A 7.2–29.8 GHz LNA With 1.35–2.67-dB NF Using Coupled-Line-Based Transformers in 0.15-μm GaN-on-SiC Technology

This paper presents a broadband low-noise amplifier (LNA) monolithic microwave integrated circuit (MMIC) in 0.15-μm GaN-on-SiC technology. The LNA circuit is designed into a three-stage topology with three coupled-line structures. The first coupled-line structure is designed at the first stage for wideband input impedance matching and noise cancellation, while the second one is employed at the inter-stage to realize the g_m-boost for gain enhancement. Then, the last coupled-line structure forms a positive feedback signal paths from the drain to the gate of the output-stage transistor, which compensates the gain degradation at the high frequency band. With these three coupled-line structures, flat gain performance and low noise figure are achieved in a broadband frequency range. For demonstration, the LNA MMIC is fabricated. The measured results show a maximum gain of 22.6 dB at 27.6 GHz and a 3-dB bandwidth of 22.6 GHz from 7.2 to 29.8 GHz. The in-band noise figure is measured as 1.35-2.67 dB, while the output 1dB gain compression point (OP1dB) and output third-order intercept point (OIP3) are 20.9 dBm and 34.8 dBm at 28.5 GHz, respectively. The fabricated LNA has a compact die area of 2.64 mm² including all test pads.