I have yet to see a trace to connector to cable interface that does not have what is effectively a 3D slot. On Mon, Nov 4, 2013 at 2:07 PM, <Ravinder.Ajmani@xxxxxxxx> wrote: > Hi Steve, > I agree. However I believe when Eric talks of tight return path, he > assumes that there are no return path discontinuities like slots. > > Regards > Ravinder Ajmani > HGST, a Western Digital Company > 5601 Great Oaks Pkwy > San Jose, CA 95119-1003 > ravinder.ajmani@xxxxxxxx > > > > > steve weir <weirsi@xxxxxxxxxx> > Sent by: si-list-bounce@xxxxxxxxxxxxx > 11/04/2013 10:45 AM > Please respond to > weirsi@xxxxxxxxxx > > > To > si-list@xxxxxxxxxxxxx > cc > > Subject > [SI-LIST] Re: Differential signals - skew - and EMC > > > > > > > Eric, those are all good points. The only exception that I take is to > statements about signals with tight return paths not radiating. They do > radiate. They don't radiate excessively. Doing foolish things like > passing signals, including differential signals, over slots increases > radiated power. > > Olive oil entrepreneur and sometimes EMC engineer Don Corleone to his > son: "Keep your signal paths close. Keep your return paths closer." > > Best Regards, > > > Steve > On 11/4/2013 8:32 AM, Eric Bogatin wrote: > > Hi folks- > > > > > > Here is an EDN blog I wrote a few weeks ago related to common currents > and > > Charles Grasso's question about how much is too much. > > > > > > > > > > http://www.edn.com/electronics-blogs/test-voices/4420453/Not-all-common-curr > > > ents-are-bad > > > > > > > > > > > > In my Advanced GigaBit Channel Design class, we go through the numbers. > Here > > is the brief analysis: > > > > > > > > It takes about 3 uA of common current on Unshielded Twisted Pair (UTP) > cable > > to fail FCC part 15 class B at about 100 MHz on a 1 m long external > cable. > > > > > > > > It takes about 1 mV of common signal driving the cable to drive 3 uA and > > fail the test. > > > > > > > > If the diff signal is 600 mV (like PCIe II), this is -55 dB of mode > > conversion from the source to the UTP front end to fail a radiated > emissions > > test. > > > > > > > > How can any product ship with an RJ45 connector for UTW cables if this > is > > the limit to mode conversion, at the ~ 100 MHz point? > > > > > > > > The solution is common mode chokes. With a 40 dB isolation, this allows > as > > much as -15 dB mode conversion before the common currents that get > through > > cause EMI problems. > > > > > > > > However, even with shielded twisted pair, a bad connector negates the > value > > of the shield proving the return for the common signal. > > > > > > > > How much radiated emissions you get is a function of how 360 degrees the > > connector is, hard to predict. > > > > > > > > This is why, as a "habit", do everything that is free to minimize > > asymmetries. When it cost more, use analysis to calculate the bang for > the > > buck. > > > > > > > > This is just one example of how common currents on external cables can > cause > > radiated emissions. > > > > > > > > --eric > > > > > > > > > > > > > > > > ******************************************************* > > Dr. Eric Bogatin, Signal Integrity Evangelist > > > > Bogatin Enterprises > > > > Setting the Standard for Signal Integrity Training > > web site: <http://www.bethesignal.com/> www.beTheSignal.com > > > > Blog: <http://www.bethesignal.com/blog> www.beTheSignal.com/blog > > > > Twitter @beTheSignal > > e: <mailto:eric@xxxxxxxxxxxxxxx> eric@xxxxxxxxxxxxxxx > > > > Laboratory: Connected Community Networks > > > > 105 S Sunset St, Suite J > > > > Longmont, CO 80501 USA > > > > cell: 913-424-4333 skype: eric.bogatin > > *********************************************** > > > > > > > > From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx] > On > > Behalf Of Grasso, Charles > > > > Sent: Friday, November 01, 2013 12:32 PM > > > > To: si-list@xxxxxxxxxxxxx > > > > Subject: [SI-LIST] Differential signals - skew - and EMC > > > > > > > > Hello, > > > > > > > > In an ideal situation differential signals will have no skew through the > > transmission path and (as I understand it) the common-signal (emi) will > be > > very low as a result. Given that EMC is very system dependent - does > any > > one have a rule of thumb or anxiety(!) factor for how much is skew is > > tolerable before becoming an emissions (regulatory) Issue? > > > > > > > > Thanks in advance. > > > > Charles Grasso > > > > > > > > > > > > ------------------------------------------------------------------ > > 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 forum is accessible at: > > http://tech.groups.yahoo.com/group/si-list > > > > List archives are viewable at: > > //www.freelists.org/archives/si-list > > > > Old (prior to June 6, 2001) list archives are viewable at: > > http://www.qsl.net/wb6tpu > > > > > > > > > -- > Steve Weir > IPBLOX, LLC > 1580 Grand Point Way > MS 34689 > Reno, NV 89523-9998 > www.ipblox.com > > (775) 299-4236 Business > (866) 675-4630 Toll-free > (707) 780-1951 Fax > > All contents Copyright (c)2013 IPBLOX, LLC. All Rights Reserved. > This e-mail may contain confidential material. > If you are not the intended recipient, please destroy all records > and notify the sender. > > ------------------------------------------------------------------ > 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 forum is accessible at: > http://tech.groups.yahoo.com/group/si-list > > List archives are viewable at: > //www.freelists.org/archives/si-list > > 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 forum is accessible at: > http://tech.groups.yahoo.com/group/si-list > > List archives are viewable at: > //www.freelists.org/archives/si-list > > Old (prior to June 6, 2001) list archives are viewable at: > http://www.qsl.net/wb6tpu > > > -- Scott McMorrow Teraspeed Consulting Group LLC 16 Stormy Brook Rd Falmouth, ME 04105 (401) 284-1827 Business http://www.teraspeed.com Teraspeed® 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 forum is accessible at: http://tech.groups.yahoo.com/group/si-list List archives are viewable at: //www.freelists.org/archives/si-list Old (prior to June 6, 2001) list archives are viewable at: http://www.qsl.net/wb6tpu