Implementation of Interface Circuit for Digital SQUID with Sub-Flux Quantum Feedback Resolution

Abstract

Digital SQUIDs with single flux quantum (SFQ) feedback have attracted much attention because of the feasibility of realizing a wide dynamic range and high slew rate for digital magnetometers. To achieve a higher resolution, we studied a digital SQUID with sub-flux quantum feedback. We studied implementation methods for an interface circuit by considering the circuit size, power consumption and signal processing to achieve high-resolution and highspeed operation of the digital SQUID magnetometer. Assuming the decimation filter and the up/down counter implemented on a FPGA board, a 1-bit to 16-bit deserializer with an output frequency of 500 MHz could be used for the interface circuit. The circuit scale was 1940 µm × 1720 µm, and the bias current was 302 mA. From the simulation results, a sufficient wide bias margin could be obtained up to 30 GHz.