Editing Electrical termination (section)

==Transmission lines==
Signal termination often requires the installation of a terminator at the beginning and end of a wire or cable to prevent an [[RF signal]] from being reflected back from each end, causing [[Interference (communication)|interference]], or power loss.  The terminator is usually placed at the end of a [[transmission line]] or [[Daisy chain (electrical engineering)|daisy chain]] [[Bus (computing)|bus]] (such as in [[SCSI]]), and is designed to [[impedance matching|match]] the [[Characteristic impedance|AC impedance]] of the cable and hence minimize signal [[Reflection (electrical)|reflections]], and power losses. Less commonly, a terminator is also placed at the driving end of the wire or cable, if not already part of the signal-generating equipment.<ref name="CTS">{{cite web |title=Clock Termination Techniques and Layout Considerations |url=https://www.ctscorp.com/wp-content/uploads/2015/10/AN1025.pdf |access-date=2021-01-03 |publisher=CTS |archive-date=2021-10-24 |archive-url=https://web.archive.org/web/20211024085900/https://www.ctscorp.com/wp-content/uploads/2015/10/AN1025.pdf |url-status=dead }}</ref>

Radio frequency currents tend to reflect from discontinuities in the cable, such as [[Electrical connector|connectors]] and joints, and travel back down the cable toward the source, causing interference as primary reflections. Secondary reflections can also occur at the cable starts, allowing interference to persist as repeated echoes of old data. These reflections also act as bottlenecks, preventing the signal power from reaching the destination.

Transmission line cables require [[impedance matching]] to carry electromagnetic signals with minimal reflections and power losses. The distinguishing feature of most transmission line cables is that they have uniform cross-sectional dimensions along their length, giving them a uniform electrical [[characteristic impedance]]. Signal terminators are designed to specifically match the characteristic impedances at both cable ends. For many systems, the terminator is a [[resistor]], with a value chosen to match the characteristic impedance of the transmission line and chosen to have acceptably low parasitic [[inductance]] and [[capacitance]] at the frequencies relevant to the system. Examples include 75-ohm resistors often used to terminate 75-ohm video transmission coaxial cables.

Types of transmission line cables include balanced line such as [[ladder line]], and [[twisted pair]]s ([[Category 6 cable|Cat-6 Ethernet]], [[Parallel SCSI]], [[ADSL]], [[Plain old telephone service|Landline Phone]], [[Balanced line#Balanced and differential|XLR audio]], [[USB]], [[IEEE 1394|Firewire]], [[RS-485|Serial]]); and unbalanced lines such as [[coaxial cable]] (Radio antenna, [[Cable television|CATV]], [[10BASE5|10BASE5 Ethernet]]).