Apparatus for receiving tone signal, apparatus for transmitting tone signal, and apparatus for transmitting or receiving tone signal
US6668057B1 · kind B1 · utility
Assignee
Inventors
Key dates
| Filing date | Nov 22, 2000 |
| Grant date | Dec 23, 2003 |
| Priority date | — |
| Expiry date | Jun 1, 2022 |
Classification
- Technology area (CPC H)Electricity
- CPC primaryH04M1/505
- WIPO fieldTelecommunications
- WIPO sectorElectrical engineering
Abstract
An arithmetic processing section is designed to repeatedly execute product-sum arithmetic processing a number of times equal to the number of samples corresponding to each of the frequencies, in which a value obtained by subtracting a product-sum arithmetic value two sampling periods before from an input signal and a value obtained by multiplying a product-sum arithmetic value one sampling period before by a coefficient corresponding to a reference frequency contained in a DTMF signal are added. A comparator extracts an output value equal to or larger than a predetermined threshold value from the product-sum arithmetic values obtained by the arithmetic processing section. A matrix section determines the type of DTMF signal on the basis of at least two output values extracted by the comparator.
Source: USPTO / EPO open patent data. Objective bibliographic and citation counts.