H - Electricity – 04 – M
Patent
H - Electricity
04
M
379/16, 379/57
H04M 3/02 (2006.01) H04M 19/02 (2006.01)
Patent
CA 1152663
PHF. 79-589 15 ABSTRACT: Apparatus for detecting the closure of a sub- scriber's telephone line in the presence of an alternating ringing voltage superimposed on a direct voltage comprises device for producing a unidirectional current from the com- bined alternating and direct voltages. When the line is open no direct current will flow and hence the peak value of successive half cycles will be equal whereas when the loop is closed and direct current flows the peak values or successive peaks will be different. A capacitor is charged by a voltage U1, which is proportional to the combined voltage, through a transistor provided that the voltage U1 is greater than the voltage across the capacitor and discharged through a resistor. The time constant of the discharge cir- cuit is selected so that when the line is looped the smaller peak is lower than the voltage to which the capacitor is discharged and hence charging current flows into capacitor on alternate peaks of the voltage U1 only. The intervals between pulses of charging current are determined by com- parator which provides an output S which indicates whether the subscriber's line is closed.
364575
Ferrieu Gilbert M.m.
Hetet Yves J.f.
Osmond Etienne J.r.
Telecommunications Radioelectriques Et Telephoniques T.r.t.
Van Steinburg C.e.
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