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 > > > > > > ------------------------------------------------------------------ > > 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: > > //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: > //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