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US 4,540,854 AGranted
Subscriber line interface circuit
AssigneeMitel Corporation
InventorPatrick R. Beirne
Life of this patent
Estimating the term…
Abstract
A transformerless, fully balanced, telephone line circuit is provided. Two differential amplifiers are employed, one for incoming signals and the other for outgoing signals. The latter drives the line with two out-of-phase, equal amplitude signals. A comparator detects grounding of either TIP or RING at the telephone to accommodate international applications.
Claims9
A telephone line circuit for connection between a balanced two-terminal port and an unbalanced terminal comprising:
- (a) first differential amplifier means for receiving incoming signals from said balanced two-terminal port and converting them to unbalanced signals;
- (b) circuit means for applying said unbalanced signals to said unbalanced terminal;
- (c) second differential amplifier means having a pair of differential input terminals coupled across said circuit means for receiving signals originating from said unbalanced terminal, and a pair of balanced output terminals for driving said balanced two-terminal port with a pair of balanced outgoing signals representative of said signals received from the unbalanced terminal;
- (d) means for detecting an imbalance in dc-current flowing into and out of said balanced two-terminal port, and indicating grounding of either side of said balanced two terminal port in response thereto;
- and
- (e) means for limiting said dc-current to a predetermined value in response to detection of said imbalance.
3 more elements
Dependencies are inferred from the claim text.