404 research outputs found
An Experiment and Detection Scheme for Cavity-based Cold Dark Matter Searches
A resonance detection scheme and some useful ideas for cavity-based searches
of light cold dark matter particles (such as axions) are presented, as an
effort to aid in the on-going endeavors in this direction as well as for future
experiments, especially in possibly developing a table-top experiment. The
scheme is based on our idea of a resonant detector, incorporating an integrated
Tunnel Diode (TD) and a GaAs HEMT/HFET (High Electron Mobility
Transistor/Heterogenous FET) transistor amplifier, weakly coupled to a cavity
in a strong transverse magnetic field. The TD-amplifier combination is
suggested as a sensitive and simple technique to facilitate resonance detection
within the cavity while maintaining excellent noise performance, whereas our
proposed Halbach magnet array could serve as a low-noise and permanent solution
replacing the conventional electromagnets scheme. We present some preliminary
test results which demonstrate resonance detection from simulated test signals
in a small optimal axion mass range with superior Signal-to-Noise Ratios (SNR).
Our suggested design also contains an overview of a simpler on-resonance dc
signal read-out scheme replacing the complicated heterodyne readout. We believe
that all these factors and our propositions could possibly improve or at least
simplify the resonance detection and read-out in cavity-based DM particle
detection searches (and other spectroscopy applications) and reduce the
complications (and associated costs), in addition to reducing the
electromagnetic interference and background.Comment: 22 pages, 7 figure
High Linearity Millimeter Wave Power Amplifiers with Novel Linearizer Techniques
Millimeter-wave communications have experienced phenomenal growth in recent
years when limited frequency spectrum is occupied by the ever-developing communication
services. The power amplifier, as the key component in the transmitter/receiver module
of communication systems, affects performance of the whole system directly and receives
much attention.
For minimized distortion and optimum system performance, the non-constant en-
velope modulation schemes used in communication systems have challenging requirements
on linearity. As linearity is related to communication quality directly, several linearization
techniques, such as predistortion and feedforward, are applied to power amplifier design.
Predistortion method has the advantages over other techniques in relatively simple struc-
ture and reasonable linearity improvement. But current predistortion circuits have quite
limited performance improvement and relatively large insertion loss, which indicate the
need for further research. In most of millimeter-wave amplifier design, great effort has
been spent on output power or gain, while linearity is often ignored. As almost all the
predistortion circuits operate at the RF frequencies, the linearized millimeter-wave com-
munication circuit is still relatively immature and very challenging.
This project is dedicated to solve the linearity problem faced by millimeter-wave
power amplifier in communication systems, which lacks of e®ective techniques in this field.
Linearity improvement with the predistortion method will be the key issue in this project
and some original ideas for predistortion circuit design will be applied to millimeter-wave
amplifiers.
In this thesis, several predistortion circuits with novel structure were proposed,
which provide a new approach for linearity improvement for millimeter-wave power am-
plifier. A millimeter-wave power ampli¯er for LMDS applications built on GaAs pHEMT
technology was developed to a high engineering standard, which works as the test bench
for linearization. Actual operation and parasitic elements at tens of gigahertz have been
taken into consideration during the design.
Firstly, two novel predistorter structures based on the amplifier were proposed, one
is based on an amplifier with a fixed bias circuit and the other is based on an amplifier with
a nonlinear signal dependant bias circuit. These novel structures can improve the linearity
while improving other metrics simultaneously, which can effectively solve the problem of
insertion loss faced by the conventional structures. Besides this, an original predistortion
circuit design methodology derived from frequency to signal amplitude transformation was
proposed. Based on this methodology, several transfer functions were proposed and related
predistortion circuits were built to linearize the power amplifier. As this methodology is
quite different from the traditional approach, it can improve the linearity signifficantly
while other metrics are affected slightly and has a broad prospect for application
High Linearity Millimeter Wave Power Amplifiers with Novel Linearizer Techniques
Millimeter-wave communications have experienced phenomenal growth in recent
years when limited frequency spectrum is occupied by the ever-developing communication
services. The power amplifier, as the key component in the transmitter/receiver module
of communication systems, affects performance of the whole system directly and receives
much attention.
For minimized distortion and optimum system performance, the non-constant en-
velope modulation schemes used in communication systems have challenging requirements
on linearity. As linearity is related to communication quality directly, several linearization
techniques, such as predistortion and feedforward, are applied to power amplifier design.
