Telephonic communications – Subscriber line or transmission line interface – Network interface device
Patent
1987-01-14
1989-09-12
Ng, Jin F.
Telephonic communications
Subscriber line or transmission line interface
Network interface device
379399, H04M 1900
Patent
active
048667684
ABSTRACT:
A telephone station subscriber line interface circuit for connecting a telephone subscriber station to a telecommunications transmission line comprises a loop current sensing circuit for providing an output signal proportionately representative of DC resistance in the telecommunications transmission line. A ring-side driving circuit is coupled to the loop current sensing circuit and is responsive to the output signal for providing an alternating current voltage source and a direct current voltage source to a transmit amplifier in periods of high constant DC resistance in the telecommunications transmission line, the ring-side driving circuit maintaining the output of the alternating current voltage source constant to the transmit amplifier and automatically transferring from a constant direct current voltage source to a constant direct current current source in the event of a decrease in the DC resistance in the telecommunications transmission line sensed by the loop curent sensing circuit.
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Ahmed Adel A.
Ng Jin F.
Siemens Corporate Research & Support, Inc.
Vaas Randall S.
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