Pulse or digital communications – Transceivers – Modems
Patent
1996-06-18
1998-07-28
Chin, Stephen
Pulse or digital communications
Transceivers
Modems
375320, 375340, 375377, 379 90, 379 93, 379 97, 379 98, 370292, H04B 138, H04L 516
Patent
active
057871167
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).
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patent: 5202905 (1993-04-01), Sakamoto et al.
patent: 5311578 (1994-05-01), Bremer et al.
patent: 5349635 (1994-09-01), Scott
patent: 5446771 (1995-08-01), Lin
Haltmaier Richard
Lam Thanh
Lis Timothy
Chin Stephen
Gamburd Nancy R.
Maddox Michael W.
Motorola Inc.
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