(19) United States
`(12) Patent Application Publication (10) Pub. No.: US 2006/0022999 A1
`(43) Pub. Date:
`Feb. 2, 2006
`Lee et al.
`
`US 20060022999A1
`
`(52) U.S. Cl. .............................................................. 345/690
`
`(57)
`
`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 rep
`resenting a color of light produced by an LED light Source
`are received. The received tristimulus values are then com
`pared 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.
`
`(54) METHODS AND APPARATUS FOR SETTING
`THE COLOR POINT OF AN LED LIGHT
`SOURCE
`(76) Inventors: Joon Chok Lee, Kuching Sarawak
`(MY); Len Li Kevin Lim, Taiping
`Perak (MY); Rizal Bin Jaffar, Masjid
`Tanah Melaka (MY)
`Correspondence Address:
`AGILENT TECHNOLOGIES, INC.
`Legal Department, DL429
`Intellectual Property Administration
`P.O. Box 75.99
`Loveland, CO 80537-0599 (US)
`(21) Appl. No.:
`10/902,409
`(22) Filed:
`Jul. 28, 2004
`Publication Classification
`
`(51) Int. Cl.
`G09G 5/10
`
`
`
`(2006.01)
`
`530
`
`LED
`DRIVERS
`
`522
`
`524
`
`CONTROLLER
`
`526
`
`C
`
`PGR2023-00016 - Home Depot
`Ex. 1031 - Page 1
`
`

`

`Patent Application Publication Feb. 2, 2006 Sheet 1 of 5
`
`US 2006/0022999 A1
`
`100
`
`
`
`RECEIVE USER-SELECTED COLOR POINT
`
`102
`
`104
`
`DERIVERGBTRISTIMULUS VALUES FOR THE USER-SELECTED COLOR POINT
`
`110
`TRANSFORM USER-SELECTED COLOR POINT TO XYZ TRISTIMULUS VALUES 1
`
`- - - - - or or - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - .2
`
`SETERROR FLAGF COLOR POINT INVALID 1
`
`- - - - - - - - - - - - - - - - - - - - - -
`
`- a
`
`- a -- a- as a
`
`- a
`
`a
`
`a
`
`- -
`
`-
`
`114
`
`CONVERT XYZ TRISTIMULUS VALUESTORGBTRISTIMULUS VALUES /
`
`-------------------------------------------------------------------
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`DETERMINE WHETHER USER-SELECTED COLOR POINT
`ISOUTSIDE THE COLOR SELECTION RANGE OF AN LED
`LIGHT SOURCE AND, IFSO, SETANERROR FLAG
`
`GENERATEPULSE WIDTH MODULATED
`SIGNALS FOR LED DRIVERS
`
`FIG. 1
`
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`
`

`

`Patent Application Publication Feb. 2, 2006 Sheet 2 of 5
`
`US 2006/0022999 A1
`
`
`
`1931 CIE Chromaticity
`Diagram
`
`FIG. 2
`
`PGR2023-00016 - Home Depot
`Ex. 1031 - Page 3
`
`

`

`Patent Application Publication Feb. 2, 2006 Sheet 3 of 5
`
`US 2006/0022999 A1
`
`300
`
`>a RECEIVE USER-SELECTED COLOR POINT
`
`104
`
`FIG. 3
`
`102
`
`DERIVERGBTRISTIMULUS VALUES FOR THE USER-SELECTED COLOR POINT
`
`-
`
`- - - - - - - - - - - - - - - m - -n - - - - - - - - - - - - - - -
`
`- - - a - as as as as a
`
`m - w m
`
`m r
`
`- a - as as up we we - - - - -
`
`- - - - m - is - - a
`
`110
`
`
`
`
`
`
`
`
`
`f14
`CONVERTXYZTRISTIMULUS VALUESTORGBTRISTIMULUS VALUES -
`
`-------------------------------------------------------------------
`
`
`
`302
`
`310
`
`
`
`COMPARE TRISTMULUS VALUES
`ACQUIRED FROM LED LIGHT SOURCE
`TORGBTRISTIMULUS VALUES FOR
`USER-SELECTED COLOR POINT
`
`312
`
`ACOURE TRISTMULUS
`VALUES FROM
`LED LIGHT SOURCE
`
`320 - . 1 N
`
`------------------
`
`SETERROR FLAGFJ-O AND
`USER-SELECTED COLOR
`POINT NOTACHIEVED
`
`322
`
`
`
`GENERATE DRIVE
`SIGNALS FOR LEDS
`
`
`
`GENERATEPULSE WIDTH
`MODULATED SIGNALS FOR
`LED DRIVERS
`
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`

