Measurement of dielectric absorption of capacitors and analysis of its effects on VCOs

In the integrators applied in A-to-D converters, smart sensors and other processing circuits, the accuracy is directly limited by the performance of the integrating element: the capacitor. An important nonideality of the capacitors concerns the short-term effects of dielectric absorption. This paper presents an 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. The special precautions to be taken to obtain the required accuracy for very short measurement times are also discussed. It is shown that the dielectric absorption of a commonly used polycarbonate capacitor causes a nonlinearity of 0.6% for a VCO in the frequency range from 1 kHz to 100 kHz. A very large dielectric-absorption effect has been found for commonly used epoxy printed-circuit boards, which means that special care has to be taken when this material is applied in accurate VCOs.