The dielectric relaxation in capacitors and dielectric material and its effect on VCOs

The linearity of accurate VCOs, sample-and-hold circuits and switched-capacitor circuits is limited by the short-term effects of dielectric relaxation in the applied capacitor. This paper presents a novel and accurate method to measure these short-term effects and discusses the measurement results for standard industrial capacitors, MOS and junction capacitors, parasitic capacitors of assembling materials and coaxial-cable capacitors. It is shown that the dielectric relaxation of a commonly used polycarbonate capacitor causes a non-linearity of 6%0 for a VCO in the frequency range from 1 kHz to 100 kHz. A very large dielectric-relaxation effect has been found for commonly used epoxy printed-circuit boards. This means that special care has to be taken when this material is applied in accurate VCOs