Bell Telephone Laboratories

DeWitt Paul Smith

Harry E Mussman

Laimons Freimanis

Irvine Keers Hetherington

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 line battery feed circuit for supplying talking current to a subscriber subset and at the same time reducing common mode interference signals. The inputs of a differential operational amplifier are coupled to a telephone line and the outputs of the differential operational amplifier are coupled to a battery feed circuit. The battery feed circuit provides talking current to the subscriber subset and the differential operational amplifier presents a high impedance between the battery and the telephone line to differential voice signals while at the same time presenting a low impedance between the telephone line and the battery for common mode interference signals thereby reducing the latter.

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Naperville, IL, United States of America

DeWitt Paul Smith