DX circuit

Details DX circuit DX circuit

1987-06-26

1989-03-21

Ng, Jin F.

Telephonic communications

Plural exchange network or interconnection

Interexchange signalling

379236, 379240, H04M 706

Patent

active

048151246

ABSTRACT:
An improved DX circuit may be connected to signaling and reference leads of a DX signaling link, without need to balance the internal impedance of the DX circuit against that of the external DX signaling link. The DX circuit senses the magnitude and direction of current flow on the leads, and operates on the principle that when a near end signaling circuit is on-hook, a positive current flow indicates that a far end signaling circuit is off-hook and a current flow of zero indicates that it is on-hook, while if the near end signaling circuit is off-hook, a negative current flow indicates that the far end signaling circuit is on-hook and a current flow of zero indicates that it is off-hook. The arrangement allows the DX circuit to properly function irrespective of the resistive load presented by the DX signaling link. To enable the DX circuit to function with various capacitive loads, it also detects the rate of change of current on the leads and, in the absence of a change in status of the near end signaling circuit, provides an output representative of a change in the on-hook/off-hook status of the far end signaling circuit, immediately upon detecting a sufficient rate of change.

REFERENCES:
patent: 3508008 (1970-04-01), Gardner et al.
patent: 3894192 (1975-07-01), Wisotzky
patent: 4476557 (1984-10-01), Knoedl, Jr.
"Basic Telephone Switching Systems", D. Talley, Hayden Book Company, New Jersey, 1979, p. 41-45.

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