1,630 research outputs found
Scheme for Attophysics Experiments at a X-ray SASE FEL
We propose a concept for production of high power coherent attosecond pulses
in X-ray range. An approach is based on generation of 8th harmonic of radiation
in a multistage HGHG FEL (high gain high harmonic free electron laser)
configuration starting from shot noise. Single-spike phenomena occurs when
electron bunch is passed through the sequence of four relatively short
undulators. The first stage is a conventional "long" wavelength (0.8 nm) SASE
FEL which operates in the high-gain linear regime. The 0.1 nm wavelength range
is reached by successive multiplication (0.8 nm 0.4 nm 0.2 nm
0.1 nm) in a stage sequence. Our study shows that the statistical properties of
the high-harmonic radiation from the SASE FEL, operating in linear regime, can
be used for selection of radiation pulses with a single spike in time domain.
The duration of the spikes is in attosecond range. Selection of single-spike
high-harmonic pulses is achieved by using a special trigger in data acquisition
system. The potential of X-ray SASE FEL at TESLA at DESY for generating
attosecond pulses is demonstrated. Since the design of XFEL laboratory at TESLA
is based on the use of long SASE undulators with tunable gap, no special place
nor additional FEL undulators are required for attophysics experiments. The use
of a 10 GW-level attosecond X-ray pulses at X-ray SASE FEL facility will enable
us to track processes inside atoms.Comment: 21 pages, 12 figures, submitted to Optics Communication
A survey on RF and microwave doherty power amplifier for mobile handset applications
This survey addresses the cutting-edge load modulation microwave and radio frequency power amplifiers for next-generation wireless communication standards. The basic operational principle of the Doherty amplifier and its defective behavior that has been originated by transistor characteristics will be presented. Moreover, advance design architectures for enhancing the Doherty power amplifier’s performance in terms of higher efficiency and wider bandwidth characteristics, as well as the compact design techniques of Doherty amplifier that meets the requirements of legacy 5G handset applications, will be discussed.Agencia Estatal de Investigación | Ref. TEC2017-88242-C3-2-RFundação para a Ciência e a Tecnologia | Ref. UIDP/50008/201
Stability analysis with Pole-zero Identification: unveiling the critical dynamics of microwave circuits
The term pole-zero identification refers to obtaining the poles and zeros of a linear (or linearized) system described by its frequency response. This is usually done using optimization techniques (such as least squares, maximum likelihood estimation, or vector fitting) that fit a given frequency response of the linear system to a transfer function defined as the ratio of two polynomials [1], [2]. This kind of linear system identification in the frequency domain has numerous applications in a wide variety of engineering fields, such as mechanical systems, power systems, and electromagnetic compatibility. In the microwave domain, rational approximation is increasingly used to obtain black-box models of complex passive structures for model order reduction and efficient transient simulation. An extensive bibliography on the matter can be found in [3]-[6]. In this article, we focus on a different application of pole-zero identification. We review the different ways in which pole-zero identification can be applied to nonlinear circuit design, for power-amplifier stability analysis, and more. We provide a comprehensive view of recent approaches through illustrative application examples. Other uses for rational-approximation techniques are beyond the scope of this article.This work was supported in part by the French Space Agency (CNES) under projects R-S10/TG-0001-019 and R-S14/TG-0001-019; by a joint Ph.D. research grant from CNES and Thales Alenia Space, France; by project TEC2015-67217-R (MINECO/FEDER); and by the Basque Country Government through project IT1104-16
Energy-Efficient Amplifiers Based on Quasi-Floating Gate Techniques
Energy efficiency is a key requirement in the design of amplifiers for modern wireless
applications. The use of quasi-floating gate (QFG) transistors is a very convenient approach to
achieve such energy efficiency. We illustrate different QFG circuit design techniques aimed to
implement low-voltage, energy-efficient class AB amplifiers. A new super class AB QFG amplifier is
presented as a design example, including some of the techniques described. The amplifier has been
fabricated in a 130 nm CMOS test chip prototype. Measurement results confirm that low-voltage,
ultra-low-power amplifiers can be designed, preserving, at the same time, excellent small-signal and
large-signal performance.Agencia Estatal de Investigación PID2019-107258RB-C32Unión Europea PID2019-107258RB-C3
Advanced design features of Doherty power amplifiers
A Doherty power amplifier (DPA) is an effective
structure born in 1936 which, after a scarce revival around year
2000), had been strengthened from 2005 because its capability
to combine linear amplification with power efficiency. Despite
the conceptual simplicity of its basic operation, a lot of practical
drawbacks shrink the theoretical behavior, thus leading a
significant number of research works to overcome them. The
main objective in DPA research is to increase efficiency while
maintaining linearity and filling the specified bandwidth. This
paper presents a survey of the state of the art of DPA advanced
design aspects. After a short review of the DPA operation
principles, aspects regarding improvements for linearity, power
efficiency and amplification bandwidth are introduced. Besides,
some alternative structures and technologies, as well as practical
design aspects and some trade-offs which the designer usually
has to face are also presented.Peer ReviewedPostprint (published version
Energy-efficient amplifiers based on quasi-floating gate techniques
Energy efficiency is a key requirement in the design of amplifiers for modern wireless applications. The use of quasi-floating gate (QFG) transistors is a very convenient approach to achieve such energy efficiency. We illustrate different QFG circuit design techniques aimed to implement low-voltage energy-efficient class AB amplifiers. A new super class AB QFG amplifier is presented as a design example including some of the techniques described. The amplifier has been fabricated in a 130 nm CMOS test chip prototype. Measurement results confirm that low-voltage ultra low power amplifiers can be designed preserving at the same time excellent small-signal and large-signal performance.This research was funded by AEI/FEDER, grant number PID2019-107258RB-C32
High-Efficiency Doherty-Based Power Amplifiers Using GaN Technology For Wireless Infrastructure Applications
abstract: The continuing advancement of modulation standards with newer generations of cellular technology, promises ever increasing data rate and bandwidth efficiency. However, these modulation schemes present high peak to average power ratio (PAPR) even after applying crest factor reduction. Being the most power-hungry component in the radio frequency (RF) transmitter, power amplifiers (PA) for infrastructure applications, need to operate efficiently at the presence of these high PAPR signals while maintaining reasonable linearity performance which could be improved by moderate digital pre-distortion (DPD) techniques. This strict requirement of operating efficiently at average power level while being capable of delivering the peak power, made the load modulated PAs such as Doherty PA, Outphasing PA, various Envelope Tracking PAs, Polar transmitters and most recently the load modulated balanced PA, the prime candidates for such application. However, due to its simpler architecture and ability to deliver RF power efficiently with good linearity performance has made Doherty PA (DPA) the most popular solution and has been deployed almost exclusively for wireless infrastructure application all over the world.
Although DPAs has been very successful at amplifying the high PAPR signals, most recent advancements in cellular technology has opted for higher PAPR based signals at wider bandwidth. This lead to increased research and development work to innovate advanced Doherty architectures which are more efficient at back-off (BO) power levels compared to traditional DPAs. In this dissertation, three such advanced Doherty architectures and/or techniques are proposed to achieve high efficiency at further BO power level compared to traditional architecture using symmetrical devices for carrier and peaking PAs. Gallium Nitride (GaN) based high-electron-mobility (HEMT) technology has been used to design and fabricate the DPAs to validate the proposed advanced techniques for higher efficiency with good linearity performance at BO power levels.Dissertation/ThesisDoctoral Dissertation Electrical Engineering 201
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