Software-defined lock-in demodulator for low-frequency resistance noise measurements

TL;DR

This paper presents a digital lock-in demodulator that enhances low-frequency resistance noise measurements by reducing 1/f noise, enabling more sensitive detection with real-time capabilities and improved low-frequency noise performance.

Contribution

The authors develop an open-source, software-based lock-in demodulator that surpasses commercial hardware in low-frequency noise performance and supports real-time analysis for resistance noise measurements.

Findings

Reduces voltage power spectral density by about two orders of magnitude.

Enables real-time preview and long acquisition at high sampling rates.

Offers superior low-frequency noise performance compared to commercial lock-in amplifiers.

Abstract

The resolution of low-frequency resistance noise measurements can be increased by amplitude modulation, shifting the spectrum of the resistance fluctuations away from the 1/f noise contributed by measurement instruments. However, commercial lock-in amplifiers used for de-modulating the fluctuations exhibit a problematic 1/f noise contribution, which imposes a hard lower limit on the relative resistance noise that can be detected. We replace the lock-in amplifier hardware by equivalent digital signal processing performed using open-source software and off-the-shelf data acquisition systems. Compared to previous implementations of the lock-in principle, our solution offers real-time preview capabilities and is resource-efficient for long acquisition times at high sampling rates. Importantly, compared to high-end commercial lock-in instruments, our system offers superior low-frequency noise performance with a reduction of the voltage power spectral density by about two orders of magnitude.