Methods and apparatus for setting the color point of an LED light source

• US 7,324,076 B2
• Filed: 07/28/2004
• Issued: 01/29/2008
• Est. Priority Date: 07/28/2004
• 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: Lee, Joon Chok, Lim, Len Li Kevin, Jaffar, Rizal Bin
• Primary Examiner(s): Hjerpe, Richard
• Assistant Examiner(s): TRAN, MY CHAU T
• Application Number:
  US10/902,409
• Publication Number:
  US 20060022999A1
• Time in Patent Office: 1,280 Days
• Field of Search: 345/82, 345/83, 345/87, 345/88, 345/102, 345/204, 345/690, 315/158, 315/159, 315/169.1, 315/169.3
• US Class Current: 345/83
• CPC Class Codes: H05B 45/20 Controlling the colour of the light
• CPC Class Codes: H05B 45/22 using optical feedback

Abstract

In one embodiment, a user-selected color point is received. RGB tristimulus values are then derived for the color point. It is also determined whether the user-selected color point is outside a color selection range of the LED light source and, if so, an error flag is set. Pulse width modulated signals for a plurality of LED drivers for the LED light source are also generated. In another embodiment, tristimulus values representing a color of light produced by an LED light source are received. The received tristimulus values are then compared to tristimulus values corresponding to a user-identified color point. In response to the comparison, pulse width modulated signals are generated for a plurality of LED drivers for the LED light source. After a predetermined number of repetitions of these actions, an error flag is set if the user-selected color point has not been achieved by the LED light source.

Claims

1. A method, comprising:

receiving a user-selected color point;

deriving red, green and blue (RGB) tristimulus values for the user-selected color point, the RGB tristimulus values being dependent on a color sensing system of a light emitting diode (LED) light source;

determining whether the user-selected color point is outside a color selection range of the LED light source and, if so, setting an error flag; and

in response to the RGB tristimulus values, generating pulse width modulated signals for a plurality of LED drivers for said LED light source.

2. The method of claim 1, wherein:

deriving RGB tristimulus values for the user-selected color point comprises;

transforming the user-selected color point into XYZ tristimulus values; and

converting the XYZ tristimulus values into RGB tristimulus values; and

the method further comprises setting an error flag if transformation of the user-selected color point reveals that the user-selected color point is invalid.

3. The method of claim 2, further comprising:

receiving tristimulus values representing a color of light produced by the LED light source;

comparing said received tristimulus values to said RGB tristimulus values;

in response to the comparison, generating said pulse width modulated signals;

repeating said receiving, comparing and generating actions; and

after a predetermined number of repetitions of said receiving, comparing and generating actions, setting an error flag if the user-selected color point has not been achieved by the LED light source.

4. The method of claim 2, further comprising:

if a color point prediction routine is active,

predicting pulse width modulated signals for the LEDs; and

maintaining said predicted pulse width modulated signals for a predetermined period; and

if the color point prediction routine is inactive,

receiving tristimulus values representing a color of light produced by the LED light source;

comparing said received tristimulus values to said RGB tristimulus values;

in response to the comparison, generating said pulse width modulated signals;

repeating said receiving, comparing and generating actions; and

after a predetermined number of repetitions of said receiving, comparing and generating actions, setting an error flag if the user-selected color point has not been achieved by the LED light source.

5. The method of claim 1, further comprising:

if a color point prediction routine is active,

predicting pulse width modulated signals for the LEDs; and

maintaining said predicted pulse width modulated signals for a predetermined period; and

if the color point prediction routine is inactive,

receiving tristimulus values representing a color of light produced by the LED light source;

comparing said received tristimulus values to said RGB tristimulus values;

in response to the comparison, generating said pulse width modulated signals; and

repeating said receiving, comparing and generating actions.

6. The method of claim 1, further comprising:

if a color point prediction routine is active,

predicting pulse width modulated signals for the LEDs; and

maintaining said predicted pulse width modulated signals for a predetermined period; and

if the color point prediction routine is inactive,

receiving tristimulus values representing a color of light produced by the LED light source;

comparing said received tristimulus values to said RGB tristimulus values;

in response to the comparison, generating said pulse width modulated signals;

repeating said receiving, comparing and generating actions; and

after a predetermined number of repetitions of said receiving, comparing and generating actions, setting an error flag if the user-selected color point has not been achieved by the LED light source.

