| 摘要 |
PURPOSE: A method and a system for controlling the gain according to light-receiving levels are provided to minimize the damage of a noise index by detecting an impedance variation of a light-receiving element, outputting the voltage varied according to the detected impedance level, and adjusting the gain of a demodulated signal level. CONSTITUTION: A resistor(R1) having a low resistance value and a resistor(R2) having a high resistance value are respectively formed at both ends of a light-receiving element(110). The light-receiving element(110) outputs a received optical signal as an electrical signal. As the electrical signal is detected at a spot(B) between the light-receiving element(110) and the resistor(R1), a smoothing condenser(C2) and a variable amplifier(120) are required between the light-receiving element(110) and the resistor(R1). Also, as the optical signal is detected at a spot(A) between the light-receiving element(110) and the resistor(R2), a voltage converter(130) is to be installed at the spot(A). At this moment, the output voltage of the voltage converter(130) is inputted to the variable amplifier(120) so that the gain of the variable amplifier(120) can be adjusted.
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