[SI-LIST] Re: Routing guidelines for 3.12Gbps LVDS pairs
- From: Dave Schaefer <dave.schaefer@xxxxxxx>
- To: <si-list@xxxxxxxxxxxxx>
- Date: Tue, 20 Oct 2009 11:27:29 -0500
Jeff,
Interesting post ...
With certain toolsets matching as you describe is no different. With others 2.5
or 5 mil matching is much more work than 100 mil matching.
Secondly, it gives a designer some perspective as to where component vendor
guidelines sometimes come from.
Dave
>
> From: FreeLists Mailing List Manager <ecartis@xxxxxxxxxxxxx>
> Date: 2009/10/20 Tue AM 10:56:41 CDT
> To: si-list digest users <ecartis@xxxxxxxxxxxxx>
> Subject: si-list Digest V9 #315
>
> si-list Digest Tue, 20 Oct 2009 Volume: 09 Issue: 315
>
> In This Issue:
> #1: From: "Loyer, Jeff" <jeff.loyer@xxxxxxxxx>
> Subject: [SI-LIST] Re: Routing guidelines for 3.12Gbps LVDS
> pairs
> #2: From: "Loyer, Jeff" <jeff.loyer@xxxxxxxxx>
> Subject: [SI-LIST] Re: Routing guidelines for 3.12Gbps LVDS
> pairs
> #3: From: <colin_warwick@xxxxxxxxxxx>
> Subject: [SI-LIST] Re: coupling calculations
> #4: From: "Joel Brown" <joel@xxxxxxxxxx>
> Subject: [SI-LIST] Re: Routing guidelines for 3.12Gbps LVDS
> pairs
>
> ----------------------------------------------------------------------
>
> Msg: #1 in digest
> From: "Loyer, Jeff" <jeff.loyer@xxxxxxxxx>
> Date: Tue, 20 Oct 2009 08:20:30 -0700
> Subject: [SI-LIST] Re: Routing guidelines for 3.12Gbps LVDS pairs
>
> After fighting this (how tightly must my diff pair be aligned?) forever, I've
> taken a more pragmatic approach. I have my CAD folks use +/-2.5 mils for ALL
> their differential pairs. This seems to be the quickest for all involved.
>
> 1) CAD folks tell me that if they're going to match within 100 mils, matching
> within 2.5 mils isn't much different. They don't care.
> 2) They use the same constraints for ALL diff pairs - less chance for messing
> that up, much quicker. They like that, A LOT!!!
> 3) I don't spend any time worrying that they didn't match some diff pair
> correctly, including accounting for multiple boards, etc.
>
> Of course, it does have the detrimental effect of lessening my workload and
> hence my innate value (providing expert guidance on exactly how much matching
> is required for each bus), but I'll take it. I have more job security when
> the design is done more reliably and quickly.
>
> Does it make anyone else giggle that someone is hoping we'll provide a
> complete Design Guide via e-mail? I would suggest to the original poster
> that you'll need some other means to supply all the guidelines you'll need to
> properly design a high-speed interface. Asking for specific clarification is
> one thing, to ask for all the guidelines necessary for a complete design is
> another.
>
> My $0.02...
>
> Jeff Loyer
>
> -----Original Message-----
> From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx] On
> Behalf Of steve weir
> Sent: Tuesday, October 20, 2009 7:43 AM
> To: Lee Ritchey
> Cc: Peterson, James F (EHCOE); si-list@xxxxxxxxxxxxx
> Subject: [SI-LIST] Re: Routing guidelines for 3.12Gbps LVDS pairs
>
> Lee, If the driver is really slow or the path very long that might be
> OK. For a clean driver on modest length links, 50ps skew can run 50% or
> more of Tr/Tf. I don't like that much mode conversion.
>
> Best Regards,
>
>
> Steve.
> Lee Ritchey wrote:
> > Actually, I was being conservative at 100 mils. A mismatch of 300 mils
> > total is acceptable throughout the total path. 300 mils is roughly 50
> > pSec.out of a 320 pSec bit interval.
> >
> >
> >
> >> [Original Message]
> >> From: Peterson, James F (EHCOE) <james.f.peterson@xxxxxxxxxxxxx>
> >> To: <si-list@xxxxxxxxxxxxx>
> >> Date: 10/20/2009 6:09:07 AM
> >> Subject: [SI-LIST] Re: Routing guidelines for 3.12Gbps LVDS pairs
> >>
> >> One comment on length matching at 100 mils : a lot of times the board
> >> we're looking at is only one section of the interface. There is often
> >> two more boards involved (a backplane and endpoint). When we say 100
> >> mils matched lengths, are we saying total matched length or at each
> >> board (so total could be 300 mils in that case)? The thread below says
> >> "matched at the receiver", which implies total, so the 100 mils should
> >> be budgeted through 3 boards.
> >>
> >> Regards,
> >> Jim Peterson
> >> Honeywell
> >>
> >> -----Original Message-----
> >> From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx]
> >> On Behalf Of steve weir
> >> Sent: Tuesday, October 20, 2009 1:13 AM
> >> To: icer world
> >> Cc: Lee Ritchey; Paul Hurst; si-list@xxxxxxxxxxxxx; chundi srikanth;
> >> Lambert Simonovich
> >> Subject: [SI-LIST] Re: Routing guidelines for 3.12Gbps LVDS pairs
> >>
> >> 1) Matching much closer than 1/4 Tr/Tf offers little value by itself.
