Monolithic Transformers for RF Electronics

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Journal Title
Journal ISSN
Volume Title
Sähkötekniikan korkeakoulu | Master's thesis
Date
2015-02-09
Department
Major/Subject
Micro and Nanotechnology
Mcode
S3010
Degree programme
EST - Master’s Programme in Micro and Nanotechnology
Language
en
Pages
61
Series
Abstract
In this thesis transformers for RF integrated circuits are investigated. Monolithic transformers are widely used in various RF and high frequency circuits. For instance, transformers are used as power combiners in power amplifiers, in small signal amplifiers they are used for advanced feedback arrangements, they enable integrated filter implementation, they are used as baluns and impedance matching networks, and they can be used as resonators in oscillators. Unfortunately foundry supported models for on-chip transformers are rarely available and circuit designers need to design and characterize their own transformers using electro magnetic (EM) field simulator. This is a time consuming and laborious task, yet rigorous optimization of transformer characteristics results in significant improvements. Therefore one of the aims of this thesis was to develop an automated EM simulator environment. The thesis starts with representation of transformer basics and then different types of structures for such devices are introduced and discussed. One structure called "Interleaved Transformer" is chosen to be the basis of the design for its good magnetic coupling, symmetry, high frequency range and need of only two layers. More than 50 samples of these devices are designed and characterized. This is done with the help of an automated layout drawing program that was developed in this thesis. Afterwards, they are compared to illustrate how changing the dimensions can help us achieve desired properties. From these comparisons we have generated guidelines on how to for instance maximize quality factor, band width, or coupling coefficient. Based on these findings we can conclude what dimensional properties are needed for a specific circuit requirement and finally find out how to choose correct transformer dimensions for given applications.
Description
Supervisor
Ryynänen, Jussi
Thesis advisor
Stadius, Kari
Keywords
monolithic transformers, on-chip transformers, on-chip inductors, electro magnetic field simulation, AEL
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