Handsfree unit

Details Handsfree unit Handsfree unit

1998-11-25

2000-11-28

Vo, Nguyen

Telecommunications

Transmitter and receiver at same station

Convertible

455431, 455553, 379 59, 379390, 379 3, H04B 140

Patent

active

061546399

ABSTRACT:
The present invention provides a cheap handsfree unit which can prevent the howling phenomenon and reduce the input sound from the loud-speaker into the microphone in both the analog and digital modes. A reception side comprises a signal level adjusting circuit constituted by a switch circuit and attenuators, and a transmission side comprises a signal level adjusting circuit constituted by a switch circuit and attenuators, to introduce the attenuation of 15 dB or 30 dB in response to the analog or digital mode. A voice switch is constituted so that the analog reception signal and the analog transmission signal are rectified respectively by rectifiers, the levels of both signals are compared by a comparator, and either switch or switch having a higher input signal level becomes conductive as a result of the comparison. The attenuation is introduced on the basis of the communication mode, only to either the analog reception signal or analog transmission signal having a smaller signal intensity.

REFERENCES:
patent: 5398281 (1995-03-01), Kurokawa
patent: 5404579 (1995-04-01), Obayashi
patent: 5416829 (1995-05-01), Umemoto
patent: 5420911 (1995-05-01), Dahlin
patent: 5475731 (1995-12-01), Rasmusson
patent: 5790957 (1998-08-01), Heidari
patent: 6002929 (1999-12-01), Bishop, Jr.

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