Investigation of Superconducting Quantum Interference Readout Electronics based on Self-feedback Differential Low-noise Amplifier

Abstract

Superconducting Quantum Interference Device (SQUID) has been widely applied in various metrology and precision applications, owing to its excellent magnetic sensitivity. The stable and accurate readout circuit is crucial for SQUID applications. In this paper, we designed the self-feedback differential low-noise amplifier (SDLA) and relied on the flux-loop lock (FLL) to construct the direct readout circuit. This weakens feedback current interferences and maintains the balance between SQUID two terminals, which in turn minimizes 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; the voltage white noise of the readout circuit is around 0.65 nV/Hz^1/2. The SQUID characteristics can be measured clearly and the total noise of the readout system remains low.