1975-06-23
1977-02-22
Cooper, William C.
H04M 150
Patent
active
040093530
ABSTRACT:
Disclosed is a method and apparatus for detecting the presence of signals, particularly touch-tone signals, of characteristic complex waveforms by comparing unknown signals with pre-specified digital formats or "masks" representative of such waveforms. The apparatus includes digital circuitry defining the masks and digital circuitry for counting the number of times during a prescribed time period there is a correlation between the digital format of the unknown signals and the masks.
REFERENCES:
patent: 3537001 (1970-10-01), Friend
patent: 3760269 (1973-09-01), Beeman
patent: 3790720 (1974-02-01), Schartmann
patent: 3912869 (1975-10-01), Ullakko
patent: 3917912 (1975-11-01), Niwa
James Randell Leland
Padden James Thomas
Cooper William C.
International Business Machines - Corporation
Jackson John L.
Popek Joseph A.
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