Patent ID: 7010117
Filing Date: 2006-03-07
Classification: H04Q

Abstract:
1. A multi-frequency tone detector comprising an analysis filter for detecting the tone energies of an input signal at a plurality of tone frequencies of interest and a decision logic block for detecting presence or absence of said tone frequencies of interest based on said detected tone energies, characterized in that a total energy calculator is provided for calculating total energy of the input signal and said decision logic block detects the presence or absence of said tone frequencies by calculating background energy as total energy minus the tone energies of said input signal at said plurality of tone frequencies of interest, and for each of said tone energies (i) calculating a roll-off signal-to-noise ratio for said analysis filter, (ii) failing any of said tone frequencies of interest for which said tone energies are less than said roll-off signal-to-noise ratio times said background energy and (iii) otherwise passing said tone frequencies.