RGB ILLUMINATOR WITH CALIBRATION
VIA SINGLE DETECTOR SERVO
BACKGROUND OF THE INVENTION
The present invention relates generally to methods and arrangements for calibrating illumination assemblies to obtain desired white-point, color balance and/or intensity. More specifically, the invention relates to using electronic storage devices and/or photodetectors and electronic circuitry to vary the current supplied to illumination devices such as light-emitting diodes, thus providing a calibrated light source for display applications.
In micro-display applications utilizing tri-color RGB (red, green and blue) light-emitting diode (LED) assemblies to illuminate a display panel, LED part-to-part illumination variation results in inconsistent brightness, white-point and color balance. Every LED's illumination output as a function of current is different, and each LED's illumination response to current across its entire current-controlled operating range may be non-linear. Manufacturing LEDs within tighter tolerances and more closely matching the three LED colors in a single assembly, thereby providing a more stable white-point and/or color balance, would be unnecessarily expensive, and would nevertheless provide unsatisfactory results.
Referring initially to FIG. 1, a prior art display system 100 providing a partial solution to the above-described problem will be described. Display system 100 includes a light modulating display 102, an illumination device 104, which provides the light source for display 102, and an adjustable current source 106 electrically connected to illumination device 104. Adjustable current source 106 is manually adjusted during manufacturing in order to cause illumination device 104 to provide calibrated light. The adjustment takes place by comparing the illumination output of illumination device 104 to a reference intensity and adjusting current source 106 until the illumination output of illumination device 104 matches the reference intensity. If illumination device 104 contains more than one light source, the process is repeated for each light source.
Display system 100 further includes a controller 108 and a display information input 110. During operation of display system 100, controller 108 receives display information via input 110 and determines the current to be supplied to illumination device 104. The setting made during manufacturing to adjustable current source 106 causes the current to vary proportionally to the setting, thereby providing partially calibrated light. Because the adjustment made to adjustable current source 106 during manufacturing calibrates the illumination output of illumination device 104 for only a single intensity, this system does not correct the non-linear illumination response to current of illumination device 104 across the device's entire current-controlled operating range.
Display system 100 includes the additional limitation that adjustable current source 106 must be manually set during manufacturing. Having to manually calibrate the current source increases the cost of producing such a device. FIG. 2 illustrates a display system that overcomes this particular limitation.
Referring now to FIG. 2, a second prior art display system 120 will be described using like reference numbers for like components. Display system 120 includes a voltage source 122 and an adjustable resistor 124. Adjustable resistor 124 may be a laser trim resistor that is capable of being adjusted
during manufacturing using an automated process to provide the desired intensity for a specific voltage. While this method overcomes one limitation of display system 100 by allowing the calibration to be accomplished by automated
5 means during manufacturing, display system 120 similarly fails to correct the non-linear illumination response to current of illumination device 104 across its entire currentcontrolled operating range. Further, neither display system 100 nor display system 120 is capable of correcting illumi
10 nation device variations that occur after manufacturing, such as illumination device aging.
The present invention discloses arrangements and methods for calibrating illumination devices to reduce both preand post-manufacturing variations, including non-linear
15 illumination output as a function of current across the current-controlled operating range and illumination device aging.
SUMMARY OF THE INVENTION
As will be described in more detail hereinafter, a display system including an arrangement for calibrating an inputdriven illumination device is disclosed. The display system includes a spatial light modulator divided into an array of individually controllable pixels and an input-driven illumination device which is adapted to receive a variable input and which is configured to direct light of variable intensity onto the modulator, depending on the input. The display system further includes an arrangement adapted for connec3Q tion with the illumination device for providing to the illumination device a specific input for a desired intensity level of the light, the specific input being provided from calibration information particular to the illumination device. The arrangement further includes a memory device for storing the calibration information.
A method of operating a display system as described above includes determining calibration information for an input driven illumination device which is adapted to receive a variable input and which is configured to direct light of
40 variable intensity onto a light modulator, depending on the input. The method further includes storing the calibration information in a memory device and establishing a specific input for a desired intensity level of the light from the calibration information. The method further includes pro
45 viding the specific input to the illumination device, and directing the light of the desired intensity level onto the light modulator.
As will be described in more detail hereinafter, an illumination assembly, including calibration information is also
50 disclosed. The illumination assembly includes an inputdriven illumination device which is adapted to receive a variable input and which is configured to produce light of variable intensity depending on the input. The illumination assembly further includes an arrangement including a
55 memory device for storing calibration information and generating from the information a specific input for causing the illumination device to produce light of a particular intensity. The arrangement is adapted to be connected with the illumination device such that the latter receives the specific
In another embodiment of a display system, the display system includes a light modulator and an input-driven illumination device which has been pre-calibrated to provide light of a given intensity in response to a particular input and 65 which is configured to direct the light onto the modulator. The display system further includes an electronic storage arrangement for storing a value which corresponds to the