Call for service and continuity sensor circuit

Details Call for service and continuity sensor circuit Call for service and continuity sensor circuit

1978-12-01

1980-02-26

Brown, Thomas W.

H04M 714

Patent

active

041907450

ABSTRACT:
A call for service and continuity sensor circuit for use in conjunction with a trunk circuit of a digital PABX telephone system interfacing with a central office via ground start signalling providing for detection of a call for service signal to the PABX by the central office. This circuit also provides the means to effect an open circuit for both signalling and transmission conditions in order to prevent excess loading of the trunk circuit during these conditions. This circuit provides a precise and stable threshold detection level necessary for accurate sensing of the trunk circuit conditions mentioned above despite parasitic leakage current, induced longitudinal power line voltages, and earth potentials sometimes existing on the line connecting the PABX to the central office.

REFERENCES:
patent: 4126765 (1978-11-01), Calder et al.
patent: 4133982 (1979-01-01), Lee et al.

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