arXiv subjects

Luca Callegaro

Publications and source records attributed to Luca Callegaro.

25 records · Page 2Linked to original sources

arXiv2013

On the synthesis of Quantum Hall Array Resistance Standards

Quantum Hall effect (QHE) is the basis of modern resistance metrology. In Quantum Hall Array Resistance Standards (QHARS), several individual QHE elements, each one having the same QHE resistance (typically half of the von Klitzing constant), are arranged in networks that realize resistance values close to decadic values (such as 1 kiloohm or 100 kiloohm), of direct interest for dissemination. The same decadic value can be approximated with different grades of precision, and even for the same approximation several networks of QHE elements can be conceived. The paper investigates the design of QHARS networks by giving methods to find a proper approximation of the resistance of interest, and to design the corresponding network with a small number of elements. Results for several decadic cases are given.

physics.ins-det↗

arXiv2013

Bridge connection of quantum Hall elementary devices

Multiple-series and multiple-parallel connections of quantum Hall elementary devices allow the realization of multiple or fractional values of the quantized Hall resistance, rejecting the effect of contact and wiring resistances. We introduce here the multiple-bridge connection, which maintains the properties of multiple-series and parallel connections and allows more freedom in the choice of the topology of networks composed of quantum Hall elements, and the design of more efficient quantum Hall array resistance standards (and other devices). As an example, a 5-element network is analyzed in detail.

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arXiv2011

Matrix method analysis of quantum Hall effect device connections

The modelling of electrical connections of single, or several, multiterminal quantum Hall effect (QHE) devices is relevant for electrical metrology: it is known, in fact, that certain particular connections allow i) the realization of multiples or fractions of the quantised resistance, or ii) the rejection of stray impedances, so that the configuration maintains the status of quantum standard. Ricketts-Kemeny and Delahaye equivalent circuits are known to be accurate models of the QHE: however, the numerical or analytical solution of electrical networks including these equivalent circuits can be difficult. In this paper, we introduce a method of analysis based on the representation of a QHE device by means of the \emph{indefinite admittance matrix}: external connections are then represented with another matrix, easily written by inspection. Some examples, including the solution of double- and triple-series connections, are shown.

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arXiv2010

Realization of the farad from the dc quantum Hall effect with digitally-assisted impedance bridges

A new traceability chain for the derivation of the farad from dc quantum Hall effect has been implemented at INRIM. Main components of the chain are two new coaxial transformer bridges: a resistance ratio bridge, and a quadrature bridge, both operating at 1541 Hz. The bridges are energized and controlled with a polyphase direct-digital-synthesizer, which permits to achieve both main and auxiliary equilibria in an automated way; the bridges and do not include any variable inductive divider or variable impedance box. The relative uncertainty in the realization of the farad, at the level of 1000 pF, is estimated to be 64E-9. A first verification of the realization is given by a comparison with the maintained national capacitance standard, where an agreement between measurements within their relative combined uncertainty of 420E-9 is obtained.

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arXiv2009

Systematic errors in the correlation method for Johnson noise thermometry: residual correlations due to amplifiers

Johnson noise thermometers (JNT) measure the equilibrium electrical noise, proportional to thermodynamic temperature, of a sensing resistor. In the correlation method, the same resistor is connected to two amplifiers and a correlation of their outputs is performed, in order to reject amplifiers' noise. Such rejection is not perfect: the residual correlation gives a systematic error in the JNT reading. In order to put an upper limit, or to achieve a correction, for such error, a careful electrical modelling of the amplifiers and connections must be performed. Standard numerical simulation tools are inadequate for such modelling. In literature, evaluations have been performed by the painstaking solving of analytical modelling. We propose an evaluation procedure for the JNT error due to residual correlations which blends analytical and numerical approaches, with the benefits of both: a rigorous and accurate circuit noise modelling, and a fast and flexible evaluation with an user-friendly commercial tool. The method is applied to a simple but very effective ultralow-noise amplifier employed in a working JNT.

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arXiv2009

An absolute Johnson noise thermometer

We developed an absolute Johnson noise thermometer (JNT), an instrument to measure the thermodynamic temperature of a sensing resistor, with traceability to voltage, resistance and frequency quantities. The temperature is measured in energy units, and can be converted to SI units (kelvin) with the accepted value of the Boltzmann constant kb; or, conversely, it can be employed to perform measurements at the triple point of water, and obtain a determination of kb. The thermometer is composed of a correlation spectrum analyzer an a calibrated noise source, both constructed around commercial mixed-signal boards. The calibrator generates a pseudorandom noise, by digital synthesis and amplitude scaling with inductive voltage dividers; the signal spectrum is a frequency comb covering the measurement bandwidth. JNT measurements at room temperature are compatible with those of a standard platinum resistance thermometer within the combined uncertainty of 60 ppm. A path towards future improvements of JNT accuracy is also sketched.

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arXiv2008

Very simple FET amplifier with a voltage noise floor less than 1 nV/sqrt(Hz)

A field-effect transistor (FET) amplifier for small voltage signals is presented. Its design is elementary and the construction can be afforded by anyone. Despite its simplicity, with a voltage noise less than 1 nV/sqrt(Hz), it outperforms commercially available integrated FET amplifiers. The amplifier has a gain flatness better than 1 dB over 1 MHz bandwidth; it can be employed as a front-end for signal analyzers or signal recovery systems.

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