To solve the problem, wherein an inverse LOG voltage generated by a transistor of a control-voltage generating circuit is less likely to agree with the LOG characteristic of a PIN diode of a variable attenuation circuit in a feedforward type AGC circuit.
The feedforward type AGC circuit in which a π-type attenuator is constituted by the PIN diode, is equipped with a variable attenuation circuit 14, which adjusts the attenuation of an RF signal; a photocurrent detection and voltage compensation circuit 16, which generates a photoelectric conversion voltage; and an inverse LOG control voltage generation circuit 17, which generates a voltage with an inverse LOG characteristic with respect to the LOG characteristic of the PIN diode from the photoelectric conversion voltage, by using the same PIN diode as the described PIN diode and linearly controls the attenuation.
ISHINO MASATO
AOYAMA HIDEJI
Daisuke Nagano
Kentaro Fujii
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