應用於紅,藍,綠發光二極體色彩穩定之控制回饋系統設計

Abstract

顯示科技蓬勃發展，液晶顯示器(Liquid Crystal Display)已成為取代陰極射線管顯示器(Cathode Ray Tube Monitor)最強大的主流產品，由於液晶顯示器並非主動發光元件，必須仰賴一個外加的光源系統，此即所謂的背光模組，而背光模組使用冷陰極射線管(Cold Cathode Fluorescent Lamp)充當光源已行之有年；發光二極體(Light Emitting Diode)因較冷陰極射線管具有壽命長,廣色域、省電、環保、反應快速等多項優點，已成為液晶顯示器背光源的新選擇。然而，長時間使用下而產生的熱，往往造成發光二極體的發光顏色偏移，此在顯示器要求高色彩品質的標準下，是最不樂見的。 本論文提出了使用光二極體感測發光二極體的光輸出訊號，經類比數位轉換的裝置，套用反覆逼近的程式，設計建立一組μA等級的電流逼近的發光二極體色彩穩定回饋系統。回饋系統在 13 位元解析下，可將對應於使用 3250, 3969, 及4462小時的紅色，藍色及綠色發光二極體的色偏值(Δu’v’)維持在內 0.005 (人眼恰可接受的範圍) 內。使用 14 位元解析下，可將紅，藍及綠色發光二極體的色偏值維持在內 0.004 之內。

LCD (Liquid Crystal Display) is the mainstream product to replace CRT (Cathode Ray Tube). Conventionally, CCFL (Cold Cathode Fluorescent Lamp) is used as a light source of LCD backlight. However, LED (Light Emitting Diode) is regarded as the candidate to replace CCFL (Cold Cathode Fluorescent Lamp) as light source of LCD backlight due to its wide color gamut, low operation voltage, mercuryfree characteristic, and fast switch response. The color shift due to heat effect after long time usage is an issue needed to resolve. In this thesis, a 14 bits recursive feedback control system is proposed and realized to stabilize the light output of RGB (red, green, and blue) LEDs by generating tiny recursive current in μA order. Whereas the just noticeable color difference (Δu’v’) of human is 0.005, feedback control system is proved that color difference (Δu’v’) of Red, Green, and Blue LEDs are kept within 0.005 under 13 bits resolution, and within 0.004 under 14 bits under aging simulation of 3250, 3969, and 4462 hours usage, respectively.