Dynamic behavior of dc SQUIDs in time-division multiplexing readout schemes
in: Superconductor Science & Technology (2013)
We have investigated the transient response of superconducting quantum interference devices (SQUIDs) used in time-division multiplexing schemes for the readout of arrays of superconducting transition-edge sensors. In time-division multiplexing the per-channel settling time is an important parameter since it limits the multiplexing frequency as well as the signal-to-noise ratio. Albeit SQUIDs in general are fast cryoelectronic devices operating at a picosecond scale, experimental evidence shows that the settling time in bias-switched SQUID multiplexers can, in the case of a low-impedance input circuit, reach several microseconds. We have confirmed this behaviour by numerical transient analysis using a Josephson circuit simulator. Within the simulation we have found that the transient response can be reduced using an extra inductor in series to the input coil of the dc~SQUID. This result in turn has been confirmed experimentally. We furthermore discuss the conflicting constraints a desired high signal bandwidth places on the parameters of the multiplexer, the readout SQUIDs, and the TES.