Analysis of the 4-junction SQUID
The circuit of the 4-junction superconducting quantum interference device (SQUID), which has two series of Josephson junctions at each side of the SQUID coil, is analyzed. The 4-junction SQUID is considered to have the advantage of a larger voltage modulation depth than that of the normal DC SQUID. The authors have tried to make its behavior clear by computer simulations. It has been found that the 4-junction SQUID has a different mode from that of the normal DC SQUID in its dynamic behavior, which causes hysteresis in the I-V characteristics. It has also been found that a large voltage modulation depth can be realized in spite of large SQUID coil inductance, so that the area of the primary coil can be more than 10 times larger. The noise performance of the 4-junction SQUID is also analyzed, and it is possible that this SQUID has higher sensitivity by virtue of circuit-parameter optimization.<<ETX>>