Subscriber line interface circuit having means for combining DC

Details Subscriber line interface circuit having means for combining DC Subscriber line interface circuit having means for combining DC

1986-09-17

1988-07-26

Ng, Jin F.

Telephonic communications

Supervisory or control line signaling

Using line or loop condition detection

379398, 379405, 379413, H04B 303, H04M 1900

Patent

active

047605952

ABSTRACT:
A subscriber line interface circuit comprises a balanced amplifier having positive and negative inputs for amplifying a voltage thereacross 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 impedence. The DC and AC feedback signals are combined in a circuit which supplies to the negative input a current corresponding to the combined signals.

REFERENCES:
patent: 4532381 (1985-07-01), Rosenbaum et al.
patent: 4600811 (1986-07-01), Hayashi et al.
patent: 4607141 (1986-08-01), Schorr
patent: 4661978 (1987-04-01), Hirata
patent: 4677667 (1987-06-01), Burns

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