Apparatus for detecting the closure of a subscriber's line durin

Details Apparatus for detecting the closure of a subscriber's line durin Apparatus for detecting the closure of a subscriber's line durin

1980-11-17

1982-10-26

Brown, Thomas W.

H04M 302

Patent

active

043563554

ABSTRACT:
Apparatus for detecting the closure of a subscriber's telephone line in the presence of an alternating ringing voltage superimposed on a direct voltage comprises circuitry for producing a unidirectional current from the combined 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 of successive peaks will be different. A capacitor (26) is charged by a voltage (U.sub.1), which is proportional to the combined voltage, through a transistor (24), provided that the voltage (U.sub.1) is greater than the voltage across the capacitor, and discharged through a resistor (27). The time constant of the discharge circuit 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 (26) on alternate peaks of the voltage (U.sub.1) only. The intervals between pulses of charging current are determined by a comparator (33) which provides an output (S) which indicates whether the subscriber's line is closed.

REFERENCES:
patent: 4037117 (1977-07-01), Carbrey
patent: 4110569 (1978-08-01), Schindler et al.
patent: 4199664 (1980-04-01), Grange et al.
patent: 4262172 (1981-04-01), Brolin

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