Current comparator for both AC and DC ratio measurements with 10- 8-level type-a uncertainty.

Accurate measurements of alternating current (AC) and direct current (DC) ratios are fundamental to electric power metrology. However, conventional current comparators for AC and DC typically rely on distinct technologies-electromagnetic induction for AC and superconducting quantum interference devices for DC. This technological divide leads to a fragmented and complex traceability system. Bridging this gap is critical for developing unified current standards that meet the demands of temperature power technologies.　In this work, we present a compact, room-temperature AC/DC current comparator that integrates a diamond-based magnetometer using nitrogen-vacancy centers. The device achieves a type-A uncertainty at [Formula: see text] level, while the expanded uncertainty is at [Formula: see text]to [Formula: see text]level, for both AC and DC signals and supports a system bandwidth up to [Formula: see text], without the need for cryogenics. It is comparable to the performance of typical AC comparators, and provides a compact and room-temperature operating platform for further performance improvement. This unified, cryogenics-free solution not only enhances precision and versatility but also expands the applicability of the system to DC resistance bridges in quantum electrical standards.