Terry - A quick check shows that your results were derived using a microstrip cross section with no mask coating. Is that correct?=20 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=20 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=20 http://www.siemc.com/SI_List.htm The link has a schematic and two simulation examples. One example is very=20 close trace to trace spacing, the other has very wide trace to trace=20 spacing. In both cases the traces are 20 inches long using a PCI Express=20 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=20 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=3D"----=3D_NextPart_002_0008_01C7B973.5B78CED0" > > > >------=3D_NextPart_002_0008_01C7B973.5B78CED0 > >Content-Type: text/plain; > > charset=3D"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. > > > > > > > > > > > >------=3D_NextPart_002_0008_01C7B973.5B78CED0 > >Content-Type: text/html; > > charset=3D"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 =3D do design=3D20 parts that other people > > >put on boards. We are working on =3D a new =3D20 (patent protected) >concept: > >the " DC-blocking =3D transmission-line". > >Basically the idea is to build a =3D pair of=3D20 capacitors that can = be > >intercalated on the differential signal =3D traces,=3D20 having a > >controlled characteristic impedance between the two capacitors, =3D > >the=3D20 obvious scope is to reduce the reflections that may show up due > >the =3D DC-blocking capacitors. > >One request, we have, is that the=3D20 characteristic impedance = between > >the two capacitors (treated as a simple =3D transmission line) should be >100 Ohm. > >Of course things are not so =3D simple; and my=3D20 question is: does > >anyone have a different approach to this =3D problem? > >Thanks for any suggestion,=3D20 George. > > > > > > > > > >------=3D_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 > > > > > >------------------------------------------------------------------ > >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.net > > > >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.net > >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.net List archives are viewable at: =20 //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 =20 ------------------------------------------------------------------ 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.net 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