The dielectric of the feedthrough capacitor it is a ceramic medium, and the capacity of the ceramic capacitor will change with the change of the ambient temperature. This capacity change will affect the filter cut-off rate of the filter. The capacity temperature change rate of ceramic capacitors is determined by the ceramic medium itself. Therefore,the dielectric of the feedthrough capacitor it is very important to choose an appropriate ceramic medium. The capacitor used in the filter is generally a ceramic capacitor. Because of its physical structure, this ceramic capacitor is also called a through-core capacitor.
The common ceramic medium and its capacity temperature change rate are as follows:
Filter inductors generally use ferrite materials, which can be easily combined with through-core capacitors to form a composite filter. In high-performance filters, wire-wound inductors are also used. However, it should be noted that the ferrite material will be magnetically saturated under high current, which will reduce the efficiency of the filter.
The self-inductance of the feedthrough capacitor is much smaller than that of the ordinary capacitor, so the self-resonant frequency is very high. At the same time, the through-core design also effectively prevents high-frequency signals from being directly coupled from the input to the output. This combination of low pass and high resistance provides excellent suppression in the 1GHz frequency range. The simplest through-core structure is one (C type) or two capacitors (Pi type) composed of inner and outer electrodes and ceramics.