34,569 research outputs found
Supercapacitor assisted LDO (SCALDO) techniquean extra low frequency design approach to high efficiency DC-DC converters and how it compares with the classical switched capacitor converters
Supercapacitor assisted low dropout regulators (SCALDO) were proposed as an alternative design approach to DC-DC converters, where the supercapacitor circulation frequency (switching frequency) is in the order of few Hz to few 10s of Hz, with an output stage based on a low dropout regulator stage. For converters such as 12â5V, 5â3.3V and 5â1.5V, the technique provides efficiency improvement factors of 2, 1.33 and 3 respectively, in compared to linear converters with same input-output combinations. In a 5â1.5V SCALDO regulator, using thin profile supercapacitors in the range of fractional farads to few farads, this translates to an approximate end to end efficiency of near 90%. However, there were concerns that this patented technique is merely a variation of well-known switched capacitor (charge pump) converters. This paper is aimed at providing a broad overview of the capability of SCALDO technique with generalized theory, indicating its capabilities and limitations, and comparing the practical performance with a typical switched capacitor converter of similar current capability
Characterization of the FE-I4B pixel readout chip production run for the ATLAS Insertable B-layer upgrade
The Insertable B-layer (IBL) is a fourth pixel layer that will be added
inside the existing ATLAS pixel detector during the long LHC shutdown of 2013
and 2014. The new four layer pixel system will ensure excellent tracking,
vertexing and b-tagging performance in the high luminosity pile-up conditions
projected for the next LHC run. The peak luminosity is expected to reach 3 x
10^34 cm^-2 s^-1 with an integrated luminosity over the IBL lifetime of 300
fb^-1 corresponding to a design lifetime fluence of 5 x 10^15 n_eq cm^-2 and
ionizing dose of 250 Mrad including safety factors. The production front-end
electronics FE-I4B for the IBL has been fabricated at the end of 2011 and has
been extensively characterized on diced ICs as well as at the wafer level. The
production tests at the wafer level were performed during 2012. Selected
results of the diced IC characterization are presented, including measurements
of the on-chip voltage regulators. The IBL powering scheme, which was chosen
based on these results, is described. Preliminary wafer to wafer distributions
as well as yield calculations are given
FPGA Design Techniques for Stable Cryogenic Operation
In this paper we show how a deep-submicron FPGA can be modified to operate at
extremely low temperatures through modifications in the supporting hardware and
in the firmware programming it. Though FPGAs are not designed to operate at a
few Kelvin, it is possible to do so on virtue of the extremely high doping
levels found in deep-submicron CMOS technology nodes. First, any PCB component,
that does not conform with this requirement, is removed. Both the majority of
decoupling capacitor types and voltage regulators are not well behaved at
cryogenic temperatures, asking for an ad-hoc solution to stabilize the FPGA
supply voltage, especially for sensitive applications. Therefore, we have
designed a firmware that enforces a constant power consumption, so as to
stabilize the supply voltage in the interior of the FPGA chip. The FPGA is
powered with a supply at several meters distance, causing significant IR drop
and thus fluctuations on the local supply voltage. To achieve the
stabilization, the variation in digital logic speed, which directly corresponds
to changes in supply voltage, is constantly measured and corrected for through
a tunable oscillator farm, implemented on the FPGA. The method is versatile and
robust, enabling seamless porting to other FPGA families and configurations.Comment: The following article has been submitted to Review of Scientific
Instruments. If it is published, it will be available on http://rsi.aip.or
Accelerated gas-liquid visible light photoredox catalysis with continuous-flow photochemical microreactors
In this protocol, we describe the construction and use of an operationally simple photochemical microreactor for gas-liquid photoredox catalysis using visible light. The general procedure includes details on how to set up the microreactor appropriately with inlets for gaseous reagents and organic starting materials, and it includes examples of how to use it to achieve continuous-flow preparation of disulfides or trifluoromethylated heterocycles and thiols. The reported photomicroreactors are modular, inexpensive and can be prepared rapidly from commercially available parts within 1 h even by nonspecialists. Interestingly, typical reaction times of gas-liquid visible light photocatalytic reactions performed in microflow are lower (in the minute range) than comparable reactions performed as a batch process (in the hour range). This can be attributed to the improved irradiation efficiency of the reaction mixture and the enhanced gas-liquid mass transfer in the segmented gas-liquid flow regime
Radiation Testing of Electronics for the CMS Endcap Muon System
The electronics used in the data readout and triggering system for the
Compact Muon Solenoid (CMS) experiment at the Large Hadron Collider (LHC)
particle accelerator at CERN are exposed to high radiation levels. This
radiation can cause permanent damage to the electronic circuitry, as well as
temporary effects such as data corruption induced by Single Event Upsets. Once
the High Luminosity LHC (HL-LHC) accelerator upgrades are completed it will
have five times higher instantaneous luminosity than LHC, allowing for
detection of rare physics processes, new particles and interactions. Tests have
been performed to determine the effects of radiation on the electronic
components to be used for the Endcap Muon electronics project currently being
designed for installation in the CMS experiment in 2013. During these tests the
digital components on the test boards were operating with active data readout
while being irradiated with 55 MeV protons. In reactor tests, components were
exposed to 30 years equivalent levels of neutron radiation expected at the
HL-LHC. The highest total ionizing dose (TID) for the muon system is expected
at the inner-most portion of the CMS detector, with 8900 rad over ten years.
