LED backlight driver synchronization and power reduction

• US 8,547,321 B2
• Filed: 07/23/2008
• Issued: 10/01/2013
• Est. Priority Date: 07/23/2008
• Status: Active Grant

• Current Assignee: Apple Inc.
• Original Assignee: Apple Inc.
• Inventors: Smith, Eric
• Primary Examiner(s): Dharia, Prabodh M
• Application Number:
  US12/178,471
• Publication Number:
  US 20100020004A1
• Time in Patent Office: 1,896 Days
• Field of Search: 345/55, 345/82, 345/589, 345/690, 345/691, 345 87-102, 345204-213, 315/169.2, 315/308, 315/185.R, 315/250, 315/122, 315/219, 315/246, 315287-297, 600/425, 600/453, 600/529, 600/534, 340/461, 349/62, 349/70, 349/71
• US Class Current: 345/102
• CPC Class Codes: G09G 2330/021 Power management, e.g. power saving
• CPC Class Codes: G09G 3/342 using several illumination sources separately controlled corresponding to different display panel areas, e.g. along one dimension such as lines

Abstract

A method and apparatus for providing a LED backlight to a LCD display screen is disclosed. In one embodiment, the apparatus includes: N LED strings, wherein N is an integer greater than or equal to two; a first circuit operable to synchronize a LED clock signal to a LCD timing signal; and a second circuit operable to generate N PWM drive signals synchronized with the LED clock signal, wherein the N PWM drive signals are phase offset from each other by a multiple of 360/N degrees and used to drive respective ones of the N LED strings.

Claims

1. A method of providing a backlight from N LED strings to a LCD screen, comprising:

generating N pulse width modulated (PWM) drive signals used to drive respective ones of the N LED strings, wherein light emitted by each of the N LED strings is diffused by a backlight diffuser prior to illuminating the LCD screen;

synchronizing an LED clock signal to an LCD timing signal to reduce or eliminate optical interference beats; and

synchronizing at least one of the N PWM drive signals with the LED clock signal;

wherein the N PWM drive signals are phase offset from each other by a multiple of 360/N degrees, where N is an integer greater than or equal to two.

2. The method of claim 1, further comprising:

generating a duty cycle signal; and

generating the N PWM drive signals such that each PWM drive signal has a pulse width corresponding to the duty cycle signal.

3. The method of claim 2 wherein the pulse width of each PWM drive signal corresponds to a duty cycle of (100/N) % such that the N LED strings cumulatively provide substantially continuous backlight illumination.

4. The method of claim 2, further comprising balancing the current provided by each of the N PWM drive signals to respective ones of the N LED strings.

5. A method of synchronizing a LED backlight to a LCD screen, comprising:

receiving an LCD timing signal;

generating an LED clock signal;

synchronizing the LED clock signal with the LCD timing signal to reduce or eliminate optical interference beats; and

generating at least one drive signal used to drive the LED backlight, wherein the at least one drive signal is synchronized with the LED clock signal, wherein light emitted by the LED backlight is diffused by a backlight diffuser prior to illuminating the LCD screen.

6. The method of claim 5 further comprising generating a duty cycle signal, wherein the at least one driving signal comprises at least one pulse width modulated (PWM) signal having a pulse width corresponding to the duty cycle signal.

7. The method of claim 5 wherein generating at least one drive signal comprises generating N PWM drive signals, where N is an integer greater than or equal to two, and offsetting each PWM drive signal with respect to another PWM drive signal by 360/N degrees in phase.

8. An apparatus for providing a LED backlight to a LCD display screen, comprising:

means for synchronizing an LED clock signal to an LCD timing signal to reduce or eliminate optical interference beats;

means for generating N PWM drive signals synchronized with the LED clock signal, wherein the N PWM drive signals are phase offset from each other by a multiple of 360/N degrees and used to drive respective ones of N LED strings provided by the LED backlight, where N is an integer greater than or equal to two; and

means for directing light emitted by the N LED strings onto a back surface of the LCD display screen, wherein the means for directing light comprises means for diffusing the light prior to illuminating the LCD screen.

9. The apparatus of claim 8 further comprising means for setting the frequency of the LED clock signal to be a desired multiple (M) of a frequency of the LCD timing signal, where M is an integer greater than or equal to one.

10. The apparatus of claim 8 further comprising:

means for generating a duty cycle signal; and

means for generating the N PWM drive signals such that each N PWM drive signal has a pulse width corresponding to the duty cycle signal.

11. The apparatus of claim 10 further comprising means for balancing a current provided by each of the N PWM drive signals to respective ones of the N LED strings.

12. An apparatus for providing a backlight from N LED strings to a LCD screen, comprising:

means for generating N pulse width modulated (PWM) drive signals used to drive respective ones of the N LED strings, wherein the N PWM drive signals are phase offset from each other by a multiple of 360/N degrees, where N is an integer greater than or equal to two, wherein light emitted by each of the N LED strings is diffused by a backlight diffuser prior to illuminating the LCD screen;

means for synchronizing an LED clock signal to an LCD timing signal to reduce or eliminate optical interference beats; and

means for synchronizing at least one of the N PWM drive signals with the LED clock signal.

13. The apparatus of claim 12, further comprising:

means for generating a duty cycle signal; and

means for generating the N PWM drive signals such that each PWM drive signal has a pulse width corresponding to the duty cycle signal.

14. An apparatus for synchronizing a LED backlight to a LCD screen, comprising:

means for receiving an LCD timing signal;

means for generating an LED clock signal;

means for synchronizing the LED clock signal with the LCD timing signal to reduce or eliminate optical interference beats;

means for generating at least one drive signal used to drive the LED backlight, wherein the at least one drive signal is synchronized with the LED clock signal, and

means for directing light emitted by the LED backlight onto a back surface of the LCD display screen, wherein the means for directing light comprises means for diffusing the light prior to illuminating the LCD screen.

15. The apparatus of claim 14 wherein the means for generating at least one drive signal comprises means for generating N PWM drive signals, where N is an integer greater than or equal to two, and means for offsetting each PWM drive signal with respect to another PWM drive signal by 360/N degrees in phase.