Telephonic communications – Subscriber line or transmission line interface – Network interface device
Patent
1989-09-20
1990-06-19
Dwyer, James L.
Telephonic communications
Subscriber line or transmission line interface
Network interface device
379399, 379324, 379405, H04M 1900
Patent
active
049359606
ABSTRACT:
A battery feed circuit including a main battery feed part and its peripheral circuits provided in a line circuit of a switching system. The peripheral circuits include the following: First, a means for forming a low impedance with respect to in-phase signals, simply realized by a capacitor; second, a bias circuit able to suppress the entry of power source noise and easily switch magnitudes of bias voltages and polarities, realized by a bias voltage generating means, a buffer means, and and AC bypass capacitor; third, a battery feed current control circuit able to suppress overflow of battery feed current when the distance to the subscriber is short, which detects an overcurrent component above a predetermined value, and, in accordance with the same, changes the bias voltage; fourth, a battery feed current supervising circuit able to detect current in both the forward and reverse directions, realized by an emitter-follower pair and a voltage/current converting resistor; fifth, a circuit for detecting bidirectional battery feed currents at a high precision, which is formed by forward direction and reverse direction current detection means provided with V.sub.BE cancelling means; and sixth, an overcurrent protection circuit, which changes the voltage applied between the inputs (+,-) of a transconductance amplifier forming the main battery feed part in accordance with an excess voltage.
REFERENCES:
patent: 4387273 (1983-06-01), Chea, Jr.
patent: 4476350 (1984-10-01), Aull et al.
patent: 4709388 (1987-11-01), Defretin
IEEE Journal of Solid-State Circuits, vol. SC-16, No. 4, Aug. 1981.
Kinoshita Kazumi
Takato Kenji
Tojo Toshiro
Yamamoto Yuzo
Dwyer James L.
Fujitsu Limited
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