| 摘要 |
The invention relates to a controllable radio-frequency amplifier with a dual-gate field-effect transistor in which one gate terminal is common both to the input circuit and to the output circuit. A control voltage is present on the second gate. To adapt the input impedance of the amplifier circuit to a predetermined characteristic impedance, it is provided in accordance with the invention that the input terminal of the amplifier is connected to the control voltage potential via a diode and a resistor connected in series with the diode so that, when the gain decreases, the diode becomes current-conducting from a particular value of the control voltage. The resistor is dimensioned in such a manner that the input impedance of the amplifier remains largely constant within the overall control range of the gain.
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