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:
Oct. 26, 1993
Filed:
Dec. 11, 1990
Yigal Brandman, Palo Alto, CA (US);
Manoj Puri, Sunnyvale, CA (US);
Octel Communications Corporation, Milpitas, CA (US);
Abstract
Dual tone multifrequency ('DTMF') signal pulses are detected and identified by subjecting the signal being analyzed to complex bandpass filtering for each of the two DTMF frequency bands. The envelope of the outputs of each of these filters are determined and subjected to a succession of different tests including a ripple or smoothness test to ensure adequate smoothness, a ratio test to ensure the occurrence of a step function, a twist test to ensure the proper amplitude ratio between the two bands, and a minimum energy test to ensure that the signal has sufficient energy. If the signal passes all of the detection tests, then the actual DTMF signal is identified by using the real and imaginary parts of each complex bandpass filter output to compute an associated complex phase angle, and comparing that phase angle to the corresponding phase angles for valid DTMF tones.