| 摘要 |
PROBLEM TO BE SOLVED: To provide an input circuit robust against noise by amplifying a signal after noise elimination not to saturate an amplifier by the noise even if the noise approximating a DC is superposed on the signal and is inputted. SOLUTION: The signal current on which the noise current generated by a light reception element 1 is superposed is shunt by base grounded transistors TRs 11 and 12. The signal from the collector of the TR 12 and the signal from the collector of the TR 11 are inputted to a differential amplification circuit 50 in the next stage and are amplified. When the frequency of the inputted noise is low, the noise is not amplified because of being inputted to the differential amplification circuit 50 as an in-phase signal, and only the signal is amplified. |
