"Grounding" according to Analog Devices - Page 1
Forum section: electronics / general

author: SiliconWizard
author_rank: Super Contributor
timestamp: February 17, 2023, 02:19:03 am
content: https://www.analog.com/en/analog-dialogue/articles/staying-well-grounded.html(Well, I don't know how the author is affiliated with AD though.)A lot of bad advice and a few reasonable points. Curious to hear about your thoughts.

author: KaneTW
author_rank: Frequent Contributor
timestamp: February 17, 2023, 02:46:45 am
content: I saw this ages ago. IMO it just doesn't hold the test of time anymore.Keep all your ground well connected. Be aware of your return currents and how/where they flow. Enclose sensitive and noisy signals between ground planes if you can.

author: Bud
author_rank: Super Contributor
timestamp: February 17, 2023, 03:02:48 am
content: Quote from: SiliconWizard on February 17, 2023, 02:19:03 amThe author's Bio is provided at the bottom of the web page.

author: BrianHG
author_rank: Super Contributor
timestamp: February 17, 2023, 03:30:43 am
content: Quote from: SiliconWizard on February 17, 2023, 02:19:03 amCant get past the stupid cookie consent. Why do they do this....

author: sleemanj
author_rank: Super Contributor
timestamp: February 17, 2023, 03:34:35 am
content: Quote from: BrianHG on February 17, 2023, 03:30:43 amBecause it's a legal requirement in europe.It's IMHO possibly the stupidest legal requirement that Europe has ever made, because it's just an annoyance and everybody just clicks ok anyway without even considering reading it. All it does is train people to click the obvious button to see the content.

author: Psi
author_rank: Super Contributor
timestamp: February 17, 2023, 03:42:48 am
content: Quote from: BrianHG on February 17, 2023, 03:30:43 amDid you try actually accepting the cookie?Or are you doing a 'homer' and holding onto the can in the vending machine while complaining you're arm is stuck?

author: SiliconWizard
author_rank: Super Contributor
timestamp: February 17, 2023, 03:50:01 am
content: Quote from: KaneTW on February 17, 2023, 02:46:45 amYep. The slits in ground planes really were too much.

author: floobydust
author_rank: Super Contributor
timestamp: February 17, 2023, 03:56:14 am
content: There are no simple one sentence answers about grounding. It's not that simple and takes many years of practical experience to know what you are doing.Entire books are written about the subject. I don't say much to anyone who asks about it (here) because I'm not offering a course on it. There is a lot of wisdom needed and every year digital circuitry goes up in speed.The AD article looks at a few specific cases, gives orders on what to do... I don't agree with all of it but at least some equivalent circuits are presented. He ignores transmission line effects which I think is a mistake. I say 'proof is in the pudding' - look at Analog Devices eval boards, how they do the PCB layout. Not that they are always well done but apparently they achieve the IC's specifications. You'll soon see lately the approach is just to use more PCB layers and panic ground everything.Because there is a disconnect between the PCB layout person and the IC engineering team and PCB layout is always a last minute rush at the end of that kind of project, it is not always done the best. When it fails EMC then people pay attention lol. But AD rarely makes product designs that far, so how can their people even know their approach is bad?

author: Bud
author_rank: Super Contributor
timestamp: February 17, 2023, 04:22:49 am
content: 10 years ago when I was speaking to an AD Lab engineer he said they use solid ground plane for characterization of their ICs and design of evaluation boards.

author: coppercone2
author_rank: Super Contributor
timestamp: February 17, 2023, 05:13:43 am
content: there is ground advicethen you run into a real life USB implementation.does anyone not care anymore? Like its not worth the stomach ache because you can... respin the board if there is a problem. I don't care about these insane grand unified theories of construction anymore.Here is a visualization exersize. Imagine for thermal and cost reasons you have to put a IC clamped to the side of a chassis that has hand soldered hook up wire attaching it to the PCB. You did it, and it got through the test lab. There are no real problems, and someone told the stickler to shut up because it made enough money. It won't be getting re designed, and the customer is happy.

author: mulcahla
author_rank: Newbie
timestamp: February 17, 2023, 02:57:42 pm
content: Quote from: SiliconWizard on February 17, 2023, 02:19:03 amWhich sections are bad advice in your opinion? I have been designing 40 input, 1.0 uV-stable ADC circuits for thermocouple measurements with their IC's (AD7793) and following their design guidelines. Still looking for ways to improve this circuit if you could offer better advice.

author: shapirus
author_rank: Super Contributor
timestamp: February 17, 2023, 03:52:37 pm
content: Quote from: KaneTW on February 17, 2023, 02:46:45 amWhat would be a good article to read on this topic these days?

author: PlainName
author_rank: Super Contributor
timestamp: February 17, 2023, 04:08:47 pm
content: QuoteYou can respin if you notice a problem. What about if it's a bit iffy but works fine on your bench - is it still going to work under different circumstances somewhere else?

author: coppercone2
author_rank: Super Contributor
timestamp: February 17, 2023, 04:49:36 pm
content: Quote from: mulcahla on February 17, 2023, 02:57:42 pmI suggest a 1/4 size prototype for testing to see if you have the right track.

author: exe
author_rank: Unknown
timestamp: February 17, 2023, 04:51:07 pm
content: So... what's wrong with the article?

