Programmable capacitors developed at NIST

NIST has produced several digitally programmable capacitance standards based on a modification of a fixed commercial fused-silica capacitance standard. The commercial device consists of 23 capacitors of roughly binary values that have been configured to combine via computer control to produce any capacitance value in the range from about 0.1 fF to 110 pF, with sub-femtofarad resolution. Upon placing the device in a custom enclosure inside an air bath, the shortterm capacitance stability achieved using a commercial capacitance bridge is approximately 5.0×10⁸ pF over the full capacitance range.