Constant current line circuit with class features

Details Constant current line circuit with class features Constant current line circuit with class features

2005-03-08

2005-03-08

Isen, Forester W. (Department: 2644)

Telephonic communications

Subscriber line or transmission line interface

Power supply

C379S400000

Reexamination Certificate

active

06865271

ABSTRACT:
A line circuit utilizing a differential amplifier whose output is regulated to zero volts D.C. (when the subscriber's set is off-hook) by a negative feedback circuit, for controlling a voltage controlled power supply which provides a constant current feed to the subscriber's loop. The differential amplifier also transmits audio signals received from the subscriber's loop directly to a PABX via an unbalanced terminal. When the loop range exceeds a predetermined threshold, the circuit reverts to a voltage feed operation thereby allowing operation over long loop lengths and the ability to provide on-hook CLASS services.

REFERENCES:
patent: 4514595 (1985-04-01), Rosenbaum et al.
patent: 4723280 (1988-02-01), Meier et al.
patent: 5329588 (1994-07-01), Willocx et al.
patent: 5864219 (1999-01-01), Fink

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