Published: 2024-09-19

Thesis defence: Analog-to-Digital Converters for High-Speed Applications

Published: 2024-06-04

This thesis delves into the multifaceted challenges of designing analog-to-digital converters (ADCs) tailored for high-speed and medium accuracy applications, particularly in deeply scaled-down complementary metal-oxide semiconductor (CMOS) technologies across five comprehensive chapters within its Introduction. Conclusively, the Introduction part briefs the challenges, achievements, and contributions of the thesis, offering insights and recommendations for future research trajectories in the realm of high-speed ADC design. Moreover, the thesis ventures into five original papers in its second part, discussing multiple designs and leveraging techniques such as time interleaving, employment of hybrid ADCs, and asynchronous clocking to attain superior performance metrics encompassing speed, resolution, and power efficiency. Notable contributions include techniques to enhance BST-SW linearity, the design of a high-speed comparator, synchronous versus asynchronous SAR ADC comparison and implementation of a 4-channel TI pipelined-SAR ADC in a 22-nm FDSOI CMOS process, capable of operating at a sampling rate of 1.4 GS/s.
 

Link to thesis i LU Research Portal:

https://portal.research.lu.se/sv/publications/analog-to-digital-converters-for-high-speed-applications

Zoom link. Zoom ID: 67608675506.

Thesis defence: Frequency Generation and Baseband Filters for mm-Wave 5G and 6G Transceivers

Published: 2024-05-29

In order to keep up with the constant demand for higher data rates, the fifth generation of mobile communication (5G) introduced the use of mm-wave carrier frequencies from 24 to 71 GHz. Plenty of new frequency spectrum then became available, which has allowed for channel bandwidths of several hundreds of MHz. 6G is projected to continue this trend with even higher carrier frequencies and wider bandwidths, reaching carrier frequencies above 100 GHz and bandwidths in the multi-GHz range. However, this creates new challenges for circuit designers, as the performance of radio circuits typically degrades with increasing frequency. Two critical components in radio transceivers whose performance are highly affected by the increase in carrier frequency and bandwidth are frequency generators and baseband filters. The former generates a local oscillator (LO) signal required for frequency translating the data signal to/from the baseband from/to the carrier frequency, and the latter is used to separate the desired signal from undesired interference and noise in a receiver and to prevent leakage of undesired spectrum content to nearby channels in a transmitter. The design of the frequency generation is also made much more complicated due to mm-wave 5G and 6G communication relying on beamforming, in which the signals from multiple antennas are combined to overcome the high path loss at these frequencies. The LO signal must then be distributed to multiple frequency converters while retaining a constant relative
phase shift. If the beamforming is done using so-called LO beamforming, this relative phase shift must also be tunable in a very accurate manner.

In this thesis, five research papers are included; two concern mm-wave frequency generation, two concern multi-GHz integrated baseband filters, and one is about system-level simulations of beamforming receivers. The thesis is divided into two parts, with the first part providing an introduction and context to the conducted research, while the second part consists of the included papers.
 

Link to thesis i LU Research Portal:

https://portal.research.lu.se/sv/publications/frequency-generation-and-baseband-filters-for-mm-wave-5g-and-6g-t

Zoom link. Zoom ID: 66635753300.

Licentiate seminar: Rohon Kundu

Published: 2024-04-10

In this thesis, we address three main security problems related to cryptography and cloud storage. To tackle the challenge posed by a quantum computer, we need encryption that is resistant to quantum computers. This category of cryptography is called post-quantum cryptography. In the first paper, we solve a challenge in one of lattice-based cryptographic protocols called Nth-degree Truncated polynomial Ring Unit (NTRU) namely how to reduce the key size while keeping the security level.  We propose a solution that reduces the key size significantly. Our proposed solution allows a practical implementation of NTRU with fast polynomial multiplications.

