Design and characteristics of common-mode choke coil for high-speed LAN port using UTP cable

A common-mode choke coil (CM coil) was developed to use for countermeasures after installation for high speed LAN systems. The relations between the magnetic permeability of ferrite core and the common-mode insertion loss were investigated. The results indicated that the ferrite core, whose permeability was large in frequency range from 0.1 MHz to 5 MHz, was appropriate to realize the CM coil. Using this core, a CM coil with two twisted pairs was developed. The results of the investigation indicated that the differential mode insertion loss of this coil satisfied requirements to use for 1000 base-T system, and the common-mode insertion loss was sufficient to use countermeasures after installation. The CM coil for 1000 base-T telecommunication port was composed with the two developed CM coils. The investigation results for transmission quality showed that the CM coil for 1000 base-T was applicable for the cable length of 100 m or less. The measurement of countermeasure effect indicated that the CM coil was effective to reduce emissions and to improve immunity at telecommunication port for 1000 base-T.