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.