| 摘要 |
The invention is to provide a DTMF decoder having a minimum power consumption. A signal inputted to a digital demodulator of the invention is respectively inputted to a bandpass filter for a DTMF signal of a low frequency band, a bandpass filter for a DTMF signal of a high frequency band, a bandpass filter for a DTMF signal of a middle frequency band, and levels of signals passed through respective filters are measured by a level measuring device for the DTMF signal of a low frequency band, a level measuring device for the DTMF signal of a high frequency band, and a level measuring device for the DTMF signal of a middle frequency band. The digital demodulator of the invention decides that the DTMF signal is included in the digital signal if it can be decided that the output level of the level measuring device for the DTMF signal of the low frequency band, and that of the level measuring device for DTMF signal of the high frequency band have respectively more than given levels and substantially the same levels and that of the level measuring device for the DTMF signal of the middle frequency band is scarcely present.
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