[SOLVED] Why cant use capacitor instead of Inductor?

[prasguy]

Hi All,

Why can't we use capacitor instead of Inductor or Ferrite bead for shorting the 2 power planes?

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[FvM]

I don't agree to the assumption, that power planes have to be "shorted". But if, ferrite beads can't be exchanged with capacitors. Posting a clear question would help a lot.

 

[prasguy]

Hi,

Thanks for the reply. To be clear, am using ferrite bead for connecting 2 different pwr planes i.e assuming like IC has got various interfaces and connecting those interfaces pwer supply through ferrite bead. Recently, i read or came across somewhere that even capactior can employ there and can be used, but there is few limiation, May i know why and what are the limitations? Hope my query is little clear this time,.

 

[FvM]

Shorting two power plane by ferrite beads means they must have the same voltage. So apparently, you have more than one power plane supplying the same voltage. This may be the case, but you didn't tell why. If there's a reason to keep the planes separated, e.g. an analog digital and ground, you won't want to short them by capacitors.

 

[embeddedlover]

If you are talking about Analog and digital ground shorting, inductor can do the job, this helps in eliminating high frequency signals from one side causing interference on the other side.

If talking about the supply path, there is no point in shorting them if they are not of same voltage...

 

[prasguy]

FvM,

I din't raise the proper question, hence the confusion. To avoid noise coupling, we connect ferrite bead between the planes and yes, it same voltage level but used for different interfaces. Now why can't we use capacitor instead of ferrite bead, bcoz it also serves to avoid noise coupling.

 

[FvM]

I don't see how. Inductors are series connected, capacitors parallel connected when acting as decoupling elements.

 

[kapilp]

why can't we use capacitor instead of ferrite bead, bcoz it also serves to avoid noise coupling.

An inductor is connected in series between points of same potential to 'block' noise. A capacitor is connected between the power point and ground to 'bypass' or 'decouple' noise. If you can appreciate the differences between bypass and block you will understand why a cap cannot be used to connect power planes.

Also a cap connected between points of same potential is practically useless and will only pass ac signals which in case of power supply means noise.

 

[prasguy]

Thanks every1 for their reply -