ИСТИНА

The DC SQUID is used in a variety of applications fabricated on low-temperature superconductors (LTS) and tunnel Josephson junctions, which have become a workhorse of modern superconducting electronics. Qualitative understanding of LTS SQUID or SQUID-based structure response can be based on the analytical approach, assuming zero SQUID inductance. However, for quantitative estimation of designed LTS circuit characteristics, accounting for a certain real value of the inductance is inevitable. Despite the fact that half a century is gone since the year of the first demonstration of quantum interference between two Josephson junctions connected in parallel by superconducting inductance, a shape of DC SQUID response still was not found analytically for practical parameters of the device at low temperature (T ~ 4.2 K). Thus, practical circuit optimization is always performed in the context of numerical analysis, which slows down the design process. We present analytical description of voltage and current responses of LTS DC SQUID with overdamped Josephson junctions. For simplicity, we neglect the junction capacitance and the noise effect. While for resistive state the responses are found for normalized SQUID inductance up to l ~ 7, the current response for superconducting state is found for arbitrary value of the inductance. The impact of small technological spread of parameters relevant to LTS technology was considered, using a generalization of the developed analytical approach, for the case of a small difference (± 20%) of critical currents and shunt resistances of the Josephson junctions, and arbitrary inequality of SQUID inductive shoulders. The developed analytical approach was applied for linearization of DC SQUID-based structures voltage response.