非遮蔽雙絞線電氣特性研究

Abstract

近年來非遮蔽雙絞線廣泛使用在高頻資料傳輸上，如網路系統及電話系統上之xDSL、ISDN。了解非遮蔽雙絞線之通道效應對於設計或維護、架設整個線導通訊系統是非常重耍的。通常通道效應可以使用量測之方法量出，但却不易有效分析其影響通道效應之主要因素。非遮蔽雙絞線之數學分析模型之產生，可使在了解通道效應之因果關係方面，提供了比完全經由量測所得方法更佳之了解。首先在文中開始，先說明差模及並模信號及信號調整耦合器在絞線傳輸系統中之功用，及信號調整耦合器之作用結果，說明那些絞線之電氣分析是重要的。導線之衰減及干擾二項絞線電氣特性是主要影響線導通訊品質之重要因素，文中先推導出衰減公式並與規範值及量測結果相比較。接著我們進行分析絞線干擾，Chain matrix之方法為本文用來分析非遮蔽雙絞線之工具。使用Chain matrix之方法可以模擬出單一直線對雙絞線所產生之共模對差模之干擾及雙絞線間共模對差模對差模之干擾之情形。本文之模擬將著重在差模干擾部分，對產生差模干擾大小之影響因素如導線長短、絞線率、導線高度…等作分析。結果為干擾之大小大致上是與導線長短成正比，而與絞線率、導線高度成反比，並且在高低頻時有不同之干擾反應。而絞線間之干擾幾乎是與絞線高度無關的. 另外我們說明了LCL (Longitudinal Conversion Loss) 及LTCL (Longitudinal Transfer Conversion Loss)兩項電氣特性之意義，及ELFEXT (Equal Level Far End Crosstalk)與FEXT (Far End Crosstalk)二者兩項電氣特性之間的關係，最後還提到絞線量測方法，一種為常用之使用balun方法，但需重複量測，效率不佳。另一種方法為modal decomposition方法，在這一種方法中我們導出比其他文獻更詳盡之說明，但我們不作實際之量測。本論文將對工程師提供一個更明白了解非遮掩雙絞線在電子裝置應用上之貢獻。

Recently, a unshielded twisted pair cable (UTP) has been widely used in high frequency data transmission such as LAN systems and telephone lines using xDSL or ISDN.The understanding of channel effects of UTP cable is very important for the development, maintenance and the cabling of wire communication system. Generally, The channel effects could be obtained by measuring of UTP, but which provide less information for understanding the main factors that affect the channel effect. The development of numerical analysis model of UTP provide more better information than measurement method for understanding the reasons that affect channel effect. At the beginning of this paper, we introduce the role of the common mode, differential mode signal and signal transformer in wired communication system. Because of the signal transformer we explain which electrical characteristics of UTP are important. It is obvious that attenuation and crosstalk are the most important characteristics, which affect the quality of wired communication. Firstly, the equation of attenuation is derived, and is compared with measured results and the limits of specification. The crosstalk characteristics of UTP are the following main topic. By using chain matrix method, we develop the analysis of generated differential crosstalk between single wire and twisted pair and between two twisted pair cables. We also analysis the factors which affect the crosstalk, such as cable length, twisted rate, cable height Etc. The simulations show that the crosstalk is increased when cable length increase, and is decreased when twisted rate and cable height increase. The most interested result is the crosstalk between two twisted cables is almost independent with cable height. The others, we explain the LCL (Longitudinal Conversion Loss) and LCTL (Longitudinal Conversion Transfer Loss) and the relation between ELFEXT (Equal Level Far End Crosstalk) and FEXT (Far End Crosstalk). The methods of cable measurement are also introduced in this paper. The most wide used method is by using balun method, which is required repeated measuring and lack of efficiency. The other method, modal decomposition method provides more quickly measuring. We explain the method more theoretical clearly than other papers, but we don’t make measures. The contents of this paper could provide a contribution to engineers with a clearer understanding about unshielded twisted pair application in electronic equipments.