> >> 100mils translates to about 16ps skew. That corresponds to a 64ns Tr/Tf
> >>
> >> for a 3.125G link which is a little to the outside, but it is not
> >> horrible. I would rephrase Lee's advice as: Don't take any
> >> extraordinary measures to match closer than 1/4 Tr/Tf as seen at the
> >> receiver. The longer the link, the slower Tr/Tf will be. There is a
> >> good treatment on this in Eric Bogatin's "Signal Integrity Simplified".
> >>
> >> If you get very tight matching truly for free, then fine. But obsessing
> >>
> >> about mechanical match to tight tolerances does not improve the design.
> >>
> >> It can in fact harm it if the matching is done with dense serpentines
> >> which introduce their own dispersion and timing skew that is not
> >> properly accounted in some tools.
> >>
> >> 2) Continuous return path is very important. Diff tolerates obscenities
> >>
> >> like crossing moats, but at undesirable costs. The best answer is don't
> >>
> >> interrupt the return path.
> >>
> >> 3) Surface ground guards are more often unintended resonators than of
> >> specific value. See if the cross-talk can be satisfied with spacing.
> >> If it can't, then consider alternatives.
> >>
> >> 4) I am not clear on what you are trying to recommend. Are you talking
> >> about termination at both ends of the link, or even and odd mode
> >> terminations?
> >>
> >> 5) An appropriate stitch density helps with EMC and signal integrity.
> >> Follow Bruce Archambeault's hierarchy on layer assignments and your life
> >>
> >> will be good:
> >> i. Route on one layer that faces a contiguous plane.
> >> ii. Switch between layers on either side of the same contiguous plane.
> >> iii. Switch between layers that reference planes on the same DC
> >> potential that are adequately stitched together. This is often
> >> misunderstood as needing to assign a return stitch via near each
> >> transition. The point is to raise the resonant frequency of the
> >> structure sufficiently so that it won't be a problem to the signal.
> >> iv. If you must switch between layers that are stitched with bypass caps
> >>
> >> and planar capacitance. Be wary of PDN resonances in the signal
> >> frequency range. These will tend to occur at much lower frequency than
> >> cavity resonances.
> >>
> >> Steve.
> >>
> >> icer world wrote:
> >>
> >>> 1) length matching must be consided seriously and mismatch should be
> >>>
> >> below 100mils;
> >>
> >>> 2) generally speaking,the differential pairs impedance must keep
> >>>
> >> 100ohm and the ground return path must not be choped ;
> >>
> >>> 3) the ground guarding trace should keep two times of differential
> >>>
> >> trace width away from the differantial pairs,which can not influences
> >> the differential pairs impedance and avoid crosstalk issues;
> >>
> >>> 4) using serial and parallel matching resistors simultaneously for
> >>>
> >> debug ;
> >>
> >>> 5) changing layers is not expected,but if necessary ,you should place
> >>>
> >> a groung via near the signal via ;
> >>
> >>> the above is just an advice ,and you'd better do a simulatiom to
> >>>
> >> decide the rules of matching resistors and crosstalk;
> >>
> >>>
> >>> ________________________________
> >>> From: Lee Ritchey <leeritchey@xxxxxxxxxxxxx>
> >>> To: Paul Hurst <paul@xxxxxxxxxxxxxxxxxxxxxx>; si-list@xxxxxxxxxxxxx
> >>> Cc: chundi srikanth <chundis@xxxxxxxxx>; Lambert Simonovich
> >>>
> >> <bertsimonovich@xxxxxxxxxx>
> >>
> >>> Sent: Mon, October 19, 2009 11:46:36 PM
> >>> Subject: [SI-LIST] Re: Routing guidelines for 3.12Gbps LVDS pairs
> >>>
> >>> Length matching does not need to be tighter than 100 mils.
> >>>
> >>> It is not necessary to back drill vias used to connect component pins
> >>>
> >> to
> >>
> >>> traces or to change layers. The 0.6 pF or so capacitance does not
> >>> adversely affect the signals at this data rate.
> >>>
> >>> It is not necessary to put "ground" vias next to routing vias as long
> >>>
> >> as
> >>
> >>> the PDS is well designed."
> >>>
> >>> "Guard" traces have no value. Proper spacing to avoid crosstalk
> >>>
> >> does.
> >>
> >>> The "rule of thumb" for spacing given, while crude, is not far off.
