Method and circuit for failsafe switch-hook detection during fau

Details Method and circuit for failsafe switch-hook detection during fau Method and circuit for failsafe switch-hook detection during fau

1995-01-30

1998-09-22

Zele, Krista M.

Telephonic communications

Supervisory or control line signaling

Using line or loop condition detection

379 26, 379 30, 379377, 379380, 379381, H04M 100

Patent

active

058126589

ABSTRACT:
A circuit and method for maintaining switch-hook detection (SHD) in the presence of a fault in a telephone system may include a comparison of one of a tip current and a ring current to a reference current. A switch-hook detection indicates that a request for service has been made. The reference current may be a conventional switch-hook detection threshold current, I.sub.SHD, times a factor (G.sub.0 +1).sup.-1, where G.sub.0 is the predetermined operating gain of the amplifier in the telephone subscriber line interface circuit. The line current may be reduced in response to detection of a fault in the telephone system without affecting the determination whether a request for service has being made.

REFERENCES:
patent: 4406929 (1983-09-01), Pace et al.
patent: 4540854 (1985-09-01), Beirne
patent: 4599494 (1986-07-01), Welty
patent: 5111497 (1992-05-01), Bliven et al.
patent: 5404401 (1995-04-01), Bliven et al.

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