Design of ultra-narrowband Q-enhanced LNAs

Abstract

Modern-day radio receivers operate in environments that are becoming increasingly dense with RF signals. As the density of the radio spectrum increases, receivers must be able to maintain successful operation despite these potential interfering signals. Two issues facing modern-day radio receivers are signal blocking issues, and the generation of intermodulation products in the LNA. These issues stem from entire bands reaching the LNA, as the power level of the signals within the service band may differ widely. This can cause the LNA to compress before a desired low-power signal receives the full gain of the LNA or allow two moderate-power signals to mix and generate an intermodulation product that is located at the same frequency of a desired low-power signal. This thesis focuses on the design, simulation, and testing of a new radio receiver architecture, using an ultra-narrowband Q-enhanced LNA, which aims to address these issues. The design is based on the fundamentals of regenerative receivers, using controlled positive feedback for control of the gain and bandwidth of the filter response. Furthermore, gain, bandwidth, and filter center frequency can be automatically tuned with the addition of an auto-tuning algorithm running on a microcontroller. Two different designs were realized, one at the board level for FM radio, the other at the chip-level for use with 802.11ax, known as Wi-Fi 6, at 2.4 GHz. This thesis details the design of the core building blocks used in an ultra-narrowband Q-enhanced LNA, including the core amplifiers, buffers, matching networks, feedback networks, and auto-tuning algorithm. The results of both physical testing and simulation are also presented, and are used to verify that the design addresses both signal blocking and intermodulation product issues.