| 摘要 |
PURPOSE:To eliminate the interference of characteristic and to improve the stability, accuracy and quick responsiveness by separating a main signal system from an AGC loop system. CONSTITUTION:The optical signal supplied to a photodetecting element 1a is amplified by a preamplifier 2 and a main amplifier 3 after receiving the photoelectric conversion with the element 1a. This amplified signal is delivered to an output OUT. While the optical signal supplied to a photodetecting element 1b is amplified by an amplifier 6 after receiving the photoelectric conversion with the element 1b. Then the peak value of the amplified signal is detected by a peak detecting circuit 7. The output of the circuit 7 is compared with the reference value V by an operational amplifier 5. This difference voltage controls the amplification degree of the amplifier 2 as well as the amplification factor of the element 1b. As a result, no interference is caused between a main signal system and an AGC loop system. This improves the stability, accuracy and quick responsiveness of an AGC system. |
