Variable-gain image-reject low-noise amplifier

摘要

A variable-gain amplifier includes an intermediate node operative to receive an electric current from a current source. A common-emitter amplifier has a collector electrically connected to the intermediate node. A first common-base amplifier has an emitter electrically connected to the intermediate node and a collector electrically connected to an output node. A base-degenerated amplifier has an emitter electrically connected to the intermediate node and a collector electrically connected to the output node. A second common-base amplifier has an emitter electrically connected to the intermediate node and a collector electrically connected to small-signal ground. The intermediate node is operative to direct the electric current to the first common-base amplifier, thereby causing the variable-gain amplifier to operate in a first mode; and the intermediate node is operative to direct the electric current to the base-degenerated amplifier and the second common-base amplifier, thereby causing the variable-gain amplifier to operate in a second mode.