Design and Analysis of Low-Power Ultra-Wideband CMOS Variable-Gain LNAs With Sub-2.5 dB NFmin Using Coupled Microstrip-Line Neutralization and AGF-Inductor

This study reports low power-dissipation (PD) and low noise-figure (NF) ultra-wideband CMOS variable-gain amplifiers (VGAs). VGA1 and VGA2 use coupled microstrip-line (CL) neutralization with an adjustable-gain-flatness inductor and multiple inductive peaking, featuring complementary common-source (CCS) input and common-source (CS) output stages to achieve low PD and NF values and wide bandwidths. The concurrent current steering of the first and second stages yields large gain-tuning ranges with low NFs. VGA1 and VGA2 with PD of 5.85 mW in the low-noise mode achieve excellent S21 bandwidths (BWs) of 32.3 GHz (2.9–35.2 GHz) and 26 GHz (3.8–29.8 GHz), maximum S21 of 11.9 dB and 13.6 dB, average NF ( $\mathrm{NF}_{\mathrm {avg}}$ ) of 4.11 and 3.93 dB, respectively, and minimum NF of 2.43 dB. The input 1-dB compression point ( $\mathrm{IP}_{\mathrm {1dB}}$ ) of VGA1 is −11.5 dBm. The chip area of both VGA1 and VGA2 is 0.356 mm2. Moreover, VGA1 attains a decent gain tunning range of 20 dB (−3.8–16.2 dB) under 1.35 dB/step for 5G NR band N257. Additionally, VGA2 attains an excellent gain tunning range of 32 dB (−14.6–17.4 dB), gain flatness of $\pm ~0.75$ dB, and NFavg of 3.62 dB between 3.8–24.1 GHz. To the authors’ knowledge, the BW and NFmin/ FOM performance are one of the best results ever reported for millimeter-wave CMOS VGAs (or low-noise amplifiers) with a PD of less than 15 mW.