Joint Research Laboratory on Superconductivity and Bioelectronics

Shanghai, China

Joint Research Laboratory on Superconductivity and Bioelectronics

Shanghai, China
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Zhang G.,CAS Shanghai Institute of Microsystem and Information Technology | Zhang G.,Joint Research Laboratory on Superconductivity and Bioelectronics | Zhang Y.,Jülich Research Center | Zhang Y.,Joint Research Laboratory on Superconductivity and Bioelectronics | And 10 more authors.
Physica C: Superconductivity and its Applications | Year: 2015

In order to set up a liquid helium-cooled practical dc SQUID system with acceptable noise figure, we employ a weakly damped dc SQUID with a large flux-to-voltage transfer coefficient ∂V/∂F{cyrillic} in a direct readout scheme (DRS) without flux modulation. Two preamplifiers are utilized: (1) AD 797 for a so-called "single chip readout electronics" (SCRE); (2) 6 parallel-connected bipolar transistors (PCBT). The latter reduces the preamplifier voltage noise V n but increases its current noise I n, which plays a leading role in the system low-frequency noise. We introduce a current feedback circuit (CFC) consisting of an inductor L i coupled to the SQUID with mutual inductance M i to improve the noise performance. In this work, the preamplifier I n contribution and CFC are analyzed. To evaluate the I n suppression with CFC, two criteria are presented. Furthermore, we establish a dimensionless parameter ξ to describe CFC quantitatively. The system noise is compared with and without CFC using the two preamplifiers. For a dc SQUID with a loop inductance of 350pH, an intrinsic noise of about 5μF{cyrillic}0/√Hz and a corner frequency at 2Hz are measured using PCBT with CFC. © 2015 Elsevier B.V.


Zeng J.,CAS Shanghai Institute of Microsystem and Information Technology | Zeng J.,Jülich Research Center | Zeng J.,Joint Research Laboratory on Superconductivity and Bioelectronics | Zeng J.,University of Chinese Academy of Sciences | And 17 more authors.
Applied Physics Letters | Year: 2013

We experimentally studied weakly damped superconducting quantum interference devices (SQUIDs) shunted by an external resistor Rs and operated in either current- or voltage-bias mode. The SQUID parameters, such as the flux-to-voltage transfer coefficient ∂V/∂Φ and the dynamic resistance Rd, are reduced due to Rs, while the SQUID intrinsic noise remains unchanged. The reduced parameters can be enhanced again by using voltage feedback circuitry. Furthermore, Rs can be used to damp the SQUID in order to avoid the appearance of hysteresis or oscillation in SQUID characteristics. SQUID shunted by small Rs is always operated in mixed-bias mode. © 2013 AIP Publishing LLC.


Zhang G.-F.,CAS Shanghai Institute of Microsystem and Information Technology | Zhang G.-F.,Jülich Research Center | Zhang G.-F.,Joint Research Laboratory on Superconductivity and Bioelectronics | Zhang Y.,Jülich Research Center | And 9 more authors.
Chinese Physics Letters | Year: 2013

The voltage biased (SQUID) bootstrap circuit (SBC) was recently introduced as an effective means to reduce the preamplifier noise contribution. We analyze the tolerances of the SBC noise suppression performance to spreads in SQUID and SBC circuit parameters. It is found that the tolerance to spread mainly caused by the integrated circuit fabrication process could be extended by a one-time adjustable current feedback. A helium-cooled niobium SQUID with a loop inductance of 350 pH is employed to experimentally verify the analysis. From this work, design criteria for fully integrated SBC devices with a high yield can be derived. © 2013 Chinese Physical Society and IOP Publishing Ltd.


Rong L.,CAS Shanghai Institute of Microsystem and Information Technology | Rong L.,Joint Research Laboratory on Superconductivity and Bioelectronics | Zhang Y.,Jülich Research Center | Zhang Y.,Joint Research Laboratory on Superconductivity and Bioelectronics | And 13 more authors.
Physics Procedia | Year: 2012

Recently, a SQUID direct readout scheme called voltage-biased SQUID Bootstrap Circuit (SBC) is introduced to reduce preamplifier noise contribution. In this paper, we describe a concept of SBC with bias reversal technique which can suppress SQUID intrinsic 1/f noise. When applying a symmetrically rectangular voltage across SBC, two I-Φcharacteristics appear at the amplifier output. In order to return to one I -Φcurve, a demodulation technique is required. Because of the asymmetry of typical SBC I-Φcurve, the demodulation method is realized by using a flux compensation of one half Φ0 flux shift. The output signal is then filtered and returned to one I-Φcurve for ordinary FLL readout. It was found, the reversal frequency fR can be dramatically enhanced when using a preamplifier consisting of two operational amplifiers. A planar Nb SQUID magnetometer with a loop-inductance of 350 pH, fR =50kHz and a second order low pass filter with 10kHz cut off frequency was employed in our experiment. Results prove the feasibility of SBC bias reversal method. Comparative experiment on noise performance will be carried out in further studies. © 2011 Published by Elsevier B.V. Selection and/or peer-review under responsibility of the Guest Editors.


Kong X.,CAS Shanghai Institute of Microsystem and Information Technology | Kong X.,Joint Research Laboratory on Superconductivity and Bioelectronics | Zhang Y.,Joint Research Laboratory on Superconductivity and Bioelectronics | Zhang Y.,Jülich Research Center | And 4 more authors.
IEICE Transactions on Electronics | Year: 2013

The voltage biased SQUID Bootstrap Circuit (SBC) was recently demonstrated for direct readout of SQUID signals. The SBC combines current- and voltage-feedbacks in one circuit to suppress the preamplifier noise. It offers not only a good noise performance, but also wide tolerance of SQUID parameters. Using SBC gradiometer, the bio-magnetic signals were successfully measured. In this paper, we overview the concept of SBC and its applications. Copyright © 2013 The Institute of Electronics, Information and Communication Engineers.


Li H.,CAS Shanghai Institute of Microsystem and Information Technology | Li H.,Joint Research Laboratory on Superconductivity and Bioelectronics | Li H.,University of Chinese Academy of Sciences | Li H.,Jülich Research Center | And 19 more authors.
Chinese Physics B | Year: 2015

SQUID gradiometer techniques are widely used in noise cancellation for biomagnetic measurements. An appropriate gradiometer baseline is very important for the biomagnetic detection with high performance. By placing several magnetometers at different heights along the vertical direction, we could simultaneously obtain the synthetic gradiometers with different baselines. By using the traditional signal-to-noise ratio (SNR) as a performance index, we successfully obtain an optimal baseline for the magnetocardiography (MCG) measurement in a magnetically shielded room (MSR). Finally, we obtain an optimal baseline of 7cm and use it for the practical MCG measurement in our MSR. The SNR about 38dB is obtained in the recorded MCG signal. © 2015 Chinese Physical Society and IOP Publishing Ltd.

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