Telephonic communications – Substation or terminal circuitry – For loudspeaking terminal
Patent
1990-04-26
1992-12-15
Dwyer, James L.
Telephonic communications
Substation or terminal circuitry
For loudspeaking terminal
379394, 379391, 379 6, 379400, H04M 100
Patent
active
051724103
ABSTRACT:
A speaker telephone comprising a microphone outputting an electrical signal, and a loudspeaker is disclosed. An amplifier has its output coupled to the loudspeaker. This amplifier has non-inverting and inverting inputs. A switch having two positions couples the microphone to the amplifier or couples the tuning signal source to one of the inputs of the amplifier. A tuning signal source and control circuit output a tuning signal. Initiation means initiates a tuning sequence by causing the switch to be in the second position and causing the tuning signal source and control circuit to generate tuning signals. A coupling device is connected to one of the inputs of the amplifier and adopted to be connected to a telephone circuit. A hybrid voltage generator circuit is responsive to the output of the microphone when the switch couples the microphone to the amplifier to generate at its output a cancellation signal which prevents transmitted voice signals from appearing at the loudspeaker.
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Dwyer James L.
Shehata M.
Sound Control Technologies, Inc.
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