Cryogenic current comparator bridge with dual SQUID detectors

The cryogenic current comparator (CCC) resistance ratio bridge provides a high accuracy over a wide range of practical resistance values. Its performance is critically dependent on the choice of detector used to achieve a voltage null in the bridge. The necessary combination of low input current and voltage noise is not widely available in commercial instruments. A SQUID is a competitive device as a voltage null detector when matched to the resistors being compared. This paper describes a CCC bridge for resistors in the range 1 Ω to 10 kΩ, as well as quantized Hall resistance plateaux, employing two SQUIDS, one for current balance and one for voltage balance.