Electronic circuit for a speakerphone

Details Electronic circuit for a speakerphone Electronic circuit for a speakerphone

1976-10-29

1978-03-28

Claffy, Kathleen H.

179 81A, 179 1HF, H04M 160

Patent

active

040816222

ABSTRACT:
The invention relates to an electronic circuit for a speakerphone which, when in the balanced condition, will eliminate acoustic feedback as between the microphone and the speaker of the speakerphone. The arrangement consists of a bridge having four legs. Input from telephone lines are fed into the bridge between two adjacent points (i.e. across one leg) of the bridge. The microphone is connected between one of the input points and a point opposite to the one input point. The legs on either side of the opposite point of the microphone connection contain equal impedances, and the fourth leg, between the input leg and one of the equal impedance legs, contains a variable impedance. To balance the bridge, the variable impedance is adjusted such that the microphone signal, appearing in opposite sides of the bridge, will be canceled out and thereby prevented from exiting on the speaker circuits. However, because of the imbalance relative thereto, the microphone signal will be passed up the telephone lines. Again, because of a similar imbalance, input from the telephone lines will be fed out to the speaker circuits.

REFERENCES:
patent: 3462560 (1969-08-01), Holzman
patent: 3748400 (1973-07-01), Ritz

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