Our results show that Commercial Off-The-Shelf (COTS) components selected for
the new electronics will operate reliably in the CMS radiation environment
Suppression of Second-Order Harmonic Current for Droop-Controlled Distributed Energy Resource Converters in DC Microgrids
Droop-controlled distributed energy resource converters in dc microgrids usually show low output impedances. When coupled with ac systems, second-order harmonics typically appear on the dc-bus voltage, causing significant harmonic currents at the converters resource side. This paper shows how to reduce such undesired currents by means of notch filters and resonant regulators included in the converters control loops. The main characteristics of these techniques in terms of harmonic attenuation and stability are systematically investigated. In particular, it is shown that the voltage control-loop bandwidth is limited to be below twice the line frequency to avoid instability. Then, a modified notch filter and a modified resonant regulator are proposed, allowing to remove the constraint on the voltage loop bandwidth. The resulting methods (i.e., the notch filter, the resonant regulator, and their corresponding modified versions) are evaluated in terms of output impedance and stability. Experimental results from a dc microgrid prototype composed of three dc-dc converters and one dc-ac converter, all with a rated power of 5kW, are reported
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The road to fully integrated DC-DC conversion via the switched-capacitor approach
This paper provides a perspective on progress toward realization of efficient, fully integrated dc-dc conversion and regulation functionality in CMOS platforms. In providing a comparative assessment between the inductor-based and switched-capacitor approaches, the presentation reviews the salient features in effectiveness in utilization of switch technology and in use and implementation of passives. The analytical conclusions point toward the strong advantages of the switched-capacitor (SC) approach with respect to both switch utilization and much higher energy densities of capacitors versus inductors. The analysis is substantiated with a review of recently developed and published integrated dc-dc converters of both the inductor-based and SC types. © 2012 IEEE
CMS Barrel Pixel Detector Overview
The pixel detector is the innermost tracking device of the CMS experiment at
the LHC. It is built from two independent sub devices, the pixel barrel and the
end disks. The barrel consists of three concentric layers around the beam pipe
with mean radii of 4.4, 7.3 and 10.2 cm. There are two end disks on each side
of the interaction point at 34.5 cm and 46.5 cm. This article gives an overview
of the pixel barrel detector, its mechanical support structure, electronics
components, services and its expected performance.Comment: Proceedings of Vertex06, 15th International Workshop on Vertex
Detector
Adaptive feedback analysis and control of programmable stimuli for assessment of cerebrovascular function
The assessment of cerebrovascular regulatory mechanisms often requires flexibly controlled and precisely timed changes in arterial blood pressure (ABP) and/or inspired CO2. In this study, a new system for inducing variations in mean ABP was designed, implemented and tested using programmable sequences and programmable controls to induce pressure changes through bilateral thigh cuffs. The system is also integrated with a computer-controlled switch to select air or a CO2/air mixture to be provided via a face mask. Adaptive feedback control of a pressure generator was required to meet stringent specifications for fast changes, and accuracy in timing and pressure levels applied by the thigh cuffs. The implemented system consists of a PC-based signal analysis/control unit, a pressure control unit and a CO2/air control unit. Initial evaluations were carried out to compare the cuff pressure control performances between adaptive and non-adaptive control configurations. Results show that the adaptive control method can reduce the mean error in sustaining target pressure by 99.57 % and reduce the transient time in pressure increases by 45.21 %. The system has proven a highly effective tool in ongoing research on brain blood flow control
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