| 摘要 |
PURPOSE:To easily set a theshold voltage and to attain the stable working of an optical receiving device by securing an AND after comparing the level of the signal current of an avalanche photodiode with the level of the control gain voltage of a variable gain amplifier circuit, the output voltage of a high voltage generating circuit, or the output voltage of a peak value detecting circuit. CONSTITUTION:A resistance 13 is provided to detect the current flowing to an avalanche photodiode 1 together with a 2nd error amplifying circuit 14, a 3rd error amplifying circuit 15, and an AND gate 16 which uses the outputs of both circuits 14 an 15 as the inputs. The the level of the current of the photo diode 1 is monitored together with the gain control voltage of a variable gain amplifying circuit 4, level of the output voltage of a high voltage generating circuit 2, or the level of the output of a peak value detecting circuit 6 respective ly. Thus it is possible of obtain an alarm circuit which can easily detect the presence or absence of an optical input signal with the stable working. |
