H - Electricity – 04 – M
Patent
H - Electricity
04
M
379/67
H04M 19/00 (2006.01)
Patent
CA 1257722
"Subscriber Line Interface Circuit Having Means for Combining DC and AC Feedback Signals" ABSTRACT OF THE DISCLOSURE A subscriber line interface circuit comprises a balanced amplifier having positive and negative inputs for amplifying a voltage thereacoss to generate a pair of mutually complementary voltages across true and complementary outputs. Four resistors of a first value are respectively connected between a subscriber tip line and the negative input, between a subscriber ring line and the positive input, between the negative input and true output and between the positive input and complementary output. Two resistors of a second value smaller than the impedance of the subscriber loop are respectively connected between the tip line and the complementary output and between the ring line and the true output. A DC feedback circuit is connected to the complementary output to generate a DC feedback signal according to a desired variable DC power feeding characteristic. An AC feedback circuit generates an AC feedback signal proportional to a differential voltage across the tip and ring lines and inversely proportional to a desired AC impedance. The DC and AC feedback signals are combined in a circuit which supplies to the negative input a current corresponding to the combined signals.
518599
Corporation Nec
Smart & Biggar
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