Filtering Capacitors
Although capacitor resonance is generally undesirable from the perspective of filtering high-frequency noise, it is not always detrimental. When the target noise frequency is known, the capacitance value can be adjusted so that the resonance point falls precisely on the disturbance frequency. In practical engineering, the frequency of electromagnetic noise that needs to be filtered often reaches several hundred MHz, or even exceeds 1GHz. To effectively suppress such high-frequency electromagnetic noise, feedthrough capacitors must be used.
On the battlefield of electromagnetic compatibility, the filtering capacitor is an indispensable “vanguard.” The prevailing view is that a capacitor’s self-resonant frequency (where its impedance is minimum and filtering performance is optimal) represents its performance limit. This is because once the frequency exceeds this resonance point, the capacitor becomes inductive due to its own parasitic inductance, causing its filtering effectiveness to drop sharply.
However, this resonance is not always harmful. When a strong noise source with a fixed and prominent frequency exists on a circuit board, conventional broadband filtering might be too costly or ineffective. In such cases, an engineer can strategically reverse this principle. By precisely adjusting the capacitance value, they can design a “frequency trap,” intentionally setting the resonance point exactly at this specific disturbance frequency.
In modern electronic devices, the extremely fast switching speeds inside chips generate electromagnetic noise that often reaches several hundred MHz and can easily surpass the 1 GHz threshold. Traditional surface-mount or leaded capacitors are largely ineffective against such high-frequency noise.
It is under these conditions, when confronting extreme high-frequency noise in the range of hundreds of MHz or even above 1 GHz, that only the LCA® feedthrough capacitor maintains its fundamental capacitive nature. It provides a low-impedance path to ground, effectively filtering out this high-frequency electromagnetic noise that ordinary capacitors cannot handle, thus becoming an indispensable “electromagnetic guardian” for high-frequency circuits and shielded enclosures.
