The Circuit Designer's Companion - diagramas.diagram...

26 The Circuit Designer’s CompanionStructured data cableOne particular cable application which forms an important aspect of datacommunications is so-called “structured” or “generic” cabling. This is general-purposedatacomms cable which is installed into the structure of a building or campus to enablelater implementation of a variety of telecom and other networks: voice, data, text, imageand video. In other words, the cable’s actual application is not defined at the time ofinstallation. To allow this, its characteristics, along with those of its connectors,performance requirements and the rules for acceptable routing configurations, aredefined in ISO/IEC 11801 (the US TIA/EIA-568 covers the same ground).Equipment designers may not be too interested in the specifications of this cableuntil they come to design a LAN or telecom port interface; then the cable becomesimportant. The TIA/EIA-568 (both ISO/IEC 11801 and EN 50173 have similarspecifications) parameters for the preferred 100Ω quad-pair cable are shown in Table1.8. The standard allows for a series of categories with increasing bandwidth. Cat 5 andCat 5e are popular and have been widely installed.Table 1.8 Characteristics of TIA/EIA-568 (ISO/IEC 11801) 100Ω quad pair cableFreq. MHz Cat 3 Cat 5 Cat 5e Cat 6Bandwidth 16MHz 100MHz 250MHzCharacteristic0.1 75 – 150 Ω N/Aimpedance≥1 100 ±15 ΩAttenuation dB per 0.256 1.3 1.1 N/A100m1.0 2.6 2.1 2.04.0 5.6 4.3 3.810 9.8 6.6 6.016 13.1 8.2 7.631.25 N/A 11.8 10.762.5 17.1 15.4100 22.0 19.8200 N/A 29.0250 32.8Capacitance unbalance 1kHz 3400 pF/km 330pF/100mDC loop resistance 19.2 Ω/100m, max unbalance 3%Return loss dBat 100m cable length1 – 10 12 23 20 + 5log(ƒ)10 – 20 12 – 23 2510log(ƒ/10)20 – 100 N/A 23 –10log(f/20)25 – 7log(ƒ/20)200 N/A 18.0250 17.3Other characteristics, particularly mechanical dimensions, crosstalk performance(extended for Cat 5e and 6), and propagation delay skew are also defined.