| 摘要 |
PURPOSE:To reduce an effect of external noise on a lead pin including an exposed part thereof, by connecting a first lead pin to one input of a differential amplifier and by connecting a second lead pin to the other input of the differential amplifier. CONSTITUTION:Elements having the same characteristic with each other are used for photodetectors 2a and 2b, and only the element 2a is so constructed as to receive a light signal, while the element 2b is used as a capacity element. Lead pins 3a and 4 are grounded and a lead pin 5a is connected to a noninversion input of a differential amplifier 6a, while a lead pin 5b is connected to an inversion input of the amplifier 6a, in use. In this case, the pins 5a and 5b are in the same noise environment substantially, and therefore noise components picked up by the pins 5a and 5b are offset in the amplifier 6a. While the effect of the noise picked up by the lead pins can be reduced, accordingly, it is easy to monitor a dark current flowing when the photodetector senses no light, and a signal of high quality can be outputted. |
