| 摘要 |
PURPOSE:To reduce the transient response time of AGC by using a comparator so as to detect the saturating state of a photodetection amplifier, eliminating the saturation of the photodetection amplifier and switching the response speed of the AGC depending on the output amplitude of the photodetection amplifier. CONSTITUTION:The output of the photodetection amplifier is inputted to a comparator 18, by which the amplitude of a prescribed value is detected and inputted to a high voltage generating circuit 7 for the bias of a photodetector, the output of the photodetection amplifier is branched into two, one output is inputted to a 1st differential amplifier 5 for the AGC through 1st peak detector 4 and the other input is inputted to a 2nd differential amplifier 16 for the AGC through a 2nd peak detector 13. Since output voltages VAGC2.VAGC2* are at a constant value, the response of the AGC is dominant by the output voltage VAGC1 to apply high speed response. Moreover, the saturating state of the photodetection amplifier is detected by the comparator 18, then the saturation of photodetection amplifier is eliminated. |
