| 摘要 |
PURPOSE:To obtain information on distance, etc., by a simple circuit without requiring a circuit for constant current removal specially by detecting the variation of an input current right after a switching circuit is opened. CONSTITUTION:While the switching circuit SW is closed, feedback is so provided that a current which is the difference between the collector current of a transistor (TR) 6 and the current of a constant current source I2 is equal to the current of a constant current source I3. In this state, the switching circuit SW is opened to turn on an infrared-ray emitting diode and then reflected light from a body whose distance is to be measured is incident on a photodetection sensor PSD, whose output current increases. At this time, when the emitter current of a TR1 increases, the collector current decreases and the base current of a TR4 is about to increase. Consequently, the collector current of a TR2 increases to lower the emitter voltage, and the collector current of the TR2 increases eventually, but the emitter potential does not vary and an increment in PSD current is all detected as an increase in the collector current of the TR6.
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