A 26.5–38-GHz Ka-Band GaN-on-Si Low-Noise Amplifier With Variable Gain Control

A broadband 26.5–38-GHz low-noise amplifier (LNA) with variable gain (VG) functionality, utilizing 100-nm gallium nitride on silicon (GaN-on-Si) process for Ka-band, is proposed. To achieve adjustable gain while minimizing noise degradation within a controllable range, a structured design procedure for device periphery and bias condition is introduced. Furthermore, a hybrid matching methodology combining low-pass and high-pass networks with a dual feedback loop in the last two stages is implemented for bandwidth enhancement. A 3-bit digital Si-CMOS controller is incorporated to modulate the gate bias of the GaN amplifier. Operating at 5 V with a quiescent current ( $I_{\mathrm {DQ}}$ ) of 60 mA, the fabricated VG-LNA exhibits the measured gain of 26.9–29.9 dB, noise figure (NF) of 1.57–2.83 dB, and output power at 1-dB compression point ( $\text{OP}_{\mathrm {1 ~dB}}$ ) of 9.2–16.5 dBm across 26.5–38 GHz. A reduction in $I_{\mathrm {DQ}}$ from 100 to 20 mA results in a decline in peak gain from 31 to 24.1 dB at 28 GHz, accompanied by an increase in the minimum NF from 1.57 to 2.03 dB, and a decrease in the maximum $\text{OP}_{\mathrm {1~dB}}$ from 18 to 14.8 dBm. To the best of our knowledge, this is the first demonstration of a GaN LNA with VG control feature.