| 摘要 |
PURPOSE:To shorten detection delay time by shaping the waveform of an input signal passed through a band-pass filter by two comparing circuits which have different threshold voltages, and detecting the presence of the signal by discriminating a time difference between the outputs of the shaping. CONSTITUTION:A burst signal applied to an input terminal 12 is seected by a band-pass filter 13 and rectified by a rectifying circuit 14. Its rectification output is converted into rectangular waves by voltage comparing circuits 15 and 16. The threshold level of the comparing circuit 15 is set low, and that of the comparing circuit 16 is set high. The rectangular wave outputs of both the circuits 15 and 16 are applied to a time comparing circuit 17 to discriminate a time difference between both the outputs. When the time difference is greater than a prescribed value, no output is generated by judging that no signal is present. When the time difference is less than the prescribed value, the output of the comparing circuit 16 appears at a terminal 18. |
