| 摘要 |
PURPOSE:To obtain a wide dynamic range by controlling the voltage of an optical attenuator with the output of a comparator and attenuating a light signal according to whether incident light is intense or not. CONSTITUTION:The comparator 6 with hysteresis characteristics is connected to the AGC control output of an AGC circuit 5 and the optical attenuator 7 capable of measuring the quantity of attenuation is installed in front of a photodetecting element 1. Then when intense light is incident on the element 1 and the output V0 of the AGC circuit exceeds a threshold voltage Voth', the comparator output rises from Vout to Vout' to increase the quantity of attenuation of the optical attenuator 7. When the intensity of the incident light decreases, on the other hand, the output of the comparator 6 is Vout' until the AGC output voltage rises to the threshold voltage Voth and Vout' after the AGC output voltage becomes below Vout' thereby decreasing the quantity of attenuation of the attenuator 7. Consequently, a wider dynamic range is obtained even when an amplification part and an equivalent amplification part are increased in gain. |
