| 摘要 |
PURPOSE:To eliminate the distortions of cross modulation produced when the gain is controlled by inserting a constant current circuit to the source side of a dual gate MOSFET and therefore keeping the 1st gate-source voltage at a constant level. CONSTITUTION:An input-side resonance circuit 1 is provided together with a dual gate MOSFET 2, a constant current circuit 3, a transistor 4 used for the circuit 3, and an output-side resonance circuit 5. The gain of a high frequency amplifying circuit is changed by reducing the potential of the 2nd gate voltage VG2. In this case, the drain current ID flowing through an MOSFET 2 is also reduced with reduction of the potential of the voltage VG2. Thus the current IB increases by the circuit 3 and the total current IDD is set at a constant level. Then the source potential VS is kept constant and therefore the 1st gate-source voltage VGIS is set at a constant level.
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