| 摘要 |
PROBLEM TO BE SOLVED: To provide a variable gain amplifier that can enhance a variable gain width without losing the linearity. SOLUTION: This invention provides a variable gain amplifier where an input amplifier consisting of FETs Q1a, Q1b connected in cascode and an output amplifier consisting of FETs Q2a, Q2b connected in cascode are connected in series via a coupling capacitor C1 and the gains of the respective amplifiers are controlled by control voltages Vc1, Vc2 supplied to the high level FETs Q1b, Q2b. A relation of Vc1<Vc2 holds between both control voltages. Thus, both amplifiers provide no decreased output at the same time, the input amplifier provides a decreased output earlier and then the output amplifier provides a decreased output so as to prevent deterioration in the linearity when the gain decreases.
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