Abstract
We have developed a hybrid flux-locked loop (FLL) system that is composed of a digital FLL and an analog FLL. The digital FLL achieves a wide dynamic range with the double-counter method for flux-quanta counting. The analog FLL on the hybrid system achieves a wide bandwidth using a differentiator. The frequency characteristics simulation revealed that the hybrid FLL system behaves like a low-pass filter in the digital part and a high-pass filter in the analog part. We carried out characteristic evaluations and a demonstration of MCG measurement using a prototype hybrid FLL system. It not only achieved great stability against high-frequency magnetic-flux noise but also enabled measurement of high-frequency magnetic-flux signals. This paper discusses the effectiveness of the hybrid FLL system.
