584 research outputs found
Nanophotonic soliton-based microwave synthesizers
Microwave photonic technologies, which upshift the carrier into the optical
domain to facilitate the generation and processing of ultrawide-band electronic
signals at vastly reduced fractional bandwidths, have the potential to achieve
superior performance compared to conventional electronics for targeted
functions. For microwave photonic applications such as filters, coherent
radars, subnoise detection, optical communications and low-noise microwave
generation, frequency combs are key building blocks. By virtue of soliton
microcombs, frequency combs can now be built using CMOS compatible photonic
integrated circuits, operated with low power and noise, and have already been
employed in system-level demonstrations. Yet, currently developed photonic
integrated microcombs all operate with repetition rates significantly beyond
those that conventional electronics can detect and process, compounding their
use in microwave photonics. Here we demonstrate integrated soliton microcombs
operating in two widely employed microwave bands, X- and K-band. These devices
can produce more than 300 comb lines within the 3-dB-bandwidth, and generate
microwave signals featuring phase noise levels below 105 dBc/Hz (140 dBc/Hz) at
10 kHz (1 MHz) offset frequency, comparable to modern electronic microwave
synthesizers. In addition, the soliton pulse stream can be injection-locked to
a microwave signal, enabling actuator-free repetition rate stabilization,
tuning and microwave spectral purification, at power levels compatible with
silicon-based lasers (<150 mW). Our results establish photonic integrated
soliton microcombs as viable integrated low-noise microwave synthesizers.
Further, the low repetition rates are critical for future dense WDM channel
generation schemes, and can significantly reduce the system complexity of
photonic integrated frequency synthesizers and atomic clocks
Enabling low cost test and tuning of difficult-to-measure device specifications: application to DC-DC converters and high speed devices
Low-cost test and tuning methods for difficult-to-measure specifications are presented in this research from the following perspectives: 1)"Safe" test and self-tuning for power converters: To avoid the risk of device under test (DUT) damage during conventional load/line regulation measurement on power converter, a "safe" alternate test structure is developed where the power converter (boost/buck converter) is placed in a different mode of operation during alternative test (light switching load) as opposed to standard test (heavy switching load) to prevent damage to the DUT during manufacturing test. Based on the alternative test structure, self-tuning methods for both boost and buck converters are also developed in this thesis. In addition, to make these test structures suitable for on-chip built-in self-test (BIST) application, a special sensing circuit has been designed and implemented. Stability analysis filters and appropriate models are also implemented to predict the DUT’s electrical stability condition during test and to further predict the values of tuning knobs needed for the tuning process. 2) High bandwidth RF signal generation: Up-convertion has been widely used in high frequency RF signal generation but mixer nonlinearity results in signal distortion that is difficult to eliminate with such methods. To address this problem, a framework for low-cost high-fidelity wideband RF signal generation is developed in this thesis. Depending on the band-limited target waveform, the input data for two interleaved DACs (digital-to-analog converters) system is optimized by a matrix-model-based algorithm in such a way that it minimizes the distortion between one of its image replicas in the frequency domain and the target RF waveform within a specified signal bandwidth. The approach is used to demonstrate how interferers with specified frequency characteristics can be synthesized at low cost for interference testing of RF communications systems. The frameworks presented in this thesis have a significant impact in enabling low-cost test and tuning of difficult-to-measure device specifications for power converter and high-speed devices.Ph.D
JamLab: Augmenting Sensornet Testbeds with Realistic and Controlled Interference Generation
Radio interference drastically affects the performance of sensor-net communications, leading to packet loss and reduced energy-efficiency. As an increasing number of wireless devices operates on the same ISM frequencies, there is a strong need for understanding and debugging the performance of existing sensornet protocols under interference. Doing so requires a low-cost flexible testbed infrastructure that allows the repeatable generation of a wide range of interference patterns. Unfortunately, to date, existing sensornet testbeds lack such capabilities, and do not permit to study easily the coexistence problems between devices sharing the same frequencies. This paper addresses the current lack of such an infrastructure by using off-the-shelf sensor motes to record and playback interference patterns as well as to generate customizable and repeat-able interference in real-time. We propose and develop JamLab: a low-cost infrastructure to augment existing sensornet testbeds with accurate interference generation while limiting the overhead to a simple upload of the appropriate software. We explain how we tackle the hardware limitations and get an accurate measurement and regeneration of interference, and we experimentally evaluate the accuracy of JamLab with respect to time, space, and intensity. We further use JamLab to characterize the impact of interference on sensornet MAC protocols
