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

  • From: steve weir <weirsp@xxxxxxxxxx>
  • To: lenaw@xxxxxxxxx, <istvan.novak@xxxxxxxxxxxxxxxx>,"Chris Cheng" <Chris.Cheng@xxxxxxxxxxxx>, <si-list@xxxxxxxxxxxxx>
  • Date: Wed, 11 Feb 2004 20:32:44 -0800

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
> >
> >
> > ------------------------------------------------------------------
> > To unsubscribe from si-list:
> > si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field
> >
> > or to administer your membership from a web page, go to:
> > //www.freelists.org/webpage/si-list
> >
> > For help:
> > si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field
> >
> > List technical documents are available at:
> >                 http://www.si-list.org
> >
> > List archives are viewable at:
> > //www.freelists.org/archives/si-list
> > or at our remote archives:
> > http://groups.yahoo.com/group/si-list/messages
> > Old (prior to June 6, 2001) list archives are viewable at:
> >   http://www.qsl.net/wb6tpu
> >
>
>------------------------------------------------------------------
>To unsubscribe from si-list:
>si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field
>
>or to administer your membership from a web page, go to:
>//www.freelists.org/webpage/si-list
>
>For help:
>si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field
>
>List technical documents are available at:
>                 http://www.si-list.org
>
>List archives are viewable at:
>                 //www.freelists.org/archives/si-list
>or at our remote archives:
>                 http://groups.yahoo.com/group/si-list/messages
>Old (prior to June 6, 2001) list archives are viewable at:
>                 http://www.qsl.net/wb6tpu
>


------------------------------------------------------------------
To unsubscribe from si-list:
si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field

or to administer your membership from a web page, go to:
//www.freelists.org/webpage/si-list

For help:
si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field

List technical documents are available at:
                http://www.si-list.org

List archives are viewable at:     
                //www.freelists.org/archives/si-list
or at our remote archives:
                http://groups.yahoo.com/group/si-list/messages
Old (prior to June 6, 2001) list archives are viewable at:
                http://www.qsl.net/wb6tpu

Other related posts:

  1. Home
  2. si-list
  3. Archive
  4. 02-2004