| 摘要 |
PURPOSE:To detect whether an input signal is a desired one or not, by shaping a waveform of the input signal through a band-pass filter rectifying circuit, and after that, inputting it to 2 comparators having opposite polarity, and synthesizing and integrating these outputs. CONSTITUTION:In case when an input signal has a single level and single frequency, this signal is inputted to an input terminal 1 through an exclusive circuit, etc., is applied to a rectifying circuit 3 through a band-pass filter 2, and its output signal 21 is applied to inputs of comparators 8, 13. In the output side of the comparator 8, a square wave which rises at the point of time when the potential of + side 22 reaches the potential of 23 is generated, and in the same way, in the output side of the comparator 13, too, a square wave which rises at some point of time is generated. A signal 28 which synthesizes output signals of the comparator 8 and 13 is inputted to an integrating circuit 14. The integrating circuit 14 lengthens a reset time T sufficiently, and sets its output signal 29 to a high level when the integral quantity exceeds a prescribed value. This signal is inputted to a starting circuit of a facsimile receiver through an output terminal 15, and is detected. |
