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:
Jul. 26, 1988
Filed:
Sep. 17, 1986
Masanobu Arai, Tokyo, JP;
NEC Corporation, , JP;
Abstract
A subscriber line interface circuit comprises a balanced amplifier having positive and negative inputs for amplifying a voltage thereacross to generate a pair of mutually complementary voltages across true and complementary outputs. Four resistors of a first value are respectively connected between a subscriber tip line and the negative input, between a subscriber ring line and the positive input, between the negative input and true output and between the positive input and complementary output. Two resistors of a second value smaller than the impedance of the subscriber loop are respectively connected between the tip line and the complementary output and between the ring line and the true output. A DC feedback circuit is connected to the complementary output to generate a DC feedback signal according to a desired variable DC power feeding characteristic. An AC feedback circuit generates an AC feedback signal proportional to a differential voltage across the tip and ring lines and inversely proportional to a desired AC impedence. The DC and AC feedback signals are combined in a circuit which supplies to the negative input a current corresponding to the combined signals.