Bravo Gert! I fully agree that a single solid return plane will cure many EMI ills. The more separate “ground” return symbols there are, the more difficult it is to keep track of all the return paths and to keep them from intermixing. As you mention, it’s important to isolate (compartmentalize) motor and power control circuit return paths from analog and normal digital return paths. Todd Hubing covers this aspect very well in his circuit board design articles at http://www.cvel.clemson.edu/emc/index.html <http://www.cvel.clemson.edu/emc/index.html>.
I think there’s one other aspect to seriously consider when designing PC boards and that is designing with a “fields” viewpoint. We’re all very familiar with the “circuits” viewpoint - that is, HF currents flow in loops and these loops make every attempt to reduce the loop area through mutual inductance effects. When we fail to define the minimum return path, EMI is usually the result. That viewpoint is fine up to a point. We also need to consider the physics of how energy moves in transmission lines - especially important when it comes to PDN design and having the ability to supply current to local storage devices (decoupling caps) to meet the current demands of switching devices. Once you realize the actual field energy moves through the dielectric between, say, the microstrip and return plane, you also realize that any interruption in that return plane (path) will cause the EM field to “leak” and go where its not supposed to go (think “water pipes”). Again, the result is EMI. I explained this in more detail in the new 2017 EMC Fundamentals Guide, produced by Interference Technology. A free copy may be downloaded from here: http://learn.interferencetechnology.com/2017-emc-fundamentals-guide/ <http://learn.interferencetechnology.com/2017-emc-fundamentals-guide/>. I also highly recommend Ralph Morrison’s excellent book, “Grounding and Shielding - Circuits and Interference” (6th edition) and “Digital Circuit Boards - Mach 1 GHz". At 92 years old and still teaching seminars on the subject, he’s just wrapping up his 14th book on the physics of EM fields, which should be released this fall. It will cover the fields viewpoint when designing PC boards in much more detail. If you’d like to learn more about this aspect of PC board design, I’ve also invited him to provide the keynote presentation for our one-day EMC Live Bootcamp series of free webinars this coming November 15th. Check https://interferencetechnology.com <https://interferencetechnology.com/> for details as we get closer to the date. Bottom line? Speaking from experience, if you design your boards and products from a fields viewpoint, you’ll usually pass EMI. If you don’t, it usually means multiple board spins and product fixes. Cheers, Ken _______________________ I'm here to help you succeed! Feel free to call or email with any questions related to EMC or EMI troubleshooting - at no obligation. I'm always happy to help! Kenneth Wyatt Wyatt Technical Services LLC 56 Aspen Dr. Woodland Park, CO 80863 Phone: (719) 310-5418 Email Me! <mailto:[email protected]> | Web Site <http://www.emc-seminars.com/> | Blog <http://design-4-emc.com/> The EMC Blog (EDN) <http://www.edn.com/blog/The-EMC-Blog> Subscribe to Newsletter <http://www.emc-seminars.com/Newsletter/Newsletter.html> Connect with me on LinkedIn <http://www.linkedin.com/in/kennethwyatt> > On Jun 28, 2017, at 11:14 PM, ce-test, qualified testing bv, Gert Gremmen > <[email protected]> wrote: > > I second that !!!! Personal experience. > Often I give the advice to get rid of all these grounds and just create one > full continuous ground plane > including DGND AGND SGND and so on. Then customer comes back and has read > manufacturers recommendations for a chip and ignored my advice, only to fail > again. > I wonder how the big chip manufacturers application guides are made up. > Certainly not with EMI in mind. > Many times the performance of the system (bits or S/N ratio) also improves > afte creating a ground plane. > > There is one situation however, where separate grounds come into view. (rule > of thumb) Once the ratio of biggest voltage/current in the design exceeds > 10^5. This happens normally only in power systems (stepper motors / smps / > frequency regulated motor drives) or in extreme low