> >>>
> >>> Lee Ritchey
> >>>
> >>>
> >>>
> >>>
> >>>> [Original Message]
> >>>> From: Paul Hurst <paul@xxxxxxxxxxxxxxxxxxxxxx>
> >>>> To: <si-list@xxxxxxxxxxxxx>
> >>>> Cc: chundi srikanth <chundis@xxxxxxxxx>; Lambert Simonovich
> >>>>
> >>>>
> >>> <bertsimonovich@xxxxxxxxxx>
> >>>
> >>>
> >>>> Date: 10/18/2009 5:45:08 PM
> >>>> Subject: [SI-LIST] Re: Routing guidelines for 3.12Gbps LVDS pairs
> >>>>
> >>>> Srikanth,
> >>>>
> >>>> Additional to Bert's comments:-
> >>>>
> >>>> 1) Match the lengths of the pairs exactly
> >>>> 2) Use a solid ground return
> >>>> 3) Avoid stubs by design or by using stub-drilling
> >>>> 4) If you have vias in the path use a small drill and a large
> >>>>
> >> anti-pad and
> >>
> >>>> place a ground via next to each signal via
> >>>>
> >>>> Regards
> >>>>
> >>>> Paul
> >>>>
> >>>> -----Original Message-----
> >>>> From: si-list-bounce@xxxxxxxxxxxxx
> >>>>
> >> [mailto:si-list-bounce@xxxxxxxxxxxxx]
> >>
> >>>>
> >>>>
> >>> On
> >>>
> >>>
> >>>> Behalf Of Lambert Simonovich
> >>>> Sent: 16 October 2009 21:57
> >>>> To: 'chundi srikanth'; si-list@xxxxxxxxxxxxx
> >>>> Subject: [SI-LIST] Re: Routing guidelines for 3.12Gbps LVDS pairs
> >>>>
> >>>>
> >>>> Srikanth,
> >>>>
> >>>> A rough rule of thumb is greater than 3 times trace width separation
> >>>>
> >>>>
> >>> between
> >>>
> >>>
> >>>> pairs. Using a 2D field solver will ultimately give you the crosstalk
> >>>> coupling factor for the exact geometry in your stackup, and dictate
> >>>>
> >> the
> >>
> >>>> routing rules you need to follow to satisfy your noise budget.
> >>>>
> >>>> Adding GND guarding will more often than not present more issues than
> >>>>
> >> it
> >>
> >>>> solves. You should stitch these guard traces at regular intervals
> >>>> approximately 1/10 of the wavelength of the highest frequency
> >>>>
> >> component of
> >>
> >>>> the aggressor signal to avoid it from resonating and coupling noise
> >>>>
> >> back
> >>
> >>>> onto other adjacent traces. This further reduces routing density of
> >>>>
> >> the
> >>
> >>>> board. By the time you factor in the additional space of one trace
> >>>>
> >> width
> >>
> >>>> between the guard trace and Diff pair, plus the additional via
> >>>>
> >> stitching,
> >>
> >>>> you will find you are already at 3 times separation between pairs and
> >>>>
> >> you
> >>
> >>>> would gain back more real estate.
> >>>>
> >>>> Regards,
> >>>>
> >>>> Bert Simonovich
> >>>>
> >>>>
> >>>>
> >>>>
> >>>>
> >>>> -----Original Message-----
> >>>> From: si-list-bounce@xxxxxxxxxxxxx
> >>>>
> >> [mailto:si-list-bounce@xxxxxxxxxxxxx]
> >>
> >>>>
> >>>>
> >>> On
> >>>
> >>>
> >>>> Behalf Of chundi srikanth
> >>>> Sent: October-16-09 12:40 PM
> >>>> To: si-list@xxxxxxxxxxxxx
> >>>> Subject: [SI-LIST] Routing guidelines for 3.12Gbps LVDS pairs
> >>>>
> >>>> Hi Techies,
> >>>> We have a 12-layer board in which we have lot of differential LVDS
> >>>>
> >> pairs
> >>
> >>>> operating at several hundreds MHz. And we have SERDES signals
> >>>>
> >>>>
> >>> (differential
> >>>
> >>>
> >>>> TX & RX pairs) operating at CPRI rate-4 i.e., 3Gbps. So can you just
> >>>>
> >> share
> >>
> >>>> me some inputs on exactly what are the guidelines to be followed
> >>>>
> >> while
> >>
> >>>> routing these signals. And is GND gaurding between the differential
> >>>>
> >> pairs
> >>
> >>>> improve the SI?Please share or refer me any documents in which i can
> >>>>
> >> get
> >>
> >>>> Good information on High-Speed design guidelines.
> >>>>
> >>>> Thanks
> >>>>
> >>>> With Best Regards
> >>>> Srikanth
> >>>>
> >>>>
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> >> --
> >> Steve Weir
> >> IPBLOX, LLC
> >> 150 N. Center St. #211
> >> Reno, NV 89501
> >> (866) 675-4630 Business
> >> (707) 780-1951 Fax
> >> http://www.ipblox.com
> >> A Teraspeed Consulting Group LLC Partner
> >>
> >> Teraspeed Consulting Group
> >> 121 North River Drive
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> >> (401) 284-1827 Business
> >> (401) 284-1840 Fax
> >>
> >> Teraspeed Labs
> >> 13610 SW Harness Lane
> >> Beaverton, OR 97008
> >> (503) 430-1065 Business
> >> (503) 430-1285 Fax
> >> A Teraspeed Consulting Group LLC Partner
> >>
> >> http://www.teraspeed.com
> >>
> >> This e-mail contains proprietary and confidential intellectual property
> >> of IPBLOX LLC
> >> ------------------------------------------------------------------------
> >> ------------------------------
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> --
> Steve Weir
> IPBLOX, LLC
> 150 N. Center St. #211
> Reno, NV 89501
> (866) 675-4630 Business
> (707) 780-1951 Fax
> http://www.ipblox.com
> A Teraspeed Consulting Group LLC Partner
>
> Teraspeed Consulting Group
> 121 North River Drive
> Narragansett, RI 02882
> (401) 284-1827 Business
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>
> Teraspeed Labs
> 13610 SW Harness Lane
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> A Teraspeed Consulting Group LLC Partner
>
> http://www.teraspeed.com
>
> This e-mail contains proprietary and confidential intellectual property of
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> ------------------------------
>
> Msg: #2 in digest
> From: "Loyer, Jeff" <jeff.loyer@xxxxxxxxx>
> Date: Tue, 20 Oct 2009 08:24:27 -0700
> Subject: [SI-LIST] Re: Routing guidelines for 3.12Gbps LVDS pairs
>
> I'd consider guard traces dead, along with "bends cause discontinuities",
> etc.). They had their short run of fame (infamy?) with the 28 ohm Rambus
> memory layout, but I haven't seen them since. If you've seen any recent
> Design Guides that still suggest it, I'd like to see those.
