[SI-LIST] Re: Placement of Decoupling Caps
- From: Ray Anderson <raymond.anderson@xxxxxxx>
- To: si-list <si-list@xxxxxxxxxxxxx>
- Date: Thu, 01 Aug 2002 16:56:34 -0700
Suresh-
It is basically a time-delay issue. It takes a finite amount
of time for the charge stored in the capacitor to transit
the PCB to the location of the device sinking the current.
If the decoupling capacitor is too far away it can't
supply the current fast enough to be useful due to
the time delay on the PCB ( C/sqrt(Er) )
-Ray Anderson
Sun Microsystems Inc.
Suresh Sivasubramaniam wrote:
>
> All,
>
> I have read that decoupling capacitors need to be place close to the
> device of interest for two main reasons.
>
> a) to minimize the loop inductance
> and
> b) For efficient energy transfer from the capacitor to the device, it is
> necessary to be "within some fraction of a quarter wavelength."
>
> I am comfortable with a) but do not quite understand b). Would someone
> care to explain the physics behind b) (assuming it is right) or point me
> to some references that can elaborate on this.
>
> Thanks in advance.
>
> Suresh
.
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