Telephonic communications – Subscriber line or transmission line interface – Network interface device
Patent
1985-08-02
1987-07-07
Rubinson, Gene Z.
Telephonic communications
Subscriber line or transmission line interface
Network interface device
379231, 379322, H04M 900
Patent
active
046792325
ABSTRACT:
When a floating battery feed circuit is used to power telephone lines, it is desirable to provide an anti-corrosion biasing circuit to keep the voltage on the tip and ring conductors from becoming positive. This can be done using an anit-corrosion circuit that sinks a dynamic amount of current from the tip conductor. A line circuit including such biasing is, however, incompatible with special lines such as PBX lines that rely on a grounded tip conductor in the talk state. In accordance with the present invention, a constant current is supplied from a ground reference circuit to the ring conductor of such special lines only when loop current is flowing. The magnitude of this supplied current is such that the anti-corrosion circuit holds the tip conductor sufficiently close to ground potential to allow the proper operation of circuits connected to the special lines.
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patent: 4593156 (1986-06-01), Martin
Brooks Kenneth L.
Bufkin Paul R.
Mihal David G.
Miller Jerry G.
American Telephone and Telegraph Company AT&T Bell Laboratories
Rubinson Gene Z.
Vaas R.
Watland Ross T.
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