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. 28, 1989
Filed:
Dec. 19, 1986
Robert Lechner, Otterfing, DE;
Norbert Wingerath, Munich, DE;
Siemens Aktiengesellschaft, Berlin and Munich, DE;
Abstract
The invention relates to a circuit arrangement for the indication of loop closure during the ringing condition for a subscriber circuit which is connected to the exchange of a digital time multiplex telephone system by way of a subscriber termination circuit comprising a subscriber line interface circuit which, in part, provides the ringing supply and signalling, and a signal processing unit which, in part, provides for analog to digital conversion and digital to analog conversion as well as for filtering. The circuit arrangement includes a changeover switch, by way of which, a signal representative of the subscriber termination line current is applied to the signal processing unit during the ringing condition, in place of the speech signal present during the speech condition. This voltage signal is subjected to analog to digital conversion and filtering as for the speech signal at other times except that the high-pass filtering otherwise employed is avoided, and in that the resulting digital signal is further summed over at least one period of the ringing signal frequency. The sum signal is compared with a reference value which provides a loop closure signal when the reference value is exceeded by the sum signal.