signal processing ( uV / > nA) systems. Care should be taken that both grounds actually become ONE for > out-of-functional (=EMI) frequencies. > Once the signal comes in the EMI frequency range, other ways of > discrimination between common mode interference currents and differential > mode signal currents are necessary. (balanced signal twisted pairs, common > mode coils, transformers). > > Gert Gremmen > > > From: Ken Wyatt [mailto:[email protected]] > Sent: Wednesday 28 June 2017 22:03 > To: [email protected] > Subject: Re: [PSES] USB dongle connector shield filtered grounding > > Bill, thanks for the complement. One of my mentors, Dr. Tom Van Doren, of the > University Missouri - Rolla, would say “the more different “ground” symbols > he saw in a schematic, the more business he knew he would get”. > > Ken > > _______________________ > > I'm here to help you succeed! Feel free to call or email with any questions > related to EMC or EMI troubleshooting - at no obligation. I'm always happy to > help! > > Kenneth Wyatt > Wyatt Technical Services LLC > 56 Aspen Dr. > Woodland Park, CO 80863 > > Phone: (719) 310-5418 > > Email Me! <mailto:[email protected]> | Web Site > <http://www.emc-seminars.com/> | Blog <http://design-4-emc.com/> > The EMC Blog (EDN) <http://www.edn.com/blog/The-EMC-Blog> > Subscribe to Newsletter > <http://www.emc-seminars.com/Newsletter/Newsletter.html> > Connect with me on LinkedIn <http://www.linkedin.com/in/kennethwyatt> > >> On Jun 28, 2017, at 1:57 PM, Bill Stumpf <[email protected] >> <mailto:[email protected]>> wrote: >> >> Truly outstanding analogies Ken, Ralph & Bill. I too cringe every time I >> hear the term "ground" bandied about in EMI circles. It's a widely >> misunderstood term that the non-initiated envision as some sort of EMI black >> hole that's by some means able to soak up all that excess RF energy. I'm >> sure we all could tell some stories from the lab. >> >> >> Bill >> >> >> From: Ken Wyatt [mailto:[email protected] >> <mailto:[email protected]>] >> Sent: Wednesday, June 28, 2017 1:29 PM >> To: [email protected] <mailto:[email protected]> >> Subject: Re: [PSES] USB dongle connector shield filtered grounding >> >> Like they say in some movies…”follow the money”. In the case of EMC issues, >> it’s usually “follow the current”. Both differential and common mode >> currents want to return to their sources in the most expedient >> (low-impedance) route. If designers fail to define a return path, >> invariably, some of that RF current radiates. Once the noise source(s) are >> identified, then what’s the return path? There will always be a return >> path…just not always the one you want. >> >> Cheers, Ken >> >> _______________________ >> >> I'm here to help you succeed! Feel free to call or email with any questions >> related to EMC or EMI troubleshooting - at no obligation. I'm always happy >> to help! >> >> Kenneth Wyatt >> Wyatt Technical Services LLC >> 56 Aspen Dr. >> Woodland Park, CO 80863 >> >> Phone: (719) 310-5418 >> >> Email Me! <mailto:[email protected]> | Web Site >> <http://www.emc-seminars.com/> | Blog <http://design-4-emc.com/> >> The EMC Blog (EDN) <http://www.edn.com/blog/The-EMC-Blog> >> Subscribe to Newsletter >> <http://www.emc-seminars.com/Newsletter/Newsletter.html> >> Connect with me on LinkedIn <http://www.linkedin.com/in/kennethwyatt> >> >>> On Jun 28, 2017, at 11:35 AM, Ralph McDiarmid >>> <[email protected] >>> <mailto:[email protected]>> wrote: >>> >>> Rather than 'ground', perhaps 'RF return' or 'counterpoise' might be better >>> terms? >>> >>> I think the thing that makes EMC mysterious is that the complete RF circuit >>> is unseen and difficult to accurately define, given all the parasitic >>> elements. The experience of 'inside' verses 'outside' the chassis envelope >>> a prime example, something I encountered some years ago, but never fully >>> understood. >>> >>> Ralph McDiarmid >>> Product Compliance >>> Engineering >>> Solar Business >>> Schneider Electric >>> >>> >>> -----Original Message----- >>> From: Bill Owsley [mailto:[email protected] >>> <mailto:[email protected]>] >>> Sent: Saturday, June 24, 2017 8:33 PM >>> To: [email protected] <mailto:[email protected]> >>> Subject: Re: [PSES] USB dongle connector shield filtered grounding >>> >>> Ancient EMC mythology, well proven to