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. 18, 1984
Filed:
Jul. 21, 1981
Patrick R Beirne, Stittsville, CA;
Mitel Corporation, Kanata, CA;
Abstract
A subscriber line interface circuit for coupling a balanced communication line with unbalanced bidirectional or a pair of unidirectional communication lines. Line current is fed to the line via a low resistance path for maximum current supply, via a circuit which matches the line impedance, and also provides high resistance protection to the output of amplifiers feeding the balanced line. Since a low resistance d.c. current feed is used, a voltage boost is not required. However lightning protection is obtained for the outputs of the amplifiers which feed the line, at the same time as virtually optimum line impedance matching and sufficient line current feed. The circuit is comprised of a balanced line including a lead pair, a pair of matched feed resistors for providing a low resistance path, each connected to one of the pair for applying a d.c. line current from a power source to the line, the total resistance of the feed resistors being a fraction of the d.c. line impedance. A circuit is provided for receiving a signal from the balanced line, and a further circuit applies a predetermined amplitude of the signal received from the balanced line back to the balanced line with a signal aiding polarity so as to raise the apparent impedance of the line for the signal at the lead pair, while allowing d.c. line current to be fed to the line via the low resistance path.