On alternative traceability chains of impedance units with digital impedance bridges

We discuss the calibration schemes for disseminating the capacitance unit farad from the reference resistance standard. The impedance ratio measurements are performed with a fully digital bridge. High stability and low crosstalk of the involved generators SWG able to perform extreme impedance ratio scaling up to 129:1. We introduce the idea of involving calculable resistance standards, which enable the laboratory to perform realization of the whole capacitance scale from DC QHE with only one DC resistance bridge and one digital bridge. Further, an alternative involvement of a single AC Josephson source is proposed. A practical example is given to demonstrate the discussed traceability chains.