be wrong and so abandoned decades ago. >>> And still it pops on occasion and often with new twists to revive the >>> mythology.So it gets ignored as those new to the stories, such that they >>> cannot figure it out, will need the lessons of 'on the job training'. >>> ps. the proper terminology needed to clearly enunciate the concepts is not >>> settled. >>> The physics is plain and simple but to describe it takes a lot words due to >>> a lack of commonly understood terminology. >>> For example 'ground' serves as the catchall term, for shielding, signal >>> return, power return, zero reference, analog return, digital return, >>> chassis, circuit, logic, cable, AND for Safety as in earth ground. >>> Now Maxwell's law's (made up by a mad Scotman back in the 1800's) dictate >>> that a so-called signal must be accompanied by its return signal, and >>> further more that return signal will couple as close as possible to the >>> original so-called signal. The two parts are inextricably intertwined and >>> cannot be considered separately, without great risk to ones grasp of >>> reality. Just as the alleged E-field and H-field are two aspects of the >>> same thing, which conveniently might be called the Poynting Vector, and are >>> related by the Impedance, the ratio of the two fields, which in free space, >>> well away from any conducting structures, is approximately 377 ohms. >>> >>> Now conducting structures, ones like a circuit 'ground', a chassis >>> 'ground', a shielding 'ground' and signal returns often called 'ground' and >>> the concept of 'inside' verses 'outside' which seems to ignore Maxwell, are >>> all going to make for a rich realm of mythology which is not well defined >>> and so, all sorts of imaginings are created to fill all the constructed >>> voids from using all these artificial concepts, when one simple concept is >>> necessary and sufficient to complete the structure. >>> >>> Aside: If that secret, the simple one, was to be 'leaked' to common >>> knowledge, we all would be out of a job in managing EMC since even the >>> simple digital guys could understand it. So we keep it under-wraps and >>> obscure by using mysterious language so that the neophytes and uninitiated >>> think that they understand and/or have no clue as to what is going on. >>> >>> Always the correct answer: "It depends!"- Bill >>> >>> >>> >>> >>> ______________________________________________________________________ >>> This email has been scanned by the Symantec Email Security.cloud service. >>> ______________________________________________________________________ >>> >>> - >>> ---------------------------------------------------------------- >>> This message is from the IEEE Product Safety Engineering Society emc-pstc >>> discussion list. To post a message to the list, send your e-mail to >>> <[email protected] <mailto:[email protected]>> >>> >>> All emc-pstc postings are archived and searchable on the web at: >>> http://www.ieee-pses.org/emc-pstc.html >>> <http://www.ieee-pses.org/emc-pstc.html> >>> >>> Attachments are not permitted but the IEEE PSES Online Communities site at >>> http://product-compliance.oc.ieee.org/ >>> <http://product-compliance.oc.ieee.org/> can be used for graphics (in >>> well-used formats), large files, etc. >>> >>> Website: http://www.ieee-pses.org/ <http://www.ieee-pses.org/> >>> Instructions: http://www.ieee-pses.org/list.html >>> <http://www.ieee-pses.org/list.html> (including how to unsubscribe) >>> List rules: http://www.ieee-pses.org/listrules.html >>> <http://www.ieee-pses.org/listrules.html> >>> >>> For help, send mail to the list administrators: >>> Scott Douglas <[email protected] <mailto:[email protected]>> >>> Mike Cantwell <[email protected] <mailto:[email protected]>> >>> >>> For policy questions, send mail to: >>> Jim Bacher: <[email protected] <mailto:[email protected]>> >>> David Heald: <[email protected] <mailto:[email protected]>> >> >> >> - >> ---------------------------------------------------------------- >> This message is from the IEEE Product Safety Engineering Society emc-pstc >> discussion list. To post a message to the list, send your e-mail to >> <[email protected] <mailto:[email protected]>> >> All emc-pstc postings are archived and searchable on the web at: >> http://www.ieee-pses.org/emc-pstc.html >> <http://www.ieee-pses.org/emc-pstc.html> >> Attachments are not permitted but the IEEE PSES Online Communities site at >> http://product-compliance.oc.ieee.org/ >> <http://product-compliance.oc.ieee.org/>can be used for graphics (in >> well-used formats), large files, etc. >> Website: http://www.ieee-pses.org/ <http://www.ieee-pses.org/> >> Instructions: http://www.ieee-pses.org/list.html (including how to >> unsubscribe) <http://www.ieee-pses.org/list.html> >> List rules: http://www.ieee-pses.org/listrules.html >> <http://www.ieee-pses.org/listrules.html> >> For help, send mail to the list administrators: >> Scott Douglas <[email protected] <mailto:[email protected]>> >> Mike Cantwell <[email protected] <mailto:[email protected]>> >> For policy questions, send mail to: >> Jim Bacher <[email protected] <mailto:[email protected]>> >> David Heald <[email protected] <mailto:[email protected]>> >> - >> ---------------------------------------------------------------- >> >> This message is from the IEEE Product Safety Engineering Society emc-pstc >> discussion list. To post a message to the list, send your e-mail to >> <[email protected] <mailto:[email protected]>> >> All emc-pstc postings are archived and searchable on the web at: >> http://www.ieee-pses.org/emc-pstc.html >> <http://www.ieee-pses.org/emc-pstc.html> >> Attachments are not permitted but the IEEE PSES Online Communities site at >> http://product-compliance.oc.ieee.org/ >> <http://product-compliance.oc.ieee.org/>can be used for graphics (in >> well-used formats), large files, etc. >> Website: http://www.ieee-pses.org/ <http://www.ieee-pses.org/> >> Instructions: http://www.ieee-pses.org/list.html (including how to >> unsubscribe) <http://www.ieee-pses.org/list.html> >> List rules: http://www.ieee-pses.org/listrules.html >> <http://www.ieee-pses.org/listrules.html> >> For help, send mail to the list administrators: >> Scott Douglas <[email protected] <mailto:[email protected]>> >> Mike Cantwell <[email protected] <mailto:[email protected]>> >> For policy questions, send mail to: >> Jim Bacher <[email protected] <mailto:[email protected]>> >> David Heald <[email protected] <mailto:[email protected]>> > > > - > ---------------------------------------------------------------- > This message is from the IEEE Product Safety Engineering Society emc-pstc > discussion list. To post a message to the list, send your e-mail to > <[email protected] <mailto:[email protected]>> > > All emc-pstc postings are archived and searchable on the web at: > http://www.ieee-pses.org/emc-pstc.html > <http://www.ieee-pses.org/emc-pstc.html> > Attachments are not permitted but the IEEE PSES Online Communities site at > http://product-compliance.oc.ieee.org/ > <http://product-compliance.oc.ieee.org/>can be used for graphics (in > well-used formats), large files, etc. > > Website: http://www.ieee-pses.org/ <http://www.ieee-pses.org/> > Instructions: http://www.ieee-pses.org/list.html (including how to > unsubscribe) <http://www.ieee-pses.org/list.html> > List rules: http://www.ieee-pses.org/listrules.html > <http://www.ieee-pses.org/listrules.html> > For help, send mail to the list administrators: > Scott Douglas <[email protected] <mailto:[email protected]>> > Mike Cantwell <[email protected] <mailto:[email protected]>> > > For policy questions, send mail to: > Jim Bacher <[email protected] <mailto:[email protected]>> > David Heald <[email protected] <mailto:[email protected]>> > - ---------------------------------------------------------------- This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. To post a message to the list, send your e-mail to <[email protected]> All emc-pstc postings are archived and searchable on the web at: http://www.ieee-pses.org/emc-pstc.html Attachments are not permitted but the IEEE PSES Online Communities site at http://product-compliance.oc.ieee.org/ can be used for graphics (in well-used formats), large files, etc. Website: http://www.ieee-pses.org/ Instructions: http://www.ieee-pses.org/list.html (including how to unsubscribe) List rules: http://www.ieee-pses.org/listrules.html For help, send mail to the list administrators: Scott Douglas <[email protected]> Mike Cantwell <[email protected]> For policy questions, send mail to: Jim Bacher: <[email protected]> David Heald: <[email protected]>