Mode-locked laser timing jitter limitation in optically enabled, spectrally sliced ADCs
Novel analog-to-digital converter (ADC) architectures are motivated by the
demand for rising sampling rates and effective number of bits (ENOB). The main
limitation on ENOB in purely electrical ADCs lies in the relatively high jitter
of oscillators, in the order of a few tens of fs for state-of-the-art
components. When compared to the extremely low jitter obtained with
best-in-class Ti:sapphire mode-locked lasers (MLL), in the attosecond range, it
is apparent that a mixed electrical-optical architecture could significantly
improve the converters' ENOB. We model and analyze the ENOB limitations arising
from optical sources in optically enabled, spectrally sliced ADCs, after
discussing the system architecture and implementation details. The phase noise
of the optical carrier, serving for electro-optic signal transduction, is shown
not to propagate to the reconstructed digitized signal and therefore not to
represent a fundamental limit. The optical phase noise of the MLL used to
generate reference tones for individual slices also does not fundamentally
impact the converted signal, so long as it remains correlated among all the
comb lines. On the other hand, the timing jitter of the MLL, as also reflected
in its RF linewidth, is fundamentally limiting the ADC performance, since it is
directly mapped as jitter to the converted signal. The hybrid nature of a
photonically enabled, spectrally sliced ADC implies the utilization of a number
of reduced bandwidth electrical ADCs to convert parallel slices, resulting in
the propagation of jitter from the electrical oscillator supplying their clock.
Due to the reduced sampling rate of the electrical ADCs, as compared to the
overall system, the overall noise performance of the presented architecture is
substantially improved with respect to a fully electrical ADC
Simulation and Design of an UWB Imaging System for Breast Cancer Detection
Breast cancer is the most frequently diagnosed cancer among women. In recent
years, the mortality rate due to this disease is greatly decreased thanks to both
enormous progress in cancer research, and screening campaigns which have allowed
the increase in the number of early diagnoses of the disease. In fact, if the tumor is
identied in its early stage, e.g. when it has a diameter of less than one centimeter,
the possibility of a cure can reach 93%. However, statistics show that more young
aged women are suered breast cancer.
The goal of screening exams for early breast cancer detection is to nd cancers
before they start to cause symptoms. Regular mass screening of all women at risk
is a good option to achieve that. Instead of meeting very high diagnostic standards,
it is expected to yield an early warning, not a denitive diagnosis. In the last
decades, X-ray mammography is the most ecient screening technique. However,
it uses ionizing radiation and, therefore, should not be used for frequent check-ups.
Besides, it requires signicant breast compression, which is often painful. In this
scenario many alternative technologies were developed to overcome the limitations
of mammography. Among these possibilities, Magnetic Resonance Imaging (MRI)
is too expensive and time-consuming, Ultrasound is considered to be too operatordependent
and low specicity, which are not suitable for mass screening. Microwave
imaging techniques, especially Ultra WideBand (UWB) radar imaging, is the most
interesting one. The reason of this interest relies on the fact that microwaves are
non-ionizing thus permitting frequent examinations. Moreover, it is potentially lowcost
and more ecient for young women. Since it has been demonstrated in the
literatures that the dielectric constants between cancerous and healthy tissues are
quite dierent, the technique consists in illuminating these biological tissues with
microwave radiations by one or more antennas and analyzing the re
ected signals.
An UWB imaging system consists of transmitters, receivers and antennas for
the RF part, the transmission channel and of a digital backend imaging unit for
processing the received signals. When an UWB pulse strikes the breast, the pulse is
re
ected due to the dielectric discontinuity in tissues, the bigger the dierence, the
bigger the backscatter. The re
ected signals are acquired and processed to create
the energy maps. This thesis aims to develop an UWB system at high resolution for the detection of carcinoma breast already in its initial phase. To favor the adoption
of this method in screening campaigns, it is necessary to replace the expensive and
bulky RF instrumentation used so far with ad-hoc designed circuits and systems.
In order to realize that, at the very beginning, the overall system environment must
be built and veried, which mainly consists of the transmission channel{the breast
model and the imaging unit. The used transmission channel data come from MRI
of the prone patient. In order to correctly use this numerical model, a simulator was
built, which was implemented in Matlab, according to the Finite-Dierence-Time-
Domain (FDTD) method. FDTD algorithm solves the electric and magnetic eld
both in time and in space, thus, simulates the propagation of electromagnetic waves
in the breast model. To better understand the eect of the system non-idealities,
two 2D breast models are investigated, one is homogeneous, the other is heterogeneous.
