400 research outputs found
A novel approach to noise shaping in digital pixels for infrared imagers using over-integration
Digital readout integrated circuits (DROICs) for small pitch infrared focal plane arrays (IR-FPAs) suffer from low in-pixel resolution owing to the limited pixel real estate. To this end, a new technique to improve the resolution of pulse frequency modulation (PFM) based pixels, using quantization charge noise shaping, is presented. Multiple integration operations are performed in a single frame and the quantization error from each integration phase is retained and effectively induced into the next integration phase. The result is a high pass noise transfer function (NTF) equivalent to what is obtained in a first order sigma delta modulator. Along with a theoretical analysis of the technique, a prototype based on a single pixel and a 2nd order decimation filter is developed to demonstrate the performance of the proposed technique. With an in-pixel circuitry generating 5 bits, a resolution of 11 bits (65 dB) is achieved with an over-integration ratio of 64. With a 100 Hz frame rate and 64 integration operations per frame, a readout noise of 1100e- is measured at full-well fill from the test pixel fabricated in a 90nm CMOS process
A highly digital microbolometer ROIC employing a novel event-based readout and two-step time to digital converters
Uncooled infrared imaging systems are a light weight and low cost alternative to their cooled counterparts. Uncooled microbolometer IR focal plane arrays (IRFPAs) for applications such as medical imaging, thermography, night vision, surveillance and industrial process control have recently been under focus. These systems have small pixel pitches ( 250 K). Low NETD demands excellent microbolometer and readout noise performance. If sensitive analog circuits, driving long metal interconnects, are part of the predigitization readout channel, this necessitates the use of power consuming buffers, potentially in conjunction with noise cancellation circuits that result in power and area overhead. Thus re-thinking at the architectural level is crucial to meet these demands. Accordingly, in this thesis a column-parallel readout architecture for frame synchronous microbolometer imagers is proposed that enables low power operation by employing a time mode digitizer. The proposed readout circuit is based on a bridge type detector network with active and reference microbolometers and employs a capacitive transimpedance amplifier (CTIA) incorporating a novel two-step integration mechanism. By using a modified reset scheme in the CTIA, a forward ramp is initiated at the input side followed by the conventional backward integrated ramp at the output. This extends the measurement interval and improves signal-to-noise ratio (SNR). A synchronous counter based TDC measures this interval providing robust digitization. This technique also provides a way of compensating for self-heating effects. Being highly digital, the proposed architecture offers robust frontend processing and achieves a per channel power consumption of 66 µW, which is considerably lower than the most recently reported designs, while maintaining better than 10mK readout NETD
Digital pixel readout integrated circuit architectures for LWIR
This paper presents and discusses digital pixel readout integrated circuit architectures for long wavelength infrared (LWIR) in CMOS technology. Presented architectures are designed for scanning and staring arrays type detectors respectively. For scanning arrays, digital time delay integration (TDI) is implemented on 8 pixels with sampling rate up to 3 using CMOS 180nm technology. Input referred noise of ROIC is below 750 rms electron meanwhile power dissipation is appreciably under 30mW. ROIC design is optimized to perform at room as well as cryogenic temperatures. For staring type arrays, a digital pixel architecture relying on coarse quantization with pulse frequency modulation (PFM) and novel approach of extended integration is presented.. It can achieve extreme charge handling capacity of 2.04Ge(-) with 20 bit output resolution and power dissipation below 350 nW in CMOS 90nm technology. Efficient mechanism of measuring the time to estimate the remaining charge on integration capacitor in order to achieve low SNR has employed
QUBIC: The QU Bolometric Interferometer for Cosmology
One of the major challenges of modern cosmology is the detection of B-mode
polarization anisotropies in the CMB. These originate from tensor fluctuations
of the metric produced during the inflationary phase. Their detection would
therefore constitute a major step towards understanding the primordial
Universe. The expected level of these anisotropies is however so small that it
requires a new generation of instruments with high sensitivity and extremely
good control of systematic effects. We propose the QUBIC instrument based on
the novel concept of bolometric interferometry, bringing together the
sensitivity advantages of bolometric detectors with the systematics effects
advantages of interferometry. Methods: The instrument will directly observe the
sky through an array of entry horns whose signals will be combined together
using an optical combiner. The whole set-up is located inside a cryostat.
Polarization modulation will be achieved using a rotating half-wave plate and
interference fringes will be imaged on two focal planes (separated by a
polarizing grid) tiled with bolometers. We show that QUBIC can be considered as
a synthetic imager, exactly similar to a usual imager but with a synthesized
beam formed by the array of entry horns. Scanning the sky provides an
additional modulation of the signal and improve the sky coverage shape. The
usual techniques of map-making and power spectrum estimation can then be
applied. We show that the sensitivity of such an instrument is comparable with
that of an imager with the same number of horns. We anticipate a low level of
beam-related systematics thanks to the fact that the synthesized beam is
determined by the location of the primary horns. Other systematics should be
under good control thanks to an autocalibration technique, specific to our
concept, that will permit the accurate determination of most of the systematics
parameters.Comment: 12 pages, 10 figures, submitted to Astronomy and Astrophysic
Enabling Technologies for Next Generation Ultraviolet Astrophysics, Planetary, and Heliophysics Missions
Our study sought to create a new paradigm in UV instrument design, detector technology, and
optics that will form the technological foundation for a new generation of ultraviolet missions.
