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:k...@emc-seminars.com] Sent: Wednesday 28 June 2017 22:03 To: EMC-PSTC@LISTSERV.IEEE.ORG 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:k...@emc-seminars.com> | 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 <bstu...@dlsemc.com> 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:k...@emc-seminars.com] Sent: Wednesday, June 28, 2017 1:29 PM To: EMC-PSTC@LISTSERV.IEEE.ORG 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 <mailto:k...@emc-seminars.com> Email Me! | <http://www.emc-seminars.com/> Web Site | <http://design-4-emc.com/> Blog <http://www.edn.com/blog/The-EMC-Blog> The EMC Blog (EDN) <http://www.emc-seminars.com/Newsletter/Newsletter.html> Subscribe to Newsletter <http://www.linkedin.com/in/kennethwyatt> Connect with me on LinkedIn On Jun 28, 2017, at 11:35 AM, Ralph McDiarmid < <mailto:ralph.mcdiar...@schneider-electric.com> ralph.mcdiar...@schneider-electric.com> 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:000000f5a03f18eb-dmarc-requ...@ieee.org> mailto:000000f5a03f18eb-dmarc-requ...@ieee.org] Sent: Saturday, June 24, 2017 8:33 PM To: <mailto:EMC-PSTC@LISTSERV.IEEE.ORG> EMC-PSTC@LISTSERV.IEEE.ORG 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. 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