I used one of those really fast TDR pulse generators into one end of both traces. They are a pair. And then using a similarly fast o'scope at the other end and two channels, looked at the results. Note, there are many ways to really screw this up - I've found several. However, you'll have to find your own. ps. It's really fun looking for femtoseconds, and if you squint just right... And so I learned to watch the layout designers and thus came to believe that yes indeed they could do what they claimed to have done. They make my job so much easier - thanks to all the layout designers here. Craig Twardy <ctwardy@xxxxxxxxxx> wrote: Lee and others. Matching the pair length to 1mil works out to about 0.16 psec skew. (if I did the math right (FR4)) How would one measure the design to verify this length matching was achieved?=20 Not sure I could measure this in the lab with the scopes I have. (at least not without spending days calibrating the setup) Perhaps there are other ways to get this resolution. Craig=20 -----Original Message----- From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx] On Behalf Of steve weir Sent: May 31, 2007 3:03 PM To: leeritchey@xxxxxxxxxxxxx Cc: Ravinder.Ajmani@xxxxxxxxxxxxxx; wdowsley@xxxxxxxxx; si-list@xxxxxxxxxxxxx Subject: [SI-LIST] Re: IEEE1394/Ethernet Routing Guidelines Lee, well FREE is the caveat, isn't it?=20 Intuitively ( because I have never tried to run a controlled experiment to prove or disprove this ) I believe there is a match requirement, maybe 50 mils, maybe 25 mils that costs just as much router time as whatever the tool resolution is.=20 Best Regards, Steve. Lee Ritchey wrote: > Ay! But ultra tight matching is not free. It requires hand routing=20 > and that takes time, which always costs money. If the matching spec=20 > is done right, the autorouter can do the job and that does save time. > > > =20 >> [Original Message] >> From: steve weir >> To: >> Cc: Ravinder.Ajmani@xxxxxxxxxxxxxx ; >> =20 > ; > =20 >> Date: 5/31/2007 10:25:11 AM >> Subject: [SI-LIST] Re: IEEE1394/Ethernet Routing Guidelines >> >> Lee, Ravinder, et-al, >> >> Sure you can't get anything remotely close to 1mil matched true=20 >> electrical length on the PCB itself, never mind what the package does. >> The variations in eR over the signal path see to that. But telling=20 >> the tool to effectively exactly match the physical length, simply=20 >> reduces an additional error term. At least on paper that is a good=20 >> thing, IF it is free. From the standpoint of entering constraints in >> the tool it might seem to be. But there are some potential hidden=20 >> gotcha's, like the coupling between adjacent segments of meanders,=20 >> and excessive real-estate for meanders. >> >> Best Regards, >> >> >> >> Steve. >> >> >> Lee Ritchey wrote: >> =20 >>> Requiring length matching to 1 mil is excessively restrictive and=20 >>> not attainable due to unknown lengths in IC packages and on die lengths. >>> =20 > The > =20 >>> fact that a layout person can do this on the PCB isn't a reason to >>> =20 > impose > =20 >>> such a restrictive matching rule. I'd be willing to bet that the=20 >>> real length matching on the PCB is not the claimed 1 mil. That's=20 >>> just what >>> =20 > the > =20 >>> tool reports. >>> >>> >>> =20 >>> =20 >>>> [Original Message] >>>> From: >>>> To: >>>> Cc: >>>> Date: 5/31/2007 9:13:25 AM >>>> Subject: [SI-LIST] Re: IEEE1394/Ethernet Routing Guidelines >>>> >>>> Bill, >>>> While I agree with almost all of your recommendations, I do not >>>> =20 >>>> =20 >>> understand >>> =20 >>> =20 >>>> the need to match the length of differential pairs to within 1 mil. >>>> =20 > Will > =20 >>>> you please give your reasoning for this. >>>> >>>> Thanks. >>>> >>>> Regards, Ravinder >>>> Server PCB Development >>>> Hitachi Global Storage Technologies >>>> >>>> >>>> Email: Ravinder.Ajmani@xxxxxxxxxxxxxx >>>> >>>> >>>> >>>> Bill Owsley >>>> Sent by: si-list-bounce@xxxxxxxxxxxxx >>>> 05/30/2007 