| 摘要 |
PROBLEM TO BE SOLVED: To provide a variable gain amplifier that suppresses an output impedance fluctuation in the event of a gain change.SOLUTION: The variable gain amplifier includes: a grounded source amplification element 3 connected to an input terminal 1 at a gate-biased gate to amplify an input signal; a ladder resistance circuit 61 having a plurality of parallel resistances 63 to which a drain bias is applied from one end, and having a plurality of series resistances 62 connecting the parallel resistances 63 on the other end; a plurality of grounded gate amplification elements 5-5having gate-biased gates grounded in a high frequency manner, drains connected to the parallel resistances of the ladder resistance circuit 61 on the other end, and sources connected to a drain of the grounded source amplification element 3; an output terminal 12 connected to the drain of any one of the plurality of grounded gate amplification elements; and a gate bias control circuit 64 connected to the gates of the plurality of grounded gate amplification elements to selectively supply a gate bias. |
