| 摘要 |
PURPOSE:To obtain the good signal of C/N by correcting the the amplitude difference of an output signal caused by the sensitivity difference of two photodetectors with the aid of a variable resistor connected between the mutual ground side terminals of two active elements and sufficiently extracting the reduction efficiency of in-phase noise caused by differential amplitude. CONSTITUTION:The output signals of the two photodetecting means 13 and 14 are inputted to a differential amplifier 15, the variable resistor Rv is inserted between the ground side terminals of the two active elements Tr1 and Tr2 of the differential amplifier 15, that means, between the emitters when the active elements Tr1 and Tr2 are bipolar transistors and the sensitivity difference of the two photodetecting means is corrected by adjusting the balance of the current of the ground side terminals of the two active elements Tr1 and Tr2, that means, the current of the emitters with the aid of the variable resistor Rv. Thus the in-phase noise of the output signal of the differential amplifier 15 is eliminated and the good signal of C/N can be obtained.
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