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Tone signal detection apparatus

  • US 20080158617A1
  • Filed: 06/04/2007
  • Published: 07/03/2008
  • Est. Priority Date: 06/09/2006
  • Status: Active Grant
First Claim
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1. A tone signal detection apparatus for detecting a tone signal of a specific frequency, comprising:

  • a time measuring unit for measuring time during which a tone signal is not detected;

    a time comparing unit for comparing the measured time with a predetermined threshold value;

    wherein the tone signal is determined to be present if the measured time is less than the threshold value.

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