New approach for a highly sensitive magnetometer utilizing a multi-stage digital SQUID

Abstract

Highly sensitive measurement of magnetic fields can be made by analogue SQUIDs with analogue-to-digital conversion in a semiconductor environment. An alternative way is the use of digital SQUIDs consisting of superconducting digital Josephson electronics. Previously we presented a full digital SQUID device based on the bidirectional single flux quantum (SFQ) technique, which featured a very high dynamic range due to intrinsic flux compensation, a high slew rate and low complexity of the superconducting digital electronics. Analogue external feedback circuitry is replaced by the internal digital feedback. The intrinsic digital processing of measured flux makes external analogue-to-digital conversion dispensable. The remaining semiconducting electronics is reduced to a high-speed up–down counter. The whole system will be clocked by a bidirectional bias signal. The achieved tristate operation ensures a serial data output stream in the range of gigabits per second. The proper function of such a single-stage digital SQUID was recently proved by experiments. This concept of flux counting suffers intrinsically from its resolution of one flux quantum, which is not sufficient for the measurement of small magnetic fields. In this paper we present investigations on novel circuit topologies utilizing digital SQUID devices to overcome the restrictions in flux resolution without losing the dynamics advantages of a full digital SQUID device.

Superconductive Digital Magnetometers with Single-Flux-Quantum Electronics

“…Also several solutions can be investigated to increase the sensitivity. The first one consists of designing a more sophisticated SFQ digitization circuit, at the price of a higher complexity [37]. Nevertheless this complexity is compatible with the state-of-the-art of SFQ technology for low-Tc superconductors.…”