PURPOSE: To make a photoelectric conversion output signal level to a constant value by providing a constant current circuit shunting a current flowing to a feedback resistor of a parallel feedback amplifier and a level detection circuit detecting an output signal level of the parallel feedback amplifier and controlling the current value of the constant current circuit in a reception circuit for an optical signal so as to widen the dynamic range.
CONSTITUTION: When the input optical signal power of a photoelectric converting element 11 is large, a current flowing to a feedback resistor 16 is large and an output signal level of a parallel feedback amplifier 12 is increased accordingly. The increase in the output signal level is detected by a level detection circuit 13 so as to control a current flowing to a transistor (TR)14 larger. Then since the current flowing to the feedback resistor 16 is small, the output signal level of the parallel feedback amplifier 12 is decreased. When the input optical signal power is decreased conversely, the current flowing to the feedback resistor 16 is decreased and the output signal level of the parallel feedback amplifier 12 is decreased. When the current flowing to the TR14 is small, the current flowing to the feedback resistor 16 is increased, then the output signal level of the parallel feedback amplifier 12 is increased.
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HANANO NAOMASA
TAKAHASHI MASAAKI
FUJINO SHIYOUJI
