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:
Feb. 26, 1980
Filed:
Dec. 01, 1978
Julius Jusinskas, Jr, Glen Ellyn, IL (US);
David Q Lee, Boca Raton, FL (US);
Richard M Rovnyak, Schaumburg, IL (US);
GTE Automatic Electric Laboratories Incorporated, Northlake, IL (US);
Abstract
A call for service and continuity sensor circuit for use in conjunction with a trunk circuit of a digital PABX telephone system interfacing with a central office via ground start signalling providing for detection of a call for service signal to the PABX by the central office. This circuit also provides the means to effect an open circuit for both signalling and transmission conditions in order to prevent excess loading of the trunk circuit during these conditions. This circuit provides a precise and stable threshold detection level necessary for accurate sensing of the trunk circuit conditions mentioned above despite parasitic leakage current, induced longitudinal power line voltages, and earth potentials sometimes existing on the line connecting the PABX to the central office.