An integrated digital SQUID magnetometer with high sensitivity input

A single chip SQUID magnetometer is described that integrates a SQUID-based pre-amplifier with a high sensitivity comparator gate and feedback circuitries on the same chip. The comparator gate is an asymmetric SQUID gate driving two SQUID quantizers in series with the feedback coil. The chip´s sensitivity and noise level are primarily determined by the pre-amplifier SQUID. The pick up coil is in series with the feedback transformer. Since the current in the feedback coil is maintained close to zero, the dynamic range of the chip can be extremely wide and is independent of the SQUID pre-amplifier or comparator architectures. The chip´s slew rate is determined by the bipolar clock biasing the comparator gate. Clocks running in the tens of MHz result in a magnetometer system with slew rate exceeding 10/sup 5/ /spl Phi//sub 0//s (/spl Phi//sub 0/=2.07/spl times/10/sup -7/ Gauss-cm/sup 2/). This chip simplifies room temperature electronics and, due to its digital output, can be easily multiplexed on-chip. A system based on this chip can be operated in a relatively high magnetic field environment without extensive magnetic shielding. The details of the chip as well as preliminary measurement results for the pre-amplifier as well as the digital circuit will be presented.<>