| 摘要 |
In a conventional variable-gain amplifier, when high-frequency signals are fed in, leak current flows through the collector-emitter parasitic capacitance of transistors, making it impossible to attenuate the gain sufficiently. A variable-gain amplifier of the invention has a controller for controlling the operation of input transistors so as to reduce the leak current that flows through transistors because of their collector-emitter parasitic capacitance when high-frequency signals are fed in and thereby prevent saturation of gain attenuation. Another variable-gain amplifier of the invention has a plurality of variable-gain amplifier circuits connected in parallel, and has a current control circuit for controlling the bias current sources provided within each of the variable-gain amplifier circuits so as to reduce the leak current that flows through transistors because of their collector-emitter parasitic capacitance when high-frequency signals are fed in and thereby prevent saturation of gain attenuation.
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