Telephonic communications – Subscriber line or transmission line interface
Patent
1992-04-16
1997-08-26
Chiang, Jack K.
Telephonic communications
Subscriber line or transmission line interface
379413, H04M 100
Patent
active
056617941
ABSTRACT:
An active impedance line interface circuit for connection to a two-wire telephone line comprises tip and ring unity gain d.c. amplifiers having outputs d.c. coupled via feed resistors to tip and ring wires respectively. Loop current and common mode current conducted via the feed resistors are monitored individually and converted to digital signals supplied to a digital control circuit, which can be programmed to provide desired operating conditions. Digital control signals produced by the control circuit are converted into analog signals and used to control currents passed by current sources through resistors at inputs of the d.c. amplifiers, thereby determining voltages at the d.c. amplifier inputs and hence on the tip and ring wires. These d.c. voltages are smoothed by capacitors used for coupling an a.c. signal to the d.c. amplifiers. The voltage control facilitates reverse battery operations without a relay, protection against faults, and adaptive adjustment of the line interface circuit to the line in dependence upon the monitored currents.
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Rosch Reinhard W.
Rosenbaum Stanley D.
Chiang Jack K.
Haley R. John
Northern Telecom Limited
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