Next, we move to solve a long-standing problem arising in any cloud storage namely the reduction of storage cost of redundant data and maintaining security and privacy at the same time. Data deduplication is considered to be a tool that can be used to eliminate redundant data and store only one of its copies. But data deduplication also means that the file cannot go through client-side encryption which opens up new possibilities of adversarial threats. In order to tackle this challenge, we propose a new architecture where we perform client-side deduplication along with dynamic erasure protection by introducing a third-party assistant. We also performed an erasure analysis to quantitatively analyze the probability of loss of a file when a large number of replicas are deleted at random.

Finally, we shift our interest to Decentralized Cloud Storage (DCS). DCS solutions like Filecoin, Storj, and Arweave are gaining more popularity in the Web 3.0 ecosystem. But they are not without challenges. The robustness of the DCS protocols remains a challenging ground. Since the file in a DCS protocol is stored in a decentralized manner among different nodes, a Distributed Denial of Service (DDoS) attack would render the system vulnerable to data loss. Therefore, it is important to analyze the robustness of decentralized architecture against DDoS attacks. In our last paper, we perform a similar erasure analysis to that of the second paper but in a decentralized setup, where the adversary aims to disrupt the system by deleting a file from the network. Storj is one of the leading players in the DCS space. We have created an adversarial model capturing the real Storj network scenario and simulated our model using real-time data obtained from the Storj network. We obtain resource budget figures for DDoS on Storj using our model. Also, we propose a better parametric value for the erasure piece distribution in Storj which suits well when there are more unvetted nodes in the network.

Thesis defence: Integrated millimeter Wave CMOS Power Amplifiers for 5G Systems

Published: 2024-04-15

This dissertation focuses on millimeter-wave power amplifiers built using a common and inexpensive silicon-based technology known as CMOS, for fifth-generation mobile systems and beyond. It comprises four scientific publications based on three measured power amplifiers with increasing complexity, where the third one essentially includes a complete transmitter and parts of a receiver. The third circuit is measured with a signal where the power amplifier sends a whopping 9.6 Gbit/s, equivalent to downloading about an hour's worth of video in just one second. To achieve high-output signal transmission at such high data rates without distorting it to the point of making it difficult or even impossible for the receiver to decode the digital bits while consuming as little power as possible, a Doherty amplifier combined with adaptive bias is used. The Doherty amplifier, invented in 1936, has the special property of consuming very little power when amplifying signals with highly varying amplitudes, a characteristic of 5G (and 6G) signals. To save power, the Doherty amplifier has two amplifiers cooperating: one is on all the time (the main amplifier), while the other (the auxiliary amplifier) is only on at high amplitudes, reducing consumption. However, constructing a Doherty amplifier at such high frequencies as millimeter waves poses a significant challenge, making it interesting from a research perspective. To ensure that the transistors amplify the signal in the desired way, it's necessary to set an appropriate operating point, known as biasing the transistors. Normally, a constant operating point is used, but with adaptive bias, the transistors' operating points are adjusted as the signal's amplitude changes. As demonstrated by the research in the dissertation, using a Doherty amplifier with adaptive bias for the auxiliary amplifier is a good way to mitigate the problems that arise when a power amplifier needs to handle the complex signals of 5G and future mobile systems in a power-efficient manner. The fourth article examines and explains the theoretical aspects of how an adaptive bias signal should be designed to work optimally with the auxiliary amplifier, and the article also contains a detailed description of the construction of a circuit capable of creating such an adaptive bias signal and thus able to change the operating point for the auxiliary amplifier very quickly, i.e., with high bandwidth. The circuit creates the adaptive bias signal by first extracting amplitude information from the Doherty amplifier's input signal. An important theoretical result is that an ideal adaptive bias signal should then be constructed through a nonlinear transfer function from the amplitude information. Measurements and simulations show that the circuit effectively achieves this.
 

Link to thesis i LU Research Portal:

https://portal.research.lu.se/sv/publications/integrated-millimeter-wave-cmos-power-amplifiers-for-5g-systems

Zoom link. Zoom ID: 63926548525.