>
> Jeff Loyer
>
> -----Original Message-----
> From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx] On
> Behalf Of Richard P EVANS
> Sent: Tuesday, October 20, 2009 7:55 AM
> To: si-list@xxxxxxxxxxxxx
> Subject: [SI-LIST] Re: Routing guidelines for 3.12Gbps LVDS pairs
>
> -----Original Message-----
> From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx] On
> Behalf Of Lee Ritchey
> Sent: Tuesday, October 20, 2009 9:33 AM
> To: icer world; Paul Hurst; si-list@xxxxxxxxxxxxx
> Cc: chundi srikanth; Lambert Simonovich
> Subject: [SI-LIST] Re: Routing guidelines for 3.12Gbps LVDS pairs
>
> Guard traces do not improve performance. Instead, the complicate layout.
> What will it take to get this myth put to rest?
>
>
> > [Original Message]
> > From: icer world <icermail@xxxxxxxxx>
> > To: Lee Ritchey <leeritchey@xxxxxxxxxxxxx>; Paul Hurst
> <paul@xxxxxxxxxxxxxxxxxxxxxx>; <si-list@xxxxxxxxxxxxx>
> > Cc: chundi srikanth <chundis@xxxxxxxxx>; Lambert Simonovich
> <bertsimonovich@xxxxxxxxxx>
> > Date: 10/19/2009 9:36:34 PM
> > Subject: [SI-LIST] Re: Routing guidelines for 3.12Gbps LVDS pairs
> >
> > 1) length matching must be consided seriously and mismatch should be
> below 100mils;
> > 2) generally speaking,the differential pairs impedance must keep
> > 100ohm
> and the ground return path must not be choped ;
> > 3) the ground guarding trace should keep two times of differential
> > trace
> width away from the differantial pairs,which can not influences the
> differential pairs impedance and avoid crosstalk issues;
> > 4) using serial and parallel matching resistors simultaneously for
> debug ;
> > 5) changing layers is not expected,but if necessary ,you should place
> > a
> groung via near the signal via ;
> > the above is just an advice ,and you'd better do a simulatiom to
> > decide
> the rules of matching resistors and crosstalk;
> >
> >
> >
> > ________________________________
> > From: Lee Ritchey <leeritchey@xxxxxxxxxxxxx>
> > To: Paul Hurst <paul@xxxxxxxxxxxxxxxxxxxxxx>; si-list@xxxxxxxxxxxxx
> > Cc: chundi srikanth <chundis@xxxxxxxxx>; Lambert Simonovich
> <bertsimonovich@xxxxxxxxxx>
> > Sent: Mon, October 19, 2009 11:46:36 PM
> > Subject: [SI-LIST] Re: Routing guidelines for 3.12Gbps LVDS pairs
> >
> > Length matching does not need to be tighter than 100 mils.
> >
> > It is not necessary to back drill vias used to connect component pins
> > to traces or to change layers. The 0.6 pF or so capacitance does not
> > adversely affect the signals at this data rate.
> >
> > It is not necessary to put "ground" vias next to routing vias as long
> > as the PDS is well designed."
> >
> > "Guard" traces have no value. Proper spacing to avoid crosstalk does.
> > The "rule of thumb" for spacing given, while crude, is not far off.
> >
> > Lee Ritchey
> >
> >
> > > [Original Message]
> > > From: Paul Hurst <paul@xxxxxxxxxxxxxxxxxxxxxx>
> > > To: <si-list@xxxxxxxxxxxxx>
> > > Cc: chundi srikanth <chundis@xxxxxxxxx>; Lambert Simonovich
> > <bertsimonovich@xxxxxxxxxx>
> > > Date: 10/18/2009 5:45:08 PM
> > > Subject: [SI-LIST] Re: Routing guidelines for 3.12Gbps LVDS pairs
> > >
> > > Srikanth,
> > >
> > > Additional to Bert's comments:-
> > >
> > > 1) Match the lengths of the pairs exactly
> > > 2) Use a solid ground return
> > > 3) Avoid stubs by design or by using stub-drilling
> > > 4) If you have vias in the path use a small drill and a large
> > > anti-pad
> and
> > > place a ground via next to each signal via
> > >
> > > Regards
> > >
> > > Paul
> > >
> > > -----Original Message-----
> > > From: si-list-bounce@xxxxxxxxxxxxx
> > > [mailto:si-list-bounce@xxxxxxxxxxxxx]
> > On
> > > Behalf Of Lambert Simonovich
> > > Sent: 16 October 2009 21:57
> > > To: 'chundi srikanth'; si-list@xxxxxxxxxxxxx
> > > Subject: [SI-LIST] Re: Routing guidelines for 3.12Gbps LVDS pairs
> > >
> > >
> > > Srikanth,
> > >
> > > A rough rule of thumb is greater than 3 times trace width separation
> > between
> > > pairs. Using a 2D field solver will ultimately give you the
> > > crosstalk coupling factor for the exact geometry in your stackup,
> > > and dictate the routing rules you need to follow to satisfy your noise
> budget.
