Optimizing Low Noise Amplifiers: A Two-Stage Approach for Improved Noise Figure and Stability

Abstract

This study introduces a new design for a low noise amplifier (LNA) consisting of two stages taking advantage of the inherent lossy properties of the input matching components. By doing this, the design balances the minimum noise figure (NF) and stability, eliminating the complexities and challenges introduced by feedback networks. Furthermore, the integration of the low-pass filter (LPF) into the design as a noise-matching network ensures improved performance across both the amplifier stages. A comprehensive analytical study is also introduced to delve deep into the relationship between critical LNA parameters, such as stability and noise figures, and the internal resistance of input-matching inductors. Two C-band LNAs are compared in terms of stability using indigenous $0.25~\mu \text{m}$ GaN technology. The designs are substantiated by fabricating two LNA MMICs for a 5–7 GHz frequency range, having a minimum NF of 1.3 dB and 1.5 dB, with a gain of 15 dB and 16 dB at 6 GHz, respectively. The study reveals that using the proposed approach, there is an overall improvement in NF of 0.2 dB within the frequency of operation. The work entails a way to remove the feedback network in the LNA leading to an improved NF.

Keywords

• C-band
• GaN
• low-noise amplifier (LNA)
• low pass filter (LPF)
• noise figure (NF)