Multi-frequency tone detector

Abstract

A multi-frequency tone detector with analysis window (i.e. filter size) chosen such that spectral nulls are located at adjacent frequencies of interest. The decision logic block of the tone detector uses the roll-off characteristics of the filter in conjunction with background noise to determine a threshold pass/fail for any tone that has deviated excessively from its nominal value. The foregoing aspects of the invention result in simple filter design (i.e. reduced order) relative to prior art tone detectors.

1 - 8 . (canceled)  
   
   
       9 . A multi-frequency tone detector comprising: 
 an analysis filter for detecting a plurality of tone frequencies; and    a decision logic block for detecting a presence or absence of each of said plurality of tone frequencies based on an output of the analysis filter; wherein    for each particular tone frequency of said plurality of tone frequencies, said analysis filter has a window having a size such that the nearest adjacent tone frequency to said each particular tone frequency is located at a spectral null of said analysis filter.    
   
   
       10 . The multi-frequency tone detector of  claim 10 , wherein said window is a rectangular window.  
   
   
       11 . The multi-frequency tone detector of  claim 10 , wherein said analysis filter is a digital filter.  
   
   
       12 . The multi-frequency tone detector of  claim 11 , wherein said analysis filter is a digital filter.  
   
   
       13 . A multi-frequency tone detector comprising: 
 an analysis filter for detecting a plurality of tone frequencies; and    a decision logic block for detecting a presence or absence of each of said plurality of tone frequencies based on an output of the analysis filter; wherein    for each particular tone frequency of said plurality of tone frequencies, the analysis filter has a window having a size such that each of the other tone frequencies is located at a spectral null of the analysis filter.    
   
   
       14 . The multi-frequency tone detector of  claim 13 , wherein said window is a rectangular window.  
   
   
       15 . The multi-frequency tone detector of  claim 13 , wherein said analysis filter is a digital filter.  
   
   
       16 . The multi-frequency tone detector of  claim 14 , wherein said analysis filter is a digital filter.