Limiting maximum gain in duplex communications devices...

Details Limiting maximum gain in duplex communications devices... Limiting maximum gain in duplex communications devices...

2006-08-15

2006-08-15

Swerdlow, Daniel (Department: 2615)

Telephonic communications

Substation or terminal circuitry

For loudspeaking terminal

C379S390030

Reexamination Certificate

active

07092513

ABSTRACT:
Duplex communication methods and systems with maximum gain limiting such as in telephone handsets and speaker phones are disclosed. The communications system such as a telephone set may generally include a digital signal processor (DSP) having a receive and transmit path in communication with a receiver and a transmitter, respectively, a volume amplifier for amplifying signals on the receive path, and a maximum gain limiter for determining a total return loss between the receive and transmit paths and for limiting a volume amplification level of the volume amplifier to a maximum depending on the total return loss. The maximum gain limiter determines the total return loss by maintaining a total loop gain for the telephone set at less than 0 dB to prevent unstable operation and howling.

REFERENCES:
patent: 5612996 (1997-03-01), Li
patent: 5867573 (1999-02-01), Wittman
patent: 6477250 (2002-11-01), Sheets
patent: 7006624 (2006-02-01), Philipsson et al.
patent: 2002/0090078 (2002-07-01), Feltstrom et al.
patent: 2004/0240664 (2004-12-01), Freed

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