> > >
> > > Adding GND guarding will more often than not present more issues
> > > than it solves. You should stitch these guard traces at regular
> > > intervals approximately 1/10 of the wavelength of the highest
> > > frequency component
> of
> > > the aggressor signal to avoid it from resonating and coupling noise
> > > back onto other adjacent traces. This further reduces routing
> > > density of the board. By the time you factor in the additional space
> > > of one trace width between the guard trace and Diff pair, plus the
> > > additional via
> stitching,
> > > you will find you are already at 3 times separation between pairs
> > > and
> you
> > > would gain back more real estate.
> > >
> > > Regards,
> > >
> > > Bert Simonovich
> > >
> > >
> > >
> > >
> > >
> > > -----Original Message-----
> > > From: si-list-bounce@xxxxxxxxxxxxx
> > > [mailto:si-list-bounce@xxxxxxxxxxxxx]
> > On
> > > Behalf Of chundi srikanth
> > > Sent: October-16-09 12:40 PM
> > > To: si-list@xxxxxxxxxxxxx
> > > Subject: [SI-LIST] Routing guidelines for 3.12Gbps LVDS pairs
> > >
> > > Hi Techies,
> > > We have a 12-layer board in which we have lot of differential LVDS
> > > pairs operating at several hundreds MHz. And we have SERDES signals
> > (differential
> > > TX & RX pairs) operating at CPRI rate-4 i.e., 3Gbps. So can you just
> share
> > > me some inputs on exactly what are the guidelines to be followed
> > > while routing these signals. And is GND gaurding between the
> > > differential
> pairs
> > > improve the SI?Please share or refer me any documents in which i can
> > > get Good information on High-Speed design guidelines.
> > >
> > > Thanks
> > >
> > > With Best Regards
> > > Srikanth
> > >
> > >
> > > ------------------------------------------------------------------
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>
> ------------------------------
>
> Msg: #3 in digest
> Subject: [SI-LIST] Re: coupling calculations
> Date: Tue, 20 Oct 2009 09:41:11 -0600
> From: <colin_warwick@xxxxxxxxxxx>
>
> Hi Craig,
>
> Sorry I don't have an answer, but I do have a question: Is your heart set on
> an analytical expression, or would you settle for scripting a 2D field solver
> to give you plots of coupling versus geometry?
>
> -- Colin Warwick
> Signal Integrity Product Marketing Manager, Agilent EEsof EDA
> Blog: http://signal-integrity.tm.agilent.com
>
> -----Original Message-----
> From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx] On
> Behalf Of Deibele, Craig Edmond
> Sent: Tuesday, October 20, 2009 9:27 AM
> To: si-list@xxxxxxxxxxxxx
> Subject: [SI-LIST] coupling calculations
>
> hi everyone,
> I have a scenario where I have four conductors enclosed inside of a tube and
> they are used as a coupled transmission line. I know what the characteristic
> impedance is of the sum mode, the two dipole modes, and of the quadripole
> mode.
>
> I've seen the equations for two coupled conductors (like for edge coupled
> microstrip/stripline or for broadside coupled transmission lines) and for the
> coupling (i.e. C *log( (Ze-Zo)/(Ze+Zo) )
>
> I've gone through some of the math to extend the theory for 4 coupled
> conductor transmission lines. I'd have expected that this be done already,
> but haven't found any references.
>
> Any ideas or can anyone point me at a good reference?
>
> Thanks
>
> Craig deibele
>
>
> ------------------------------
>
> Msg: #4 in digest
> From: "Joel Brown" <joel@xxxxxxxxxx>
> Subject: [SI-LIST] Re: Routing guidelines for 3.12Gbps LVDS pairs
> Date: Tue, 20 Oct 2009 08:54:21 -0700
>
> We use a similar approach but use 5 mils. It is a number I have seen in
> various design guidelines including PCI express published by Intel.
> I think Jeff is right it's easier and faster to have a one size fits all
> rule even if it is overly conservative than to have to scrutinize each route
> to see if the length matching is below some number related to rise time.
> Our layout guy never has complained.
>
> Joel
>
>
> -----Original Message-----
> From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx] On
> Behalf Of Loyer, Jeff
> Sent: Tuesday, October 20, 2009 8:21 AM
> To: steve weir; Lee Ritchey
> Cc: si-list@xxxxxxxxxxxxx
> Subject: [SI-LIST] Re: Routing guidelines for 3.12Gbps LVDS pairs
>
> After fighting this (how tightly must my diff pair be aligned?) forever,
> I've taken a more pragmatic approach. I have my CAD folks use +/-2.5 mils
> for ALL their differential pairs. This seems to be the quickest for all
> involved.
