Low-Noise Amplifier Design for Ultra-Wideband Systems

University dissertation from Linköping : Linköpings universitet

Abstract:  The low-noise amplifier (LNA) remains a critical block in every receiver front-end. As the development of the wideband, low-power and low-cost wireless systems continues, new LNA topologies and design methodologies have become one of the most interesting challenges in the field of radio frequency system design. Optimally, wideband LNA design methodologies should provide improved receiver sensitivity and thus accurate low-level signal processing. The LNA design must handle trade-offs among LNA topology selection, wideband matching for low noise figure, flat power gain and wideband bias aspects. Another key factor of the wideband radio front-end design refers to the antenna-LNA co-design. Any loss that occurs before the LNA in the system will substantially degrade the overall receiver sensitivity. In order to reduce losses and thus minimize the noise figure of the front-end, the LNA and the antenna or antenna-system should be designed simultaneously.The main focus of this thesis has been LNA design for ultra-wideband (UWB) applications. Firstly, an overview of the design techniques for wideband matching networks is given. Then, the way in which some classical single-stage LNA topologies are adapted to UWB specifications is analyzed. To verify the wideband amplifier design principles, both a narrowband LNA for 5.25 GHz and a UWB LNA for 3-5 GHz based on microstrip matching networks were designed, manufactured, and measured. Advanced design techniques, for example electromagnetic simulations of the entire layout of the LNA module were utilized. Optimization techniques and statistical analyses were also used in the design flow. Moreover, a co-design of an antenna-UWB LNA front-end was performed for the minimum noise figure and maximum flat power gain within the entire frequency band. Finally, UWB bias networks implemented with different microstrip elements were studied. It has been shown that, without accurate high-frequency component models and without including high-frequency electromagnetic coupling and component parasitics, LNA and particularly UWB LNA design can result in large errors. A good design approach has large potential to improve the performance and manufacturing yield of LNAs, especially UWB LNAs.  

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