HIGH-SENSITIVITY DIGITAL SQUID MAGNETOMETERS

A single-chip digital SQUID magnetometer integrates a sensitive analog SQUID sensor with a comparator gate and feedback circuitry an the sam e chip, The comparator gate is an asymmetric SQUID gate driving two DC -to-SFQ converters in series with the feedback coil. In an optimized d igital magnetometer chip, sensitivity and noise level are determined b y the input analog SQUID. The dynamic range of such digital chips is e xtremely wide enabling them to be operated in;a relatively high magnet ic field environment without extensive magnetic shielding, Their slew rate is determined by the frequency of an external two-phase clock. Th is chip simplifies room temperature electronics and, due to its digita l output, sam be easily multiplexed on-chip. In this paper, we describ e this digital SQUID magnetometer chip and summarize our experimental results demonstrating a digital SQUID chip with sensitivity of 20 mu P hi(0)/root Hz and a system slew rate of 5 x 10(6) Phi(0)/s at the pick up coil.