A Hybrid Circuit with High Isolation for a Two-Wire Full Duplex Cable Modem to Adapt to Variations in Line Impedance

Jeich MAR  Guan-Chiun CHEN  Ming-Yi LAN  Luo-Shing LUO  

Publication
IEICE TRANSACTIONS on Communications   Vol.E85-B   No.1   pp.352-354
Publication Date: 2002/01/01
Online ISSN: 
DOI: 
Print ISSN: 0916-8516
Type of Manuscript: LETTER
Category: Electromagnetic Compatibility(EMC)
Keyword: 
hybrid circuit,  full duplex,  cable modem,  binary frequency shift keying,  

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Summary: 
A high isolation hybrid circuit composed of a pair of transformers, a voltage control resistance (VCR) circuit and an automatic impedance control device is designed for a two-wire full duplex cable modem to adapt variable line impedance. A binary frequency shift keying (BFSK) cable modem using the new hybrid circuit with an isolation of 52 dB to 58 dB in the line impedance variation range of 400 to 950 ohm is demonstrated. The isolation of the new hybrid circuit is increased by more than 30 dB over the traditional hybrid circuit for a two-wire full duplex modem in the preset line impedance range.