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@ARTICLE{Hong:809116,
      author       = {Hong, Tao and Wang, Hai and Zhang, Yi and Krause,
                      Hans-Joachim and Braginski, Alexander and Xie, Xiaoming and
                      Offenhäusser, Andreas and Jiang, Mianheng},
      title        = {{F}lux modulation scheme for direct current {SQUID} readout
                      revisited},
      journal      = {Applied physics letters},
      volume       = {108},
      number       = {6},
      issn         = {1077-3118},
      address      = {Melville, NY},
      publisher    = {American Inst. of Physics},
      reportid     = {FZJ-2016-02506},
      pages        = {062601 -},
      year         = {2016},
      abstract     = {The flux modulation scheme (FMS) is the standard readout
                      technique of dc SQUIDs, where a step-up transformer links
                      the SQUID to the preamplifier. The transformer's primary
                      winding shunts the SQUID via a large capacitor while the
                      secondary winding connects it to the preamplifier. A
                      modulation flux having a frequency of typically 100 kHz
                      generates an ac voltage across the SQUID, stepped up by the
                      transformer. The SQUID with FMS is customarily operated in
                      the current bias mode, because a constant dc bias current
                      flows only through the SQUID due to the capacitor isolation.
                      With FMS, however, the transformer ac shunts the SQUID so
                      that in reality the operating mode is neither purely
                      current-biased nor voltage-biased but rather nominal
                      current-biased or “mixed biased.” Our objective is to
                      experimentally investigate the consequences of ac shunting
                      of the dc SQUID in FMS and the transformer's transfer
                      characteristics. For different shunt values we measure the
                      change in the SQUID bias current due to the ac shunt using
                      another SQUID in the two-stage readout scheme, and
                      simultaneously monitor the SQUID output voltage signal. We
                      then explain our measurements by a simplified graphic
                      analysis of SQUID intrinsic current-voltage (I–V)
                      characteristics. Since the total current flowing through the
                      SQUID is not constant due to the shunting effect of the
                      transformer, the amplitude of SQUID flux-to-voltage
                      characteristics V(Φ) is less as compared to the direct
                      readout scheme (DRS). Furthermore, we analyze and compare
                      V(Φ) obtained by DRS and FMS. We show that in FMS, the
                      transfer characteristics of the SQUID circuit also depend on
                      the isolation capacitance and the dynamic resistance of the
                      SQUID.},
      cin          = {PGI-8 / ICS-8 / JARA-FIT},
      ddc          = {530},
      cid          = {I:(DE-Juel1)PGI-8-20110106 / I:(DE-Juel1)ICS-8-20110106 /
                      $I:(DE-82)080009_20140620$},
      pnm          = {523 - Controlling Configuration-Based Phenomena (POF3-523)},
      pid          = {G:(DE-HGF)POF3-523},
      typ          = {PUB:(DE-HGF)16},
      UT           = {WOS:000373056300029},
      doi          = {10.1063/1.4941665},
      url          = {https://juser.fz-juelich.de/record/809116},
}