[SI-LIST] Re: DC-blocking transmission-line

  • From: Terry Fox <tfox@xxxxxxxxx>
  • To: "Grasso, Charles" <Charles.Grasso@xxxxxxxxxxxx>, <tfox@xxxxxxxxx>, <si-list@xxxxxxxxxxxxx>
  • Date: Mon, 02 Jul 2007 16:09:25 -0700

Charles,

The simulation was made with both differential signal traces on the top 
layer of the PCB.

There was 0.5 oz solder mask (Er of 3.3) on top of a
0.5 oz copper trace that was 5 mills wide.
3 mills of dielectric Er 4.3 loss tangent 0.02
1 oz solid plane.

The two pictures showed a trace to trace separation of  1 mills ... ie 1X 
trace to plane distance and 30 mills ... ie 10X trace to plane distance.

In both cases the traces were 5 mills wide and 3 mills above the ground plane.


TFox

  At 03:43 PM 7/2/2007, Grasso, Charles wrote:

>Terry - A quick check shows that your results were derived using a
>microstrip cross section with no mask coating. Is that correct?
>
>Best Regards
>Charles Grasso
>Compliance Engineer
>Echostar Communications Corp.
>Tel: 303-706-5467
>Fax: 303-799-6222
>Cell: 303-204-2974
>Pager/Short Message: 3032042974@xxxxxxxxx
>Email: charles.grasso@xxxxxxxxxxxx
>
>-----Original Message-----
>From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx]
>On Behalf Of Terry Fox
>Sent: Monday, July 02, 2007 4:17 PM
>To: si-list@xxxxxxxxxxxxx
>Subject: [SI-LIST] Re: DC-blocking transmission-line
>
>Aubrey, Ron,
>
>I always appreciate learning something through the experience of others
>rather than having to get it the hard way.
>
>I suspect there is a certain amount of conflict in our terminology.
>
>I placed a short explanation about what I was talking about on
>http://www.siemc.com/SI_List.htm
>
>The link has a schematic and two simulation examples.  One example is
>very
>close trace to trace spacing, the other has very wide trace to trace
>spacing.  In both cases the traces are 20 inches long using a PCI
>Express
>driver.
>
>The difference between the two is about 10% in eye opening.
>
>I am happy to do more simulations to illustrate your points, I just want
>a
>common picture from which we can all work.
>
>TFox
>
>   At 12:22 PM 6/28/2007, Aubrey_Sparkman@xxxxxxxx wrote:
>
> >I don't believe in public stoning....
> >
> >What you have said is pretty much true for the special case where the
> >two 50 Ohm traces are far enough appart to have negligible coupling.
> >Take a look at cases where there is significant coupling.  For
>instance,
> >make a 100 Ohm diff pair from two 60 Ohm traces.  Let me know...
> >
> >
> >Aubrey Sparkman
> >Enterprise Engineering Signal Integrity Team
> >Dell, Inc.
> >Aubrey_Sparkman@xxxxxxxx
> >(512) 723-3592
> >
> >The Greatest Pleasure in Life is Doing what People say can't be done...
> >
> >-----Original Message-----
> >From: si-list-bounce@xxxxxxxxxxxxx
>[mailto:si-list-bounce@xxxxxxxxxxxxx]
> >On Behalf Of Terry Fox
> >Sent: Thursday, June 28, 2007 12:29 PM
> >To: gkorony@xxxxxxxxx; Si-List
> >Subject: [SI-LIST] Re: DC-blocking transmission-line
> >
> >At risk of being stoned...the "differential impedance" has very little
> >to do with anything.
> >
> >The key issues is the impedance of the individual lines to their
> >reference.
> >
> >The number "differential impedance" comes from 2 X Z0 which is the
> >characteristic impedance of each of the individual lines.
> >
> >If these lines are balanced mirror images, the current through each of
> >the two Z0 50 ohm resistors cancels and there is no net current out the
> >reference...hence you can use a single 100ohm resistor rather than two
> >50 ohm resistors.
> >
> >The out fall of this is that everyone thinks differential imp[edance is
> >some magical thing.
> >
> >In my experience it is not.
> >
> >He has touched the holy thing...let us now begin the stoning.
> >
> >TFox
> >
> >At 07:59 AM 6/28/2007, George Korony wrote:
> >
> > >Content-Type: multipart/alternative;
> > >         boundary="----=_NextPart_002_0008_01C7B973.5B78CED0"
> > >
> > >------=_NextPart_002_0008_01C7B973.5B78CED0
> > >Content-Type: text/plain;
> > >         charset="iso-8859-1"
> > >Content-Transfer-Encoding: 7bit
> > >
> > >BlankHi All,
> > >I am not a board designer, but I do design parts that other people
>put
> > >on boards. We are working on a new  (patent protected) concept: the "
> > >DC-blocking transmission-line".
> > >Basically the idea is to build a pair of capacitors that can be
> > >intercalated on the differential signal traces, having a controlled
> > >characteristic impedance between the two capacitors, the obvious
>scope
> > >is to reduce the reflections that may show up due the DC-blocking
> >capacitors.
> > >One request, we have, is that the characteristic impedance between
>the
> > >two capacitors (treated as a simple transmission line) should be 100
> >Ohm.
> > >Of course things are not so simple; and my question is: does anyone
> > >have a different approach to this problem?
> > >Thanks for any suggestion, George.
> > >
> > >
> > >
> > >
> > >
> > >------=_NextPart_002_0008_01C7B973.5B78CED0
> > >Content-Type: text/html;
> > >         charset="iso-8859-1"
> > >Content-Transfer-Encoding: quoted-printable
> > >
> > ><!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN"> Hi
>All,
> > >I am not a board designer, but I = do design=20 parts that other
>people
> >
> > >put on boards. We are working on = a new =20 (patent protected)
> >concept:
> > >the " DC-blocking = transmission-line".
> > >Basically the idea is to build a = pair of=20 capacitors that can be
> > >intercalated on the differential signal = traces,=20 having a
> > >controlled characteristic impedance between the two capacitors, =
> > >the=20 obvious scope is to reduce the reflections that may show up
>due
> > >the = DC-blocking capacitors.
> > >One request, we have, is that the=20 characteristic impedance between
> > >the two capacitors (treated as a simple = transmission line) should
>be
> >100 Ohm.
> > >Of course things are not so = simple; and my=20 question is: does
> > >anyone have a different approach to this = problem?
> > >Thanks for any suggestion,=20 George.
> > >
> > >
> > >
> > >
> > >------=_NextPart_002_0008_01C7B973.5B78CED0--
> > >
> > >
> > >-- Binary/unsupported file stripped by Ecartis --
> > >-- Type: image/gif
> > >-- File: Blank Bkgrd.gif
> > >
> > >
> > >
> > >-- Binary/unsupported file stripped by Ecartis --
> > >-- Type: text/x-vcard
> > >-- File: George Korony.vcf
> > >
> > >
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