107 research outputs found
Circuit models and SPICE macro-models for quantum Hall effect devices
Quantum Hall effect (QHE) devices are a pillar of modern quantum electrical
metrology. Electrical networks including one or more QHE elements can be used
as quantum resistance and impedance standards. The analysis of these networks
allows metrologists to evaluate the effect of the inevitable parasitic
parameters on their performance as standards. This paper presents a systematic
analysis of the various circuit models for QHE elements proposed in the
literature, and the development of a new model. This last model is particularly
suited to be employed with the analogue electronic circuit simulator SPICE. The
SPICE macro-model and examples of SPICE simulations, validated by comparison
with the corresponding analytical solution and/or experimental data, are
provided
A correlation noise spectrometer for flicker noise measurement in graphene samples
We present a high-resolution digital correlation spectrum analyzer for the measurement of low frequency resistance fluctuations in graphene samples. The system exploits the cross-correlation method to reject the amplifiers' noise. The graphene sample is excited with a low-noise DC current. The output voltage is fed to two two-stage low-noise amplifiers connected in parallel; the DC signal component is filtered by a high-pass filter with a cutoff frequency of 34 mHz. The amplified signals are digitized by a two-channel synchronous ADC board; the cross-periodogram, which rejects uncorrelated amplifiers' noise components, is computed in real time. As a practical example, we measured the noise cross-spectrum of graphene samples in the frequency range from 0.153 Hz to 10 kHz, both in two- and four-wire configurations, and for different bias currents. We report here the measurement setup, the data analysis and the error sources
A three-arm current comparator bridge, for impedance comparisons over the complex plane
We present here the concept of three-arm current comparator impedance bridge,
which allows comparisons among three unlike impedances. Its purpose is the
calibration of impedances having arbitrary phase angles, against calibrated
nearly-pure impedances. An analysis of the bridge optimal setting and proper
operation is presented. To test the concept, a two terminal-pair
digitally-assisted bridge has been realized; measurements of an air-core
inductor and of an RC network versus decade resistance and capacitance
standards, at kHz frequency, have been performed. The bridge measurements are
compatible with previous knowledge of the standards' values with relative
deviations in the 10^-5 -- 10^-6 range
Update: On the synthesis of quantum Hall array resistance standards (2015 Metrologia 52 31)
This work provides an update, according to the revised SI, to table 1 of Ortolano et al (2015 Metrologia 52 31–9). The table reports fractions of the quantized Hall resistance approximating decadic values and the associated deviations. In several cases, the deviations have become smaller in the revised SI
Primary Realization of Inductance and Capacitance Scales With a Fully Digital Bridge
This article describes an automated electronic fully digital bridge for the comparison of four-terminal-pair (4TP) impedance standards in the audio frequency range. The bridge relative accuracy, which is on the order of 10-6, makes it suitable as a reference bridge for the realization of primary scales of inductance and capacitance in metrology institutes and calibration laboratories. The performances of this bridge were validated by comparing the results of the calibrations of inductance and capacitance standards with those obtained from an existing analog reference system based on the three-voltage method. The article also reports the results of this validation
A Capacitance Build-Up Method to Determine LCR Meter Errors and Capacitance Transfer
We present a capacitance build-up method suitable for the determination of the measurement error of a capacitance meter. The method requires only a small number of uncalibrated base capacitors, to be connected in parallel in various combinations, and a single calibrated capacitor, which provides measurement traceability. The outcome of the method is both the determination of the meter error and the calibration of all the base capacitors; it can therefore be also considered a capacitance scaling method. The method's equations, cast in matrix form, express estimates and uncertainties for all the quantities of interest. As an example of application, a commercial LCR meter is calibrated in the ranges of (100-1000) pF and (1-10) nF at 1.6 and 10 kHz, with an accuracy at the level of a few parts in 10(6). The calibration is validated by comparison with an ultrahigh accuracy capacitance bridge
A fully digital bridge towards the realization of the farad from the quantum Hall effect
This paper presents the implementation of an electronic fully-digital impedance bridge
optimized for RC comparisons with equal impedance magnitudes, together with an evaluation
of the uncertainty. This bridge has been designed with the goal of realizing the farad directly
from the quantum Hall effect with a bridge uncertainty component at the 1E-7 level. Thanks to
its simple design, ease of operation and affordability, this bridge is suitable to be industrially
manufactured. Together with the increasing availability of graphene quantum Hall resistance
standards, this can provide an affordable quantum realization of the unit farad for metrology
institutes and calibration centres.
In this paper we present the uncertainty budget of an example measurement and the results of
the validation of the bridge against a suitably modified version of the traceability chain of the
Italian national standard of capacitance. The combined uncertainty of the bridge resulted from
repeated measurements (overall measurement time of about 200 min) is 9.2 × 10^−8, suitable for
the primary realization of the unit of capacitance from a quantized Hall resistance standard. The
crosstalk among the channels of the electrical generator is the most significant uncertainty
component, possibly reducible with internal shielding and filtering of the electronic generator
Smart Glasses for Visually Evoked Potential Applications: Characterisation of the Optical Output for Different Display Technologies
Off-the-shelf consumer-grade smart glasses are being increasingly used in extended reality and brain–computer interface applications that are based on the detection of visually evoked potentials from the user’s brain. The displays of these kinds of devices can be based on different technologies, which may affect the nature of the visual stimulus received by the user. This aspect has substantial impact in the field of applications based on wearable sensors and devices. We measured the optical output of three models of smart glasses with different display technologies using a photo-transducer in order to gain insight on their exploitability in brain–computer interface applications. The results suggest that preferring a particular model of smart glasses may strongly depend on the specific application requirements
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