>
> 1) CAD folks tell me that if they're going to match within 100 mils,
> matching within 2.5 mils isn't much different. They don't care.
> 2) They use the same constraints for ALL diff pairs - less chance for
> messing that up, much quicker. They like that, A LOT!!!
> 3) I don't spend any time worrying that they didn't match some diff pair
> correctly, including accounting for multiple boards, etc.
>
> Of course, it does have the detrimental effect of lessening my workload and
> hence my innate value (providing expert guidance on exactly how much
> matching is required for each bus), but I'll take it. I have more job
> security when the design is done more reliably and quickly.
>
> Does it make anyone else giggle that someone is hoping we'll provide a
> complete Design Guide via e-mail? I would suggest to the original poster
> that you'll need some other means to supply all the guidelines you'll need
> to properly design a high-speed interface. Asking for specific
> clarification is one thing, to ask for all the guidelines necessary for a
> complete design is another.
>
> My $0.02...
>
> Jeff Loyer
>
> -----Original Message-----
> From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx] On
> Behalf Of steve weir
> Sent: Tuesday, October 20, 2009 7:43 AM
> To: Lee Ritchey
> Cc: Peterson, James F (EHCOE); si-list@xxxxxxxxxxxxx
> Subject: [SI-LIST] Re: Routing guidelines for 3.12Gbps LVDS pairs
>
> Lee, If the driver is really slow or the path very long that might be
> OK. For a clean driver on modest length links, 50ps skew can run 50% or
> more of Tr/Tf. I don't like that much mode conversion.
>
> Best Regards,
>
>
> Steve.
> Lee Ritchey wrote:
> > Actually, I was being conservative at 100 mils. A mismatch of 300 mils
> > total is acceptable throughout the total path. 300 mils is roughly 50
> > pSec.out of a 320 pSec bit interval.
> >
> >
> >
> >> [Original Message]
> >> From: Peterson, James F (EHCOE) <james.f.peterson@xxxxxxxxxxxxx>
> >> To: <si-list@xxxxxxxxxxxxx>
> >> Date: 10/20/2009 6:09:07 AM
> >> Subject: [SI-LIST] Re: Routing guidelines for 3.12Gbps LVDS pairs
> >>
> >> One comment on length matching at 100 mils : a lot of times the board
> >> we're looking at is only one section of the interface. There is often
> >> two more boards involved (a backplane and endpoint). When we say 100
> >> mils matched lengths, are we saying total matched length or at each
> >> board (so total could be 300 mils in that case)? The thread below says
> >> "matched at the receiver", which implies total, so the 100 mils should
> >> be budgeted through 3 boards.
> >>
> >> Regards,
> >> Jim Peterson
> >> Honeywell
> >>
> >> -----Original Message-----
> >> From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx]
> >> On Behalf Of steve weir
> >> Sent: Tuesday, October 20, 2009 1:13 AM
> >> To: icer world
> >> Cc: Lee Ritchey; Paul Hurst; si-list@xxxxxxxxxxxxx; chundi srikanth;
> >> Lambert Simonovich
> >> Subject: [SI-LIST] Re: Routing guidelines for 3.12Gbps LVDS pairs
> >>
> >> 1) Matching much closer than 1/4 Tr/Tf offers little value by itself.
> >> 100mils translates to about 16ps skew. That corresponds to a 64ns Tr/Tf
> >>
> >> for a 3.125G link which is a little to the outside, but it is not
> >> horrible. I would rephrase Lee's advice as: Don't take any
> >> extraordinary measures to match closer than 1/4 Tr/Tf as seen at the
> >> receiver. The longer the link, the slower Tr/Tf will be. There is a
> >> good treatment on this in Eric Bogatin's "Signal Integrity Simplified".
> >>
> >> If you get very tight matching truly for free, then fine. But obsessing
> >>
> >> about mechanical match to tight tolerances does not improve the design.
> >>
> >> It can in fact harm it if the matching is done with dense serpentines
> >> which introduce their own dispersion and timing skew that is not
> >> properly accounted in some tools.
> >>
> >> 2) Continuous return path is very important. Diff tolerates obscenities
> >>
> >> like crossing moats, but at undesirable costs. The best answer is don't
> >>
> >> interrupt the return path.
> >>
> >> 3) Surface ground guards are more often unintended resonators than of
> >> specific value. See if the cross-talk can be satisfied with spacing.
> >> If it can't, then consider alternatives.
> >>
> >> 4) I am not clear on what you are trying to recommend. Are you talking
> >> about termination at both ends of the link, or even and odd mode
> >> terminations?
> >>
> >> 5) An appropriate stitch density helps with EMC and signal integrity.
> >> Follow Bruce Archambeault's hierarchy on layer assignments and your life
> >>
> >> will be good:
> >> i. Route on one layer that faces a contiguous plane.
> >> ii. Switch between layers on either side of the same contiguous plane.
> >> iii. Switch between layers that reference planes on the same DC
> >> potential that are adequately stitched together. This is often
> >> misunderstood as needing to assign a return stitch via near each
> >> transition. The point is to raise the resonant frequency of the
> >> structure sufficiently so that it won't be a problem to the signal.
