| 摘要 |
PROBLEM TO BE SOLVED: To provide a variable gain amplifier which maintains input matching and gets a high order distortion property not to deteriorate when changing gain in a variable gain amplifier used at a receiving front end portion for digital wireless communication instruments. SOLUTION: The bias circuit maintains input matching when changing gain, and gets a high order distortion property not to deteriorate by cascade connect to a collector of the first transistor 1 and the second transistor 2 which ground an emitter and an emitter of the transistor 5 which grounds base in a high frequency way; providing a bias switching circuit 107 which chooses either the first transistor or the second transistor and provides a base bias, the first impedance compensating circuit 20 which controls input impedance of the second transistor 2, and the second impedance compensating circuit 102 which connects between the first transistor base and the second transistor base; and letting the first impedance compensating circuit 20 operate at the same time as a bias electronic switch 107. COPYRIGHT: (C)2005,JPO&NCIPI
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