| 摘要 |
PURPOSE:To obtain a maximum SN ratio, by keeping the photodetector of a negative feedback amplifier for optical reception to a given temperature and changing the gain of amplifier corresponding to the amplification factor. CONSTITUTION:An optical digital signal from an optical buffer 1 is received at an APD3 in a constant temperature tank 2. A negative feedback amplifier 4 consisting of an amplifier 5, automatic resistor attenuator 6 and amplifier 7 is connected to the APD3. To the automatic resistor attenuator 6, a level shift circuit 12 is connected, and an outpuf of a high voltage generating circuit 11 and a peak detection circuit 9 is applied to the circuit 12. With this constitution, when an output of the photodetector is greater, the gain of the amplifier 4 is changed accordingly to obtain the maximum SN ratio according to the photodetection level. |
