| 摘要 |
PURPOSE:To suppress the decrease in a reverse bias voltage of an avalanche photodiode(APD) against the increase of a photoelectric current by clipping a voltage drop across a protection resistor by a forward voltage in an optical reception circuit provided with the protection resistor protecting the APD. CONSTITUTION:A high voltage generating circuit 9 is controlled by a gain control circuit 8 at a photodetection area over a gain switching point and its output voltage is changed. A current I1 flowing to a diode 10 is much larger than a current I2 flowing to the protection resistor 1, resulting that the voltage V of a parallel circuit comprising the diode 10 and the protection resistor 1 is very small. Thus, the voltage from a high voltage generating circuit 9 is clipped to the voltage drop by the forward voltage component only of the diode 10 connected in parallel with the protection resistor 1 with respect to the increase in the photoelectric current attended with the average photoelectric current and given as a reverse bias voltage of the APD. As a result, the decrease in the reverse bias voltage of the APD and the reduction in the multiple factor M of the APD are suppressed. |