> >> iv. If you must switch between layers that are stitched with bypass caps
> >>
> >> and planar capacitance. Be wary of PDN resonances in the signal
> >> frequency range. These will tend to occur at much lower frequency than
> >> cavity resonances.
> >>
> >> Steve.
> >>
> >> icer world wrote:
> >>
> >>> 1) length matching must be consided seriously and mismatch should be
> >>>
> >> below 100mils;
> >>
> >>> 2) generally speaking,the differential pairs impedance must keep
> >>>
> >> 100ohm and the ground return path must not be choped ;
> >>
> >>> 3) the ground guarding trace should keep two times of differential
> >>>
> >> trace width away from the differantial pairs,which can not influences
> >> the differential pairs impedance and avoid crosstalk issues;
> >>
> >>> 4) using serial and parallel matching resistors simultaneously for
> >>>
> >> debug ;
> >>
> >>> 5) changing layers is not expected,but if necessary ,you should place
> >>>
> >> a groung via near the signal via ;
> >>
> >>> the above is just an advice ,and you'd better do a simulatiom to
> >>>
> >> decide the rules of matching resistors and crosstalk;
> >>
> >>>
> >>> ________________________________
> >>> From: Lee Ritchey <leeritchey@xxxxxxxxxxxxx>
> >>> To: Paul Hurst <paul@xxxxxxxxxxxxxxxxxxxxxx>; si-list@xxxxxxxxxxxxx
> >>> Cc: chundi srikanth <chundis@xxxxxxxxx>; Lambert Simonovich
> >>>
> >> <bertsimonovich@xxxxxxxxxx>
> >>
> >>> Sent: Mon, October 19, 2009 11:46:36 PM
> >>> Subject: [SI-LIST] Re: Routing guidelines for 3.12Gbps LVDS pairs
> >>>
> >>> Length matching does not need to be tighter than 100 mils.
> >>>
> >>> It is not necessary to back drill vias used to connect component pins
> >>>
> >> to
> >>
> >>> traces or to change layers. The 0.6 pF or so capacitance does not
> >>> adversely affect the signals at this data rate.
> >>>
> >>> It is not necessary to put "ground" vias next to routing vias as long
> >>>
> >> as
> >>
> >>> the PDS is well designed."
> >>>
> >>> "Guard" traces have no value. Proper spacing to avoid crosstalk
> >>>
> >> does.
> >>
> >>> The "rule of thumb" for spacing given, while crude, is not far off.
> >>>
> >>> Lee Ritchey
> >>>
> >>>
> >>>
> >>>
> >>>> [Original Message]
> >>>> From: Paul Hurst <paul@xxxxxxxxxxxxxxxxxxxxxx>
> >>>> To: <si-list@xxxxxxxxxxxxx>
> >>>> Cc: chundi srikanth <chundis@xxxxxxxxx>; Lambert Simonovich
> >>>>
> >>>>
> >>> <bertsimonovich@xxxxxxxxxx>
> >>>
> >>>
> >>>> Date: 10/18/2009 5:45:08 PM
> >>>> Subject: [SI-LIST] Re: Routing guidelines for 3.12Gbps LVDS pairs
> >>>>
> >>>> Srikanth,
> >>>>
> >>>> Additional to Bert's comments:-
> >>>>
> >>>> 1) Match the lengths of the pairs exactly
> >>>> 2) Use a solid ground return
> >>>> 3) Avoid stubs by design or by using stub-drilling
> >>>> 4) If you have vias in the path use a small drill and a large
> >>>>
> >> anti-pad and
> >>
> >>>> place a ground via next to each signal via
> >>>>
> >>>> Regards
> >>>>
> >>>> Paul
> >>>>
> >>>> -----Original Message-----
> >>>> From: si-list-bounce@xxxxxxxxxxxxx
> >>>>
> >> [mailto:si-list-bounce@xxxxxxxxxxxxx]
> >>
> >>>>
> >>>>
> >>> On
> >>>
> >>>
> >>>> Behalf Of Lambert Simonovich
> >>>> Sent: 16 October 2009 21:57
> >>>> To: 'chundi srikanth'; si-list@xxxxxxxxxxxxx
> >>>> Subject: [SI-LIST] Re: Routing guidelines for 3.12Gbps LVDS pairs
> >>>>
> >>>>
> >>>> Srikanth,
> >>>>
> >>>> A rough rule of thumb is greater than 3 times trace width separation
> >>>>
> >>>>
> >>> between
> >>>
> >>>
> >>>> pairs. Using a 2D field solver will ultimately give you the crosstalk
> >>>> coupling factor for the exact geometry in your stackup, and dictate
> >>>>
> >> the
> >>
> >>>> routing rules you need to follow to satisfy your noise budget.