Moreover, the modeling takes into account all critical aspects, including
stability and medium dispersion. Given the types of tissues under examination, the
frequency dependence of tissue dielectric properties is incorporated into wideband
FDTD simulations using Debye dispersion parameters. A performed further study
is in the implementation of the boundary conditions. The Convolution Perfectly
Matched Layer (CPML) is used to implement the absorbing boundaries.
The objective of the imaging unit is to obtain an energy map representing the
amount of energy re
ected from each point of the breast, by recombining the sampled
backscattered signals. For this purpose, the study has been carried out on various
beamforming in the literature. The basic idea is called as "delay and sum", which
is to align the received signals in such a way as to focus a given point in space and
then add up all the contributions, so as to obtain a constructive interference at that
point if this is a diseased tissue. In this work, Microwave Imaging via Space Time
(MIST) Beamforming algorithm is applied, which is based on the above principle
and add more elaborations of the signals in order to make the algorithm less sensitive
to propagation phenomena in the medium and to the non-idealities of the system.
It is divided into two distinct steps: the rst step, called SKin Artifact Removal
(SKAR), takes care of removing the contributions from the signal caused by the
direct path between the transmitter and receiver, the re
ection of skin, as they are
orders of magnitude higher compared to the re
ections caused by cancers; the second
step, which is BEAmForming (BEAF), performs the algorithm of reconstruction by
forming a weighted combination of time delayed version of the calibrated re
ected
signals.
As discussed above, more attention must be paid on the implementation of the
ad-hoc integration circuits. In this scenario, due to the strict requirements on the
RF receiver component, two dierent approaches of the implementation of the RF
front-end, Direct Conversion (DC) receiver and Coherent Equivalent Time Sampling
(CETS) receiver are compared. They are modeled behaviorally and the eects of
various impairments, such as thermal, jitter, and phase noise, as well as phase inaccuracies, non-linearity, ADC quantization noise and distortion, on energy maps
and on quantitative metrics such as SCR and SMR are evaluated. Dierential
Gaussian pulse is chosen as the exciting source. Results show that DC receiver
performs higher sensitivity to phase inaccuracies, which makes it less robust than
the CETS receiver. Another advantage of the CETS receiver is that it can work
in time domain with UWB pulses, other than in frequency domain with stepped
frequency continuous waves like the DC one, which reduces the acquisition time
without impacting the performance.
Based on the results of the behavioral simulations, low noise amplier (LNA)
and Track and Hold Amplier (THA) can be regarded as the most critical parts
for the proposed CETS receiver, as well as the UWB antenna. This work therefore
focuses on their hardware implementations. The LNA, which shows critical performance
limitation at bandwidth and noise gure of receiver, has been developed based
on common-gate conguration. And the THA based on Switched Source Follower
(SSF) scheme has been presented and improved to obtain high input bandwidth,
high sampling rate, high linearity and low power consumption. LNA and THA
are implemented in CMOS 130nm technology and the circuit performance evaluation
has been taken place separately and together. The small size UWB wide-slot
antenna is designed and simulated in HFSS.
Finally, in order to evaluate the eect of the implemented transistor level components
on system performance, a multi-resolution top-down system methodology
is applied. Therfore, the entire
ow is analyzed for dierent levels of the RF frontend.
Initially the system components are described behaviorally as ideal elements.
The main activity consists in the analysis and development of the entire frontend
system, observing and complementing each other blocks in a single
ow simulation,
clear and well-dened in its various interfaces. To achieve that the receiver is modeled
and analyzed using VHDL-AMS language block by block, moreover, the impact
of quantization, noise, jitter, and non-linearity is also evaluated. At last, the behavioral
description of antenna, LNA and THA is replaced with a circuit-level one
without changing the rest of the system, which permits a system-level assessment
of low-level issues
Impact of Background Traffic on Speech Quality in VoWLAN
This paper describes measurements of the impact of background traffic on speech quality in an environment of WLANs (IEEE 802.11). The simulated background traffic consists of three types of current traffics in telecommunication networks such as data transfer service, multimedia streaming service, and Web service. The background traffic was generated by means of the accomplished Distributed Internet Traffic Generator (D-ITG). The impact of these types of traffic and traffic load on speech quality using the test sequence and speech sequences is the aim of this paper. The assessment of speech quality is carried out by means of the accomplished Perceptual Evaluation of Speech Quality (PESQ) algorithm. The proposal of a new method for improved detection of the critical conditions in wireless telecommunication networks from the speech quality point of view is presented in this paper. Conclusion implies the next application of the method of improved detection of critical conditions for the purpose of algorithms for link adaptation from the speech quality point of view in an environment of WLANs. The primary goal of these algorithms is improving speech quality in the VoWLAN connections, which are established in the competent link
Novel Multicarrier Memory Channel Architecture Using Microwave Interconnects: Alleviating the Memory Wall
abstract: The increase in computing power has simultaneously increased the demand for input/output (I/O) bandwidth. Unfortunately, the speed of I/O and memory interconnects have not kept pace. Thus, processor-based systems are I/O and interconnect limited. The memory aggregated bandwidth is not scaling fast enough to keep up with increasing bandwidth demands. The term "memory wall" has been coined to describe this phenomenon.
