H - Electricity – 04 – M
Patent
H - Electricity
04
M
379/57
H04M 3/22 (2006.01) H04M 7/00 (2006.01) H04Q 1/38 (2006.01)
Patent
CA 1190680
CURRENT SINK FOR DPT CHANNEL UNIT by Gregor D. McGibbon and Kenneth K. Yu ABSTRACT OF DISCLOSURE DC saturation effects in the VF transformer of a DPT are re- duced or eliminated with apparatus diverting central office battery loop current away from windings of the transformer when a trunk circuit is seized for an off-hook condition of a calling parties telephone handset. A physically smaller transformer having increased inductance may then be employed for providing increased return loss at low fre- quencies. The apparatus comprises a current amplifier that is electri- cally connected across tip and ring lines, with a first switch means in its feedback path, and second switch means for AC coupling a transfor- mer winding to the lines. When the trunk is idle for an on-hook condi- tion of the handset, the amplifier is disabled and the lines are termi- nated with a large resistance. When the trunk is seized for an off- hook condition of the handset, binary PF and CF signals cause the cur- rent amplifier to shunt the resistor and to draw a prescribed amount of DC loop current on the lines for energizing a central office A-relay. This also turns on the second switch means for passing VF signals on the lines to and from the transformer, while blocking DC current from the winding, and terminating the lines with a prescribed impedance. When the calling party is dialing, the CF signal opens the feedback path so that the amplifier is turned hard on and off by pulsing of the PF signal for changing the termination impedance and causing resistive pulsing in the central office. -17-
424547
Mcgibbon Gregor D.
Yu Kenneth K.
Gte Automatic Electric Incorporated
R. William Wray & Associates
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