| 摘要 |
PURPOSE:To measure a distance accurately by detecting a state before light emission with a window comparator, keeping the state before light emission by the output voltage from a D/A converter when pulse light is emitted, and taking out the change in current output of a PSD. CONSTITUTION:The output of a semiconductor position detector 3 is inputted into a difference detecting circuit 6 through detecting circuit 4 and 5. The input signal is imparted into the emitter of a transistor Q 20 and the inverted input of an operation amplifier 21. The collector of a Q 20 is connected to the collector of a Q 22 and the base of a Q 23. The collector current of the Q 23 is detected with a current detecting circuit 24 and imparted into the difference detecting circuit 6. When the output Vout of the detecting circuit 24 has the specified difference from a reference value Vr2, a window comparator 25 drives an up/down counter 26. The logic output of the counter 26 drives the Q 22 through a DAC 27. Said operation is repeated until the comparator 25 is not operated. During this period, the output current of the PSD 3 is changed, and the input current for the Q 23 approaches 0. In this constitution, voltage change due to leakage does not occur, and a distance can be measured accurately. |
