Reduced Power Displays

• US 20120113167A1
• Filed: 07/21/2010
• Published: 05/10/2012
• Est. Priority Date: 07/23/2009
• Status: Active Grant

• Current Assignee: Dolby Laboratories Licensing Corporation (Dolby Laboratories Incorporated)
• Original Assignee: Dolby Laboratories Licensing Corporation (Dolby Laboratories Incorporated)
• Inventors: Messmer, Neil W., Margerm, Steve
• Granted Patent: US 9,373,287 B2
• Time in Patent Office: Days
• US Class Current: 345/690
• CPC Class Codes: G09G 2310/066 Waveforms comprising a gently increasing or decreasing portion, e.g. ramp
• CPC Class Codes: G09G 2320/064 by time modulation of the brightness of the illumination source
• CPC Class Codes: G09G 2320/0646 Modulation of illumination source brightness and image signal correlated to each other
• CPC Class Codes: G09G 2330/021 Power management, e.g. power saving
• CPC Class Codes: G09G 2330/025 Reduction of instantaneous peaks of current
• CPC Class Codes: G09G 2360/16 Calculation or use of calculated indices related to luminance levels in display data
• CPC Class Codes: G09G 3/3426 the different display panel areas being distributed in two dimensions, e.g. matrix

Abstract

A backlight for a display comprises a plurality of independently controllable groups of light emitters. The brightness levels of the groups of light emitters are controllable by pulse width modulation (PWM) signals generated by PWM driving circuits. The phases of PWM signals to different groups of light emitters are configured to be offset by different amounts, so as to stagger the start times of light emitters of different groups. Such phase-shifting of PWM signals may result in total power consumption that ramps up more gradually, is distributed more evenly over time, and is held to a lower maximum value than if the same PWM signals were not phase-shifted. The duration of a first PWM cycle of PWM signals for an image may also be made longer than subsequent PWM cycles for the image so as to extend the initial power ramp-up time.

Claims

1. A backlight for a display, the backlight comprising:

a plurality of groups of light emitters, each group comprising at least one light emitter;

a power supply, the power supply configured to supply power to the groups of light emitters; and

one or more controllers, the controllers configured to control brightness levels of the light emitters within the groups by applying pulse width modulation (PWM) driving signals to each light emitter, the PWM driving signals having a period T, a duty cycle proportional to the brightness level, and a phase offset that varies between the groups;

wherein the brightness levels depend upon received image data representing an image to be displayed and wherein the brightness levels of at least two light emitters are independently controllable.

2. A backlight according to claim 1 wherein the duration of a first PWM cycle of the PWM driving signals for the image is controllable to be different from the period T of subsequent PWM cycles for the image.

3. A backlight according to claim 2 wherein the duration of the first PWM cycle for the image is controllable to be 2T.

4. A backlight according to claim 1 wherein the phase offsets associated with each group are configurable to differ by increments of 360/N where N is the number of groups of light emitters.

5. A backlight according to claim 1 wherein each group comprises a tile comprising an array of light emitters.

6. A backlight according to claim 4 wherein each tile comprises a printed circuit board.

7. A method for controlling light emitters of a backlight, the method comprising:

determining brightness values for groups of the light emitters based on image data representing an image to be displayed;

determining PWM duty cycles for the groups of light emitters based on the brightness values;

applying PWM driving signals having the determined duty cycles and having phase offsets that are different for each group to the light emitters;

wherein a duration of a first PWM cycle of the PWM driving signals for the image is longer than the duration of subsequent PWM cycles for the image.

8. A method according to claim 7 wherein each PWM cycle of the applied PWM driving signals comprises a first percentage of time that corresponds to the duty cycle in an ON state preceding a remaining percentage of time in an OFF state.

9. A method according to claim 8 wherein each PWM cycle of the applied PWM driving signals comprises a first percentage of time in an OFF state preceding a remaining percentage of time that corresponds to the duty cycle in an ON state.

10. A backlight comprising a plurality of light emitters and a power supply, the power supply having a maximum power surge capacity that is less than a combined current draw of all of the light emitters of the backlight.

11. A display comprising N light emitters, each of the light emitters, when driven, drawing an in-rush current A, and a power supply connected to supply electrical power to the N light emitters, the power supply having a maximum out-rush current M where M<

(N)(A).

12. A display according to claim 11 wherein M<

0.75(N)(A).

13. A display according to claim 11 wherein M<

0.5(N)(A).

14. A display comprising:

a spatial light modulator;

a backlight comprising a plurality of groups of light emitters for illuminating the spatial light modulator, each group comprising at least one light emitter;

a power supply, the power supply configured to supply power to the groups of light emitters; and

one or more controllers, the controllers configured to control brightness levels of the light emitters within the groups by applying pulse width modulation (PWM) driving signals to each light emitter, the PWM driving signals having a period T, a duty cycle proportional to the brightness level, wherein the one or more controllers are configured to apply a different phase offset to the PWM driving signals for the light emitters of each of the groups;

wherein the brightness levels depend upon received image data representing an image to be displayed and wherein the brightness levels of at least two light emitters are independently controllable.

15. A lighting apparatus comprising a plurality of PWM driving circuits, each PWM driving circuit configured to generate PWM signals to drive one or more light emitters, wherein the PWM signals of each PWM driving circuit are configured to have a different phase offset.

16. A lighting apparatus according to claim 15 wherein the phase offset of each PWM driving circuit is controlled by a clock signal connected to the PWM driving circuit.

17. A lighting apparatus comprising a plurality of PWM driving circuits, each PWM driving circuit configured to generate PWM signals to drive one or more light emitters, wherein the PWM signals of each PWM driving circuit are configured to be time multiplexed.