| 摘要 |
PROBLEM TO BE SOLVED: To provide a variable gain amplifier capable of suppressing variation in the output impedance when its gain is changed. SOLUTION: A variable gain amplifier includes: a source-grounded amplification element 3 whose gate is connected to an input terminal, a gate bias being supplied to the gate, for amplifying an input signal; a ladder resistor circuit 61 having a plurality of parallel resistors 63 to which a drain bias is applied from one terminal, and a plurality of series resistors 62 connecting other terminals of the parallel resistors 63; a plurality of gate-grounded amplification elements 5<SB>1</SB>-5<SB>n</SB>whose gates are grounded in a high frequency manner, a gate bias being supplied to the gates, whose drains are connected with other terminals of the parallel resistors in the ladder resistor circuit 61, and whose sources are connected with a drain of the source-grounded amplification element 3; an output terminal 12 connected to a drain of any one of the plurality of gate-grounded amplification elements; and a gate bias control circuit 6 connected with the gates of the plurality of gate-grounded amplification elements for selectively supplying the gate bias. COPYRIGHT: (C)2011,JPO&INPIT
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