| 摘要 |
PURPOSE:To remove a malfunction due to the shot noise of an APD (avalanche photodiode), and to improve stability by providing a logical circuit to take the logical sum of the output signal of a comparison circuit and the output signal of a monostable multivibrator circuit. CONSTITUTION:A timing signal is extracted from a received signal inputted by a tank circuit 1, and a peak level is detected by a peak detection circuit 3, and is compared with a reference level by a comparator 4. The monostable multivibrator circuit 5 is triggered by the rise of the output signal of the comparator 4, and is made to output the pulse of a prescribed pulse width, and the logical sum of this pulse and the output signal of the comparator 4 is taken by an OR gate 6, and an optical input interruption detection signal is obtained. At the time of the interruption of the optical input, when an error due to the shot noise generated by the APD as a photodetector is generated in the output of the comparator 4, the monostable multivibrator circuit 5 outputs the output after removing this error, and when the error is not generated, it outputs the output of the comparator 4. Thus, the optical input interruption can be stably detected without being influenced by the APD shot noise. |
