Browse Prior Art Database

VEHICULAR 'HANDS FREE' CIRCUIT WITH NOISE MONITORING MICROPHONE

IP.com Disclosure Number: IPCOM000007387D
Original Publication Date: 1995-Mar-01
Included in the Prior Art Database: 2002-Mar-21
Document File: 1 page(s) / 71K

Publishing Venue

Motorola

Related People

Zami Schwartzman: AUTHOR [+3]

Abstract

Hands free operation of mobile radios in tele- phone conversations is very popular, because of driver convenience and for safety reasons.

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MOIY)ROLA Technical Developments Volume 24 March 1995

VEHICULAR 'HANDS FREE' CIRCUIT WITH NOISE MONITORING MICROPHONE

by Zami Schwartzman, Claude Hassan and Ariel Goldfarb

  Hands free operation of mobile radios in tele- phone conversations is very popular, because of driver convenience and for safety reasons.

  Most cellular mobile radios provide a full duplex channel, with a speakerphone circuit, that by voice activation switches attenuators between transmit and receive paths, which practically results in half duplex hands free operation.

  Most of the circuits that are used to carry out hands free speakerphone operation use voice enve- lope detection schemes, that can distinguish between voice and any constant envelope noise, like wind noise and engine noise at cruising speed. Such schemes cannot distinguish the voice from vehicular noise if the noise has a non-constant envelope nature such as the vehicle horn, rough road noise, sudden acceleration, etc.

  Very directional microphones are too bulky to implement in a vehicle, they are too expensive and will not provide satisfactory results, since the vehic- ular space is very resonant, which gives rise to noise coming from many directions.

  Noise cancelling microphones with digital audio signal processing can eliminate vehicle noise after a training process, but this is quite a complicated and costly method.

  It is proposed that a hands free speakerphone circuit uses a noise monitoring microphone to help distinguish the driver's voice from other vehicular noises.

  Two microphones are used together with the v...