`

`Patent Application Publication Feb. 2, 2006 Sheet 4 of 5
`
`US 2006/0022999 A1
`
`400
`
`N RECEIVE USER-SELECTED COLOR POINT
`
`102
`
`DERIVERGBTRISTIMULUS VALUES FOR THE USER-SELECTED COLOR POINT
`
`104
`
`DETERMINE WHETHER USER-SELECTED COLOR POINT SOUTSIDE
`THE COLOR SELECTION RANGE OF AN LED LIGHT SOURCE
`
`106
`
`404
`
`406 N
`
`
`
`
`
`
`
`COLOR
`CONFIRMED
`BYUSER2
`
`
`
`
`
`MAKE DRIVE
`SIGNAL PREDICTION
`
`PREDICT LED
`DUTY FACTORS
`
`
`
`
`
`
`
`
`
`Y1PREDICT
`ON
`
`402
`
`N
`
`COMPARE TRISTIMULUS VALUES
`ACQUIRED FROM LEDLIGHT SOURCE
`TO RGBTRISTIMULUS VALUES FOR
`ER-SELECT
`LOR POINT
`USERSELECTED COLOR POINT
`
`
`
`-rr was war -
`
`w
`
`- -
`
`-
`
`-
`
`-
`
`-
`
`-
`
`-
`
`- we we w w s - - - - - - as a
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`SETERROR FLAGF
`JEO AND USER
`SELECTED COLOR
`POINT NOT
`ACHIEVED
`
`FIG. 4
`
`302
`
`ACOUIRE TRISTIMULUS
`VALUES FROM LED
`LIGHT SOURCE
`
`GENERATE DRIVE
`SIGNALS FOR LEDS
`
`GENERATEPULSE
`WOTHMODULATED
`SIGNALS FOR LED
`DRIVERS
`
`
`
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`

`

`Patent Application Publication Feb. 2, 2006 Sheet 5 of 5
`
`US 2006/0022999 A1
`
`
`
`530
`
`522
`
`FIG. 5
`
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`

