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:
Jul. 28, 1998
Filed:
Jun. 18, 1996
Thanh Lam, Grafton, MA (US);
Timothy Lis, Framingham, MA (US);
Richard Haltmaier, West Newton, MA (US);
Motorola Inc., Schaumburg, IL (US);
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 been detected (205) but when the discrimination value is not greater than a predetermined threshold, a non-amplitude modulated signal (or a signal having amplitude modulation less than a predetermined modulation index), such as ANS, has been detected (255, 265).