| 摘要 |
PURPOSE:To suppress noise component by using a positive and a negtive voltage sources provided with voltages which are far beyond the input level range of a voltage comparator for signal detection, and generating a sufficiently high signal level from a high-impedance sensor. CONSTITUTION:Both terminals of the sensor 1 which has high resistance when input light present and low resistance when not are coupled with a detecting circuit 9 through a transmission line 3. Then, one conductor is coupled with the voltage comparator 10 through a resistance R2 of the transmission line 3 and also connected to the 1st voltage source +VCC2 through a resistance R1, and the other conductor 3b is connected to the 2nd voltage source -VCC. The value of the resistance R1 is so set that when the sensor 1 turns on or off, the potential at a coupling point A is almost +VCC2 or -VCC. Then, an input signal containing no noise is supplied to the voltage comparator 10.
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