`

`US 2006/0022999 A1
`
`Feb. 2, 2006
`
`METHODS AND APPARATUS FOR SETTING THE
`COLOR POINT OF AN LED LIGHT SOURCE
`
`BACKGROUND
`Light from a plurality of light emitting diodes
`0001
`(LEDs) of different colors (e.g., red, green and blue) has
`been used to create a light Source of predetermined spectral
`balance (e.g., a “white' light Source). See, for example, the
`U.S. Pat. No. 6,448,550 of Nishimura entitled “Method and
`Apparatus for Measuring Spectral Content of LED Light
`Source and Control Thereof. At times, a user may wish to
`Set the color point of an LED light Source-especially in
`applications Such as liquid crystal display (LCD) backlight
`ing and decorative lighting.
`SUMMARY OF THE INVENTION
`0002. A first method comprises receiving a user-selected
`color point. Red, green and blue (RGB) tristimulus values
`are then derived for the user-selected color point, with the
`RGB tristimulus values being dependent on a color Sensing
`system of an LED light source. 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.
`0003) A second method comprises receiving tristimulus
`values representing a color of light produced by an LED
`light Source. The received tristimulus values are then com
`pared 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.
`0004. An integrated circuit for controlling an LED light
`Source comprises an interface for receiving a user-Selected
`color point Specified in a device independent color Space, a
`memory for Storing an indication of Said user-Selected color
`point, and a controller. The controller is configured to 1)
`derive RGB tristimulus values for the user-selected color
`point, 2) determine whether the user-selected color point is
`outside a color Selection range of the LED light Source and,
`if so, set an error flag, and 3) in response to the RGB
`tristimulus values, generate pulse width modulated Signals
`for a plurality of LED drivers for the LED light source.
`0005. Other embodiments of the invention are also dis
`closed.
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`0006 Illustrative and presently preferred embodiments of
`the invention are illustrated in the drawings, in which:
`0007 FIGS. 1, 3 & 4 illustrate alternate exemplary
`methods for Setting the color point of an LED light Source;
`0008 FIG. 2 illustrates a 1931 CIE Chromaticity Dia
`gram; and
`0009 FIG. 5 illustrates an integrated circuit having a
`controller for Setting the color point of an LED light Source.
`DETAILED DESCRIPTION OF AN
`EMBODIMENT
`0010 FIG. 1 illustrates a first exemplary method 100 for
`setting the color point of an LED light source. The method
`
`100 begins with the receipt 102 of a user-selected color
`point. A user may specify the color point in a variety of
`ways, and may often specify the color point in a device
`independent color Space Such as a 1931 Commission Inter
`nationale de I Eclairage (CIE) XYZ color space, a Yxy color
`space, an RGB color space, or a 1976 Yu'v' color space.
`Device independent color Spaces often provide a wide range
`of colors from which a user may select a color point. In Some
`cases, the user may provide the color point by clicking (e.g.,
`with a mouse) on a color representing a desired color point.
`In other cases, the user may input Specific luminance and
`chrominance values.
`0011. After receiving the user-selected color point, the
`method 100 continues with the derivation 104 of RGB
`tristimulus values (e.g., new RGB colorimetric tristimulus
`values) for the user-selected color point. Unlike the received
`color point, which may be device independent, the derived
`RGB tristimulus values will be dependent on the color
`Sensing System of the LED light Source.
`0012. When deriving the RGB tristimulus values, it is
`determined 106 whether the user-selected color point is
`outside the color Selection range of the LED light Source.
`The color Selection range of an LED light Source is the Set
`of all possible color points that may be produced by the light
`Source. By way of example, FIG. 2 provides a 1931 CIE
`Chromaticity Diagram (with the 1931 CIE color space being
`represented by the bounded area A). If a light Source is
`comprised of RGB LEDs having respective wavelengths of
`R1, G1 and B1, then the color selection range of the RGB
`light source is represented by the triangular area B. Point U1
`represents a user-Selected color point that is within the color
`Selection range of the RGB light Source, and point U2
`represents a user-Selected color point that is outside the color
`Selection range of the RGB light Source. If a user-Selected
`color point is determined to be outside the color Selection
`range of an LED light Source, an error flag may be Set 106.
`The error flag may then be retrieved by the user, or the user's
`Software or control device, Such as a microcontroller or
`computer. Alternately, a control System associated with the
`LED light Source may notify the user that the error flag has
`been set (e.g., by sending an alert to the user's Software or
`computer).
`0013 By way of example, RGB tristimulus values may
`be derived from the user-selected color point by first trans
`forming 110 the user-selected color point into XYZ tris
`timulus values (e.g., CIE 1931 XYZ tristimulus values).
`These XYZ tristimulus values may then be converted 114
`into RGB tristimulus values using a conversion matrix. By
`way of example, one way to determine whether the user
`Selected color point is outside the color Selection range of the
`LED light Source is via a mathematical equation based on
`the LED light Source's color coordinates and the user
`Selected color point.
`0014. During transformation 110 of the user-selected
`color point, it may be determined whether the user-Selected
`color point is invalid. With reference to the 1931 CIE color
`space shown in FIG. 2, point U3 would be an invalid color
`point, as it is outside of the 1931 CIE color space. If a
`user-Selected color point is determined to be invalid, an error
`flag may be set 112.
`0.015 The method 100 continues with the generation 108
`of pulse width modulated signals for a plurality of LED
`drivers for an LED light source.
`
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`

