Analog Pixel Memory Circuit of Low Temperature Polycrystalline Silicon TFTs and Radio Frequency Identification Demodulator of Amorphous Silicon for Liquid Crystal Display
|關鍵字:||液晶顯示器;低溫複晶矽;非晶矽;畫素儲存電路;解調器;Liquid Crystal Display;Low Temperature Polycrystalline Silicon;Amorphous Silicon;Pixel Memory Circuit;Demodulator|
|摘要:||薄膜電晶體液晶顯示器(thin-film transistor liquid-crystal display,簡稱TFT-LCD)是利用兩片玻璃基板中間夾雜著一層液晶分子,上層的玻璃基板主要是和彩色濾光片做結合,而下層的基板則有電晶體嵌於基板上方,當電晶體打開,電流通過電晶體時會對液晶分子產生電場變化,液晶分子隨著電場變化做不同角度的偏轉,藉以改變光線的偏極性,配合固定背光源的光度,再透過濾光片來決定不同畫素的明暗狀態,最後經過彩色濾光片,構成了面板出現的影像。為了確保電晶體產生的電場絕大部分能夠被液晶分子利用,以及避免液晶分子內的可移動離子產生內建電場而造成直流殘留(DC residue)而讓畫面失真,目前一般的方法是利用交流的電壓施加在液晶分子上造成分子的極性偏轉,但在TFT-LCD中,提供此交流電壓所消耗的功率佔了整體消耗功率的一大部分。然而,當畫面處在待機畫面(如手機或電腦)而無畫面變換時,交流電壓仍然要維持一定的頻率做輸入,意味著持續的消耗功率。因此,如何能夠在不輸入交流電壓的情況下又能夠維持著一定的頻率的反轉電壓來減少輸入交流電壓所產生的功率消耗是目前在正被廣泛研究的課題。
在本篇論文中,提出了兩種畫素儲存電路來解決上述的問題,而電路是用低溫多晶矽薄膜電晶體(Low Temperature Polycrystalline Silicon TFTs,簡稱LTPS-TFTs)來作為電路的驅動元件。然而,LTPS-TFTs電子遷移率高,可以讓設計的元件尺寸縮小,並降低操作電壓進而減小功率消耗;另外,兼具p和n型的電晶體讓電路設計更多元。利用這兩種畫素補償電路在一定時間範圍內可以穩定的提供固定的反轉電壓,並可以減低面板在靜態影像的更新速度,對於實現低功耗的TFT-LCD的目標前進了一大步。
另外, RFID (Radio Frequency Identification ) －「無線射頻識別系統」是針對接觸式系統的缺點而發展出來，利用射頻訊號以無線方式傳送及接收數據資料且同時使用此射頻訊號來做無線傳能，識別工作無須人工干預，可工作於各種惡劣環境。此外,RFID技術可識別高速運動的物體並可同時識別多個標籤,速度上比傳統條碼式的辨識高出很多。然而,隨著技術的改進和價格上的降低,目前已逐漸取代傳統條碼式的辨識系統,並廣泛的應用在資料儲存和安全系統中,例如:門禁系統,貨物監控與管理等。若將此無線辨識系統的接收器(電子標籤)嵌入面板的應用之中比如說手機,就可以直接以此類電子產品來代替其他額外的電子標籤,大幅增加生活的便利性,但由於目前無線辨識系統中都是搭配著單晶矽的電晶體做設計,不僅會增加繞線上的困難,也大大的增加製作的成本。因此,利用非晶矽薄膜電晶體以及多晶矽薄膜電晶體來設計無線辨識系統電路來結合在系統面板上也是近年來所追尋的目標。
在本篇論文中,提出了在無線射頻辨識系統中的解調器電路,並利用非晶矽薄膜電晶體(Amorphous Silicon TFTs,簡稱A-Si TFTs)來做為驅動元件,其功用是將接收的類比資料轉成數位資料給後端的數位電路解讀,其適用的頻率範圍符合辨識系統的界定頻率(135KHz~13.56MHz) 。藉由此電路設計的可行性,可逐漸將非晶矽電晶體擴展至整個系統中的各個數位電路層面,取代一般IC的黏接,並可大幅增加產能,降低成本,漸近地實現嵌入式辨識系統於面板上的目標。|
Thin-film transistor liquid-crystal display(TFT-LCD) uses a layer of liquid crystal molecules placed between two pieces of glass, the upper glass is mainly bound with color filters, while the transistors are embedded in the top of lower glass, when the transistor is turned on, the current which pass through the transistor change the electric field for liquid crystal molecules. With the different variation of electric field, the molecules are rotated for different angles and change the polarity of light 。By cooperating with fixed backlight and filters determines the light and dark condition in pixels, finally the light through the color filters produces the image which appears in a panel. To ensure most of electric field which is produced by transistor can be used by liquid crystal molecules and to avoid producing built-in electric field made by mobile ions in liquid crystal molecules (the built-in electric field causes DC residue which would distorted the image), using the AC voltage applies to the liquid crystal molecules and inverse their polarity is the general way at present, but the AC power consumption in TFT-LCD occupies a large part of the overall power consumption. However, when the screen is in standby mode (exists in some technologies such as mobile phones or computers) and no image changing, the AC voltage is needed to input with a certain frequency, which means continuous increasing power consumption. Therefore, how to reducing the power consumption by maintaining the inversion voltage with certain frequency when no AC voltage inputting is the main subject which is being extensively studied. In this paper, two pixel memory circuits are proposed to solve the above problem. However, the circuits use low-temperature poly-silicon TFT, referred to as LTPS-TFTs as the driving devices. LTPS-TFTs have high mobility which can reduce the size of device and lower the operating voltage which reduces power consumption; In addition, LTPS-TFTs have both p-type and n-type that can fit the circuit design more. Using the pixel memory can provide stable inversion voltage and would reduce the update rate in static mode. It is a advancement for achieving the goal for low power consumption TFT-LCDs. Besides, RFID (Radio Frequency Identification) system is developed for the disadvantage of contact systems, the system uses radio frequency signals to send and receive data and also uses this wireless communication to transmit wireless energy and identify goods that need no human’s intervention, it can work in variety of harsh environments. RFID technology can identify moving objects with high speed and can also recognize multiple electric tags. However, as improvement of RFID technology and lower of cost, it has gradually replaced the traditional identification system with bar code and widely used in data storage and security systems, such as access control systems, cargos monitoring and management and so on. If this wireless identification system receivers (RFID tag) embedded panel applications nowadays such as mobile phones, they can directly in use without taking another electric tags, and enhance the convenience in life. However, most of identification system circuits are designed with single crystal silicon transistors, it will not only increase the routing difficulties, but also greatly increase the cost of production. Therefore, using amorphous silicon thin film transistors and polysilicon thin film transistors to design wireless identification system circuits combined with system on panel(SOP) is a goal which is pursued recently In this paper, we propose a wireless radio frequency identification system demodulator circuit, the circuit is used with amorphous silicon thin film transistor as the driving device, the function is analog data receiving and changes to digital data to back-end digital circuits. The suitable frequency range consistent with the definition of the frequency identification system (135KHz ~ 13.56MHz). By the feasibility of this circuit, it is possible that all digital circuits utilize amorphous silicon transistors gradually and replace the general bonding of IC. It’s not merely increases productivity significantly, but also achieves target that the RFID system on panel.