| 摘要 |
The method provides a method and device for detecting in a single or multi frequency signal, one or more frequencies from a predetermined set of frequencies. The Signal is subjected to a complex filter substantially passing all of the frequencies in the predetermined set of frequencies. For each of one or more pairs of members of the complex filtered signal, a complex number Y<SUB>d </SUB>is determined having a phase indicative of a phase difference between the two members of the pair. The one or more frequencies are then determined based upon the one or more complex numbers. The method and device of the invention may be used in an apparatus such as a call indicator (CI) detector or a DTMF detector.
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