`US 2006/0022999 A1
`
`Feb. 2, 2006
`
`0016. Using the method 100, a user may select an LED
`light Source's color point in a device independent color
`Space which is easy for the user to comprehend, and then
`receive an error notification if the Selected color point is
`invalid or unachievable.
`0017 FIG. 3 illustrates a second exemplary method 300
`for setting the color point of an LED light source. The
`method 300 extends the method 100 by providing details as
`to how an LED light Source is controlled using a user
`selected color point. In the method 300, a set of tristimulus
`values representing a color of light produced by an LED
`light Source are acquired 302. By way of example, this may
`be accomplished by means of a color Sensor 304, low-pass
`filter 306 and analog-to-digital converter (ADC) 308. The
`color sensor 304 may comprise three filtered photodiodes
`that receive incident light from the light source's LEDs. For
`example, for a light Source comprised of red, green and blue
`LEDs, three photodiodes may be respectively provided with
`color filters for red, green and blue light. In this manner, the
`different photodiodes may sense different wavelengths of
`light. The color sensor 304 may also comprise amplifier
`circuitry to convert photonic light readings to output Volt
`ages. The low-pass filter 306 may be used to average the
`Sensor's output voltages and provide low-ripple direct cur
`rent (DC) output voltages that correspond to the time
`average of the sensor's output voltages. The ADC 308 may
`then convert the DC output voltages to digital representa
`tions thereof.
`0018. The method 300 continues with a comparison 310
`of the tristimulus values acquired from the light Source to the
`RGB tristimulus values for the user-selected color point. In
`response to the comparison 310 of tristimulus values, pulse
`width modulated signals for LED drivers are generated 108.
`For example, as a byproduct of comparing tristimulus Val
`ues, drive signal duty factors may be set 312 for the LEDs
`(e.g., by looking them up, calculating them, or by basing
`them on a fixed increment/decrement over previous duty
`factors). The duty factors may then be used to generate 108
`pulse width modulated signals for the LED drivers. Depend
`ing on the nature of the LED light Source, a set of drive
`Signals may be then be generated 314 for the light Source as
`a whole (e.g., a single set of red, green and blue drive
`Signals), or sets of drive signals may be generated for
`various groups of the light Source's LEDS.
`0019. In one embodiment of the method 300, pulse width
`modulated Signals are generated for LED driverS So as to
`cause the tristimulus values acquired from an LED light
`Source to match the tristimulus values corresponding to the
`user-identified color point. In an alternate embodiment of the
`method 300, pulse width modulated signals are generated
`for LED drivers So as to cause the tristimulus values
`acquired from an LED light Source to fall within an accepted
`range of tristimulus values (i.e., a range of tristimulus values
`about the tristimulus values corresponding to the user
`identified color point).
`0020. The method 300 further comprises an optional
`error-reporting routine 316, 318,320,322. By means of the
`error-reporting routine 316-322, the method 3001) receives
`tristimulus values from the LED light Source, 2) compares
`310 the tristimulus values to those corresponding to user
`selected color point, and 3) generates 108 pulse width
`modulated signals for LED drivers for a predetermined
`
`number of repetitions. After the predetermined number of
`repetitions (i.e., J=0), the method 300 sets 322 an error flag
`if the user-Selected color point has not been achieved by the
`LED light source.
`0021. Using the method 300, the color point of the
`combined light produced by a plurality of LEDs may be
`maintained even though individual LEDs are Subject to
`manufacturing variance, or drift in their light output as a
`result of temperature, aging and other effects.
`0022 FIG. 4 illustrates a third exemplary method 400 for
`setting the color point of an LED light source. The method
`400 extends the method 300 by providing a color point
`prediction routine 402, 404, 406, 408, 410, 412. If the
`prediction routine is active, drive signals generated for a
`light source's LEDs are based on predicted 408 pulse width
`modulated Signals, rather than on a comparison 310 of
`acquired and desired tristimulus values. In one embodiment,
`the drive signal prediction 408 comprises a predication of
`LED duty factors 410. These duty factors may be predicted
`by, for example, looking them up in a table, or calculating
`them using a conversion matrix. Predicted pulse width
`modulated Signals are then maintained for a predetermined
`period (e.g., until I=0). Optionally, if a user confirms 406
`their color point selection, the prediction routine 402-412
`may be exited. Once the prediction routine 402-412 is
`exited, drive signals for an LED's light Source may be
`generated in response to a comparison 310 of acquired and
`desired tristimulus values.
`0023 FIG. 5 shows an integrated circuit 500 for control
`ling an LED light source 502. In one embodiment, the LED
`light source 502 comprises red, green and blue LEDs
`504-520. However, the LED light source could also com
`prise additional and/or other colors of LEDs. Further, the
`LED light Source could take various forms, Such as that of
`a display backlight, accent lighting, or other form of light
`SOCC.
`0024. As shown, the integrated circuit 500 comprises an
`interface 522 for receiving a user-Selected color point. By
`way of example, the interface 522 may comprise an Inter-IC
`(I°C) or System Management Bus (SMBus) interface. A
`user-Selected color point may be received via Such an
`interface by coupling the interface to a control device Such
`as the user's computer, a microcontroller, or one or more
`control Switches (e.g., buttons or sliders).
`0025 The integrated circuit 500 also comprises a
`memory 524 for Storing an indication of the user-Selected
`color point. In some embodiments, the memory 524 may be
`a random access memory (RAM) or an electrically erasable
`programmable read-only memory (EEPROM). The indica
`tion of the user-Selected color point may variously comprise
`the user-Selected color point (e.g., in the form of chromi
`nance and luminance values), or tristimulus values or inter
`mediate data based thereon.
`0026. The integrated circuit 500 further comprises a
`controller 526. In one embodiment, the controller 526 is
`configured to 1) derive RGB tristimulus values for the
`user-selected color point, 2) determine whether the user
`Selected color point is outside the color Selection range of the
`LED light source 502 and, if so, set an error flag, and 3) in
`response to the RGB tristimulus values, generate drive
`signals for a plurality of LEDs 504-520 forming the LED
`
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`

