薄膜電晶體液晶顯示器
维基百科，自由的百科全书
薄膜電晶體液晶顯示器（TFT LCD, Thin Film Transistor Liquid Crystal Display）是液晶顯示器的一種變型，採用薄膜電晶體技術來改善影像品質，應用在平面顯示器與投影機上。薄膜電晶體液晶顯示器目前正快速取代傳統的陰極射線管顯示器，市面上常見顯示器尺寸有從30到77公分(約12到30英吋)，並往電視市場邁進。
目录 |
[编辑] 架構
尋常的液晶顯示器好比-{zh-tw:計算機;zh-cn:計算器}-(calculator)的顯示面版，其圖像元素是由電壓直接驅動；當控制一個單元時不會影響到其他單元。當畫素數量增加到極大如以百萬計時，這種方式就變得不實際，注意到每個畫素的紅、綠、藍三色都要有個別的連接線。 為了避免這種困境，將畫素排成行與列則可將連接線數量減至數以千計。如果一列中的所有畫素都由一個正電位驅動，而一行中的所有畫素都由一個負電位驅動，則行與列的交叉點畫素會有最大的電壓而被切換狀態。然而此法仍有些問題，即是同一行或同一列的其他畫素雖然受到的電壓僅為部分值，但這種部份切換仍可使畫素變暗(以不切換為亮的液晶顯示器而言。)解決方法是每個畫素都添加一個配屬於它的電晶體開關，使得每個畫素都可被獨立控制。電晶體所擁有的低漏電流特徵所代表的意義乃是當畫面更新之前，施加在畫素的電壓不會任意喪失掉。每個畫素是個小的電容器，前方有著透明的氧化銦錫(ITO)層，後方也有透明層，並有絕緣性的液晶處在其中。
此種電路佈置方式很類似於動態存取記憶體，只不過整個架構不是建在矽晶圓上，而是建構在玻璃上。許多矽晶圓製程技術所需的溫度會超過玻璃的熔點。尋常半導體的矽基質是利用液態矽長出很大的單晶，具有電晶體的良好特質。而薄膜電晶體液晶顯示器所用到的矽層是利用矽化物氣體製造出非晶矽層或多晶矽層，這種製造方法較不適合做出高等級的電晶體。
[编辑] 種類
[编辑] TN+Film
TN(TN指的是液晶扭轉角度為90度)薄膜 (Twisted Nematic 扭轉向列型液晶) 顯示器是多數顧客所需要的顯示器形式, 由於價格低. The pixel response time on modern TN panels is sufficiently fast to avoid the shadow-trail artifacts that were a cause for complaint in the past. This fast response time has been a heavily marketed aspect of TN displays, although in most cases this number does not reflect performance across the entire range of possible color transitions. However this marketing strategy, combined with the relatively lower cost of production for TN panels, has lead to the dominance of TN in the consumer market.
The TN display suffers from limited viewing angles, especially in the vertical direction, and some are unable to display the full 16.7 million colors (24-bit truecolor) available from modern graphics cards. These particular panels, with 6 bits per color channel as opposed to 8, can approach true 24-bit color using a dither method which quickly cycles pixels to simulate a given shade, which are noticeable to some and discomfiting to others. Overall, color reproduction and linearity on TN panels is poor. Shortcomings in display color gamut (often referred to as a percentage of the NTSC color gamut) can also be attributed to backlighting technology. It is not uncommon for displays with CCFL (Cold Cathode Flourescent Lamps) based lighting to range from 40% to 76% of the NTSC color gamut, whereas displays utilizing white LED backlights may extend past 100% of the NTSC color gamut -a difference quite perceivable by the human eye.
[编辑] IPS
IPS (In-Plane Switching) was developed by Hitachi in 1996 to improve on the poor viewing angles and color reproduction of TN panels. These improvements came at a loss of response time, which was initially on the order of 50ms. IPS panels were also extremely expensive.
IPS has since been superceded by S-IPS (Super-IPS), which has all the benefits of IPS technology with the addition of improved pixel refresh timing. Though color reproduction approaches that of CRTs, the contrast ratio remains relatively weak. S-IPS technology only appears in larger displays aimed at professionals, though pricing has come down to the reach of the typical consumer.
[编辑] MVA
MVA (Multi-domain Vertical Alignment，垂直排列)最先是由富士通公司於1998年開發的，作為TN與IPS的折衷方案。It achieved fast pixel response (at the time), wide viewing angles, and high contrast at the cost of brightness and color reproduction.
Analysts predicted that MVA would corner the mainstream market, but instead, TN has risen to dominance. A contributing factor was the higher cost of MVA, along with its slower pixel response (which rises dramatically for small changes in brightness).
PVA (Patterned Vertical Alignment，垂直排列) is a more advanced version of MVA technology offered by 三星公司. 雖獨立發展，但和MVA面臨相同的問題，不過boasts the best contrast ratios of any TFT technology.
[编辑] 顯示器工業
Due to the immense cost of building TFT factories, the number of major OEM panel vendors probably does not exceed four or five. Several of the most well-known are Samsung, LG.Philips LCD and AU Optronics.
Raw LCD TFT panels are usually factory-sorted into three categories, with regards to the number of dead pixels, backlight evenness and general product quality. Additionally, there may be up to +/- 2ms maximum response time differences between individual panels that came off the same assembly line on the same day. The poorest-performing screens are then sold to no-name vendors or used in "value" TFT monitors (often marked with letter V behind the type number), the medium performers are incorporated in gamer-oriented or home office bound TFT displays (sometimes marked with the capital letter S), and the best screens are usually reserved for use in "professional" grade TFT monitors (usually marked with letter P or S after their type number).
Value TFT screens and most 38 cm (~15 in.) sized LCDs usually fail to include a digital signal compatible DVI interface, thus their future proofing may be limited. The upper end of 43 cm (~17 in.) or 48 cm (~19 in.) gamer and office TFT screens may have dual analog-VGA and DVI sockets; almost all professional screens have DVI and pivot mode for letter-mode display. However, the use of a DVI video signal does not automatically guarantee better image quality: a good video card RAMDAC and properly shielded analogue VGA cable may produce the same display.
[编辑] 外部連結
另見：液晶電視
