Numerical and Analytical Methodologies in High-Frequency Low-Noise Amplifier Design

The world-wide sales of cellular phones, home satellite networks and all equipment and services for wireless communications have enormously expanded in the last few years, entering several aspects of our lives.
This has been possible trough the availability of suitable and sophisticated radio-frequency systems. Two factors have greatly helped to enable the development of these circuits.
Semiconductor companies are continuously exploiting and improving the technology for the manufacture of high frequency circuits, boards and systems capable to handle signals up to several GHz.
Design techniques have been constantly evolving toward a more rational and systematic design approach, certainly more practical and powerful than many years ago, when the RF and microwave design domain was barely supported by a few, poorly organised principles and techniques.
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The main focus of this dissertation regards design techniques of high frequency low noise amplifiers, developed by the author after several investigations into the problem of the impedance matching between the active device and a signal source or between the device and its load or, finally, between two or more active devices.
The formalism of the scattering parameter analysis has been adopted since it is, at the moment, the most convincing postulate for the analysis, the design and the a priori optimisation of a high frequency mplifier. In Chapter 1, such a formalism is introduced and described.
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Particular emphasis has been put on the sensitivity of a high frequency circuit, PCB or system to parametric variations of the lo ad, being the core analysis based on the tunability factor, introduced and fully investigated in Chapter 2. Methodologies are described and explained through a couple of case studies. In the first, a good design from the point of view of tunability is compared with a more sensitive choice of the output matching. In the second, the design of a potentially unstable device is considered.
The importance of the tunability analysis derives from the fact that a parametric load variation has a direct influence on the output matching network, but also has indirect effects on the input reflection plane.
Fortunately, this does not make the noise matching worse, if there is one, but may heavily degrade the input power matching, resulting in an undesired response of the circuit in some corner conditions.
In Chapter 3, a new algorithm for the mathematical determination of the noise-optimum input reflection coefficient is presented. Both cases of single stage and multi-stage low-noise amplifier have been considered: in the former, the minimisation of the noise figure is the core of the algorithm; in the latter, the noise figure is replaced by the more meaningful noise measure, which has a big relevance in cascaded circuits when the same active device appears in all stages. In order to clarify all parts of the method, a third case study completes the section.
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The present thesis is the result of a four-years academic Ph.D. course on Microelectronics developed at Polytechnic of Bari, Engineering Faculty, under the supervision of Prof. B. Castagnolo and the co-ordination of Prof. M. De Sario.