Thesis defence: Dude, Where's My Car? Cellular Navigation for Autonomous Driving

Published: 2024-03-21

Position and direction estimation is useful for numerous engineering applications for commercial, scientific, and military purposes. Technology that fuses observations of signals broadcast by Global Navigational Satellite Systems (GNSS) with inertial measurements is standard for electronic devices, but this requires at least a periodically unobstructed view of the sky to perform reliably. This has motivated the use of terrestrial radio signals as navigation references to complement or as an alternative to satellite systems, but environments with obstructions, specular reflectors, and scatterers of electromagnetic waves create challenges for any wireless navigation system.

This thesis is about how wireless signals other than those transmitted by GNSS might be used for navigation in complex propagation environments, particularly for safety-critical systems, and conversely how position and orientation information can be used to better understand electromagnetic wave propagation. The thesis is split into introductory chapters that provide broad background on the researched subjects, and five papers published in or submitted to scientific conferences and journals.\par
The first paper offers a broad analysis of the requirements for a cellular navigation system to meet the unique and particularly challenging operating requirements of an autonomous vehicle. Aspects of the problem that are not frequently addressed in literature on terrestrial positioning, particularly requirements for safety-critical operation, are included in the analysis. \par
The second, third, and fourth papers propose methods for position estimation for a passenger vehicle operating in a dense urban canyon environment, tested with a specially-designed measurement system that makes passive (opportunistic), high-resolution observations of down-link synchronization signals transmitted by commercial cellular base stations that are paired with highly accurate pose estimates. Inspired by the prominence and success of Artificial Neural Networks (ANNs) in computer vision, ANNs are used for wireless navigation. The results show that meter-level position estimates and accurate heading estimation can be achieved simultaneously when receiving only reflected and scattered signals from a single transmitter that is never within line-of-sight of the receiving antenna array, relying entirely on multipath propagation.

Finally, in the fifth paper, the link between geometry and multipath propagation is explored from a different perspective. Known navigation states are used to study and characterize multipath propagation. A method for multipath component clustering for statistical channel modeling is proposed, where knowledge about the receiver position is used to gain insight into channel statistics. The algorithm is shown to provide consistent results and to be scalable to large data sets.
 

Link to thesis i LU Research Portal:

https://portal.research.lu.se/sv/publications/dude-wheres-my-car-cellular-navigation-for-autonomous-driving

Zoom link. Zoom ID: 69963010473.

Thesis defence: Computational Methods and Measurements for Direct and Inverse Scattering of Microwaves

Published: 2024-03-18

The problem of electromagnetic scattering has long been important in radar, where it is the mechanism for detection. This is often called the direct scattering problem, where a known object is illuminated by an incident wave and the scattered wave is computed. In Paper I, a computational code implementing the finite element-boundary integral method is presented. The code, which is publicly available at https://www.github.com/nwingren/fe2ms, was developed using open-source software to accelerate the development process. While this code is verified in Paper I, there were no comparisons to measurements. In Paper II, a complete design process was performed using the code from Paper I, with manufacturing using 3D printing and measurements of the performance to validate the computations. This acted both as a demonstration of using the code practically, and as a validation. One advantage of the finite element-boundary integral method used in the code is that problems with highly complex media can be solved. This was utilized in Paper III where characteristic modes were computed for a an inhomogeneous, bianisotropic, and nonreciprocal object.

A different problem is that of inverse scattering, for which the scattered wave is known but the object or incident wave is unknown. This is a more complicated problem which requires the modern computational methods available today, and can be used to discern properties of an object, for example for nondestructive testing. In Paper IV, a method for nondestructive testing of singly curved composite panels using millimeter waves is presented together with measurements of real panels. The method is based on computational electromagnetics and was designed specifically for detection of sparsely distributed flaws in such panels. Microwaves and millimeter waves are relatively new in nondestructive testing compared to other methods like ultrasound. One possible development would be to combine the new and the old by utilizing interaction between acoustic and electromagnetic waves. As a way to demonstrate that this might be possible, microwaves scattered by ultrasound were measured in Paper V in air, where the interaction would be much weaker than in nondestructive testing settings.
 

