Telephonic communications – Centralized switching system – With generating of call associated substation signal
Patent
1992-08-17
1995-03-28
Dwyer, James L.
Telephonic communications
Centralized switching system
With generating of call associated substation signal
379254, 379255, 379418, 363 44, 363 89, 363127, H04M 150
Patent
active
054024803
ABSTRACT:
A call signal generating circuit includes a step-up transformer having a primary winding and secondary windings and a first switching circuit coupled between the primary winding of the step-up transformer and a D.C. power source for turning ON/OFF at a frequency higher than a frequency of a call signal. A rectifying circuit is coupled to the secondary windings of the step-up transformer for rectifying voltages induced at the secondary windings into a positive polarity voltage and a negative polarity voltage. A second switching circuit is coupled to the rectifying circuit for alternatively outputting the positive polarity voltage and the negative polarity voltage with a quiescent time in which both the positive and negative polarity voltages are not output. A capacitor is coupled to the second switching circuit for receiving the positive and negative polarity voltages output from the second switching circuit. A third switching circuit is provided in the call signal generating circuit for discharging the capacitor during the quiescent time. A pair of output terminals are coupled to the capacitor for outputting the generated call signal.
REFERENCES:
patent: 4436960 (1984-03-01), Harmon
patent: 4656659 (1987-04-01), Chea
patent: 4703500 (1987-10-01), Pollard
patent: 4866585 (1989-09-01), Das
patent: 5122760 (1992-06-01), Nishijima
patent: 5134355 (1992-07-01), Hastings
Dwyer James L.
Fujitsu Limited
Lau Michael N.
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