Loudspeaking telephone with a variable gain circuit

Details Loudspeaking telephone with a variable gain circuit Loudspeaking telephone with a variable gain circuit

1988-07-05

1990-02-06

Dwyer, James L.

Telephonic communications

Supervisory or control line signaling

Using line or loop condition detection

379390, H04M 160, H04M 908

Patent

active

048993808

ABSTRACT:
A loudspeaker telephone has a circuit which is much less likely to go into singing or howling during the change over time while it is switching between transmit and receive modes. This is done by using FETs as variable resistors during the change over period. As a result of the resistance variation during change over, the total gain of both the transmit and receive channels added together does not exceed the gain during either the transmit or the receive modes.

REFERENCES:
patent: 3725585 (1973-04-01), Moniak
patent: 4025728 (1977-05-01), Jacobson
patent: 4629829 (1986-12-01), Puhl et al.
A. Busala, "Fundamental Consideration in the Design of a Voice--Switched Speakerphone," The Bell System Technical Journal, vol. XXXIX, 3-1960, pp. 265-294.
W. F. Clemency et al., "Functional Design of a Voice--Switched Speakerphone", The Bell System Technical Journal, vol. XL, May 1961, pp. 649-668.

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