Developments for the high frequency power transformer design and implementation

The thesis considers design and manufacturing of ferrite based high frequency power transformers. The primary aim of the work was to study core and winding losses and in particular thermal modeling of high frequency power transformers and to determine appropriate loss and temperature rise modeling methods for power converter applications. The secondary aim of the work was to study improved, mass manufacturable winding methods for toroidal, tube-type planar and disc-type planar high frequency power transformers. The analytical high frequency power transformer design equations for core and winding losses and transformer temperature rise were reviewed from literature, formulated for spreadsheet type calculations using excitation, material, geometry and winding implementation parameters and validated by in circuit temperature rise comparisons between calculated and measured values using regression analysis. The core and winding loss calculation methods in literature were found to provide appropriate accuracy for the practical design purposes. Thermal test block tests suggested a slight modification for analytical convective heat transfer equation from the literature. The results from in circuit temperature rise comparisons suggest that the transformer total losses can be predicted with the average standard error below 0.2 W with datasheet type information only. Further, if conductive thermal resistance from transformer via printed circuit board substrate to ambient is available the transformer operating temperature could be predicted with appropriate accuracy (5.6 °C) as well. The new manufacturing methods developed for toroidal, tube and disc-type transformer geometries were proved to be suitable for high frequency operation. With a common mode choke with static shield and windings deposited and etched directly on the toroidal NiZn core a transfer loss resonant frequency above 1.2 GHz was achieved. A multilayer foil winding with interleaved primary and secondary layers resulted resulted leakage inductance of 10 % of the value achieved using a wire-wound winding. The new developments for Z-folded inductive components resulted material cost savings, reduction of winding resistance and adjustability of leakage inductance and winding capacitances.reviewe

Analysis and modeling of monolithic on-chip transformers on silicon substrates

Passive components, including spiral inductors and transformers, fabricated on silicon-based substrates are placing an increasing demand on radio-frequency integrated circuit (RFIC) design. Performance of the RFIC suffers from several non-ideal effects that must be taken into account in order to create a successful design. In particular, monolithic transformers can be a major obstacle for Low-Noise Amplifiers (LNAs), mixers, Voltage Controlled Oscillators (VCOs), and other RFIC circuits. For designers to correctly analyze their designs that include monolithic transformers, lumped-element models suitable for circuit simulation and design optimization are required. This thesis work is mainly concerned with the analysis and the methodology of developing a wide-band compact equivalent circuit model for monolithic transformers fabricated on silicon substrates. A new wide-band compact equivalent circuit model for monolithic transformers fabricated on silicon substrates is presented. The model achieves high wide-band accuracy through the use of the newly developed "Frequency-Dependent Transformer" (FDT) cell, which effectively takes into account the frequency-dependent conductor losses associated with the transformer's windings. A fast extraction technique that allows extraction of the circuit parameters from simulated or measured data is also described. Results are presented for various RFIC transformer configurations including stacked and interleaved topologies. This research provides a complete measurement or simulation-based modeling methodology for four-port transformers on lossy silicon substrates

Analysis and Design Methodology For Pcb and Integrated Circuit Pulse Transformer

This thesis work aims to establish a design procedure for the Coreless pulse transformers based on the design equations determined from the Low and high frequency models for the transformer after making suitable assumptions. These models are used to develop the pulse waveform structure and hence determine the effect of various circuit parameters on the performance of the transformer. The leakage inductance and the parasitic capacitance are major factors affecting the performance of the transformer. Based on the developed equations the appropriate values for the inductance for the given of rise time are determined .With these values as guidelines the PCB /IC transformer has been designed and simulated in the high frequency electromagnetic software. Based on the simplified models and the simulation data the PCB transformer has been fabricated and measured to validate the design methodology.School of Electrical & Computer Engineerin

Study and design of topologies and components for high power density DC-DC converters

Size reduction of low power electronic DC–DC converters is a topic of major interest for power electronics which requires the study and design of circuits and components working under redefined requirements. For this purpose, novel circuital topologies provide advantages in terms of power density increment, especially where a single chip design is feasible. These concepts have been applied to design and implement an integrated high step-down multiphase buck converter and to study the miniaturization of a stackable fiflyback architecture. Particular attention has been dedicated to power inductors, focusing on the modeling and measurement of magnetic materials’ hysteresis and core losses

Monolithic Transformers for RF Electronics

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

Microelectronic Design with Integrated Magnetic and Piezoelectric Structures

This thesis investigates the possibility of integrating the standard CMOS design process with additional microstructures enhancing circuit functionalities. More specifically, the thesis faces the problem of miniaturization of magnetic and piezoelectric devices mostly focused on the application field of EH (Energy Harvesting) systems and ultra-low power and ultra-low voltage systems. It shows all the most critical aspects which have to be taken into account during the design process of miniaturized inductors for PwrSoC (Power System on Chip) or transformers. Furthermore it shows that it is possible to optimize the inductance value and also performances by means of a proper choice of the size of the planar core or choosing a different layout shape such as a serpentine shape in place of the classic toroidal one. A new formula for the correct evaluation of the MPL (Magnetic Path Length) was also introduced. Concerning the piezoelectric counterpart, it is focused on the design and simulation of various MEMS PTs based on a SOI (Silicon on Insulator) structure with AlN (Alluminum Nitride) as active piezoelectric element, in perspective of having a SoC with embedded MEMS devices and circuitry. Furthermore it demonstrates for the first time the use of a PT (Piezoelectric Transformer) for ultra-low voltage EH applications. A new boost oscillator based on a discrete PZT (Lead Zirconate Titanate) PT instead of a MT (Magnetic Transformer) has been modelled and tested on a circuit made up by discrete devices, showing performances comparable to commercial solutions like the LTC3108 from Linear. Furthermore this novel boost oscillator has been designed in a 0.35μm technology by ST Microelectronics, showing better performances as intuitively expected by the developed mathematical model of the entire system