| 摘要 |
PURPOSE:To perform fine AGC (automatic gain control) to both AC and DC components of the output of a photodetector, by separating the AC and DC components of a converted output signal each other and controlling the levels of the AC and DC components respectively. CONSTITUTION:Out of the output of an adder 4 which is the sum of four conversion outputs from a four-division type photodetector 1, the DC component is extracted by an LPF 6 and the AC component is extracted by a DC interrupting capacitor C3. The LPF 6 is an integrating type filter consisting of a resistor R1 and a capacitor C2 and the DC output from the LPF 6 is compared with a reference level 8 by a differential amplifier 7. The AC component is converted into a DC signal by a rectifier and smoothing circuit 13 consisting of a diode D1, a capacitor C4 and a resistor R7 and the DC signal is compared with a reference level 15 by a differential amplifier 14. The impedance of variable impedance elements 9-12 is controlled by respective outputs of the differential amplifiers 7, 14. |
