Telephonic communications – Supervisory or control line signaling – Signal receiver
Patent
1993-07-01
1995-06-20
Dwyer, James L.
Telephonic communications
Supervisory or control line signaling
Signal receiver
379282, 379283, 379290, H04M 322
Patent
active
054266963
ABSTRACT:
A method of improving the sensitivity and speech immunity of a receiver in conjunction with DTMF-reception is disclosed. The number of zero-crossings of the input signal are counted during one of a number of measuring intervals in real time at frequencies which occur in the low frequency group and the high frequency group of a DTMF-signal. At the end of each of the measuring intervals, the number of zero-crossings in a current measuring interval is compared for each frequency group, with a corresponding number of zero crossing in a number of nearest preceding measuring intervals, and the magnitude of any difference is established. The input signal is treated as a DTMF-signal when the difference is at most equal to a permitted limit value.
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Dwyer James L.
Saint-Surin Jacques M.
Telefonaktiebolaget LM Ericsson
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