A 1-4GHz LNA for Convenient Cascade Application

A design methodology of broadband LNA (low noise amplifier) for convenient cascade application is proposed. This method solved two main problems in cascade LNA, i.e. the impedance match between two same modules and the stability after cascade. The single stage LNA has a good performance with over 10 dB of S₂₁, the typical 2.5-2.7 dB of the NF (noise figure) in 1-4 GHz band, and it is unconditionally stable in the whole band. Especially, S₁₁ is approximately equal to S₂₂ at any frequency point. This characteristic can make a good match between two same modules. The simulation results show that the LNA with directly cascade of two same single modules can also achieve good performance in 1-4 GHz, the NF keeps nearly unchanged, S₂₂ is two times larger than the single one, and the whole LNA is unconditionally stable, S₁₁ and S₂₂ decrease, and Sn is also almost equal to S₂₂ at any frequency point.