Telephonic communications – Subscriber line or transmission line interface – Network interface device
Patent
1987-09-23
1989-05-09
LaRoche, Eugene R.
Telephonic communications
Subscriber line or transmission line interface
Network interface device
379398, 379405, H04M 1900
Patent
active
048295671
ABSTRACT:
A line interface circuit supplies energizing current for operation of a two wire communication line and couples a.c. signals between the communication line and a telephone facility. Tip and ring rails are resistively connected to the communication line by matched feed resistors in a resistance network also including tip and ring taps. Active impedance circuits in an a.c. signal coupling circuit terminate the tip and ring rails with a predetermined impedance, via the feed resistors, in response to voltages at the tip and ring taps. Active resistance valving circuits in a direct current feed circuit supply the communication line with energizing direct current via the tip and ring rails and feed resistors. The valving circuits may be controlled to limit current for shorter lines and the functions of the a.c. signals coupling circuit may be optimally altered in response thereto. In one example, operating band width is extended into ISDN frequencies by providing a secondary resistance network with secondary feed resistors coupling secondary tip and ring rails to the tip and ring rails. In this structure, the a.c. signal coupling circuit is responsive to a.c. signals at secondary tip and ring taps for terminating the secondary rails and a supervisory circuit is responsive to the voltages at the tip and ring taps for generating supervisory signals for the telephone facility.
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LaRoche Eugene R.
Lee Benny
Moorhouse J. E.
Northern Telecom Limited
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