Subscriber line interface circuit with improved d.c. balance

Details Subscriber line interface circuit with improved d.c. balance Subscriber line interface circuit with improved d.c. balance

1985-09-24

1988-02-23

Ng, Jin F.

Telephonic communications

Subscriber line or transmission line interface

Network interface device

379400, H04M 1908

Patent

active

047275740

ABSTRACT:
A SLIC includes controlled current circuits (CCCs) which simulate feed resistors for controlling d.c. feed to a two-wire telephone subscriber line which is coupled to two terminals, control being achieved via a feedback loop. A differential amplifier has an inverting input coupled to the tapping point of a potential divider connected between the terminals, and a non-inverting input connected to a reference potential of half of the supply battery voltage. For suppressing longitudinal currents on the line, the amplifier output is connected to each terminal via a d.c. blocking capacitor in series with a resistor, the resistors having closely matched resistances. For maintaining d.c. balance, the output of the amplifier is coupled via a low pass filter to control a current splitter included in the feedback loop, to control the relative proportions of control currents for the CCCs.

REFERENCES:
patent: 4300023 (1981-11-01), Kelley et al.
patent: 4375015 (1983-02-01), Chambers, Jr.
patent: 4445006 (1984-04-01), Scholich
patent: 4467310 (1984-08-01), Jakab
patent: 4476350 (1984-10-01), Aull et al.
patent: 4525602 (1985-06-01), Robra et al.
patent: 4600811 (1986-07-01), Hayashi et al.
patent: 4631359 (1986-12-01), Johansson et al.
"One Chip Closes in on SLIC Functions", L. Brown et al., Electronic Design, Sep. 27, 1980, pp. 85-91.

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