K-band Mmic Low Noise Amplifier Design

This paper discusses the total design flow of a K-band MMIC LNA. Thecircuit design, layout design and simulation result is introduced. A novelfeedback configuration is presented to achieve the requirement of gain andgain flatness.A K-band MMIC LNA based on 0.25μm GaAs PHEMT process is designed. Astructure with three cascaded circuits is used for low noise figure (NF) andhigh gain. Bias circuits are designed for each stage. Microstrip lines areused for matching networks. Input and output ports are both matched to 50ohm.Source feedback microtrip line is adopted in the first and second stage forbetter stability.An improved feedback network is used in the last stage to obtain a bettergain flatness and a enough gain. It consists of a parallel RC and a seriesinductor. The gain of this improved feedback network is 2～3 dB higher thanthe classical structure's. The stability factor of the LNA is decreased. Butthe LNA is still keeping absolute stability. Finally, the layout is optimizedfor best simulating result.As a result, the K-band MMIC LNA achieved a low noise figure of less than2.9 dB, a high small signal gain of over 23 dB, a good gain flatness of lessthan±0.5 dB, as well as good input VSWR and output VSWR of less than 2from 21 to 25 GHz. The chip areas are also small and all components areintegrated on a GaAs chip of 1.79mm×0.98mm×0.1mm. The simulating resultsindicate that the circuit satisfies the design demands.