| 摘要 |
<P>PROBLEM TO BE SOLVED: To prevent malfunction due to shot noise caused by a photodiode. <P>SOLUTION: An amplifier circuit AMP 1 amplifies a bias voltage and an output voltage of a current voltage conversion circuit 1 for converting an optical current of the photodiode PD for detecting an input light into a voltage, and a gm-amplifier AMP 2 charges / discharges a capacitor C1 by a current in accordance with a difference between a reference voltage V3 and the output voltage of the amplifier circuit AMP 1. A field effect transistor M3 supplies a drain current controlled by a voltage across the capacitor C1 to the photodiode PD, so that the output voltage of the amplifier circuit AMP 1 is not fluctuated by the effect of a DC optical current flowing through the photodiode PD. A level of a gate of a field effect transistor M1 connected in parallel with a current voltage conversion resistor R1 is the same as a level of the gate of the field effect transistor M3, and when the DC optical current increases, the resistance of the transistor M1 is decreased to decrease the resistance of current voltage conversion thereby a noise voltage due to shot noise is decreased. <P>COPYRIGHT: (C)2005,JPO&NCIPI |
