Speakerphone for cellular telephones with howl prevention, detec

Telephonic communications – Having light wave or ultrasonic link for speech or paging... – Including fiber optic link within telephone network

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379 56, 455 68, 455 70, H04M 1100, H04B 100

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active

050142941

ABSTRACT:
A unique speakerphone for celluar telephones includes in the transmit audio path between microphone 112 and transmitter 118, a transmitter mute switch which disconnects the audio path to the transmitter from the microphone 112, and a transamit gain amplifier that is controlled to lower the feedback the microphone can pickup from the speaker 110. In the feedback path to the radiotelephone receiver 120 from the cellular base station 122 and the land line telephone system 124, the speakerphone includes the controlled amplifier 106 which is fed into the speaker mute gate, and the speaker 110 to close the feedback loop. De-emphasized audio is sampled by the A/D 102 on both the microphone-to-transmittr side of the loop and the receiver-to-speaker side of the loop. The microcomputer 104 is able to detect and eliminate howl, as well as determine whether howl exists, from the A/D sampling.

REFERENCES:
patent: 4627098 (1986-12-01), Dolikiar et al.
patent: 4629829 (1986-12-01), Puhl et al.
patent: 4682957 (1987-07-01), Young
patent: 4737976 (1988-04-01), Borth et al.
patent: 4741018 (1988-04-01), Potratz et al.
patent: 4843621 (1989-06-01), Potratz
IBM Technical Disclosure Bulletin vol. 33 #1B Jun. 1990.

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