| 摘要 |
PROBLEM TO BE SOLVED: To stabilize operation without depending on a means for increasing the capacitance of a capacitor for sample-and-hold by connecting a resistor between the reference signal input terminal and output corresponding signal input terminal of a comparing means for comparing a reference signal and an output corresponding signal. SOLUTION: By connecting a resistor (RX) 11 between the positive input and negative input of an input amplifier 7 in a light quantity control circuit, operation is performed only by the impedance of a resistor (RM) 5 in DC manner. The quantity of light is set by the resistance value of the RM 5 and when an error occurs, operation is performed as the parallel impedance of RM 5 and RX 11. Concerning an input error current, the impedance is reduced, an input error current/voltage converting gain is dropped and a feedback gain is reduced. Further, since the impedance can be reduced to the input error current, a time constant with the capacity of a photodiode (PD) 2 can be reduced at the time of error occurrence so that the phase delay of feedback can be reduced as well.
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