Digital SQUID Sensor Based on SFQ Technique

For high sensitive measurements of small magnetic fields a Digital SQUID is superior to conventional analog SQUIDs in terms of dynamic properties, but recent realizations as single-flux-quantum (SFQ) circuit suffers from high complexity. A new kind of Digital SQUID as a full digital sensor device with the advantage of a small number of Josephson junctions and a large slew rate was developed. The circuit consists of basic SFQ cells and an internal digital feedback loop. The operation with a bidirectional clock signal ensures a decreased effort on superconducting electronics. The SFQ/dc converter and an additional voltage driver provides a processable digital output signal for hybrid systems including semiconductor electronics. The sensor circuit was simulated, optimized and fabricated in niobium technology. From investigation of dynamic properties of the circuit we expect a flux slew rate in the gigahertz range.