The patent badge is an abbreviated version of the USPTO patent document. The patent badge does contain a link to the full patent document.
The patent badge is an abbreviated version of the USPTO patent document. The patent badge covers the following: Patent number, Date patent was issued, Date patent was filed, Title of the patent, Applicant, Inventor, Assignee, Attorney firm, Primary examiner, Assistant examiner, CPCs, and Abstract. The patent badge does contain a link to the full patent document (in Adobe Acrobat format, aka pdf). To download or print any patent click here.
Patent No.:
Date of Patent:
Sep. 05, 1989
Filed:
Mar. 08, 1988
John Ramsay, Herndon, VA (US);
Thomas Ouellette, Fairfax, VA (US);
International Telesystems Corp., Herndon, VA (US);
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.