08:13 PM >>>> Please respond to >>>> wdowsley@xxxxxxxxx >>>> >>>> >>>> To >>>> Sam.Charles@xxxxxxxx, jeff.loyer@xxxxxxxxx cc=20 >>>> si-list@xxxxxxxxxxxxx, si-list-bounce@xxxxxxxxxxxxx,=20 >>>> weirsi@xxxxxxxxxx Subject [SI-LIST] Re: IEEE1394/Ethernet Routing=20 >>>> Guidelines >>>> >>>> >>>> >>>> >>>> >>>> >>>> I went below to check what Mr.Voorhies asked for; >>>> "...have had a very difficult time finding exact numbers for=20 >>>> trace spacing/individual trace impedence and so on." >>>> =20 >>>> And now I don't find in any of the suggestions (or in Mr.Voorhies >>>> =20 > note) > =20 >>>> anything about copper weight, dielectric constant at what=20 >>>> frequency, >>>> =20 >>>> =20 >>> trace >>> =20 >>> =20 >>>> width, distance above or between reference planes, length matching, >>>> =20 >>>> =20 >>> number >>> =20 >>> =20 >>>> of vias across how many layers, crosstalk coupling factor and it's >>>> =20 > effect > =20 >>>> on even/odd mode impedance, pre-emphasis to compensate for longer >>>> =20 > lengths > =20 >>>> at higher frequencies, various "cute tricks" to emulate=20 >>>> differential signals (one I really like, nearly eliminates most of=20 >>>> the above), differential drivers or complementary drivers or=20 >>>> current steering >>>> =20 >>>> =20 >>> drivers, >>> =20 >>> =20 >>>> differential to common mode conversion factor, terminations, >>>> =20 > decoupling, > =20 >>>> and so on. All the books/sources referenced have all the=20 >>>> conflicting information that Mr. Voorhies has already discovered. >>>> For us, immersed in the culture (or lack of it on my part) the >>>> =20 > references > =20 >>>> are like preaching to the choir, we nod our collective heads in >>>> =20 > agreement > =20 >>>> that those are indeed good sources and Mr. Voorhies says to=20 >>>> himself, >>>> =20 > Hey > =20 >>>> =20 >>>> =20 >>> I >>> =20 >>> =20 >>>> can catch lightning in a jar, but I still don't WTF they just said, >>>> =20 > thus > =20 >>>> the reason for his request. Everyday we work with digit heads,=20 >>>> okay, digital guys, who connect to the dots and then look to the SI >>>> and EMC >>>> =20 >>>> =20 >>> guys >>> =20 >>> =20 >>>> to make the board work. ps. we work well together cuz the only=20 >>>> dots I connect are in my granddaughters coloring book. >>>> So given the dearth of details here's one answer (of many) he can >>>> =20 > use; > =20 >>>> 50 ohm surface traces (no vias), spaced 5 times the distance to=20 >>>> the reference plane, no breaks in the plane below the traces,=20 >>>> matched >>>> =20 > lengths > =20 >>>> to within 1 mil. (my layout guys can do that in about 30 seconds=20 >>>> all >>>> =20 > day, > =20 >>>> another "cute trick"), and all added parts are absolute mirrow >>>> =20 > symmetric > =20 >>>> (the parts might need vias).=20 >>>> =20 >>>> =20 >>>> =20 >>>> =20 >>>> =20 >>>> =20 >>>> =20 >>>> Sam.Charles@xxxxxxxx wrote: >>>> I second that. >>>> >>>> >>>> >>>> >>>> >>>> "Loyer, Jeff"=20 >>>> >>>> Sent by: To >>>> si-list-bounce@xxxxxxxxxxxxx >>>> cc >>>> >>>> 05/30/2007 02:24 PM Subject >>>> [SI-LIST] Re: IEEE1394/Ethernet Routing Guidelines >>>> >>>> Please respond to >>>> jeff.loyer@xxxxxxxxx >>>> >>>> >>>> >>>> >>>> >>>> >>>> >>>> THANK YOU!!! >>>> >>>> A response absent of sarcasm and/or scorn, and with some useful=20 >>>> information. A pleasant change from the recent postings on the forum. >>>> >>>> Thanks Steve, >>>> >>>> Jeff Loyer >>>> >>>> -----Original Message----- >>>> From: si-list-bounce@xxxxxxxxxxxxx >>>> =20 > [mailto:si-list-bounce@xxxxxxxxxxxxx] > =20 >>>> On Behalf Of steve weir >>>> Sent: Wednesday, May 30, 2007 1:39 PM >>>> To: voorhies@xxxxxxx >>>> Cc: si-list@xxxxxxxxxxxxx >>>> Subject: [SI-LIST] Re: IEEE1394/Ethernet Routing Guidelines >>>> >>>> Randolph, I suggest any of the following four books would be=20 >>>> helpful to y=3D3D >>>> ou: >>>> >>>> Signal Integrity Simplified, Bogatin High Speed Signal Propagation, >>>> Johnson and Graham Digital