|Título/s:||Towards a quantum sampling system|
|Autor/es:||Iuzzolino, Ricardo; Behr, Ralf; Bierzychudek, Marcos E.; Palafox, Luis|
|Institución:||Instituto Nacional de Tecnología Industrial. INTI-Física y Metrología. Buenos Aires, AR |
Physikalisch-Technische Bundesanstalt. PTB. Braunschweig, DE
|Palabras clave:||Teoría cuántica; Metrología; Voltaje; Voltametría; Instrumentos de medición; Convertidores digital-analógico; Metrología|
| Ver+/- |
Towards a Quantum Sampling System
Ricardo Iuzzolino1, Ralf Behr2, Marcos Bierzychudek1 and Luis Palafox2
1Instituto Nacional de Tecnologı´a Industrial (INTI), Buenos Aires, Argentina
2Physikalisch-Technische Bundesanstalt (PTB), Braunschweig, Germany
Abstract—This summary paper describes the development
of a system based on the Josephson effect, to calibrate and
characterize voltage standards and digital sampling systems.
In particular, this work includes the test of a digital-to-analog
converter as a source to bias the segments of the programmable
Index Terms—Voltage measurement, Josephson effect,
Measurement standards, Analog-digital conversion, Metrology.
Application of Josephson Voltage Standards (JVS) to
reproduce the unit volt is nowadays widely spread within the
National Metrology Institutes. It is also the cornerstone of
modern precision instrumentation due to its unique capabilities
to characterize analog-to-digital converters. The Josephson
effect and its application to the electrical metrology is well
described in the bibliography, see  as an example.
INTI has started in June 2015 to upgrade its Josephson
system to a Programmable Josephson Voltage Standard (PJVS)
and towards a quantum sampling system based on a previous
work . The first step was to test a 1 V programmable
Josephson array modifying the conventional Josephson system
available at INTI. Second a self-made fully programmable
current source has been tested as a bias source for the binary
segments of the Josephson array. Third, a digital sampling
system based on sigma-delta ADC has been verified with AC
and DC voltages.
II. SYSTEM OVERVIEW
The upgrade of the INTI conventional Josephson system to
a 1 V programmable Josephson voltage standard is ongoing.
The first tasks are described in this section.
A. Upgrade of the conventional 1 V Josephson system
The INTI conventional Josephson system has been upgraded
to a 1 V PJVS. To accomplish this, the cryoprobe was slightly
modified as follows: the high frequency filters at the front-end
were bypassed and the connections to the bias sources were
removed to use all the remaining wires to connect the array
segments. Then, the bias sources were replaced by a new
model which can deliver more current. The 70 GHz Gunn
diode oscillator, the phase locked loop and the microwave
attenuator were kept unchanged.
B. Programmable Josephson array configuration
The 1 V programmable array , built at PTB, has 8192
SNS Josephson junctions (JJ) divided into 14 binary segments
in the sequence shown in Fig. 1. Since the cryoprobe of the
conventional JVS system has 8 wires, only 6 bias connections
are available. The voltage across the complete array uses two
additional wires. The chosen configuration allows to perform
the projected tests and is depicted in Fig. 1.
I1 I4 I2 I3 I5 I6
Fig. 1. Arrangement of the array segments sequence. The connections to the
bias source are indicated as I1 to I6. VA and VB indicate the output voltage
C. Programmable current source
The current source is constructed connecting a 50 Ω resistor
in series to the output of a real-time programmable voltage
source, designed for a cryogenic current comparator and
described in . This source can generate DC voltages, square
and triangle waveforms using a commercially available R-2R
DAC with 20-bits resolution, ±5 V dynamic range and a slew
rate of 50 V/µs. On this application the working sampling
frequency is set to 100 kHz with an output amplitude of
±1.2 V. The DAC is controlled by a CPLD running at 66 MHz
clock frequency via an isolated serial communication of 121 ns
III. PRELIMINARY MEASUREMENT RESULTS
Different tests were performed in order to check the
modified system capabilities.
A. Zener comparison
The system was configured to obtain an output voltage of
1.018 V using the segments I1-I2 (7168 JJ, see Fig. 1), biased
manually, and I3-I5 (136 JJ) biased with the DAC. The center
of the step has been checked with a high resolution voltmeter.
Then, using a sequence which includes polarity reversals,
gave a result of:
δ = UZPJV S − UZJV SUZJV S
= 85 nV/V, (1)
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where UZPJV S is the Zener voltage obtained with the
programmable system and UZJV S is the last voltage calibrated
with the conventional system one month before with an
uncertainty of 100 nV/V (k=2).
B. Thermal voltages measurement
In order to characterize the system the thermal voltage has
been measured in both polarities. To do so, segments I1-I4
and I4-I6 were connected in series-opposition. The resulting
voltage was measured using a digital nanovoltmenter. Then,
the bias currents through the segments have been reversed and
the voltage was measured. Table I presents the results for both
THERMAL E.M.F. RESULTS. MEASURED VALUES ARE THE AVERAGE OF
THE NANOVOLTMETER READOUTS.
Polarity Measured Values Standard(nV) deviation (nV)
POL- -29.3 2.3
POL+ -10.5 1.3
Signal transients were measured in order to establish the
frequency limit. The current source was applied to the full
array in order to produce a 2 V peak-to-peak change. The step
transients have been observed and measured using a digital
oscilloscope. A transient of 5 µs was obtained as depicted in
0 1 2 3 4 5 61.5
Fig. 2. Step transient of a square waveform. The settling time is around 5 µs.
D. Sigma-Delta ADC sampling system verification
The sampling system based on a 24-bits sigma-delta ADC
described in  was calibrated with the PJVS for AC and
DC voltages as follows: for AC voltage a square waveform of
100 Hz has been synthesized to obtain the AC correction, δAC .
Then, the amplitude of the square waveform was applied as a
DC voltage and a DC correction, δDC , was calculated with a
standard deviation of 8 µV/V. Finally, an AC/DC calibration
difference was obtained as:
δDC − δDC
= −1.2 µV/V. (2)
This value is in agreement with the results presented in ,
, where the sampling system measured a signal of 1 V peak
voltage at 125 Hz with a combined uncertainty of 4.5 µV/V.
IV. CONCLUSION AND FUTURE TRENDS
The tests presented in this summary have fulfilled our
expectations. The development is ongoing on a two year
schedule. The next step is to add more channels to
the programmable current source in order to use all the
segments which are now connected. These channels will
act synchronously in real-time to obtain different signal
waveforms at different frequencies and amplitudes. Finally,
a new cryoprobe will be constructed in order to use the 14
segments in the array. At the conference we will report the
progress of the work.
The authors would like to thank the MINCyT and BMBF
for financial support of scientist exchanges within the frame of
a two years bilateral cooperation project Voltrace (AL/14/05)
between Germany and Argentina.
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current comparator,” in CPEM 2016 Conf. Digest, July 2016.
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