[SI-LIST] Re: DC-blocking transmission-line
- From: Terry Fox <tfox@xxxxxxxxx>
- To: <si-list@xxxxxxxxxxxxx>
- Date: Mon, 02 Jul 2007 15:17:22 -0700
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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