| 摘要 |
A variable attenuator is provided with a plurality of amplifiers each comprising an emitter grounded or common source amplifier circuit. The amplifiers have different emitter degeneration impedances. One of the amplifiers is selected in accordance with a gain control signal under control of a current switch controller. The selected amplifier is connected to a current source and supplied with an operating current, and thus the selected amplifier is set in an operating state. The other amplifiers are not supplied with an operating current and thus do not operate. The gain of the variable attenuator is determined by a ratio between the emitter degeneration impedance of the selected amplifier and a load impedance.
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