| 摘要 |
PURPOSE:To prevent the titled device from generation of an output even with reception of consecutive noise, by constituting a comparison circuit with one comparison circuit having a specified level of threshold and the other comparison circuit making a picked up output of frequency of a multi-frequency signal as the threshold value. CONSTITUTION:Each frequency component of a multi-frequency signal inputted to a terminal 10 is picked up at a low group filter 21 and a high group filter 22 and it is rectified at rectifying circuits 31 and 32. The output of the circuits 31 and 32 is applied to comparison circuits 41-44. The circuits 41 and 44 cause an output when the output of the circuits 31 and 32 is greater than the reference voltage Vs. On the other hand, a full band signal is given to the input of a rectifying circuit 33 via an attenuator 23. If white noise over the entire band is incoming consecutively, an output is obtained at the circuits 31-33, high threshold value is given to the circuits 42 and 43 and no output is obtained from the circuits 42 and 43. When a signal given to the terminal 10 is a normal multi-frequency signal, an output is obtained from the circuits 41-43 and when this state continues for a specified time or more, an output is transmitted to a terminal 80. |