A new memory bus concept that has the potential to push double data rate (DDR) memory speed to 30 Gbit/s is presented. We propose to map the conventional DDR bus to a microwave link using a multicarrier frequency division multiplexing scheme. The memory bus is formed using a microwave signal carried within a waveguide. We call this approach multicarrier memory channel architecture (MCMCA). In MCMCA, each memory signal is modulated onto an RF carrier using 64-QAM format or higher. The carriers are then routed using substrate integrated waveguide (SIW) interconnects. At the receiver, the memory signals are demodulated and then delivered to SDRAM devices. We pioneered the usage of SIW as memory channel interconnects and demonstrated that it alleviates the memory bandwidth bottleneck. We demonstrated SIW performance superiority over conventional transmission line in immunity to cross-talk and electromagnetic interference. We developed a methodology based on design of experiment (DOE) and response surface method techniques that optimizes the design of SIW interconnects and minimizes its performance fluctuations under material and manufacturing variations. Along with using SIW, we implemented a multicarrier architecture which enabled the aggregated DDR bandwidth to reach 30 Gbit/s. We developed an end-to-end system model in Simulink and demonstrated the MCMCA performance for ultra-high throughput memory channel.
Experimental characterization of the new channel shows that by using judicious frequency division multiplexing, as few as one SIW interconnect is sufficient to transmit the 64 DDR bits. Overall aggregated bus data rate achieves 240 GBytes/s data transfer with EVM not exceeding 2.26% and phase error of 1.07 degree or less.Dissertation/ThesisDoctoral Dissertation Electrical Engineering 201
An On-chip PVT Resilient Short Time Measurement Technique
As the CMOS technology nodes continue to shrink, the challenges of developing manufacturing tests for integrated circuits become more difficult to address. To detect parametric faults of new generation of integrated circuits such as 3D ICs, on-chip short-time intervals have to be accurately measured. The accuracy of an on-chip time measurement module is heavily affected by Process, supply Voltage, and Temperature (PVT) variations. This work presents a new on-chip time measurement scheme where the undesired effects of PVT variations are attenuated significantly. To overcome the effects of PVT variations on short-time measurement, phase locking methodology is utilized to implement a robust Vernier delay line. A prototype Time-to-Digital Converter (TDC) has been fabricated using TSMC 0.180 µm CMOS technology and experimental measurements have been carried out to verify the performance parameters of the TDC. The measurement results indicate that the proposed solution reduces the effects of PVT variations by more than tenfold compared to a conventional on-chip TDC. A coarse-fine time interval measurement scheme which is resilient to the PVT variations is also proposed. In this approach, two Delay Locked Loops (DLLs) are utilized to minimize the effects of PVT on the measured time intervals. The proposed scheme has been implemented using CMOS 65nm technology. Simulation results using Advanced Design System (ADS) indicate that the measurement resolution varies by less than 0.1ps with ±15% variations of the supply voltage. The proposed method also presents a robust performance against process and temperature variations. The measurement accuracy changes by a maximum of 0.05ps from slow to fast corners. The implemented TDC presents a robust performance against temperature variations too and its measurement accuracy varies a few femto-seconds from -40 ºC to +100 ºC. The principle of robust short-time measurement was used in practice to design and implement a state-of-the-art Coordinate Measuring Machine (CMM) for an industry partner to measure geometrical features of transmission parts with micrometer resolution. The solution developed for the industry partner has resulted in a patent and a product in the market. The on-chip short-time measurement technology has also been utilized to develop a solution to detect Hardware Trojans
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