Telephone trunk interface circuit

Details Telephone trunk interface circuit Telephone trunk interface circuit

1988-03-08

1989-09-05

Dwyer, James L.

Telephonic communications

Supervisory or control line signaling

Using line or loop condition detection

379380, 379382, 379377, 379265, H04M 342

Patent

active

048646059

ABSTRACT:
A solid-state telephone trunk interface circuit provides high isolation between a central office and telephone equipment. Opto-isolator transistors and a transformer are used to isolate the central office and the local equipment portions of the circuit. A switching transistor (Q4) is connected between a ring connector (3) and turned on and off via an opto-isolator transistor connected to a control connector (9). A ring detector (11) comprising a first diode bridge is connected between tip and ring connectors (2 and 3) via an opto-isolator transistor to a ring signal connector (13). First and second parallel and opposite sign line condition detectors are respectively connected between tip and ring connectors and via opto-isolator transistors to battery-reverse and battery-forward signal connectors (19 and 17). The voice circuit includes a second diode bridge connecting tip and ring connectors to a first winding of a transformer (T1). The circuit between the diode bridge and the first winding is completed by a high voltage transistor (Q3) which is turned on and off via an opto-isolator transistor connected to an off-hook connector ( 21). A second winding of the transformer is connected to first and second operational amplifiers respectively connected to voice signal input and output connectors (23 and 25). A feedback cancelling circuit is connected between the voice signal input connector and the input of the second operational amplifier for cancelling a portion of the voice signal input to the voice signal output.

REFERENCES:
patent: 4126765 (1978-11-01), Calder et al.
patent: 4203006 (1980-05-01), Mascia
patent: 4303804 (1981-12-01), Johnson et al.
patent: 4723267 (1988-02-01), Jones et al.

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