Design of GaN-based X-band LNAs to achieve sub-1.2 dB noise figure
GaAs and SiGe technologies take an edge over GaN-based devices in terms of better noise figure (NF). In this article, we present HEMT topologies and design techniques to achieve a sub-1.2 dB NF for a GaN-based X-band low-noise amplifier (LNA). This NF is comparable with state-of-the-art reported works in competitive GaAs and SiGe technologies. Moreover, this is the best reported NF in X-band using GaN technology to date. Two LNAs are fabricated using in-house 0.15 μm AlGaN/GaN on the SiC HEMT process. LNA-1 has inductive source degenerated (ISD) HEMTs at both stages, while LNA-2 has ISD HEMT at the first and common source at the second stage. The significance of ISD HEMT, for the first or subsequent stages in a multi-stage design, towards NF improvement is addressed. The criticality of stability networks towards NF contribution and its design is discussed in detail. Furthermore, even-mode stability of each HEMT after complete LNA design is assured using the S-probe method in Pathwave Advanced Design Systems.