Precision computer-controlled decade capacitor

A precision computer-controlled decade capacitor is described that is capable of switching capacitances from 100 pF to 1 /spl mu/F in steps of 100 pF. These capacitances can be realized with a relative uncertainty of better than 1/spl times/10/sup -4/ and repeated selection of a given capacitance can be achieved with a relative uncertainty of the order of 1/spl times/10/sup -6/. To minimize temperature dependence of the capacitances, special ceramic capacitors with temperature coefficients of the order of 1/spl times/10/sup -6/ K and low loss factor are used. The effect of switching impedances is minimized by a four terminal-pair definition of capacitors and quasicoaxial connection. The capacitor can be used for automatic calibrations of capacitance bridges with relative uncertainties in the range of 1/spl times/10/sup -6/ to 1/spl times/10/sup -4/.