H - Electricity – 04 – L
Patent
H - Electricity
04
L
340/104
H04L 27/00 (2006.01) H04L 12/26 (2006.01) H04Q 1/448 (2006.01)
Patent
CA 1209666
ABSTRACT A TONE RECEIVER FOR DIGITAL DATA COMMUNICATION SYSTEMS A device for detecting the presence of an alarm tone of a given frequency within a received signal carrying digital data in addition to said tone. The receiver comprises an analog-to-digital converter the output of which is applied to a first recursive bandpass filter centered at the frequency of the alarm tone and the feedback loop of which includes a limiter. In addition, an input feedforward loop is provided for adding the output signal from the converter, as multiplied by a coefficient ?, to the output signal from the limiter. The output signal from the adder is hard limited, then passed through a second bandpass filter. The energy of the signal obtained at the output of said second filter is then measured to provide indication of a tone being received when said energy exceeds a predetermined threshold,
425790
Barrett B.p.
International Business Machines Corporation
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