Patent ID: 6813350
Filing Date: 2004-11-02
Classification: H03L,H04J,H04L

Abstract:
An apparatus for detecting an alert signal containing first and second tones in a telephone system capable of caller id off hook mode operation, said apparatus comprising:a) a first processing channel comprising: (i) a bandsplit filter for passing said first tone and providing limited attenuation of said second tone; (ii) a first comparator for comparing the output of said first bandsplit filter with a first varying threshold value to reject speech and music imitations; and (iii) a first adaptive threshold generator for generating said first varying threshold value that adapts to a characteristic of the output of said first bandsplit filter; b) a second processing channel comprising: (i) a second bandsplit filter for passing the second tone and providing limited attenuation of said first tone; (ii) a second comparator for comparing the amplitude of the output of said second bandsplit filter with a second varying threshold value to reject speech and music imitations; and (ii) a second adaptive threshold generator for generating said second varying threshold value that adapts to said characteristic of the output of said second bandsplit filter; and c) a detect decision circuit for detecting the presence of said alert signal based on the output of said first and second comparators of said first and second processing channels.