Patent ID: 6710659
Filing Date: 2004-03-23
Classification: H03F,H03G

Abstract:
A variable-gain amplifier comprising:a first differential amplifier circuit having first and second transistors, a differential input voltage being applied between bases of the first and second transistors; a second differential amplifier circuit having third and fourth transistors of which emitters are connected to a collector of the first transistor, the second differential amplifier circuit outputting a signal amplified by the first transistor after attenuating the signal according to a voltage applied between bases of the third and fourth transistors; a third differential amplifier circuit having fifth and sixth transistors of which emitters are connected to a collector of the second transistor, the third differential amplifier circuit outputting a signal amplified by the second transistor after attenuating the signal according to a voltage applied between bases of the fifth and sixth transistors; a first controller for controlling operation of the first transistor; and a second controller for controlling operation of the second transistor, wherein the first controller controls the operation of the first transistor stepwise from an active state to an off state, and the second controller controls the operation of the second transistor stepwise from an active state to an off state.