7. The method of claim 1, further comprising:

receiving tristimulus values representing a color of light produced by the LED light source;

comparing said received tristimulus values to said RGB tristimulus values;

in response to the comparison, generating said pulse width modulated signals;

repeating said receiving, comparing and generating actions; and

after a predetermined number of repetitions of said receiving, comparing and generating actions, setting an error flag if the user-selected color point has not been achieved by the LED light source.

8. The method of claim 1, wherein the device independent color space is a 1931 Commission Internationale de I'"'"'Eclairage (CIE) XYZ color space.

9. A method, comprising:

receiving tristimulus values representing a color of light produced by a light emitting diode (LED) light source;

comparing said received tristimulus values to tristimulus values corresponding to a user-identified color point;

in response to the comparison, generating pulse width modulated signals for a plurality of LED drivers for said LED light source;

repeating said receiving, comparing and generating actions; and

after a predetermined number of repetitions of said receiving, comparing and generating actions, setting an error flag if the user-selected color point has not been achieved by the LED light source.

10. The method of claim 9, further comprising:

as a byproduct of said comparison, setting drive signal duty factors for the LEDs, said pulse width modulated signals being generated in response to the drive signal duty factors.

11. The method of claim 9, wherein said pulse width modulated signals are generated to match said tristimulus values representing the color of light produced by the LED light source to said tristimulus values corresponding to the user-identified color point.

12. The method of claim 9, wherein said pulse width modulated signals are generated to cause said tristimulus values representing the color of light produced by the LED light source to fall within an accepted range of tristimulus values about said tristimulus values corresponding to the user-identified color point.

13. An integrated circuit for controlling a light emitting diode (LED) light source, comprising:

an interface for receiving a user-selected color point;

a memory for storing an indication of said user-selected color point; and

a controller, configured to;

derive red, green and blue (RGB) tristimulus values for the user-selected color point;

determine whether the user-selected color point is outside a color selection range of said LED light source and, if so, set an error flag; and

in response to the RGB tristimulus values, generate pulse width modulated signals for a plurality of LED drivers for said LED light source.

14. The integrated circuit of claim 13, wherein:

the controller derives RGB tristimulus values for the user-selected color point by;

transforming the user-selected color point into XYZ tristimulus values; and

converting the XYZ tristimulus values into RGB tristimulus values; and

the controller is further configured to set an error flag if transformation of the user-selected color point reveals that the user-selected color point is invalid.

15. The integrated circuit of claim 13, wherein the controller is further configured to:

receive tristimulus values representing a color of light produced by the LED light source;

compare said received tristimulus values to said RGB tristimulus values;

in response to the comparison, generate said pulse width modulated signals;

repeat said receiving, comparing and generating actions; and

after a predetermined number of repetitions of said receiving, comparing and generating actions, set an error flag if the user-selected color point has not been achieved by the LED light source.

16. The integrated circuit of claim 13, wherein the controller is further configured to implement a color point prediction routine, wherein:

if the color point prediction routine is active, the controller;

predicts pulse width modulated signals for LEDs of the light source; and

maintains said predicted pulse width modulated signals for a predetermined period; and

if the color point prediction routine is inactive, the controller;

receives tristimulus values representing a color of light produced by the LED light source;

compares said received tristimulus values to said RGB tristimulus values;

in response to the comparison, generates said pulse width modulated signals;

repeats said receiving, comparing and generating actions; and

after a predetermined number of repetitions of said receiving, comparing and generating actions, sets an error flag if the user-selected color point has not been achieved by the LED light source.

17. The integrated circuit of claim 13, wherein the pulse width modulated signals comprise three pulse width modulated signals, respectively corresponding to red, green and blue LEDs of the LED light source.

18. The integrated circuit of claim 13, wherein the interface is an Inter-IC (I²C) interface.

19. The integrated circuit of claim 13, wherein the interface is a System Management Bus (SMBus) interface.