| 摘要 |
PURPOSE:To eliminate the influence of an external light by executing on-off control of a gate circuit for controlling the output of a light emitting element driving circuit and a photodetector by a prescribed discriminating signal, and inserting an external light input portion cancelling capacitor into an output side of the photodetector. CONSTITUTION:At the time of a low level in which no discriminating signal exists, transistor (TR) Q2 is off, light emitting diode is not turned on, and as for a phototransistor, an external light current portion flows to a load resistance R1, and a capacitor C is charged. A TRQ4 of an output gate circuit 3 is on, grounded directly, and an output component by an external light is not led out to the output side. On the other hand, at the time of a high level in which a discriminating signal exists, the TRQ2 becomes on, the light emitting diode is turned on, its light quantity is detected by a photodetecting phototransistor in accordance with whether an object exists or not, and as for the output gate circuit 3, the TRQ4 is off, the capacitor C cancels an output component by an external light, and only the light quantity by the light emitting diode is led out as an output signal 7 from a buffer 8. In this way, the influence of an external light component can be eliminated by a simple constitution. |
