Investigation of Superconducting Quantum Interference Readout Electronics Based on Self-Feedback Differential Low-Noise Amplifier

Superconducting quantum interference device (SQUID) has been widely used in various metrological and high-precision-demanding applications, owing to its excellent magnetic flux resolution. Nevertheless, the SQUID with nonlinear flux-to-voltage characteristics makes the stable and accurate readout circuit crucial for applications. In this paper, we design a self-feedback differential low-noise amplifier (SDLA) which relies on the flux-loop lock (FLL) to construct the direct readout circuit. This weakens the feedback current and maintains the balance between two-terminals SQUID, thus minimizing the influence of wire resistors. The SDLA is composed of matched transistors and two amplifiers that maintain stable amplification performance and low noise performance through current feedback. In a series of experiments, the feedback current is reduced to the pA level, minimizing wire resistor influences. And, the white input voltage noise of the readout circuit is around 0.65 nV/Hz^1/2.