Office line interface circuits

Details Office line interface circuits Office line interface circuits

1988-04-27

1989-08-08

Ng, Jin F.

Telephonic communications

Substation or terminal circuitry

Impedance matching or line equalizing

379387, 379402, 379392, H04M 700

Patent

active

048560588

ABSTRACT:
An office line interface circuit includes a DC circuit for extracting a DC signal component from the office line current, an AC circuit for extracting an AC signal component from the office line current to supply the extracted AC signal component to the receiver of a telephone set, an impedance circuit switchably connected to the office line, and a switching circuit for connecting the impedance circuit to the office line when the extracted DC signal component exceeds a predetermined level to maintain at a substantially constant value the impedance of the office line as viewed from the telephone set. With this interface circuit, the sidetone preventing circuit for the telephone system can operate satisfactorily without complicating the construction under any office line condition.

REFERENCES:
patent: 1756816 (1930-04-01), Dolmago
patent: 3748399 (1973-07-01), Matsuda et al.
patent: 3914560 (1975-10-01), Greene
patent: 3953676 (1976-04-01), Brown
patent: 4004102 (1977-01-01), Ott
patent: 4056688 (1977-11-01), Stiefel
patent: 4132863 (1979-01-01), Smith
patent: 4359609 (1982-11-01), Apfel
patent: 4515996 (1985-05-01), Burgin
patent: 4538032 (1985-08-01), Ballatore et al.
"Understanding Telephone Electronics", Radio Shack, Fort Worth, Tex., 76102, 1983, FIG. 1-2, FIG. 2-23, pp. 2-24.

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