High-Precision DC-Current Source

For applications in the field of high-precision electrical measurements, specially on superconducting circuits, a dc-current source has been developed, which supplies two dc currents with selectable ratios in the range between 10 mA and 5 A. The performance of the instrument relies on the combination of conventional dc-current comparators with low ripple sampling detectors and ironless cryogenic current comparators with a SQUID as zero detector. Thus the current ratio is stabilized to 1 X 10-9 of its value.