Audio Cards for High-Resolution and Economical Electronic Transport Studies

TL;DR

This paper introduces a cost-effective method using commercial audio cards to measure electronic transport properties with high resolution, demonstrating applications in spin-valve nanopillars and GMR devices.

Contribution

It presents novel circuits and techniques leveraging audio cards for high-precision transport measurements, including a lock-in amplifier and digitally-compensated bridge.

Findings

Audio cards achieve spectral purity with >16 effective bits and >110 dB dynamic range.

The basic circuit functions as a digital lock-in amplifier.

Application demonstrated on spin-valve nanopillars with GMR.

Abstract

We report on a technique for determining electronic transport properties using commercially available audio cards. Using a typical 24-bit audio card simultaneously as a sine wave generator and a narrow bandwidth ac voltmeter, we show the spectral purity of the analog-to-digital and digital-to-analog conversion stages, including an effective number of bits greater than 16 and dynamic range better than 110 dB. We present two circuits for transport studies using audio cards: a basic circuit using the analog input to sense the voltage generated across a device due to the signal generated simultaneously by the analog output; and a digitally-compensated bridge to compensate for nonlinear behavior of low impedance devices. The basic circuit also functions as a high performance digital lock-in amplifier. We demonstrate the application of an audio card for studying the transport properties of spin-valve nanopillars, a two-terminal device that exhibits Giant Magnetoresistance (GMR) and whose nominal impedance can be switched between two levels by applied magnetic fields and by currents applied by the audio card.