| 摘要 |
PURPOSE:To accurately monitor a light receiving power even when the power is very small by separating a DC current component from an information signal outputted from a photodetector and applying current/voltage conversion thereto so as to obtain a monitoring voltage. CONSTITUTION:A light beam emitting from an optical space transmitter is received by a photodiode PD, where the beam is subjected to photoelectric conversion and the result is inputted to a preamplifier via a capacitor C2 as an RF signal modulated by an information signal. Since a load resistor RL is connected to ground via a capacitor C1, a DC current component DC separated from the current obtained by the photodiode PD is obtained from the load resistor RL. Then the DC current component DC inputted to an operational amplifier OP is subjected to current/voltage conversion and the result is outputed as a monitoring voltage Vm. Even when the receiving power in the photodiode PD is minute, accurate monitoring is attained. |
