Apparatus and method for detecting amplitude modulated answer back toned signals
US5787116A · kind A · utility
Assignee
Inventors
Key dates
| Filing date | Jun 18, 1996 |
| Grant date | Jul 28, 1998 |
| Priority date | — |
| Expiry date | Jun 18, 2016 |
Classification
- Technology area (CPC H)Electricity
- CPC primaryH04M11/06
- WIPO fieldDigital communication
- WIPO sectorElectrical engineering
Abstract
An apparatus and method are provided for a data communications device, such as a modem (100,101), software modem, or facsimile machine, to detect and discriminate various amplitude modulated signals, such as an ANS signal of the ITU V.25 protocol and an ANSam signal of the ITU V.8 protocol. The apparatus and method embodiments first determine the presence of a first frequency component in a received signal, such as the 2100 Hz component of ANS and ANSam signals (205). The received signal is then demodulated (215) and low pass filtered (220), followed by removing any resulting direct current component (225) to form an inclusive signal. A second frequency component, such as the frequency of the 15 Hz amplitude modulating component of an ANSam signal, is removed from the inclusive signal (235), and its resulting magnitude is determined, as a filtered signal magnitude (240). The filtered signal magnitude is subtracted from the magnitude of the inclusive signal (230) to form a discrimination value (245). When the discrimination value is greater than a predetermined threshold, an amplitude modulated signal such as ANSam has been detected (255, 260). When the first frequency component has…
Source: USPTO / EPO open patent data. Objective bibliographic and citation counts.