Dial pulsing circuit

Details Dial pulsing circuit Dial pulsing circuit

H - Electricity

04

M

379/26

H04M 1/31 (2006.01)

Patent

CA 1190679

- 17 - DIAL PULSING CIRCUIT Abstract In order to provide push-button telephone service to those telephone systems not equipped to respond to multifrequency dialing signals, it is necessary to convert push-button dialed digits into conventional dial pulses. A pulse train consisting of make and break intervals representing the dialed digit is electronically converted into a corresponding series of make and break intervals on the telephone line by switching a pulsing transistor that is in series with the telephone line ON and OFF. In order to keep the pulsing transistor ON during nondialing intervals and during each make interval, and not attenuate the voice signal, the pulsing transistor is biased by an adjustable current source. The current needed to bias the pulsing transistor ON is linearly related to the telephone line current flowing through the emitter collector path of the transistor, and which varies considerably from station-to-station. In order to minimize the current needed to bias the pulsing transistor, a current sensor derives a signal proportional to the line current which, in turn, is fed back to the current source in order to adjust the bias current to be proportional to the line current.

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