| 摘要 |
PROBLEM TO BE SOLVED: To provide a gain control circuit having a low NF at the maximum gain and functioning as a variable gain circuit even at a low voltage. SOLUTION: The gain control circuit includes a variable impedance circuit unit made up of a bipolar type transistor 8, in which the base is connected to a control terminal 5 for applying an input voltage under gain control, the collector is connected to a power terminal 11 for applying a constant voltage, and the emitter is connected to the ground, and a variable gain amplifier circuit unit made up of an amplifier circuit 1, in which the input is connected to an input terminal 3 connected though a capacitor 9 in serial for feeding an input signal, an output terminal 4 is connected to the output side, while a point between the input terminal 3 and the capacitor 9 is connected to the emitter side of the transistor 8 and the diode 2. In the diode 2, the positive electrode side is connected to the emitter side of the transistor 8 and the negative electrode side is connected to the ground.
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