Telephonic communications – Subscriber line or transmission line interface – Network interface device
Patent
1987-07-01
1988-08-16
Ng, Jin F.
Telephonic communications
Subscriber line or transmission line interface
Network interface device
379412, 379347, H04M 176, H04M 1900
Patent
active
047649569
ABSTRACT:
A typical active impedance line feed circuit includes tip and ring amplifiers being controlled in response to signals at tip and ring voltage taps by control circuit to exhibit a.c. impedance and d.c. resistance characteristics for the purpose of supplying energizing current via tip and ring terminals for tip and ring leads of a two wire communication line. In one example of the active impedance line feed circuit, improved operational tolerance of longitudinal interference and of a ground fault condition is provided by a d.c. amplifier being responsive to voltages at the tip and ring terminals. The circuit is characterized in that an inverting input of the d.c. amplifier is connected via resistors to the tip and ring voltage taps. In operation, the d.c. amplifier provides complete cancellation of all common mode signals at the tip and ring voltage taps and a compensation circuit is also connected between the tip and ring voltage taps and is responsive to the output of the control circuit for compensating for non-symmetrical current, the non-symmetrical current being introduced between the tip and ring voltage taps by normal operation of the control circuit, thereby, a threshold of ground fault current limiting action is substantially constant under all operating conditions. The d.c. amplifier is conveniently manufacturable in integrated circuit technology along with the remaining amplifiers in the active impedance line feed circuit.
REFERENCES:
patent: 4476350 (1984-10-01), Aull et al.
patent: 4540854 (1985-09-01), Beirne
patent: 4571460 (1986-02-01), Rosenbaum et al.
Holy Zdenek
Plett Calvin
Rosch Reinhard
Rosenbaum Stanley D.
Moorhouse J. E.
Ng Jin F.
Northern Telecom Limited
Vaas Randall S.
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