| 摘要 |
PROBLEM TO BE SOLVED: To easily and reliably realize improvement of the quality of a signal to be reference and a signal to be compared at the time of binarizing an optical signal combined with differential signal processing. SOLUTION: The optical signal processing circuit is provided with an automatic gain control circuit which inputs the output of an optical signal sending device or a weak signal obtained by converting information included in reflected light from an information recording medium to electric signal by a photodiode, obtains an electric signal of a fixed amplitude without regard to the magnitude of the signal and outputs it to a comparator. The gain control amplifier 10 of this automatic gain controlling circuit receives a control signal generated by applying set voltage to the amplitude of the output of a differential signal processing circuit 20 detected by a peak detecting circuit 30 from a level shift circuit 40 by a controlled input terminal 11. Then, with the difference between the control signal and the reference voltage of a reference voltage circuit 50 inputted to a reference input terminal 12, the amplifier 10 lowers the gain when the output of the circuit 20 is increased and executes negative feedback control for raising the gain when the output of the circuit 20 is reduced.
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