| 摘要 |
A variable impedance circuit includes a capacitor and a MOSFET and is connected between the base of a bipolar transistor and a ground node. The capacitor acts to the open for a direct-current component. The MOSFET varies impedance for an alternate-current component. A base voltage ration portion includes first and second resistors, which set a bias applied to the base of the bipolar transistor. More specifically, the base voltage generation portion divides an operating voltage supplied through a voltage terminal by a ratio of the first and second resistors to generate a base voltage of the bipolar transistor.
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