[SI-LIST] Re: Bypassing on Passive Backplane
- From: Istvan Novak <istvan.novak@xxxxxxx>
- To: Joel Brown <joel@xxxxxxxxxx>
- Date: Wed, 09 Sep 2009 20:11:12 -0400
Hi Joel,
As it was said, 'it depends', but let me give you a few generic
considerations that may help you.
If by passive backplane you mean you dont even need to assign plane
layers for carrying power,
a useful thing you can do is stitch together your ground layers with
vias as frequently as
conveniently you can. If you need to allocate plane layers to carry
power and you have to go through
the power-ground plane cavities with sensitive signals, you need to go
through the usual bypass
exercise because the signal vias can both excite the planes and can pick
up noise from the planes.
If your geometry allows you to physically separate the power
distribution and high-speed signaling
(for instance by putting power shapes into areas where no signal via
goes through them and you
also make sure that there is no horizontal coupling mechanism to link
your planes to areas where
signal vias exist), you are then lucky and dont need to worry about
bypassing the backplane.
Regards,
Istvan Novak
SUN Microsystems
Joel Brown wrote:
> Looking for advice, published guidelines, books, etc on PDN for passive
> backplane.
> In the past I was told to always bypass both sides of power connectors with
> bulk and high frequency capacitors to prevent AC currents flowing through
> the connector.
>
> If the plug in cards have sufficient bypassing then why would it be needed
> on the backplane?
>
> Should power planes be bypassed to ground planes on some grid interval?
>
> If high speed signals are always surrounded by ground planes, are the power
> planes free of signal return currents?
>
>
>
> Thanks - Joel
>
>
>
>
>
>
>
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