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Suppose I want to suppress the noise at around 100Mhz on a signal line. I can do that using a EMI filter capacitor or a ferrite bead. The frequency characteristics for both show suppression of noise at around 100 Mhz:

enter image description here

Left fig.: EMI capacitor
Right fig.: Ferrite bead

If I want to combine these two to have more attenuation, how does putting them in series change the frequency characteristics? Can I expect higher suppression of 100 MHz noise?

Should ferrite bead follow capacitor or other way round or doesn't matter?

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  • \$\begingroup\$ Don't do this, you won't get what you want. \$\endgroup\$
    – Matt Young
    Sep 30, 2015 at 16:25

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As Matt said in the comment, don't do this. Together, they form an LC circuit, with resonance at a frequency other than 100MHz. Beside that, the bead is suitable for power lines, and the NFM41 (A ceramic filter, not actually a cap) is suitable for 50Ohm transmission lines.

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  • \$\begingroup\$ Is there a way to estimate how does the new frequency characteristics look like? If I have to choose ferrite vs capacitor filter, which would be better in my case? \$\endgroup\$
    – zud
    Oct 1, 2015 at 10:03
  • \$\begingroup\$ Do you need to filter a power line or a 50 Ohm transmission line? It is that simple to choose. \$\endgroup\$
    – Lior Bilia
    Oct 1, 2015 at 21:27

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