| 摘要 |
PROBLEM TO BE SOLVED: To prevent frequency components included in voice response signals from being erroneously recognized as CNG (calling tone) signals in a facsimile equipment. SOLUTION: A telephone line interface circuit 1 removes DC components for signals inputted from a public telephone line and sends them to a frequency component detection circuit 2. The frequency component detection circuit 2 detects whether or not the components of 1,100 Hz are present in the signals, and at the time of detecting the components of 1,100 Hz, sends the signals for reporting that to a timer circuit 3 and a counting circuit 4. When the time of detecting the components of 1,100 Hz exceeds about 300 ms, for about 3.5 s from the point of time at which the time passes for about 2.5 s, the timer circuit 3 sends the signals for reporting that to the counting circuit 4. The counting circuit 4 judges that CNG tones are detected at the time of detecting the signals composed of the time width of about 300 ms and the stop period of 2.5-3.5 s for two times based on the signals from the frequency component detection circuit 2 and the timer circuit 3.
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