H - Electricity – 04 – M
Patent
H - Electricity
04
M
379/81
H04M 1/60 (2006.01) H04M 9/10 (2006.01)
Patent
CA 1134522
A VOICE SWITCH FOR HANDS FREE COMMUNICATION APPARATUS Abstract of the Disclosure First syllable clipping typically associated with simple control circuits in hands free telephony, is substantially reduced by using a voice switch with non-linear response characteristics. The voice switch includes field effect devices in transmit and receive variolossers for providing handsfree operation in communication apparatus. The field effect devices are non-linear in their response to a control voltage, and are thus controllable to provide rapid switching from an idle mode of operation, to an opposite mode of operation. The control circuit generates a control signal for operating the voice switch in response to a.c. signals in a microphone circuit connected with a transmit path and in response to a.c. signals in a loudspeaker circuit connected with a receive path. A circuit including another field effect device similar to the above mentioned field effect devices, is responsive to the control signal for generating a control voltage for controlling attenuation introduced in the transmit and receive paths by the respective variolossers. This circuit generates the control voltage having first and second limits. The first limit corresponds to operation of the voice switch in a quiescent or idle state and is adjusted with respect to operating temperatures such that the field effect devices are maintained at or near a threshold of conductance. As a result, the variolossers are hyper-responsive to excursions in the control voltage from the first limit toward the second limit, substantially reducing first syllable clipping. - i -
350901
Moorhouse J. E.
Northern Telecom Limited
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