17,896 research outputs found
1.5V fully programmable CMOS Membership Function Generator Circuit with proportional DC-voltage control
A Membership Function Generator Circuit (MFGC) with bias supply of 1.5 Volts and independent DC-voltage programmable functionalities is presented. The realization is based on a programmable differential current mirror and three compact voltage-to-current converters, allowing continuous and quasi-linear adjustment of the center position, height, width and slopes of the triangular/trapezoidal output waveforms. HSPICE simulation results of the proposed circuit using the parameters of a double-poly, three metal layers, 0.5 μm CMOS technology validate the functionality of the proposed architecture, which exhibits a maximum deviation of the linearity in the programmability of 7 %
High Gain Amplifier with Enhanced Cascoded Compensation
A two-stage CMOS operational amplifier with both, gain-boosting and indirect current feedback frequency compensation performed by means of regulated cascode amplifiers, is presented. By using quasi-floating-gate transistors (QFGT) the supply requirements, the number of capacitors and the size of the compensation capacitors respect to other Miller schemes are reduced. A prototype was fabricated using a 0.5 μm technology, resulting, for a load of 45 pF and supply voltage of 1.65 V, in open-loop-gain of 129 dB, 23 MHz of gain-bandwidth product, 60o phase margin, 675 μW power consumption and 1% settling time of 28 ns
High spatial resolution and high contrast optical speckle imaging with FASTCAM at the ORM
In this paper, we present an original observational approach, which combines,
for the first time, traditional speckle imaging with image post-processing to
obtain in the optical domain diffraction-limited images with high contrast
(1e-5) within 0.5 to 2 arcseconds around a bright star. The post-processing
step is based on wavelet filtering an has analogy with edge enhancement and
high-pass filtering. Our I-band on-sky results with the 2.5-m Nordic Telescope
(NOT) and the lucky imaging instrument FASTCAM show that we are able to detect
L-type brown dwarf companions around a solar-type star with a contrast DI~12 at
2" and with no use of any coronographic capability, which greatly simplifies
the instrumental and hardware approach. This object has been detected from the
ground in J and H bands so far only with AO-assisted 8-10 m class telescopes
(Gemini, Keck), although more recently detected with small-class telescopes in
the K band. Discussing the advantage and disadvantage of the optical regime for
the detection of faint intrinsic fluxes close to bright stars, we develop some
perspectives for other fields, including the study of dense cores in globular
clusters. To the best of our knowledge this is the first time that high
contrast considerations are included in optical speckle imaging approach.Comment: Proceedings of SPIE conference - Ground-based and Airborne
Instrumentation for Astronomy III (Conference 7735), San Diego 201
An X-ray study of the SNR G344.7-0.1 and the central object CXOU J170357.8-414302
Aims. We report results of an X-ray study of the supernova remnant (SNR)
G344.7-0.1 and the point-like X-ray source located at the geometrical center of
the SNR radio structure. Methods. The morphology and spectral properties of the
remnant and the central X-ray point-like source were studied using data from
the XMM-Newton and Chandra satellites. Archival radio data and infrared Spitzer
observations at 8 and 24 m were used to compare and study its multi-band
properties at different wavelengths. Results. The XMM-Newton and Chandra
observations reveal that the overall X-ray emission of G344.7-0.1 is extended
and correlates very well with regions of bright radio and infrared emission.
The X-ray spectrum is dominated by prominent atomic emission lines. These
characteristics suggest that the X-ray emission originated in a thin thermal
plasma, whose radiation is represented well by a plane-parallel shock plasma
model (PSHOCK). Our study favors the scenario in which G344.7-0.1 is a 6 x 10^3
year old SNR expanding in a medium with a high density gradient and is most
likely encountering a molecular cloud on the western side. In addition, we
report the discovery of a soft point-like X-ray source located at the
geometrical center of the radio SNR structure. The object presents some
characteristics of the so-called compact central objects (CCO). However, its
neutral hydrogen absorption column (N_{H}) is inconsistent with that of the
SNR. Coincident with the position of the source, we found infrared and optical
objects with typical early-K star characteristics. The X-ray source may be a
foreground star or the CCO associated with the SNR. If this latter possibility
were confirmed, the point-like source would be the farthest CCO detected so far
and the eighth member of the new population of isolated and weakly magnetized
neutron stars.Comment: 9 pages, 8 figures, accepted for publication in Astronomy and
Astrophysics. Higher resolution figures can be seen on A&
On the Effect of Correlation on the Capacity of Backscatter Communication Systems
We analyse the effect of correlation between the forward and backward links
on the capacity of backscatter communication systems. To that aim, we obtain an
analytical expression for the average capacity under a correlated Rayleigh
product fading channel, as well as closed-form asymptotic expressions for the
high and low signal-to-noise ratio (SNR) regimes. Our results show that
correlation is indeed detrimental for a fixed target SNR; contrarily to the
common belief, we also see that correlation can be actually beneficial in some
instances when a fixed power budget is considered.Comment: This work has been submitted for publication. Copyright may be
transferred without notice, after which this version may no longer be
accessibl
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