發光二極體背光模組之光學回授設計

Optical feedback design for Light Emitting Diode backlight module

周智勤(Chih-Chin Chou)

指導教授 ： 黃惠良 ； 黃忠民

國立清華大學/電機資訊學院/積體電路設計產業研發碩士專班/碩士(2007年)

摘要

隨著LED(發光二極體)亮度的提高與其飽和的色彩，LED開始被運用為液晶顯示器的背光模組光源，採用RGB三色LED取代傳統的冷陰極螢光燈管作為發光源可以大幅改善液晶顯示器的明亮度和色彩表現。然而RGB-LED 背光模組與其光學設計需要一些特殊考量:如個別LED的色彩必須適當混合以獲得良好的色彩均勻度，同時要使RGB LED的光強度可以得到穩定的白光輸出。RGB三色LED背光模組額外的好處還有寬廣的色域範圍、較長的生命週期、節省能源以及符合環保等。RGB三色LED背光模組令人困擾的問題是由於LED在長時間使用下，其元件隨溫度的變化會影響亮度和色溫穩定性，因此光學回饋控制成為LED背光模組的一項關鍵技術。 在本論文中，我們採用了利用光二極體來作回授補償，以使其穩定性提高，並且針對不同顏色LED光找出其和光二極體之間特性的關係，經由類比數位轉換器將兩者關係線性化，再經由微處理器運算所得的最佳值做為參考，以做為回饋控制的依據。

關鍵字

LED

並列摘要

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.

參考文獻

[3] Gerard Harbers, Christoph Hoelen, “High Performance LCD Backlighting using High Intensity Red, Green and Blue Light Emitting Diodes.” SID’01 Digest, LP-2,702(2001).

[7] E. Fred Schubert, “Light-Emitting Diodes”, 2nd ed, 2006

[9] Ian Ashdown, “Extended Parallel Pulse Code Modulation of LEDs”, TIR Systems Limited, 7700 Riverfront Gate, Burnaby, British Columbia, Canada V5J 5M4

[10] Marc Dyble, Nadarajah Narendran, Andrew Bierman, and Terence Klein, “Impact of Dimming White LEDs: Chromaticity Shifts Due to Different Dimming Methods”, Lighting Research Center, Rensselaer Polytechnic Institute, Troy, NY 12180

[20] Ljubisa Ristic, “Sensor Technology and Devices”, Artech House, 1994, Chapter 9,Planar Silicon Photosensors, page 317~322.