Dual tone multifrequency signal detection and identification methods and apparatus
US5257309A · kind A · utility
Assignee
Inventors
Key dates
| Filing date | Dec 11, 1990 |
| Grant date | Oct 26, 1993 |
| Priority date | — |
| Expiry date | Dec 11, 2010 |
Classification
- Technology area (CPC H)Electricity
- CPC primaryH04L27/30
- WIPO fieldTelecommunications
- WIPO sectorElectrical engineering
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.
Source: USPTO / EPO open patent data. Objective bibliographic and citation counts.