| Summary: | 碩士 === 國立清華大學 === 產業研發碩士積體電路設計專班 === 95 === Light Emitting Diode (LED) is light source with high efficient and vivid colors. The illuminance of LED is increasing year by year, so LED is considered to be
integrated into a direct backlight. By using red, green, and blue (RGB) LEDs instead of cold cathode fluorescent lamps (CCFL) in LCD backlights brightness and color
performance LCD displays can be improved considerably. However, the design of an RGB-LED backlight and optical design need some special attention: the colors of the
separate LEDs need to be mixed well to obtain good color uniformity while a good balance between the red, green and blue LED has to be maintained to stabilize the white light. Additional features of an RGB-LED backlight solution are large color range, long lifetime, energy saving and environmental friendliness. An inconvenient property of LED backlight module is the dependence of light output on temperature and lifetime thus resulting in varying chromaticity and luminance. Optical feedback control system is a key technology for LED backlighting module.
In this paper, we use the photodiode of an optical color sensing feedback system for an LED backlight module to improve the stability. Moreover, we find out the
relationship between different colors LED and photodiode characteristic, through A/D converter to linearization the relationship. Refer to the optimum values calculate by microcomputer for the basis to operation the optical feedback control system.
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