Predistortion method has the advantages over other techniques in relatively simple struc-
ture and reasonable linearity improvement. But current predistortion circuits have quite
limited performance improvement and relatively large insertion loss, which indicate the
need for further research. In most of millimeter-wave amplifier design, great effort has
been spent on output power or gain, while linearity is often ignored. As almost all the
predistortion circuits operate at the RF frequencies, the linearized millimeter-wave com-
munication circuit is still relatively immature and very challenging.
This project is dedicated to solve the linearity problem faced by millimeter-wave
power amplifier in communication systems, which lacks of e®ective techniques in this field.
Linearity improvement with the predistortion method will be the key issue in this project
and some original ideas for predistortion circuit design will be applied to millimeter-wave
amplifiers.
In this thesis, several predistortion circuits with novel structure were proposed,
which provide a new approach for linearity improvement for millimeter-wave power am-
plifier. A millimeter-wave power ampli¯er for LMDS applications built on GaAs pHEMT
technology was developed to a high engineering standard, which works as the test bench
for linearization. Actual operation and parasitic elements at tens of gigahertz have been
taken into consideration during the design.
Firstly, two novel predistorter structures based on the amplifier were proposed, one
is based on an amplifier with a fixed bias circuit and the other is based on an amplifier with
a nonlinear signal dependant bias circuit. These novel structures can improve the linearity
while improving other metrics simultaneously, which can effectively solve the problem of
insertion loss faced by the conventional structures. Besides this, an original predistortion
circuit design methodology derived from frequency to signal amplitude transformation was
proposed. Based on this methodology, several transfer functions were proposed and related
predistortion circuits were built to linearize the power amplifier. As this methodology is
quite different from the traditional approach, it can improve the linearity signifficantly
while other metrics are affected slightly and has a broad prospect for application
Distributed Circuit Analysis and Design for Ultra-wideband Communication and sub-mm Wave Applications
This thesis explores research into new distributed circuit design techniques and topologies, developed to extend the bandwidth of amplifiers operating in the mm and sub-mm wave regimes, and in optical and visible light communication systems. Theoretical, mathematical modelling and simulation-based studies are presented, with detailed designs of new circuits based on distributed amplifier (DA) principles, and constructed using a double heterojunction bipolar transistor (DHBT) indium phosphide (InP) process with fT =fmax of 350/600 GHz. A single stage DA (SSDA) with bandwidth of 345 GHz and 8 dB gain, based on novel techniques developed in this work, shows 140% bandwidth improvement over the conventional DA design. Furthermore, the matrix-single stage DA (M-SSDA) is proposed for higher gain than both the conventional DA and matrix amplifier. A two-tier M-SSDA with 14 dB gain at 300 GHz bandwidth, and a three-tier M-SSDA with a gain of 20 dB at 324 GHz bandwidth, based on a cascode gain cell and optimized for bandwidth and gain flatness, are presented based on full foundry simulation tests. Analytical and simulation-based studies of the noise performance peculiarities of the SSDA and its multiplicative derivatives are also presented. The newly proposed circuits are fabricated as monolithic microwave integrated circuits (MMICs), with measurements showing 7.1 dB gain and 200 GHz bandwidth for the SSDA and 12 dB gain at 170 GHz bandwidth for the three-tier M-SSDA. Details of layout, fabrication and testing; and discussion of performance limiting factors and layout optimization considerations are presented. Drawing on the concept of artificial transmission line synthesis in distributed amplification, a new technique to achieve up to three-fold improvement in the modulation bandwidth of light emitting diodes (LEDs) for visible light communication (VLC) is introduced. The thesis also describes the design and application of analogue pre-emphasis to improve signal-to-noise ratio in bandwidth limited optical transceivers
Design, fabrication and testing of a novel W-band monolithic millimetre-wave integrated circuit mixer
Abstract available: p. [1
Very Low-Noise Differential Radiometer at 30 GHz for the PLANCK LFI
The PLANCK mission of the European Space Agency is devoted to produce sky maps of the cosmic microwave background radiation. The low-frequency instrument is a wide-band cryogenic microwave radiometer array operating at 30, 44, and 70 GHz. The design, test techniques, and performance of the complete differential radiometer at 30 GHz are presented. This elegant breadboard 30-GHz radiometer is composed of a front-end module (FEM) assembled at the Jodrell Bank Observatory, Cheshire, U.K., and a back-end module assembled at the Universidad de Cantabria, Cantabria, Spain, and Telecomunicacio/spl acute/, Universitat Polite/spl acute/cnica de Catalunya, Barcelona, Spain. The system noise temperature was excellent, mainly due to the very low noise performance of the FEM amplifiers, which achieved an average noise temperature of 9.4 K.Peer Reviewe
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