Telephonic communications – Supervisory or control line signaling – Signal receiver
Reexamination Certificate
2005-10-14
2009-10-13
Smith, Creighton (Department: 2614)
Telephonic communications
Supervisory or control line signaling
Signal receiver
C379S282000, C379S283000, C379S284000
Reexamination Certificate
active
07602902
ABSTRACT:
A method for decoding a DTMF tone which includes collecting the width of serial signals by measuring the time interval between zero-crossing points within a predetermined time; counting within the predetermined time the number of signal zero-crossing points; performing interpolation on the data produced by the collecting and counting steps with a Fourier transform; identifying a first frequency that has the strongest magnitude from the resulting data; and calculating the lower frequency of the tone being decoded by subtracting the first frequency from the average frequency of the digitized signal. The invention also includes apparatus that utilizes a zero-crossing detector for receiving a DTMF tone to be decoded and producing a digitized output; apparatus for collecting the width of serial signals by measuring the time interval between zero-crossing points within a predetermined time; apparatus for counting within the predetermined time the number of signal zero-crossing points; apparatus for performing interpolation on the data produced by the collecting and counting steps with a Fourier transform; apparatus for identifying a first frequency that has the strongest magnitude from the resulting data; and apparatus for calculating the lower frequency of the tone being decoded by subtracting the first frequency from the average frequency of the digitized signal.
REFERENCES:
patent: 5144626 (1992-09-01), Funatsu et al.
patent: 5265097 (1993-11-01), Funatsu et al.
patent: 6771767 (2004-08-01), Li et al.
patent: 2002/0038210 (2002-03-01), Yajima et al.
Beninati John
Grimberg Dalia S.
Honeywell International , Inc.
Smith Creighton
Smith Robert S.
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