VARIABLE GAIN AMPLIFIER CIRCUIT

摘要

PROBLEM TO BE SOLVED: To prevent a distortion characteristic from being deteriorated when a low gain is set in a variable gain amplifier circuit.

SOLUTION: A variable capacity 5 is connected instead of a fixed capacity connected to an output terminal 4 in order to attenuate an interference wave signal and an undesired signal, such as intermodulation distortion, an RF leakage signal and an LO leakage signal. A capacity value C5 of the variable capacity 5 is controlled by a control circuit 6 for controlling the gain of variable gain mixer 1. This makes the cutoff frequency fc of the variable gain mixer 1 constant even though the resistance value R7 of a variable resistor 7 fluctuates at the time of gain control. As a result, the undesired signal is attenuated and the distortion characteristic deterioration of the variable gain mixer 1 and a poststage block is suppressed even when a low gain is set.

COPYRIGHT: (C)2005,JPO&NCIPI