[SI-LIST] Re: Simulating SI and PI through a "passive" backplane
- From: "Brad Brim" <bradb@xxxxxxxxxxx>
- To: "'steve weir'" <weirsi@xxxxxxxxxx>, "'Cuong P Nguyen'" <cuong@xxxxxxxxxxxxx>
- Date: Tue, 2 Mar 2010 21:23:57 -0800
hi Steve,
You seem to be focusing on AC PI rather than DC IR drop.
I believe you and I would say pretty much the same thing if we both typed
more text, but I beg to differ with your brief text that says referencing to
only one pwr or gnd net will preclude PDN issues.
Whether you are defining a "rail" as a single net or a pair of nets I
disagree. You can have resonances of the pair of nets, one or both of which
you reference your signal to. These resonances couple noise in a more global
sense into the signal from the PDN. Also, since there are other nets this
global coupling implies you will have greatly enhanced signal-to-signal
coupling near resonances. The PDN definitely enters into the picture for PDN
resonances.
Further, your signal may be referenced to a single net but if your have
multi-layer transitions you may not have a clean return path local to the
signal vias. Even if you have return current vias there can be a parasitic
effects and if you pass through another plane you will launch noise into the
PDN as parallel plate modes. If you don't have local return current vias for
every signal via you will connect between planes through non-local vias or
possibly decoupling capacitors. In any case, the PDN is entering into the
picture.
cheers,
-Brad
> -----Original Message-----
> From: si-list-bounce@xxxxxxxxxxxxx
> [mailto:si-list-bounce@xxxxxxxxxxxxx] On Behalf Of steve weir
> Sent: Tuesday, March 02, 2010 9:03 PM
> To: Cuong P Nguyen
> Cc: si-list@xxxxxxxxxxxxx
> Subject: [SI-LIST] Re: Simulating SI and PI through a
> "passive" backplane
>
> Cuong, as with many things: it depends. If any given signal
> references only one rail through the entire channel path,
> then the PDN never enters into the picture. If on the other
> hand signals change or share references between multiple
> power rails, then the PDN performance becomes a big issue,
> biggest near the transitions.
>
> Steve
> Cuong P Nguyen wrote:
> > Content-Type: text/plain;
> > charset="us-ascii"
> > Content-Transfer-Encoding: 7bit
> > Anyone has any comments on simulating crosstalk on high speed diff
> > pairs running through a "passive" backplane?
> >
> > The topology is as follow:
> >
> >
> >
> > 1. The driver resides on board #1.
> >
> > 2. This board connects to a passive backplane with
> only connectors.
> > No other components (incl. decoupling)
> >
> > 3. The receiver is on board #2.
> >
> >
> >
> > My question is really on the effects of the GND and PWR
> planes (on the
> > passive backplane) on the diff pairs and
> >
> > whether or not the crosstalk analysis will be accurately modeled.
> >
> >
> >
> > For Power Integrity Analysis, if the driver is on 1st board and
> > receiver is on 2nd board and there are 2 connectors
> >
> > in between (with many pins inter-connecting the PWR and GND of the
> > back plane to the PWR and GND of the
> >
> > 1st and 2nd board), how will the DC drop analyzed?
> >
> >
> >
> > Thanks for your feedback.
> >
> >
> >
> > ----------------------------
> >
> > Cuong Nguyen
> >
> > <http://www.edadirect.com/> edasmall2
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