| 摘要 |
PROBLEM TO BE SOLVED: To implement a precise adjustment of detection sensitivity to an optical signal.SOLUTION: A differential amplification circuit 11 differentially amplifies a differential signal Tout input via coupling capacitors C1, C2. A differential current addition circuit 12 adds a DC current depending on an offset adjustment voltage Vos to a normal phase signal and a reverse phase signal of a resultant amplified output signal Fout to regulate a DC offset voltage of the normal phase signal and the reverse phase signal. A comparator 13 compares voltage values of a normal phase signal and a reverse phase signal of a resultant current-added output signal Aout. A holding circuit 14 holds a resultant comparison output signal Cout as a DC holding voltage Vhd. A hysteresis comparator circuit 15 compares the holding voltage Vhd with two different determination threshold voltages Vth_SD, Vth_LOS determined by a sensitivity adjustment voltage Vsens, and outputs a comparison result as an optical signal detection signal SD/LOS. |
