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 highfrequency 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-μm 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 × 0.7 mm2, including test pads.