| 摘要 |
A circuit arrangement, suitable for a burglar security device, has coincidence operation of two Doppler alarm devices. The difference frequency signal of the two Doppler frequency signals which are produced by the movement of an object within a protected area is employed as an alarm-triggering signal. The circuit arrangement has a product detector for the formation of the difference frequency signals, a subsequently connected low pass filter and a threshold value detector. The threshold value detector is designed such that the amplitude value of its detection threshold can be changed in dependence upon the frequency of a control signal supplied thereto, the frequency of the control signal being derived from one of the Doppler frequency signals, the dependence being designed such that the frequency dependence of the amplitude value of the detection threshold is fundamentally equal to the frequency-dependent attenuation characteristics of the low pass filter. |
