CASCODE LOW-NOISE AMPLIFIER

摘要

A cascode low-noise amplifier for enhancing linearity is provided. The cascode low-noise amplifier has a two-stage structure in which a common-emitter stage cascaded to a common-base stage, wherein a phase difference of 180 is produced between a third-order intermodulation signal resulting from a fundamental signal input to the common-base stage and a third-order intermodulation signal previously generated at the common-emitter stage. Accordingly, the fundamental signal and the third-order intermodulation signal can be adjusted to have a phase difference of 180 by disposing an impedance matching circuit between a common-emitter (or a common-source) stage of a buffer transistor and a common-base (or a common-gate) stage of an amplifier transistor, and the magnitude difference can be adjusted as well. In addition, the entire linearity of the cascode low-noise amplifier is enhanced by adjusting the impedance value of the impedance matching circuit to an appropriate value so as to cancel the impedance with the third- order intermodulation signal in the subsequent stage.