Telephonic communications – Subscriber line or transmission line interface – Protective circuit
Patent
1995-06-07
1997-06-03
Zele, Krista M.
Telephonic communications
Subscriber line or transmission line interface
Protective circuit
379252, 379377, 379382, H04M 302
Patent
active
056362730
ABSTRACT:
An apparatus for determining a power cross condition during a ringing state of a telephone. The apparatus also is capable of distinguishing a true power cross condition from a short loop ringing condition, by including a first path for receiving a signal indicative of a voltage across a ring feed resistor exceeding a predetermined value, and determining if that voltage is in an active state for a predetermined amount of time (i.e., 14 milliseconds). The apparatus also includes a second path for receiving a first and second current that flow respectively across a first and second sense resistor connected to opposite ends of the ring feed resistor. On the second path, the first and second currents are subtracted, converted to a digital value, filtered, and compared to a threshold value to determine if a ring trip has occurred. If so, the potential ring trip is sent to a persistence timer circuit, for checking if it is in an active state for a predetermined amount of time (i.e., 104 milliseconds). If either of the first and second paths indicate a ring trip, then the apparatus outputs a ring trip detection signal. The apparatus also is configured to work with a power cross validation circuit, which may be connected on a third path for switching ring relays quickly to save components on the telephone lines during a power cross occurrence.
REFERENCES:
patent: 3996426 (1976-12-01), Lancaster
patent: 4079210 (1978-03-01), Sanderson
patent: 4995111 (1991-02-01), Tojo et al.
patent: 5038375 (1991-08-01), Sinberg
patent: 5323461 (1994-06-01), Rosenbaum et al.
patent: 5426695 (1995-06-01), Misu
Ramirez Sergio R.
Schopfer Walter S.
Saint-Surin Jaques M.
Zele Krista M.
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