Link to thesis i LU Research Portal:

https://portal.research.lu.se/sv/publications/computational-methods-and-measurements-for-direct-and-inverse-sca

Zoom link. Zoom ID: 62684643819.

An inclusive work environment - Norm awareness in practice

Published: 2024-02-26

The workshop combines basic theory with humour, practical exercises and everyday examples of how different norms affect our treatment of each other. The different grounds for discrimination are linked together and you will gain knowledge about how they interact and the mechanisms that lie behind and create inequality.
We all have different experiences and values that affect how we treat each other - often unconsciously. This workshop aims wants to stimulate people's desire to change because they themselves feel that they are developing, not because someone else demands it. This requires a large portion of humour and humility. It is about creating inspiration and seeing things outside your own normative bubble. We all have a lot to gain from counteracting prejudices and seeing the norms that exist in our workplaces.
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Mingle after the workshop: Coffee and cake will be served in the foyer. 
Registration is not needed but will be appreciated. Please use this link  ??  https://www.eit.lth.se/ws-jamstallt

Thesis defence: Navigating the Future: Intersection of Safety, Efficiency, and Resilience in Autonomous Traffic Systems

Published: 2024-02-29

This thesis embarks on a journey in the advancement of urban traffic management, centering around the innovative integration of Autonomous Intersection Management (AIM) systems. The research encompasses a comprehensive exploration of various facets of AIM implementation, significantly contributing to the evolution of a more efficient and safer urban transport system.
The research investigates the dynamic and complex environment of city transportation, addressing the myriad of challenges and opportunities that arise with the advancement of autonomous vehicle technology. It synthesizes a broad spectrum of dimensions in AIM implementation, collectively contributing to the vision of a more streamlined and safer urban transportation network.
A pivotal aspect of this thesis is the exploration of the interplay between autonomous and non-autonomous vehicles in urban settings. The study assesses the robustness and resilience of AIM systems across diverse and unpredictable scenarios, with a focus on adaptive control strategies, wireless communication challenges, and efficient traffic flow management. This emphasis highlights the crucial role of these systems in ensuring safety and efficiency, especially in mixed-traffic environments.
A notable contribution of this work is the integration of cutting-edge technologies like machine learning with AIM, proposing innovative solutions for traffic management. These solutions are designed to reduce operational complexities and enhance scalability, showcasing potential to transform traditional traffic management practices. This aspect of the research not only demonstrates innovation but also practical applicability in urban contexts.
The thesis culminates in demonstrating the practical application and effectiveness of AIM systems in real-world urban contexts. Besides underscoring the relevance and utility of the research, it also showcases the practical applicability of the model. The findings and developments presented in this work pave the way for future advancements in the field.
In summary, this thesis offers a substantial contribution to urban transportation management by providing innovative insights and practical solutions for the integration and optimization of AIM systems. It lays a foundational framework for future research, steering towards advanced transportation networks, which are both safe and efficient.
 

Link to thesis i LU Research Portal:
https://portal.research.lu.se/en/publications/navigating-the-future-intersection-of-safety-efficiency-and-resil

Zoom link.  Zoom ID: 66179207826.

