H - Electricity – 04 – M
Patent
H - Electricity
04
M
379/67
H04M 7/00 (2006.01) H04M 19/00 (2006.01)
Patent
CA 1154185
SUBSCRIBER LINE INTERFACE CIRCUIT ABSTRACT OF THE DISCLOSURE 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 to 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.
369226
Mitel Corporation
Pascal & Associates
LandOfFree
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