| 摘要 |
PURPOSE:To increase the dynamic range by switching the gain of a preamplifier depending on the optical input level. CONSTITUTION:The circuit consists of a photodetector 1, a gain switching circuit 3, a peak value detection circuit 4 and a switching control circuit 5. The gain switching circuit 3 consists of a 1st resistor 7, a triac 8 applying switch operation by the switching control circuit 5 and a 2nd resistor 9 and when the triac 8 is turned on, the resistors 7, 9 and an ON resistance of the triac 8 are combined and the resistance is decreased, then the gain is decreased. Then the gain of a preamplifier is changed by using a prescribed optical input level to increase a maximum light reception level without varying a minimum light reception level. Thus, the light receiving dynamic range is expanded. |
