A Broadband Cascode Low-Noise Amplifier Using Transformer Feedback and Darlington Techniques

In this brief, a three-stage broadband cascode low noise amplifier (LNA) is proposed with transformer feedback and Darlington techniques. The first two stages use transformer feedback to provide low-frequency gain, and the Darlington structure is employed in the third stage to compensate for high-frequency gain. The additional transmission poles introduced by the transformer feedback increase the freedom of gain tuning with little effect on low-frequency gain, therefore facilitating the design of broadband LNAs. To verify the feasibility of bandwidth expansion of these two structures, the proposed LNA is designed and fabricated in a 0.15-mu m GaAs pseudomorphic high electron mobility transistor (pHEMT) technology. The measured results show that the proposed LNA achieves an average gain of 23.4 dB and a minimum noise figure (NF) of 2.1 dB in the operating band from 0.5 GHz to 30 GHz. The power consumption of the LNA is 246 mW at 6 V/ -0.6 V DC bias. The LNA has a compact chip size with an area of 2.2 x 0.7 mm(2), including test pads.