Residual Charge
Charge retention in dielectrics represents a critical performance limitation when capacitors must discharge completely during rapid signal transitions. Dielectric absorption causes a capacitor that has been discharged to gradually recover a portion of its voltage after the discharge circuit is disconnected. This voltage recovery happens because the dielectric material does not release its polarization instantly.
Molecular Mechanism
Dipolar relaxation and molecular polarization processes in the polymer or ceramic material control the rate of charge recovery. When an electric field is applied, the dipoles align, but some do not return to their random states immediately when the field is removed. Teflon and polypropylene exhibit extremely low dielectric absorption, while ceramic and electrolytic materials exhibit much higher values.
Circuit Distortion
Voltage errors resulting from this residual charge affect precision analog circuits like sample-and-hold stages or dual-slope converters. The slow recovery of voltage introduces non-linearity and offset errors that disrupt signal digitization. Engineers must specify low-absorption dielectric materials for these sensitive applications to ensure that the analog voltages settle to their intended values within the required clock cycle.
This becomes especially problematic in high-speed, multi-channel data acquisition systems where the residual charge from a previous measurement can bleed into the subsequent channel reading, creating artificial crosstalk that calibration software cannot easily correct.