Techniques for High Speed Design,=20 >>>> Granberg Right the First Time Vol II, Ritchey >>>> >>>> Lee Ritchey self publishes so if you want Right the First Time you=20 >>>> will =3D3D >>>> >>>> need to go to www.speedingedge.com. Your alternative is to rely on=20 >>>> PHY=3D3D20 manufacturer guidelines. >>>> >>>> The basic guide that I can offer you is this: >>>> >>>> * Loosely coupled pairs are easier to manage than tightly=20 >>>> coupled=3D3D20 pairs. If you don't specifically need tight coupling = >>>> for density=3D3D20 reasons, you will be less likely to go wrong = with=20 >>>> loosely coupled >>>> =20 > pairs. > =20 >>>> =3D3D >>>> >>>> >>>> * The crude approximation for a loosely coupled pair is Zodd = =3D3D3D=20 >>>> 2*Zeven.=3D3D =3D3D20 Ie two loosely coupled 50 ohm traces will = have=20 >>>> about a 100ohm odd mode=3D3D20 impedance.=3D3D20 >>>> >>>> * Maintaining a uniform impedance and matched electrical length=20 >>>> will do=3D3D20 much to get you were you need to go. If you are a = tiny >>>> bit sloppy, it=3D3D20 shouldn't matter for a student project. Your=20 >>>> project doesn't have =3D to=3D3D20 pass FCC part B, and it is = unlikely=20 >>>> that you have to support =3D maximal=3D3D20 length links. >>>> >>>> Eric Bogatin's book has some impedance nomographs. However, there=20 >>>> are a =3D3D >>>> >>>> number of free calculators around some better than others. Google=20 >>>> for=3D3D20 impedance calculator and take your pick.=3D3D20 >>>> >>>> Good luck. >>>> >>>> Steve. >>>> >>>> >>>> >>>> Randolph Voorhies wrote: >>>> =20 >>>> =20 >>>>> Hi Everyone, >>>>> I'm brand new not just to this list, but to the world of PCB >>>>> =20 >>>>> =20 >>>> product=3D3D >>>> ion in general. I'm currently a masters student at USC in robotics=20 >>>> and h=3D3D ave been producing some relatively simple PCBs for the=20 >>>> past few months us=3D3D ing Eagle. I'm now working on a fairly=20 >>>> complex project that involves crea=3D3D ting a custom baseboard for = >>>> an XTX module (xtx-standard.org). My formal =3D3D training is in=20 >>>> digital electronics, computer architecture, and computer s=3D3D=20 >>>> cience, so when it comes to signal integrity I'm pretty much at a loss. >>>> =3D3D >>>> Does anyone know where to find specific routing guidlines for=20 >>>> differentia=3D3D l pair lines such as firewire and ethernet? I have = >>>> read all sorts of conf=3D3D licting advice (differential impedence = is >>>> crucial vs. differential impede=3D3D nce couldn't matter less,=20 >>>> etc..), and have had a very difficult time find=3D3D ing exact=20 >>>> numbers for trace spacing/individual trace impedence and so = on.=3D3D=20 >>>> If anyone with experience has any advice that has worked for them=20 >>>> it wou=3D3D ld be very very very much appreciated. >>>> =20 >>>> =20 >>>>> Thanks so much, >>>>> Rand Voorhies >>>>> ------------------------------------------------------------------ >>>>> To unsubscribe from si-list: >>>>> si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject=20 >>>>> 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: =3D3D20=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 >>>>> =3D3D20 >>>>> >>>>> >>>>> >>>>> =3D3D20 >>>>> =20 >>>>> =20 >>>> ------------------------------------------------------------------ >>>> To unsubscribe from si-list: >>>> si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject=20 >>>> 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: =3D20 >>>> //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 >>>> =3D20 >>>> ------------------------------------------------------------------ >>>> To unsubscribe from si-list: >>>> si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject=20 >>>> 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=20 >>>> 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 >>>> --------------------------------- >>>> Need Mail bonding? >>>> Go to the Yahoo! 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