A CMOS Variable-Gain Low-Noise Amplifier Achieving a 33.5 dB Gain Tuning Range for Ka-Band Receiver Applications

We present a 14.2 mW, 17.7–25.1 GHz differential CMOS low-noise amplifier (LNA) featuring a wide gain tuning range of 33.5 dB and a low average noise figure (NFavg) of 3 dB. These characteristics are enabled by the combined use of a body-to-ground floating technique, coupled transmission-line (TL) feedback, and multiple inductive-peaking techniques. The proposed LNA consists of an input transformer, a common-source (CS) input stage, current-reused CS gain and output stages, and an output transformer. The body-to-ground floating technique connects the transistor body to ground through a large body-floating resistor (RB) of 3.2 kΩ, thereby suppressing substrate noise and leakage while enhancing the gain and reducing the NF. Moreover, coupled-TL feedback is introduced in the input stage to further improve the gain and NF, while multiple inductive-peaking techniques are adopted to extend the 3 dB gain bandwidth (f3dB). In the maximum-gain mode, with the transistor switches turned off, the LNA consumes 14.2 mW and achieves a measured S21 of 17 ± 1.5 dB over 17.7–25.1 GHz, corresponding to an f3dB of 7.4 GHz. The measured minimum NF is 2.37 dB at 17 GHz, with an NFavg of 2.71 dB over 17–21 GHz. The LNA also achieves a figure of merit (FoM1) of 12.27 GHz and a normalized figure of merit (FoM2) of 1.55 mm−2. Furthermore, a wide gain tuning range of 33.5 dB, from 16.7 to −16.8 dB, is obtained. To the best of the authors’ knowledge, the proposed LNA achieves one of the lowest NFavg values and the highest FoM1 and FoM2 among reported K- and Ka-band CMOS LNAs.