| 摘要 |
PROBLEM TO BE SOLVED: To provide a high frequency amplification circuit, contained in a high frequency circuit block of a mobile communication terminal supporting a plurality of communication systems, capable of conducting gain control easily, in order to reduce variation in gain due to fluctuation of a threshold voltage of a FET contained in a gain control circuit. SOLUTION: A gain control circuit 12 comprises a FET 41 operating as a variable resistance. A control voltage VC impressed at a gain control terminal 23 is applied to a gate terminal of the FET 41. A reference voltage Vref1 determined at a reference potential circuit 13 is applied to a source terminal and a drain terminal of the controlling FET 41. The reference voltage Vref1 is controlled so as to compensate variation in a threshold voltage of the FET 41. A resistance value of the FET 41 changes continuously, according to the control voltage VC. Thereby, gain of a high frequency amplification circuit 10 also changes continuously. COPYRIGHT: (C)2006,JPO&NCIPI
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