Telephonic communications – Substation or terminal circuitry – Sidetone control or hybrid circuit
Reexamination Certificate
2005-12-27
2005-12-27
Isen, Forester W. (Department: 2644)
Telephonic communications
Substation or terminal circuitry
Sidetone control or hybrid circuit
C379S392000, C379S406010
Reexamination Certificate
active
06980644
ABSTRACT:
There is disclosed an echo canceller circuit for use in a full duplex transceiver of the type comprising a line driver capable of sending analog transmit signals through a cable and comprising a line receiver capable of receiving analog receive signals from the cable. An echo canceller impedance model circuit is coupled to an output of the line driver and is coupled to an input of the line receiver. The echo canceller impedance model circuit generates an echo canceller current that is equal in magnitude and opposite in phase to a current that represents signal echoes that are present in the analog receive signals. The echo canceller impedance model circuit has a variable impedance for generating the echo canceller current. The variable impedance has at least one variable resistor and at least one variable capacitor. The values of resistance and capacitance in the echo canceller impedance model circuit are varied in response to control signals from a echo canceller control circuit to compensate for and cancel signal echoes.
Manickam Thulasinath G.
Raghavan Sreen
Sallaway Peter J.
Isen Forester W.
National Semiconductor Corporation
Singh Ramnandan
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