Noise-optimized ultrastable low-noise current amplifier.

C Krause,D Drung,M Götz,H Scherer

doi:10.1063/1.5078572

Abstract

We have developed a noise-optimized ultrastable low-noise current amplifier (ULCA) aimed at reducing the uncertainty at low currents. It involves a thin-film resistor network with 6.75 GΩ at the high-ohmic path which reduces the noise level to 1.6 fA/Hz. Noise investigations as well as short-term and long-term stability studies were carried out. The stability of the input current gain was measured using a cryogenic current comparator at ±6.1 nA. Methods for investigating the measurement accuracy at low input currents of about 100 pA at a level of below one part in 107 are introduced and experimentally verified. The performance of the noise-optimized ULCA is compared with that of the standard variant introduced in 2014. It is shown that the reduced noise floor is achieved without impairing the stability of the transresistance.

Highlights

In various fields of research and industry, for example in dosimetry, the interest in the metrology of electric currents in the femtoampere to nanoampere range is increasing.1 pushing the sensitivity and accuracy limits of related small-current instrumentation is highly relevant
The uncertainty budget of the calibration assumes a uniformly distributed error flux of ±0.5 μΦ0, where Φ0 is the flux quantum.18. This value was deduced from the nonlinearity measurements in Ref. 16 and implies an error current within about ±350 aA for the 16 000 turns of the cryogenic current comparator (CCC) winding connected to the ultrastable low-noise current amplifier (ULCA) input
A noise-optimized ULCA was compared to the standard variant

Summary

INTRODUCTION

In various fields of research and industry, for example in dosimetry, the interest in the metrology of electric currents in the femtoampere to nanoampere range is increasing. pushing the sensitivity and accuracy limits of related small-current instrumentation (meters and sources) is highly relevant. Until 2014, achieving such a low current measurement uncertainty was not possible, neither with commercial equipment nor with special metrological setups.4,5 This lack gave rise to a new type of small-current meter, the ultrastable low-noise current amplifier (ULCA).. This lack gave rise to a new type of small-current meter, the ultrastable low-noise current amplifier (ULCA).6,7 This instrument enables the highest current measurement performance, and is very versatile and allows the generation of small currents with high accuracy. The ULCA demonstrated its performance in several low-current applications It enabled the measurement of SEP generated currents of about 100 pA with uncertainties down to 0.16 μA/A9 (all uncertainties quoted in this paper are standard uncertainties, with coverage factor k = 1).

NOISE OPTIMIZATION

CCC-BASED STABILITY EVALUATION

LOW-CURRENT PERFORMANCE

CONCLUSION