Method of providing d.c. feed to a telephone line

Details Method of providing d.c. feed to a telephone line Method of providing d.c. feed to a telephone line

1995-04-21

1996-04-23

Hofsass, Jeffery

Telephonic communications

Subscriber line or transmission line interface

379413, H04M 100

Patent

active

055111181

ABSTRACT:
A two-wire telephone line is supplied with d.c. feed from a drive circuit including two amplifiers via which a transmission signal is supplied to the line. Output potentials of the two amplifiers determine a loop current on the line, which is monitored and used to control a supply voltage for the drive circuit, the amplifier output potentials being offset from the supply potentials by headroom voltages to accommodate the transmission signal. The resulting current limiting voltage control acts iteratively to converge the supply voltage and a target voltage which is inversely dependent on an amount by which the loop current exceeds a predetermined value, the rate of convergence being fast for high loop currents for rapid response and slow for small differences to provide stable operation. The headroom voltages can be increased to nearly the supply voltage to reverse the polarity of the d.c. feed while maintaining current limiting.

REFERENCES:
patent: 4130735 (1978-12-01), Chambers et al.
patent: 4254305 (1981-03-01), Treiber
patent: 4315106 (1982-02-01), Chea, Jr.
patent: 4317963 (1982-03-01), Chea, Jr.
patent: 4343971 (1982-08-01), Beene
patent: 4431868 (1984-02-01), Bolus et al.
patent: 4631359 (1986-12-01), Johansson et al.
patent: 4837818 (1989-06-01), Pieters et al.
patent: 5103387 (1992-04-01), Rosenbaum et al.
patent: 5175764 (1992-12-01), Patel et al.

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