Thesis defence: Ferroelectric memristors: materials, interfaces and applications

Published: 2024-02-28

The backbone of modern computing systems rely on two key things: logic and memory, and while computing power has
seen tremendous advancements through scaling of the fundamental building block ? the transistor, memory access hasn?t
evolved as rapidly, leading to significant memory-bound systems. Additionally, the rapid evolution of machine learning
and deep neural network (DNN) applications, has exposed the fundamental limitations of the traditional von Neumann
computing architecture, due to its heavy reliance on memory access. The physical separation between the computing unit
and the memory in von Neumann architectures is limiting performance and energy efficiency. A promising solution to
address these challenges is the development of emerging non-volatile memory technologies that provide significant scaling
and integration possibilities, fast switching speeds, and highly energy-efficient operations. Additionally, by integrating
?memory resistors? (memristors) in large crossbar arrays, the computation can take place in-memory which can resolve the
bottleneck in traditional von Neumann architectures.
This thesis investigates the implementation of ferroelectric HfO2 in ferroelectric tunnel junctions (FTJs) and ferroelectric
field effect transistors (FeFETs) as potential candidates for emerging non-volatile memories and memristors.
Initially, the thesis focuses on the integration of ferroelectric HfO2 onto the high mobility III-V semiconductor InAs for
the fabrication of metal-oxide-semiconductor (MOS) capacitors. Moreover, optimization of the processing conditions on the
critical interface between the semiconductor and high-k oxide is extensively studied using both electrical characterization and
synchrotron radiation techniques. After optimization of the annealing treatment and top electrode texturing, the fabrication
of vertical InAs nanowire FeFETs is successfully implemented. The FeFET shows encouraging initial results with limitations
solvable by further process engineering.
 

Link to thesis i LU Research Portal:

https://portal.research.lu.se/en/publications/ferroelectric-memristors-materials-interfaces-and-applications

Zoom link. Zoom ID: 63504410836

Thesis defence: III-V Devices for Emerging Electronic Applications

Published: 2024-02-05

Today?s digitalized society relies on the advancement of silicon (Si) Complementary Metal Oxide Semiconductor (CMOS) technology, but the limitations of down-scaling and the rapidly increasing demand for added functionality that is not easily achieved in Si, have pushed efforts to monolithically 3D-integrate III-V devices above the Si-CMOS technology. In addition, the demand for increased computational power and handling of vast amounts of data is rapidly increasing. This has led to an increased interest in quantum computing, offering the potential to solve specific complex problems more efficiently than conventional computers. Superconducting transmon Quantum Bits (qubits) are promising for the realization of quantum computers, which has led to an increased interest in cryogenic electronics. For these applications, III-Vs are suitable as their high carrier mobility enables low power consumption, low noise, and highly transparent superconductor-semiconductor interfaces. High-quality interfaces between superconductors and semiconductors are crucial for the implementation of gate-tunable hybrid superconductor-semiconductor qubits known as gatemon qubits.

This thesis explores the potential of utilizing indium arsenide (InAs) and indium gallium arsenide (InGaAs) nanowire and quantum well devices in these emerging electronic applications. Both as an add-on in Si-CMOS technology, as well as the channel material in electronic devices for cryogenic applications.

The electron transport in near surface quantum wells is studied by DC-measurements in combination with applied magnetic fields, from room temperature down to cryogenic temperatures. Several different ways to extract the carrier mobility are investigated, such as standard current-voltage sweeps, the Geometrical Magnetoresistance Effect (gMR), as well as the Hall effect. A deeper understanding of electron transport at cryogenic temperatures is obtained by the development of a model for the current characteristics of long-channel InGaAs quantum well Metal-Oxide Semiconductor Field-Effect Transistors (MOSFETs), which includes the effects of band tail states, electron concentration-dependent mobility, and interface trap density. The model shows an increased effect of remote impurity scattering associated with mobility degradation in the subthreshold region.
A demultiplexer based on an InGaAs nanowire network was fabricated, to enable routing of DC-currents on-chip and reduce the number of connections to the cryostat. To facilitate system-level investigation of circuits containing Josephson Field-Effect Transistors (JoFETs), a compact model was developed which by circuit simulations accurately reproduced the measured data from our JoFET.
Finally, a process for the growth of InAs nanowires on tungsten was developed. This novel approach is based on Template-Assisted Selective Epitaxy (TASE) and allows for easy 3D-integration of III-V devices in Si-CMOS technology.

Link to thesis i LU Research Portal:

https://portal.research.lu.se/en/publications/iii-v-devices-for-emerging-electronic-applications