| 摘要 |
A tone detection circuit of a voice mailing system is provided, which includes a low pass filter (20) for filtering a calling signal input from the interface circuit part (10) to output, a tone frequency detecting member (30) for providing a valid/non-valid frequency detection signal according to whether the tone frequency is detected for a predetermined time period with relation to the calling signal output from the low pass filter (20), a tone cadence detecting member (40) for providing a valid/non-valid cadence detection signal according to whether the cadence state is detected or not in the calling signal output from the low pass filter (20), a tone validity state detecting member (50) for output a tone validity detection signal by logic arithmetic of the valid/non-valid frequency detection signal and the valid/non valid cadence detection signal, and a control member (60) for controlling calling loop of the interface part, wherein the calling state which is transmitted from the switch board is precisely detected, for thereby improving the speech quality of the voice mailing system.
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