> >>>>
> >>>> Adding GND guarding will more often than not present more issues than
> >>>>
> >> it
> >>
> >>>> solves. You should stitch these guard traces at regular intervals
> >>>> approximately 1/10 of the wavelength of the highest frequency
> >>>>
> >> component of
> >>
> >>>> the aggressor signal to avoid it from resonating and coupling noise
> >>>>
> >> back
> >>
> >>>> onto other adjacent traces. This further reduces routing density of
> >>>>
> >> the
> >>
> >>>> board. By the time you factor in the additional space of one trace
> >>>>
> >> width
> >>
> >>>> between the guard trace and Diff pair, plus the additional via
> >>>>
> >> stitching,
> >>
> >>>> you will find you are already at 3 times separation between pairs and
> >>>>
> >> you
> >>
> >>>> would gain back more real estate.
> >>>>
> >>>> Regards,
> >>>>
> >>>> Bert Simonovich
> >>>>
> >>>>
> >>>>
> >>>>
> >>>>
> >>>> -----Original Message-----
> >>>> From: si-list-bounce@xxxxxxxxxxxxx
> >>>>
> >> [mailto:si-list-bounce@xxxxxxxxxxxxx]
> >>
> >>>>
> >>>>
> >>> On
> >>>
> >>>
> >>>> Behalf Of chundi srikanth
> >>>> Sent: October-16-09 12:40 PM
> >>>> To: si-list@xxxxxxxxxxxxx
> >>>> Subject: [SI-LIST] Routing guidelines for 3.12Gbps LVDS pairs
> >>>>
> >>>> Hi Techies,
> >>>> We have a 12-layer board in which we have lot of differential LVDS
> >>>>
> >> pairs
> >>
> >>>> operating at several hundreds MHz. And we have SERDES signals
> >>>>
> >>>>
> >>> (differential
> >>>
> >>>
> >>>> TX & RX pairs) operating at CPRI rate-4 i.e., 3Gbps. So can you just
> >>>>
> >> share
> >>
> >>>> me some inputs on exactly what are the guidelines to be followed
> >>>>
> >> while
> >>
> >>>> routing these signals. And is GND gaurding between the differential
> >>>>
> >> pairs
> >>
> >>>> improve the SI?Please share or refer me any documents in which i can
> >>>>
> >> get
> >>
> >>>> Good information on High-Speed design guidelines.
> >>>>
> >>>> Thanks
> >>>>
> >>>> With Best Regards
> >>>> Srikanth
> >>>>
> >>>>
> >>>> ------------------------------------------------------------------
> >>>> To unsubscribe from si-list:
> >>>> si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field
> >>>>
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> >>>> //www.freelists.org/webpage/si-list
> >>>>
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> >>>>
> >>>>
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> >>>> http://www.qsl.net/wb6tpu
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> >>>> or to administer your membership from a web page, go to:
> >>>> //www.freelists.org/webpage/si-list
> >>>>
> >>>> For help:
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> >>>>
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> >>>> List technical documents are available at:
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> >>>> 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:
> >>> //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
> >>>
> >>>
> >>>
> >>>
> >>>
> >> --
> >> Steve Weir
> >> IPBLOX, LLC
> >> 150 N. Center St. #211
> >> Reno, NV 89501
> >> (866) 675-4630 Business
> >> (707) 780-1951 Fax
> >> http://www.ipblox.com
> >> A Teraspeed Consulting Group LLC Partner
> >>
> >> Teraspeed Consulting Group
> >> 121 North River Drive
> >> Narragansett, RI 02882
> >> (401) 284-1827 Business
> >> (401) 284-1840 Fax
> >>
> >> Teraspeed Labs
> >> 13610 SW Harness Lane
> >> Beaverton, OR 97008
> >> (503) 430-1065 Business
> >> (503) 430-1285 Fax
> >> A Teraspeed Consulting Group LLC Partner
> >>
> >> http://www.teraspeed.com
> >>
> >> This e-mail contains proprietary and confidential intellectual property
> >> of IPBLOX LLC
> >> ------------------------------------------------------------------------
> >> ------------------------------
> >> Teraspeed(R) is the registered service mark of Teraspeed Consulting
> >> Group LLC
> >>
> >> ------------------------------------------------------------------
> >> 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:
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> >>
> >> For help:
> >> si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field
> >>
> >>
> >> List technical documents are available at:
> >> http://www.si-list.net
> >>
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> >> 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
> >>
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> >> 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:
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> >
> > 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
> >
> >
> >
> >
>
>
> --
> Steve Weir
> IPBLOX, LLC
> 150 N. Center St. #211
> Reno, NV 89501
> (866) 675-4630 Business
> (707) 780-1951 Fax
> http://www.ipblox.com
> A Teraspeed Consulting Group LLC Partner
>
> Teraspeed Consulting Group
> 121 North River Drive
> Narragansett, RI 02882
> (401) 284-1827 Business
> (401) 284-1840 Fax
>
> Teraspeed Labs
> 13610 SW Harness Lane
> Beaverton, OR 97008
> (503) 430-1065 Business
> (503) 430-1285 Fax
> A Teraspeed Consulting Group LLC Partner
>
> http://www.teraspeed.com
>
> This e-mail contains proprietary and confidential intellectual property of
> IPBLOX LLC
> ----------------------------------------------------------------------------
> --------------------------
> Teraspeed(R) is the registered service mark of Teraspeed Consulting Group
> LLC
>
> ------------------------------------------------------------------
> 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
>
>
>
> ------------------------------
>
> End of si-list Digest V9 #315
> *****************************
>
>
------------------------------------------------------------------
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
Other related posts:
