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:
Aug. 18, 1992
Filed:
May. 01, 1991
James L Fry, San Rafael, CA (US);
Larry Martin, Sebastopol, CA (US);
Robert B Johnston, Petaluma, CA (US);
Light Logic, Ltd., San Rafael, CA (US);
Abstract
An added main line system is disclosed with particular utility in connection with equipment for providing the services of two telephone lines on a single conductor pair. The ring generator of the added main line system has two transistor bridges, one for the ringing signal on each of two subscriber lines. In each bridge, diagonally opposed pairs of transistors are turned on in alternation, providing alternating current for the ringing signal. The two bridges, each of which has four transistors, share two transistors. Comparators provide off-hook detection during the ringing cycle. Off-hook detection circuits are provided in series with selected driver transistors of the bridges, so that the condition of customer equipment going off-hook may be detected even though limited power is available for testing for the off-hook condition. Ring detectors at the central office are coupled digitally to ring generators at the subscriber equipment, and bit-message protocols are provided so that the added main line apparatus is able to replicate, at the customer line, the ringing cadence provided at the central office.