Digital dtmf tone detector

Details Digital dtmf tone detector Digital dtmf tone detector

H - Electricity

04

M

379/59

H04M 3/22 (2006.01) H04Q 1/457 (2006.01)

Patent

CA 1289281

ABSTRACT A digital DTMF tone receiver comprised of a detector circuit for scanning incoming audio signals for possible presence of DTMF tones, and a verifier circuit for verifying the presence of the detected DTMF tones. The detector circuit performs successive discrete Fourier transforms on the incoming signal at a first level of accuracy, and in response generates a tone verify flag signal for indicating whether or not a DTMF tone has been detected. The verifier circuit is enabled in the event that the tone verify flag signal indicates detection of a DTMF tone. The verifier circuit then performs further discrete Fourier transforms on the incoming signal at the detected DTMF frequencies as well as frequencies adjacent thereto, at a second level of accuracy greater than that provided by the detection circuit. The verifier circuit generates a tone present flag signal for indicating whether or not the detected DTMF tone is actually present. The detector and verifier circuits are preferably implemented algorithmically within a digital signal processor.

566003

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