Ultrastable low-noise current amplifier: a novel device for measuring small electric currents with high accuracy

Area of Science:

• Electrical Metrology
• Instrumentation Science

Background:

• Accurate measurement of small electrical currents is crucial for various scientific and technological applications.
• Existing instruments may face limitations in stability, noise performance, or temperature dependence.

Purpose of the Study:

• To develop and characterize an ultrastable low-noise current amplifier (ULCA).
• To provide a non-cryogenic instrument for precise current amplification and conversion.
• To establish traceability for current measurements to fundamental standards.

Main Methods:

• Design of a two-stage amplifier using specialized operational amplifiers and resistor networks.
• Implementation of current-to-voltage conversion with internal or external reference resistors.
• Calibration using a cryogenic current comparator for traceability to the quantum Hall effect.

Main Results:

• The ULCA demonstrates high stability in its transfer coefficient across time, temperature, and current amplitude (±5 nA).
• Achieved a low noise level of 2.4 fA/√Hz, enabling efficient averaging for small currents.
• Transresistance uncertainty of approximately 0.1 ppm within one week post-calibration, with a long-term drift of 5 ppm/yr.

Conclusions:

• The developed ULCA is a highly stable and low-noise instrument suitable for precise current measurements.
• The instrument facilitates traceable generation of small currents and calibration of high-ohmic resistors.
• A high-accuracy variant offers improved gain stability at a slightly increased noise level.