| 摘要 |
PURPOSE:To reduce the size of a device extremely on the whole by using the voltage of a power source which is used by a photodetecting element and a signal processing part even as a power source for a visible light semiconductor laser driving circuit and sharing the power source. CONSTITUTION:A positive source voltage +V which is used by the photodetecting element 7 and signal processing part 8 is used even for the visible light semiconductor laser driving circuit 11. Here, an operational amplifier 80 converts the output current of a photoelectric converting element 72 into a voltage signal by a resistance 90 and then the differentiating circuit composed of a capacitor 91 and a resistance 92 removes a DC component; and only the variation of the signal is compared with a comparison voltage VR5/(R4+R5) determined by resistance R4 and R5 by a comparator 100 and when the variation of the input signal is larger than the comparison voltage, a defect signal 9 is outputted. Thus, the visible light semiconductor laser is used as the light source to reduce the light source and driving circuit in size, so the device can be reduced in size on the whole.
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