This study brought together scientists and technologists representing the broad community of
astrophysicists, planetary and heliophysics physicists, and technologists working in the UV.
Next generation UV missions require major advances in UV instrument design, optics and
detector technology. UV offers one of the few remaining areas of the electromagnetic spectrum
where this is possible, by combining improvements in detector quantum efficiency (5-10x),
optical coatings and higher-performance wide-field spectrometers (5-10x), and increasing
multiplex advantage (100-1000x).
At the same time, budgets for future missions are tightly constrained. Attention has begun to turn
to small and moderate class missions to provide new observational capabilities on timescales that
maintain scientific vitality. Developments in UV technology offer a comparatively unique
opportunity to conceive of small (Explorer) and moderate (Probe, Discovery, New Millennium)
class missions that offer breakthrough science.
Our study began with the science,
reviewing the breakthrough science
questions that compel the development of
new observational capabilities in the next
10-20 years. We invented a framework for
highlighting the objectives of UV
measurement capabilities: following the
history of baryons from the intergalactic
medium to stars and planets. In
astrophysics, next generation space UV missions will detect and map faint emission and
tomographically map absorption from intergalactic medium baryons that delineate the structure
of the Universe, map the circum-galactic medium that is the reservoir of galaxy-building gas,
map the warm-hot ISM of our Galaxy, explore star-formation within the Local group and beyond,
trace gas in proto-planetary disks and extended atmospheres of exoplanets, and record the
transient UV universe. Solar system planetary atmospheric physics and chemistry, aurorae,
surface composition and magnetospheric environments and interactions will be revealed using
UV spectroscopy. UV spectroscopy may even detect life on an exoplanet.
Our study concluded that with UV technology developments within reach over the next 5-
10 years, we can conceive moderate-class missions that will answer many of the compelling
science questions driving the field.
We reviewed the science measurement requirements for these pioneering new areas and
corresponding technology requirements. We reviewed and evaluated the emerging technologies,
and developed a figure of merit based on potential science impact, state of readiness, required
investment, and potential for highly leveraged progress in a 5-10 year horizon. From this we
were able to develop a strategy for technology development. Some of this technology
development will be subject to funding calls from federal agencies. A subset form a portfolio of
highly promising technologies that are ideal for funding from a KISS Development Program.
One of our study’s principal conclusions was that UV detector performance drives every aspect
of the scientific capability of future missions, and that two highly flexible detector technologies
were at the tipping point for major breakthroughs. These are Gen-2 borosilicate Atomic Layer
Deposition (ALD) coated microchannel plate detectors with GaN photocathodes, and ALDantireflection
(AR) coated, delta-doped photon-counting CCD detectors. Both offer the potential
for QE>50% combined with large formats and pixel counts, low background, and sky-limited
photon-counting performance over the 100-300 nm band. Ramped AR coatings for
spectroscopic detectors could achieve QE’s as high as 80%!
A second conclusion was that UV coatings are on the threshold of a major breakthrough. UV
coatings permeate every aspect of telescope and instrument design. Efficient, robust, ultra-thin
and highly uniform reflective coatings applied with Atomic Layer Deposition (ALD) offer the
possibility of high-performance, wide-field, highly-multiplexed UV spectrometers and a broadband
reach covering the scientifically critical 100-120 nm range (home of 50% of all atomic and
molecular resonance lines). Our study concluded that UV coating advances made possible by
ALD is the principle technology advance that will enable a joint UV-optical general
astrophysics and exoEarth imaging flagship mission.
A third conclusion was that the revolution in micro- and nano-fabrication technology offers a
cornucopia of new possibilities for revolutionary UV technology developments in the near future.
An immediate example is the application of new microlithography techniques to patterning UV
diffraction gratings that are highly efficient and designed to enable wide-field, high-resolution
spectroscopy. These techniques could support the development of new detectors that could
discriminate optical and UV photons and potentially energy-resolving detection.
Relatively modest investments in technology development over the next 5-10 years could
provide advances in detectors, coatings, diffractive elements, and filters that would result
in an effective increase in science capability of 100-1000!
