| 摘要 |
PURPOSE:To detect light with a high SN ratio, by using >2 photodetectors having equivalent electric characteristics and covering at least one of the surfaces of the photodetectors with a member attenuating or shutting the light. CONSTITUTION:An output of a photodetecting circuit consisting of series circuits 13, 23 comprising photodiodes 11, 21 and resistors 12, 22 is outputted as a photodetecting signal via a comparison amplifier 15. The diodes 11, 21 consists of N layers 32, 34 and P layers 36, 37 on the same semiconductor substrate 31 and the resistors 21, 22 are constituted with N layers 33, 35 as shown in a figure. The photodetecting plane comprising the N and P layers constituting the diode 11 is covered with a light shielding member 38. The comparison amplifier 15 cancels a detecting signal from the diode 21 receiving the light with a signal of the diode 11 covered with the light shielding member for the difference of characteristics such as leakage current and temperature change and the like and outputs the photodetecting signal having a high SN ratio. |
