可適性即時背光亮度控制之積體電路設計

A Content Adaptive Backlight Control VLSI Design for Monitors

陳雕龍(Tiao-Lung Chen)

指導教授 ： 陳世綸

中原大學/工學院/電子工程研究所/碩士(2014年)

https://doi.org/10.6840/cycu201400696

摘要

液晶顯示器以其低成本、低能耗與高解析等優勢成為現今大多數電子產品所採用的平面顯示器。但隨著其普及化，尤其是在可攜式電子產品如智慧型手機、平板電腦等日漸普及的情況下，勢必長時間被一般大眾使用，如此縱然液晶顯示器相較於其他顯示器擁有低功耗特性，然而在人們習慣長時間使用下，其所造成的能量耗損也非常可觀。
為了降低液晶顯示器的能耗，首先針對主要核心進行分析。由於液晶顯示器的顯示原理是使用背光顯示原理，即無法透過自身通電主動發光，需依靠背光模組發光，故主要能耗是在背光模組上。過去有不少文獻探討如何降低背光模組的能耗，像是針對背光與液晶穿透率進行調整，或是從欲顯示之圖像本身的灰階值與背光亮度之相關性進行調整。
一般而言，提高穿透率去換取背光節能效果能得到較佳的影像品質，但會得到較差的節能效果(除非最大灰階值很低)，並且在計算上必須使用到開n次方根的計算，大大增加運算複雜度，不利積體電路的實現；至於透過提升像素灰階值來達到節能效果的方式，雖然能得到較佳的節能效果與使用較低複雜度的計算，然而最後得到的圖失真情況比較嚴重。
本論文將結合此二種概念，並改善各自的缺點，發展出二種創新的演算法。第一種演算法會使用標準差來調整穿透率，以獲得較好的節能效果且維持圖像低失真度；而第二種則帶入變異數，並嘗試以查表方式來取代開根號的複雜運算，雖然節能效果略遜於第一種演算法，但較易於積體電路實現且合成之晶片面積亦會小於第一種方法。本論文使用0.18 μm　CMOS製程技術進行實現，其操作頻率可達200 MHz，邏輯閘數目為7.3 K，晶片面積為88.7 K μm2 。

關鍵字

背光 ； 穿透率 ； 節能 ； 灰階

並列摘要

Since the TFT LCD with advantages of low cost, low power, and high resolution, it is popularly used in most of electronic products. But with its popularity, especially the portable electronic products such as smart phones are also popularly used in human life. Since the TFT LCD always operates for a long time, it consumes a lot of energy.
To reduce power consumption of LCD, it is necessary to understand which part of LCD consumes the most energy. Since LCD needs backlight to display images, it is clear that decreasing the backlight power can solve the problem of energy consumption. There are so many dimming algorithms to discuss how to save backlight power, such as using transmittance to affect backlight power, or enhancing the gray level of image to decrease the driving current of backlight.
In general, increasing the transmittance to save power can get good image quality, but power reduction rate is not so good. Moreover, the equation of such kind of algorithm is high-complexity that it is difficult to be realized by the integrated circuits. In the other case, improving gray level to reduce power consumption might have high reduction rate, but the distortion of image is large.
In this thesis, two algorithms which combine ideas of increasing the transmittance and improving gray level of image are proposed. First one involves standard deviation in the transmittance to get better result of power reduction rate and still keeps high image quality. Another one involves variance in the transmittance, and uses look up table to replace all equations, which include calculation of root. Although this way might not get result as good as first algorithm, it can be easier to be realized by integrated circuit.

並列關鍵字

backlight ； power saving rate ； PSNR ； gray level ； transmittance

參考文獻

[1] Won-Sik Oh , Daeyoun Cho, Kyu-Min Cho ,Gun-Woo Moon, Byungchoon Yang, and Taeseok Jang, ” A novel two-dimensional adaptive dimming technique of X-Y channel drivers for LED backlight system in LCD TVs”, IEEE Journal of display technology. , vol. 5, no. 1, pp.20-26 ,Jan. 2009.

[2] Daeyoun Cho,Won-Sik Oh, and Gun Woo Moon, ” A novel adaptive dimming LED backlight system with current compensated X-Y channel drivers for LCD TVs”, IEEE Journal of display technology.,vol. 7, no. 1,pp.29-35, Jan. 2011.

[4] Y. T. Kim, “Contrast enhancement using brightness preserving bi-histogram equalization”, IEEE Transactions on Consumer Electronic., vol. 43, no. 1, pp. 1-8, Feb. 1997.

[5] Chi-Chia Sun, Shanq-Jang Ruan, Mon-Chau Shie, and Tun-Wen Pai, “Dynamic contrast enhancement based on histogram specification” , IEEE Trans. Consumer Electron., vol. 51, no. 4, pp. 1300-1305, Nov. 2005.

[6] Chih-Chang Lai and Ching-Chih Tsai, ” Backlight power reduction and image contrast enhancement using adaptive dimming for global backlight applications”, IEEE Trans. Consumer Electron., vol. 54, no. 2, pp.669-674, May. 2008.