Bell Telephone Laboratories

Laimons Freimanis

Harry E Mussman

DeWitt Paul Smith

A communication line interface circuit including a floating current source supplying a constant current substantially independent of loop length is disclosed. The line interface circuit is provided with circuitry for line supervision and the detection of dial pulse signaling.

Telephone subscriber line circuit

A telephone ringing circuit responds to both conventional high voltage 20Hz ringing signals and low voltage tone alerting signals. A conventional electromechanical ringer is connected across the telephone line and is responsive to high voltage 20Hz ringing signals. A high capacitance capacitor is charged by the dc voltage present on the telephone line and is discharged across the electromechanical ringer when a tone detector circuit connected across the line detects a tone alerting signal, thereby activating the electromechanical ringer.

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Chicago, IL, United States of America

Laimons Freimanis