Telephonic communications – Subscriber line or transmission line interface – Network interface device
Patent
1990-04-30
1993-02-23
Dwyer, James L.
Telephonic communications
Subscriber line or transmission line interface
Network interface device
379399, 379345, 379404, H02H 320, H04M 1900
Patent
active
051896974
ABSTRACT:
A line interface circuit supplies energizing direct current from a power source via tip and ring leads of a two wire communications line connected with a telephone apparatus, and also couples alternating current signals between the telephone line and an associated telephone facility. The line interface circuit is provided with tip and ring terminals for connection to the tip and ring leads, and power terminals for connection to the power source. Coupling circuitry is connected in series with the tip and ring terminals for providing paths for the energizing direct current and for the alternating current signals. An active tip feed circuit is connected in series between the tip terminal and the coupling circuitry for providing a tip feed path having a predetermined resistance while the telephone apparatus is in an OFF HOOK state and having a much higher resistance in response to an excess of voltage at the tip terminal. An active ring feed circuit is connected in series between the ring terminal and the coupling circuitry for providing a ring feed path having a predetermined resistance while the telephone apparatus is in the OFF HOOK state and having a much higher resistance in response to an excess of voltage at the ring terminal.
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Das Tapan K.
Fung George S.
Ozkan Oguz
Dwyer James L.
Moorhouse J. E.
Northern Telecom Limited
Shehata M.
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