What is this ting called "Chassis Ground" that everyone keeps referring to? Last I remember it was just the green wire on the AC cord that UL requires. How does that play into discussion of EMI? > [Original Message] > From: <chen_jinhua@xxxxxxx> > To: <erdinih@xxxxxxxxx>; <xileil@xxxxxxxxxxx> > Cc: <si-list@xxxxxxxxxxxxx> > Date: 8/15/2006 9:16:30 AM > Subject: [SI-LIST] Re: Cable grounding scheme > > Ihsan > > If I understand your email correctly, you still use separate chassis and > logic grounds. But you use many many stitching points to connect them > together. If you consider the high speed cable application. It will > impact SI. If the cable does not have separate logic and chassis > grounds. Cable reference is chassis ground when it connects to the board > connector. From connector to semiconductor chips, there will be a > reference interruption because chip references to logic ground. Depends > on how bad of the reference interruption, the SI impacts will vary. If > the signal-point connection is used, I would guess the SI impact is > huge. > > This brings an old question: single-point connection vs. many many > points of connections, which one we prefer for high speed SI and EMI? Or > it depends ... > > Thanks! > > Jinhua > ________________________________ > > From: Ihsan Erdin [mailto:erdinih@xxxxxxxxx] > Sent: Tuesday, August 15, 2006 9:40 AM > To: Xilei Liu > Cc: chen, jinhua; si-list@xxxxxxxxxxxxx > Subject: Re: [SI-LIST] Re: Cable grounding scheme > > > Celine, > > First of all, I want to express my apologies to Jinhua for -kind of- > hijacking his topic for a potentially flaring issue. > I think this issue goes as far back as the debate over single-point > vs.multi-point connection between chassis and digital grounds. As such, > it is more of an conducted/radiated emission problem than SI. The > dilemma is while single-point connection could be justified by the fact > that it avoids very low frequency common mode (noise) currents from > creeping into the power line, in order to cut down on the radiated > emissions at high frequencies, multi-point connection is strictly > required between the two reference systems. In his "EMC and printed > Circuit board design theory and layout made simple" book, for example, > M. Montrose suggests stitching the two reference systems at a distance > of lambda/20, with lambda being the wavelength of the highest frequency > component of the spectrum of the system. The book was published in 1999. > With today's multi-gigahertz systems, it's impossible to achieve such a > design goal and it's an overkill at any rate. But the necessity of > multi-point connection is not a debate any more. Some designers try to > find a mid-way by connecting the reference systems with high frequency > caps but the boards are already overly-populated by the same type of > caps used for decoupling and there's the issue of parasitic inductances > that defeat the purpose. Today, the commonplace approach, at least in > the designs that I observe, is to suppress the low frequency CM currents > with power line filters and directly connect the chassis and digital > grounds at practically as many points as possible against radiated > emissions. > If you want to see some numbers and charts to support these ideas, in > "EMI and Troubleshooting Techniques" book, M. Mardiguian gives a very > good example that compares the two grounding strategies. > > Regards, > > Ihsan > > > On 8/15/06, Xilei Liu <xileil@xxxxxxxxxxx> wrote: > > Hey, Ihsan, > > I've ever seen notes that published in the past in 2002, saying > that"we > learned from NRAO engineers that it is both feasible and > advisable to > physically separate digital circuits from analog systems, and to > interpose a > minimum of two levels of Faraday shielding acting in series." > From my point > of view, it should be easier to employ different EMI solutions > for power > line and signal line separately when the digital/analog grounds > are > separated and connected somehow at a single-point. What will be > the problems > in terms of SI? Welcome your 'fight back' so that I can learn > more ;) > > Regards, > Celine > > > >From: "Ihsan Erdin" <erdinih@xxxxxxxxx> > >Reply-To: erdinih@xxxxxxxxx > >To: chen_jinhua@xxxxxxx > >CC: si-list@xxxxxxxxxxxxx > >Subject: [SI-LIST] Re: Cable grounding scheme > >Date: Tue, 15 Aug 2006 06:29:32 -0400 > > > >This question makes me wonder if there're any designers left > who still > >separate logic ground from the chassis ground in high-speed > digital circuit > >design -and on what basis? I thought this whole issue of > chassis vs. logic > >ground was something of the past. > >Regards, > > > >Ihsan > > > >On 8/14/06, chen_jinhua@xxxxxxx <chen_jinhua@xxxxxxx > wrote: > > > > > > Hi, > > > > > > I have a few general questions about the high speed cable > grounding > > > scheme. It could impact both SI and EMI. I would like to > have your > > > inputs about this issue. > > > > > > Scheme 1: cable does not separate logic ground and chassis > ground. But > > > when it connects the system/boards, the system/boards have > separate > > > logic ground and chassis ground. How do you separate/connect > the logic > > > ground to chassis ground in boards? What is the pros and > cons for SI > > > and/or EMI?=20 > > > > > > Scheme 2: Cable keeps separate logic ground and chassis > ground. > > > System/boards also keep the separate logic and chassis > ground. Cable > > > logic ground and board logic ground connects, and chassis > connects the > > > chassis ground. How do you separate/connect the logic ground > to chassis > > > ground in boards? What is the pros and cons for SI and/or > EMI? > > > > > > Do you prefer scheme 1 or scheme 2? What is the pros and > cons of scheme > > > 1 vs. scheme 2 for SI and/or EMI? Does SI and EMI have > conflict > > > requirements? > > > > > > Thanks! > > > > > > Jinhua Chen > > > SI of Hardware Engineering > > > EMC Corp. > > > > ------------------------------------------------------------------ > > > 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 FAQ wiki page is located at: > > > http://si-list.org/wiki/wiki.pl?Si-List_FAQ > > > > > > List technical documents are available at: > > > http://www.si-list.org > > > > > > 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 FAQ wiki page is located at: > > http://si-list.org/wiki/wiki.pl?Si-List_FAQ > > > >List technical documents are available at: > > http://www.si-list.org > > > >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 FAQ wiki page is located at: > http://si-list.org/wiki/wiki.pl?Si-List_FAQ > > List technical documents are available at: > http://www.si-list.org > > 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 FAQ wiki page is located at: http://si-list.org/wiki/wiki.pl?Si-List_FAQ List technical documents are available at: http://www.si-list.org 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