Automatic gain and return loss compensating line circuit

Details Automatic gain and return loss compensating line circuit Automatic gain and return loss compensating line circuit

1977-12-20

1979-01-02

Claffy, Kathleen H.

179 81R, H04M 176

Patent

active

041328639

ABSTRACT:
The disclosed T-type line compensation circuit reduces the gain and return loss variations when customer equipment is connected to a central office or PBX over telephone lines of various lengths. A linear resistor of a first series leg is thermally coupled, as a heat source, to a positive temperature coefficient (PTC) resistor of a second series leg. The shunt leg consists of a series connection of a bilateral zener diode, linear resistor, and varistor. The resistance value of both the second series leg and the shunt leg of the line circuit vary automatically with the direct current in the line to minimize gain variation due to telephone line length variation. The thermal feedback to the PTC resistor varies automatically with the direct current in the line to minimize return loss variations seen by the customer equipment.

REFERENCES:
patent: 2620402 (1952-12-01), Botsford et al.
patent: 2629783 (1953-02-01), Hopkins
patent: 2777994 (1957-01-01), Hurault
patent: 3436488 (1969-04-01), Barbato et al.
patent: 3810247 (1974-05-01), Ono
patent: 4027259 (1977-05-01), Zellmer
"Automatic Level Control Telephone Circuits with Nonlinear Resistances," Kakehi, Review of the Electrical Communications Labs, vol. 22, No. 11-12, Nov.-Dec. 1974, pp. 1004-1018.
"An Improved Circuit for the Telephone Set", Bennett, Bell System Technical Journal, May 1953, pp. 611-626.

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