse,

wherein the specific reference brightness is determined by an experimental result and a statistical result in accordance with the characteristics of the liquid crystal display panel, wherein the brightness of the lamp can be compensated to correspond to the specific reference brightness,

wherein during the scanning period, after determining a specific output power in accordance with the specific reference brightness, adjust the amplitude of the pulse of the Pulse Width Modulator controller to correspond to the determined specific output power, and

wherein during the scanning period, if the on-time duty cycle ratio of the pulse is unchanged, adjust the amplitude of the pulse to correspond to the determined specific output power.