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. 01, 1990
Filed:
Mar. 25, 1988
Christian Hubert, Paderborn, DE;
Rainer Janssen, Paderborn, DE;
Nixdorf Computer AG, Paderborn, DE;
Abstract
A circuit is described for recognition of two-tone compound signals of two frequency ranges (F1 to F4, F5 to F8) in telephone installations with a limited transmission band width. Band pass filters (11, 12) whose output signals are added up and weighted individually are provided in a number corresponding to the number of possible single tones. The weighted output signals are each compared with the output signal sum of one of two frequency ranges (F1 to F4, F5 to F8 ) in order to signal a valid single tone. To increase the certainty of speech, another summand (Su, So) that is derived from a summation of the output signals of at least two other band pass filters (13) whose mid-band frequencies (F9 to F11) are outside the two frequency ranges (F1 to F4, F5 to F8) is also sent to the summation circuit.