`US 2006/0022999 A1
`
`Feb. 2, 2006
`
`light source 502. In another embodiment, the controller 526
`is configured to 1) receive tristimulus values representing a
`color of light produced by the LED light source 502, 2)
`compare the received tristimulus values to desired tristimu
`lus values, 3) in response to this comparison, generate pulse
`width modulated signals for the LEDs 504-520, and 4)
`repeat the above actions a predetermined number of times,
`and then Set an error flag if the user-Selected color point has
`not been achieved by the LED light source 502. The
`controller 526 may also be configured to implement any of
`the methods 100, 300, 400 disclosed herein.
`0027. As shown, the controller 526 may receive the
`tristimulus values representing a color of light produced by
`the LED light source 502 from a color sensor 528. The color
`Sensor 528 may be a separate device, or may be variously
`included within (or on) the integrated circuit 500 or display
`502.
`0028. The pulse width modulated signals produced by the
`controller 526 may be provided to one or more LED drivers
`530 (e.g., three LED drivers to respectively drive the red,
`green and blue LEDs of the display 502). The LED drivers
`530 may be a separate device or devices, or may be variously
`included within (or on) the integrated circuit 500 or display
`502.
`
`What is claimed is:
`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 val
`ues being dependent on a color Sensing System of a
`light emitting diode (LED) light Source;
`determining whether the user-Selected color point is out
`Side 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 tri
`Stimulus values, and
`converting the XYZ tristimulus values into RGB tristimu
`lus 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 receiv
`ing, 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 Sig
`nals 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 Sig
`nals 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 Sig
`nals 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,
`
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`US 2006/0022999 A1
`
`Feb. 2, 2006
`
`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 receiv
`ing, 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
`IEclairage (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 receiv
`ing, 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 tris
`timulus 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 con
`troller 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 receiv
`ing, 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 con
`troller is further configured to implement a color point
`prediction routine, wherein:
`if the color point prediction routine is active, the control
`ler:
`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 con
`troller:
`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
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`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 modu-
`lated Signals, respectively corresponding to red, green and
`blue LEDs of the LED light source.
`
`18. The integrated circuit of claim 13, wherein the inter
`face is an Inter-IC (I°C) interface.
`19. The integrated circuit of claim 13, wherein the inter
`face is a System Management Bus (SMBus) interface.
`
`k
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