Catherine C Tsang

US Patent:

57683646, Jun 16, 1998

Filed:

Feb 10, 1997

Appl. No.:

8/797853

Inventors:

Mark J. Karnowski - Westminster CA
Frank Sacca - West Covina CA
Catherine Tsang - Monterey Park CA

Assignee:

Casio PhoneMate, Inc. - Torrance CA

International Classification:

H04M 900

US Classification:

379388

Abstract:

In a speakerphone, which operates under software control, transmit and receive signal levels are sampled and compared against one another, with hysteresis, to enable one of two speakerphone modes of operation--either a transmit mode or a receive mode. A single peak detector is multiplexed to sense the transmit and receive signal levels. Fixed attenuators are switched into either the receive signal path or into the transmit signal path, depending upon the current speakerphone operation mode. Signal compression is used to provide for improved mode determination over a wide dynamic range. The level detection and/or attenuation may be performed in software. The speakerphone functions are readily implemented using standard line interfaces and control circuitry. Automatic gain control in the receive mode ensures a constant level of signals at the speakerphone loudspeaker, regardless of telephone line conditions.