| 摘要 |
PURPOSE:To enable AGC to be applied even when an incoming level is a level in which an amplifier is saturated, by controlling a current being permitted to flow on a photodetector corresponding to the level of an incoming beam of light. CONSTITUTION:When an optical signal arrives at the photodetector 10, a voltage proportional to the light quantity of the signal appears on the output of a preamplifier 12. When the output voltage of the preamplifier 12 arrives at a prescribed voltage, an output signal representing that it is forced to be operated in a range outside a linear range is generated. Corresponding to the output signal, a switching circuit 34 prevents the saturation of the preamplifier 34, and also, connects circuits 361-36n to the output of the photodetector 10 so as to stay the output voltage within a prescribed level. |
