Methods and apparatus for regulating the drive currents of a plurality of light emitters

• US 20060054776A1
• Filed: 09/10/2004
• Published: 03/16/2006
• Est. Priority Date: 09/10/2004
• Status: Active Grant

• Current Assignee: Avago Technologies International Sales Pte Limited (Broadcom, Inc.)
• Original Assignee: Avago Technologies ECBU IP Singapore Pte Limited (Broadcom, Inc.)
• Inventors: Nishimura, Ken A.
• Granted Patent: US 7,759,622 B2
• Time in Patent Office: Days
• US Class Current: 250/206
• CPC Class Codes: H05B 45/22 using optical feedback

Abstract

In one embodiment, ones of a plurality of drive currents are modulated in accordance with ones of a plurality of unique modulation sequences. The modulated drive currents are then applied to a plurality of light emitters. Thereafter, a stream of optical measurements is obtained from a photosensor that is positioned to sense the aggregate light emitted by the light emitters. The stream of optical measurements is then correlated with the modulation sequences to extract optical responses to each of the plurality of drive currents. Finally, each drive current is regulated based on its relationship to its corresponding optical response. Related apparatus, and other methods for regulating the drive currents of a plurality of light emitters, is also disclosed.

Claims

1. Apparatus, comprising:

a plurality of light emitters;

a photosensor, positioned to sense an aggregate light emitted by the light emitters; and

a control system to i) modulate ones of a plurality of drive currents in accordance with ones of a plurality of unique modulation sequences, ii) apply the modulated drive currents to the light emitters, iii) correlate a stream of optical measurements taken by the photosensor with the unique modulation sequences to extract optical responses to each of the plurality of drive currents, and iv) regulate each drive current based on its relationship to its corresponding optical response.

2. The apparatus of claim 1, wherein the light emitters comprise emitters that emit light of different wavelengths.

3. The apparatus of claim 1, wherein the light emitters are solid-state light emitters.

4. The apparatus of claim 3, wherein the light emitters are light emitting diodes (LEDs).

5. The apparatus of claim 1, wherein the plurality of light emitters forms a backlight for a liquid crystal display (LCD).

6. The apparatus of claim 1, wherein the plurality of light emitters forms a display.

7. The apparatus of claim 1, wherein the unique modulation sequences are based on pseudo-random bit sequences (PRBSs).

8. The apparatus of claim 1, wherein the unique modulation sequences are orthogonal to one another.

9. The apparatus of claim 1, wherein the unique modulation sequences are based on Haddamarand-Walsh sequences.

10. The apparatus of claim 1, wherein the unique modulation sequences are based on Gold sequences.

11. The apparatus of claim 1, wherein the unique modulation sequences are periodic in nature.

12. The apparatus of claim 1, wherein the control system modulates ones of the plurality of drive currents with a pilot tone that is modulated by ones of the plurality of unique modulation sequences

13. The apparatus of claim 12, wherein the pilot tone, in combination with each unique modulation sequence, has an amplitude that is within two percent (2%) of the nominal operating value of the drive current to which it is applied.

14. The apparatus of claim 1, wherein the control system applies each drive current to a different one of the light emitters.

15. The apparatus of claim 1, wherein the control system applies each drive current to a subset of the light emitters.

16. The apparatus of claim 1, wherein the control system extracts the optical responses serially.

17. The apparatus of claim 1, wherein the control system extracts the optical responses in parallel.

18. A method, comprising:

modulating ones of a plurality of drive currents in accordance with ones of a plurality of unique modulation sequences;

applying the modulated drive currents to a plurality of light emitters;

obtaining a stream of optical measurements from a photosensor that is positioned to sense an aggregate light emitted by the light emitters;

correlating the stream of optical measurements with the unique modulation sequences, to extract optical responses to each of the plurality of drive currents; and

regulating each drive current based on its relationship to its corresponding optical response.

19. The method of claim 18, wherein the plurality of drive currents are modulated in accordance with ones of the plurality of unique modulation sequences by modulating the drive currents with a pilot tone that is modulated by ones of the plurality of unique modulation sequences

20. The method of claim 18, wherein the unique modulation sequences are orthogonal pseudo-random bit sequences (PRBSs).

21. Apparatus, comprising:

a plurality of light emitters;

a photosensor, positioned to sense an aggregate light emitted by the light emitters; and

a control system to i) apply a plurality of drive currents to the light emitters, ii) periodically alter one of the drive currents by a predetermined amount for a predetermined time, iii) for each drive current alteration, obtain readings from the photosensor with and without the drive current alteration, and iv) regulate each drive current based on its relationship to its corresponding photosensor readings.

22. The apparatus of claim 21, wherein the light emitters comprise emitters that emit light of different wavelengths.