The study brought together a diverse community, led to many new ideas and collaborations, and
brought cohesion and common purpose to UV practitioners. This will have a lasting and positive
impact on the future of our field
An overview of lidar imaging systems for autonomous vehicles
Lidar imaging systems are one of the hottest topics in the optronics industry. The need to sense the surroundings of every autonomous vehicle has pushed forward a race dedicated to deciding the final solution to be implemented. However, the diversity of state-of-the-art approaches to the solution brings a large uncertainty on the decision of the dominant final solution. Furthermore, the performance data of each approach often arise from different manufacturers and developers, which usually have some interest in the dispute. Within this paper, we intend to overcome the situation by providing an introductory, neutral overview of the technology linked to lidar imaging systems for autonomous vehicles, and its current state of development. We start with the main single-point measurement principles utilized, which then are combined with different imaging strategies, also described in the paper. An overview of the features of the light sources and photodetectors specific to lidar imaging systems most frequently used in practice is also presented. Finally, a brief section on pending issues for lidar development in autonomous vehicles has been included, in order to present some of the problems which still need to be solved before implementation may be considered as final. The reader is provided with a detailed bibliography containing both relevant books and state-of-the-art papers for further progress in the subject.Peer ReviewedPostprint (published version
Cosmic Origins Program Annual Technology Report
What is the Cosmic Origins (COR) Program? From ancient times, humans have looked up at the night sky and wondered: Are we alone? How did the universe come to be? How does the universe work? COR focuses on the second question. Scientists investigating this broad theme seek to understand the origin and evolution of the universe from the Big Bang to the present day, determining how the expanding universe grew into a grand cosmic web of dark matter enmeshed with galaxies and pristine gas, forming, merging, and evolving over time. COR also seeks to understand how stars and planets form from clouds in these galaxies to create the heavy elements that are essential to life starting with the first generation of stars to seed the universe, and continuing through the birth and eventual death of all subsequent generations of stars. The COR Programs purview includes the majority of the field known as astronomy, from antiquity to the present
Advanced photon counting techniques for long-range depth imaging
The Time-Correlated Single-Photon Counting (TCSPC) technique has emerged as a
candidate approach for Light Detection and Ranging (LiDAR) and active depth imaging
applications. The work of this Thesis concentrates on the development and
investigation of functional TCSPC-based long-range scanning time-of-flight (TOF)
depth imaging systems. Although these systems have several different configurations
and functions, all can facilitate depth profiling of remote targets at low light levels and
with good surface-to-surface depth resolution. Firstly, a Superconducting Nanowire
Single-Photon Detector (SNSPD) and an InGaAs/InP Single-Photon Avalanche Diode
(SPAD) module were employed for developing kilometre-range TOF depth imaging
systems at wavelengths of ~1550 nm. Secondly, a TOF depth imaging system at a
wavelength of 817 nm that incorporated a Complementary Metal-Oxide-Semiconductor
(CMOS) 32×32 Si-SPAD detector array was developed. This system was used with
structured illumination to examine the potential for covert, eye-safe and high-speed
depth imaging. In order to improve the light coupling efficiency onto the detectors, the
arrayed CMOS Si-SPAD detector chips were integrated with microlens arrays using
flip-chip bonding technology. This approach led to the improvement in the fill factor by
up to a factor of 15. Thirdly, a multispectral TCSPC-based full-waveform LiDAR
system was developed using a tunable broadband pulsed supercontinuum laser source
which can provide simultaneous multispectral illumination, at wavelengths of 531, 570,
670 and ~780 nm. The investigated multispectral reflectance data on a tree was used to
provide the determination of physiological parameters as a function of the tree depth
profile relating to biomass and foliage photosynthetic efficiency. Fourthly, depth
images were estimated using spatial correlation techniques in order to reduce the
aggregate number of photon required for depth reconstruction with low error. A depth
imaging system was characterised and re-configured to reduce the effects of scintillation
due to atmospheric turbulence. In addition, depth images were analysed in terms of
spatial and depth resolution
EXIST: Mission Design Concept and Technology Program
The Energetic X-ray Imaging Survey Telescope (EXIST) is a proposed very large
area coded aperture telescope array, incorporating 8m^2 of pixellated Cd-Zn-Te
(CZT) detectors, to conduct a full-sky imaging and temporal hard x-ray (10-600
keV) survey each 95min orbit. With a sensitivity (5sigma, 1yr) of ~0.05mCrab
(10-150 keV), it will extend the ROSAT soft x-ray (0.5-2.5keV) and proposed
ROSITA medium x-ray (2-10 keV) surveys into the hard x-ray band and enable
identification and study of sources ~10-20X fainter than with the ~15-100keV
survey planned for the upcoming Swift mission. At ~100-600 keV, the ~1mCrab
sensitivity is 300X that achieved in the only previous (HEAO-A4, non-imaging)
all-sky survey. EXIST will address a broad range of key science objectives:
from obscured AGN and surveys for black holes on all scales, which constrain
the accretion history of the universe, to the highest sensitivity and
resolution studies of gamma-ray bursts it will conduct as the Next Generation
Gamma-Ray Burst mission. We summarize the science objectives and mission
drivers, and the results of a mission design study for implementation as a free
flyer mission, with Delta IV launch. Key issues affecting the telescope and
detector design are discussed, and a summary of some of the current design
concepts being studied in support of EXIST is presented for the wide-field but
high resolution coded aperture imaging and very large area array of imaging CZT
detectors. Overall mission design is summarized, and technology development
needs and a development program are outlined which would enable the launch of
EXIST by the end of the decade, as recommended by the NAS/NRC Decadal Survey.Comment: 14 pages, 8 figures, 2 tables. PDF file only. Presented at SPIE (Aug.
2002) and to appear in Proc. SPIE, vol. 485
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