| 摘要 |
PURPOSE:To perform stable AGC operation with simple circuit constitution by connecting a photocoupler in parallel with a load resistor which is connected in series to a pin photodiode and driving the photocoupler with output voltage. CONSTITUTION:The signal from an optical fiber 1 is converted to a voltage signal by a pin photodiode PD2 and a load resistor 3 and this converted voltage is outputted after it is amplified 4. The amplified output is smoothed 7, 8 after rectification 6, and drives the LED5b of the photocoupler 5 via a transistor 9. According to the quantity of the light emitted by the LED5b, the resistance value of a variable resistor 5a changes. Since the resistor 5a is connected in parallel with the resistor 3, the input voltage signal level is controlled and the AGC function for the amplifier 4 is obtained. |
