| 摘要 |
PURPOSE:To enable detection without error with a simple constitution, by inputting a binary output of an audible tone signal to a monostable multivibrator having a specific output time and discriminating an audible tone signal on the basis of the difference of interrupted period. CONSTITUTION:Noise or the like are eliminated out of an audible tone signal (a) from an incoming exchanger at a band pass filter 1 and the signal is applied to a full wave rectifying circuit 2 and the rectified output is binarized by an integral binary circuit 3. For example, if the audible signal (a) is as a busy tone shown in figure (a), the binarized signal (b) is as shown in figure (b), and if a call tone signal is inputted, the binarized signal (b) is as shown in figure (e). The binary signal (b) is applied to a monostable multivibrator in which the output time is longer than the short intermittent period of the busy tone signal and shorter than the long intemittent period of the call tone signal, and FFs 6, 7, and the Q output of the monostable multivibrator 4 is respectively continuous or discontinuous at the time of input of busy tone or call tone. Thus, when the Q terminal output (d) of the FF6 is 1 or 0, it is judged as a busy tone or as a call tone, respectively. |
