Design and Analysis of CMOS LNAs with Transformer Feedback for Wideband Input Matching and Noise Cancellation

This paper presents a new transformer-feedback technique for RF and millimeter-wave (mmW) low-noise amplifiers (LNAs). The working principle of conventional LNAs using transformers is analyzed to show their underlying performance trade-off between input matching and noise figure (NF). To mitigate this issue, a new feedback technique is developed by constructing a drain-to-gate feedback path around the input transistor with a transformer and then further demonstrated by two LNA prototypes. In the first LNA aiming for software-defined radio (SDR) applications, the proposed technique not only achieves wideband input matching but also enables noise cancellation through an auxiliary out-of-phase forward path. Fabricated in 0.13-μm CMOS, the LNA measures voltage gain >14 dB, minimum NF of 1.8 dB, IIP3 of 1.8-3.8 dBm, and S₁₁< -10 dB over a frequency range of 1.2-6.6 GHz, while consuming 13.2 mW. The second LNA implemented in 65-nm CMOS operates from 55 to 65 GHz and achieves a 16.4-dB conversion gain and a 6.8-dB minimum NF, with power dissipation of 33.6 mW. Particularly, the measured S₁₁ remains below -10 dB from 49.5 to 67 GHz.