| 摘要 |
A variable gain amplifier circuit 1 includes an amplifier A 1 , an amplifier A 2 , an inductor L 1 , and an inductor L 2 . The amplifier A 1 has a predetermined gain and is connected at a terminal to a circuit output section. The amplifier A 2 has a different gain from the amplifier A 1 and is connected at a terminal to the circuit output section. The inductor L 1 is connected at an end to a circuit input section and at the other end to the input terminal of the amplifier A 1 . The inductor L 2 is connected at an end to ground and at the other end to the input terminal of the amplifier A 2 . The inductors L 1 and L 2 form a transformer T. The configuration restricts input impedance variations which are dependent on the signal path taken by an input signal Vin. The input impedance and the signal source impedance remain matched. Impedance matching is preformed with the signal source with variable gain.
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