[SI-LIST] Re: Stack up for EMI reduction, plane resonance and u-strip radiation etc etc

From: steve weir <weirsp@xxxxxxxxxx>
To: "lenaw" <lenaw@xxxxxxxxx>, <istvan.novak@xxxxxxxxxxxxxxxx>,"Chris Cheng" <Chris.Cheng@xxxxxxxxxxxx>, <si-list@xxxxxxxxxxxxx>
Date: Wed, 11 Feb 2004 20:48:59 -0800
MC, it appears that we are talking about different issues.  I was reacting 
to this statement:

  >Istvan:
 > >            On (b) my opinion is that if you want to reduce the
power/ground
 > >bounce, you have to reduce the total effective inductance of the
 > >power/ground planes

It sounds like you are discussing reduction of inductance looking from the 
package I/O out.

Regards,


Steve.
At 10:41 PM 2/11/2004 -0600, lenaw wrote:
>Steve:
>           Please try to locate one of those papers published in IEEE by Dr.
>John Prince and his students from University of Arizona in Tuscon in the
>early 90s related to calculation of effective inductance in SSO simulation.
>In general the effective inductance of a power or ground pin is the sum of
>the partial self inductance of itself minus the sum of all the partial
>mutual inductance of the signal pins that share the common power or ground
>pin. That is why PEEC is wonderful to handle SSO analysis in spice as long
>as you connect the ideal ground node correctly. Correct me if it is not
>right.
>
>Regards,
>MC
>
>----- Original Message -----
>From: "steve weir" <weirsp@xxxxxxxxxx>
>To: <lenaw@xxxxxxxxx>; <istvan.novak@xxxxxxxxxxxxxxxx>; "Chris Cheng"
><Chris.Cheng@xxxxxxxxxxxx>; <si-list@xxxxxxxxxxxxx>
>Sent: Wednesday, February 11, 2004 10:32 PM
>Subject: [SI-LIST] Re: Stack up for EMI reduction, plane resonance and
>u-strip radiation etc etc
>
>
> > MC, how are you going to reduce inductance other than by reducing plane
> > separation?
> >
> > Regards,
> >
> >
> > Steve.
> > At 10:22 PM 2/11/2004 -0600, lenaw wrote:
> > >Istvan:
> > >            On (b) my opinion is that if you want to reduce the
>power/ground
> > >bounce, you have to reduce the total effective inductance of the
> > >power/ground planes ( assume you have no bond wire and use flip-chip
> > >technology to connect the die to the package ) and it depends on what
>kind
> > >of buffer technology you are using, signals on top of a pair of closely
> > >coupled power/ground reference may not be the best solution because you
>need
> > >the strong mutual inductance between the signal and power or ground
>planes
> > >to reduce your total effective inductance during SSO. Just my 2cents.
> > >
> > >
> > >Regards,
> > >MC
> > >
> > >----- Original Message -----
> > >From: "Istvan NOVAK" <istvan.novak@xxxxxxxxxxxxxxxx>
> > >To: "Chris Cheng" <Chris.Cheng@xxxxxxxxxxxx>; <si-list@xxxxxxxxxxxxx>
> > >Sent: Wednesday, February 11, 2004 9:59 PM
> > >Subject: [SI-LIST] Re: Stack up for EMI reduction, plane resonance and
> > >u-strip radiation etc etc
> > >
> > >
> > > > Chris,
> > > >
> > > > > a) If your plane reference is so limited and crowed with highspeed
> > >traces
> > > > > that it can not provide the effective capacitance, it will exhibit
> > >itself
> > > > as
> > > > > both xtalk and power/gnd bounce problem. The image current starts to
> > > > overlap
> > > > > each other and either add or subtract from each other. This is an
> > > > observable
> > > > > problem in most signal traces in organic packages. But I will turn
>the
> > > > table
> > > > > around and ask you, how could your fancy capacitor or thin core
>plane
> > >help
> > > > > if they are electrically further from the reference planes ? It's
>like
> > > > > challenging my Covertte saying "hey, I bet you can't drive this car
>at
> > > > > 300mph" while you are sitting on a pintle.
> > > >
> > > > So I think we are in agreement here that if trace density is
>increases,
> > > > beyond
> > > > a certain point we will have power/ground bounce issues on the planes.
> > > > You are correct that crosstalk among traces will probably go up at
> > > > a similar rate, but it is a matter of system design, which will pose a
> > > > limitation first.
> > > > If you hit the power/ground bounce limit first, and crosstalk is still
>not
> > > > harmful,
> > > > a thinner power/ground laminate may help to reduce power/ground
>bounce.
> > > > If in the new stackup you still reference the same power plane, what
>has
> > > > changed is that the traces will be 'outside' of the power/ground
>cavity,
> > >not
> > > > inside as before.  In this case only the ground reference plane for
>the
> > > > traces is
> > > > what is further away from the power/ground plane pair.  If the
>components
> > > > on the board force you to have a large number of ground vias anyway,
>you
> > > > can get the sufficiently tight stitching between the ground planes
>without
> > > > extra
> > > > expence.
> > > >
> > > >
> > > > > b) At extreme high edge rate, the skin effect is limiting both the
> > >signal
> > > > > trace and the image current that flows on the reference plane, your
> > > > infinity
> > > > > argument doesn't exist. I can't answer an argument that cannot
>exist.
> > > >
> > > > OK, let me rephrase the question that may be easier to answer.  Say
>you
> > > > have a working board, and you are satisfied with it.  It has a given
> > >number
> > > > of traces referencing the correct plane.  Say the transition times on
> > >those
> > > > traces are all around 1 nsec.  And lets suppose the power/gnd bounce
> > > > is acceptable: not much lower than your target, but safely below your
> > > > limit.  Suppose the only thing you change next is the silicon, and it
>puts
> > > > out
> > > > 200psec transition times instead of 1nsec.  There is no other change
> > > > on the board.
> > > > The 200psec edges are 'slow' enough that within an inch radius we cant
> > > > really
> > > > expect any absorption due to skin effect, and the one inch radius
> > > > approximately
> > > > represents the distance the signals can go within 200psec.  So the
> > > > question is: if you want to maintain about the same level of
>power/ground
> > > > bounce,
> > > > would you change the plane structure; would you put the power/ground
> > >planes
> > > > closer, further apart, or leave them where they are?
> > > >
> > > > Regards,
> > > > Istvan
> > > >
> > > >
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References:
- [SI-LIST] Re: Stack up for EMI reduction, plane resonance and u-strip radiation etc etc
  - From: Chris Cheng
- [SI-LIST] Re: Stack up for EMI reduction, plane resonance and u-strip radiation etc etc
  - From: Istvan NOVAK
- [SI-LIST] Re: Stack up for EMI reduction, plane resonance and u-strip radiation etc etc
  - From: steve weir
- [SI-LIST] Re: Stack up for EMI reduction, plane resonance and u-strip radiation etc etc
  - From: lenaw
[SI-LIST] Re: Stack up for EMI reduction, plane resonance and u-strip radiation etc etc

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