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 oth er processing circuits, the accuracy is directly limited by the perfor mance of the integrating element: the capacitor, An important nonideal ity of the capacitors concerns the short-term effects of dielectric ab sorption, This paper presents an accurate method to measure these shor t-term effects and discusses the measurement results for standard indu strial capacitors, MOS and junction capacitors, parasitic capacitors o f assembling materials and coaxial-cable capacitors. The special preca utions to be taken to obtain the required accuracy for very short meas urement times are also discussed. It is shown that the dielectric abso rption of a commonly used polycarbonate capacitor causes a nonlinearit y of 0.6% for a VCO in the frequency range from 1 kHz to 100 kHz. A ve ry 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 VCO's.