An ultra-wideband Darlington low noise amplifier design based on SiGe HBT

A design methodology of Darlington low noise figure (LNA) for application at ultra wide bandwidth using a resistive feedback scheme is proposed. The packaged SiGe heterojunction bipolar transistors (HBTs) BFP740 and chip type passive components were used for this direct-coupled LNA. The Darlington amplifier has high gain of 20 dB with variation of 0.5 dB over 3.1-6 GHz, which is twice of single stage LNA. The typical noise figure is 1.8 dB at 3.1 GHz, 2.9 dB at 6 GHz and the circuit keeps unconditional stable for whole 3.1 GHz-6 GHz frequency band. General design procedures are also given in this paper in order to better understand the roles of the various key issues for the LNA.