Adaptive expander for telephones

Details Adaptive expander for telephones Adaptive expander for telephones

1987-12-11

1989-07-11

Ng, Jin F.

Telephonic communications

Substation or terminal circuitry

For loudspeaking terminal

381 94, 379388, H04M 160

Patent

active

048478970

ABSTRACT:
An adaptive expander for telephones reduces the gain of a transmitting amplifier in proportion to the intensity of the background noise. Gain reduction occurs when the user is not speaking into the handset microphone. When the user is speaking, however, the gain of the transmitting amplifier is restored to its normal level. Noise is distinguished from speech via long-term averaging of the microphone output signal, and a circuit that precludes the magnitude of the long-term average voltage from ever exceeding the short-term average voltage. The present invention is used in full duplex arrangements where simultaneous transmission in both directions is possible rather than in half duplex arrangements, such as a speakerphone, where transmission occurs only in one direction at a time.

REFERENCES:
patent: 3889059 (1975-06-01), Thompson et al.
patent: 3963868 (1976-06-01), Randmere et al.
patent: 4076968 (1978-02-01), Wattenbarger
patent: 4461025 (1984-07-01), Franklin
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patent: 4506381 (1985-03-01), Ono
patent: 4531228 (1985-07-01), Noso et al.
patent: 4609878 (1986-09-01), Rodgers
patent: 4628529 (1986-12-01), Borth et al.
patent: 4630304 (1986-12-01), Borth et al.
patent: 4696032 (1987-09-01), Levy

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