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:
May. 02, 1989
Filed:
Oct. 20, 1987
Applicant:
Inventors:
Kenji Takato, Kawasaki, JP;
Kazumi Kinoshita, Yokohama, JP;
Toshiro Tojo, Kawasaki, JP;
Yuzo Yamamoto, Kawasaki, JP;
Assignee:
Fujitsu Limited, Kanagawa, JP;
Attorney:
Primary Examiner:
Int. Cl.
CPC ...
H04M / ;
U.S. Cl.
CPC ...
379373 ; 379375 ; 379418 ;
Abstract
A constant current circuit, including a constant current source which draws a current and a constant current source which sends a current, is connected to a two-wire subscriber line. A ringing signal made up of constant stream of positive and negative current signals is transmitted to the telephone line. The OFF-hook condition of a telephone set is detected by comparing the output voltage of a constant current circuit with a reference voltage for ring trip.