| 摘要 |
PROBLEM TO BE SOLVED: To provide a preamplifier which has flat gain characteristic over a high-frequency range and a wide dynamic range as a high-conversion-gain and wide-band trans-impedance type preamplifier for optical communications, by suppressing very remarkable peaking, even when a large current is inputted. SOLUTION: The trans-impedance type preamplifier comprises an amplifying circuit part, a feedback circuit part, and a control circuit part. The amplifying circuit part is provided with a source-grounded input FET which amplifies an electrical signal, a resistance element, and a cascaded FET, comprises an FET to which the output signal from the drain of the cascaded FET is inputted, a level shift diode, and a current source FET, and has its output on the drain side of the current source FET. The feedback circuit part has a 1st feedback resistance connected between the input side and the output side of the amplifying circuit part, has a circuit part constituted by connecting a feedback FET, connected to the 1st feedback resistance in parallel and a 2nd feedback resistance in series, and further has a capacity element provided in parallel to the 2nd feedback resistance. The output signal of the control part is inputted to the gate of the feedback FET of the feedback circuit part.
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