author: Infraviolet
author_rank: Super Contributor
timestamp: February 17, 2023, 08:17:19 pm
content: If you're still having a cookie popup problem, try NoScript or another script blocker, page loads fine for me using those, no pop-ups in the way anywhere.

author: SiliconWizard
author_rank: Super Contributor
timestamp: February 17, 2023, 10:21:50 pm
content: Quote from: Bud on February 17, 2023, 04:22:49 amNot surprised. Anyone sane does that. You don't cut your planes with slits or worse (in most cases), separate ground planes and connect them in a single point.That's a case of: do what I do, not what I say.

author: EPAIII
author_rank: Super Contributor
timestamp: February 18, 2023, 07:13:01 am
content: They do it because the people who write code are tyrants. Their way or the highway! Period. Ever try to get one to do a simple project? No way Jose! Gotta have all the latest bells and whistles when all you want it to do is ring a doorbell.Been there! They won! Overnight project took 1.5 years.Quote from: BrianHG on February 17, 2023, 03:30:43 am

author: wraper
author_rank: Unknown
timestamp: February 18, 2023, 07:56:31 am
content: Ground splitting is a sure way how to fail EMI tests and have random operation failures. In some cases causing IC latch-up, personally seen that in a commercial device that brand new cost like $100k. Replacing ADC or even swapping the whole board did not fix the issue of ADC latching up and heating like hell like 1-3 times in a year (sat on both analog and digital GND connected in other place on PCB). The only fix that worked was connecting grounds under this IC. It more or less worked in the past when digital part was slow. But now with very fast digital signals making slits in GND is intentionally making good antennas. I'm not saying is should never be done, however it only makes things worse in 99% of cases. Digital/analog ground splitting is not the worst though. The most popular thing seems to be splitting GND at USB shield. Many app notes suggest that too. The funny thing is that some suggest adding a cap in series, others a ferrite bead, making them do exactly opposite thing. And some even add a cap in parallel with inductor making a nice LC circuit. Just look on this abomination from Arduino UNO. A nice way how to divert ESD from USB shield into data lines through devices which are supposed to protect from it.

author: JohanH
author_rank: Frequent Contributor
timestamp: February 18, 2023, 08:16:47 am
content: "How to Achieve Proper Grounding" - Rick HartleyDefinitely recommended to watch this training. This is an expert with 50 years of experience of signal integrity and EMI and he assists companies in these matters.

author: JohanH
author_rank: Frequent Contributor
timestamp: February 18, 2023, 08:25:19 am
content: Here's a list of literature that Rick Hartley recommends:https://resources.altium.com/p/reading-list-emi-noise-control

author: JohanH
author_rank: Frequent Contributor
timestamp: February 18, 2023, 08:27:13 am
content: To be noted that @RobertFeranec on Youtube has many sessions and interviews with Rick Hartley.

author: exe
author_rank: Unknown
timestamp: February 18, 2023, 09:15:59 am
content: I quickly skimmed through the article and I don't see horrors that you guys suggest. Their example of adding slits makes perfect sense to me: to prevent high currents going through sensitive analog part where space is at premium and relocating components away from current paths is not an option ("due to the realities of the mechanical design").I guess what we are talking here is that modern best practice is to have an uninterrupted ground plane, use of 4+ layers pcb, route digital signals on adjacent to gnd layer, and minimize interference between components by carefully placing them so their "return" paths do not overlap.

author: wraper
author_rank: Unknown
timestamp: February 18, 2023, 09:27:46 am
content: Quote from: exe on February 18, 2023, 09:15:59 amThe thing is that return path at high frequencies go only right under the traces if there is a solid ground plane, so they will not travel to somewhere far away into the analog part. And if you have traces which go over a slit in the ground plane, you create more problems than you solve as energy somehow needs to travel in the return path and it won't go over remote connection between analog and digital grounds. Note that frequency is not a frequency of digital signals but a rise time.

author: exe
author_rank: Unknown
timestamp: February 18, 2023, 10:27:54 am
content: Quote from: wraper on February 18, 2023, 09:27:46 amFor digital signals yes, but that doesn't apply to low frequency analog signals. So no digital traces should go between analog parts, right?

author: buta
author_rank: Contributor
timestamp: February 18, 2023, 10:48:16 am
content: Quote from: BrianHG on February 17, 2023, 03:30:43 amcookie consent popup->cookie details->decline cookies at bottomrightleft

author: m k
author_rank: Super Contributor
timestamp: February 18, 2023, 11:01:34 am
content: What am I seeing, electricity or heat?If electricity then how it is measured?

author: Siwastaja
author_rank: Super Contributor
timestamp: February 18, 2023, 07:21:01 pm
content: Quote from: wraper on February 18, 2023, 09:27:46 am... but the return currents of low-frequency signals (down to DC; including power!) do not follow the track on the top, but distribute over larger area, in the ratio of path resistances.While solid, uncut, single ground plane is known to be optimal forEMCandEMIin almost all cases, the exception where cuts can increase performance is high-resolution, high-accuracy low-frequency single-ended analog signals. It does not help with EMI; but it helps with accuracy, simply by removing or reducing the DC supply return current from the measurement path.Careful placement of parts is of course super important. When one reaches a solution which minimizes the DC level problem even without cutouts, that placement also carries least EMC risk if/when the cuts are added. In other words, the separate area where the "ground" acts like a pseudo-differential signal, should be at some corner of the PCB, far away from any fast signals. Crossing a plane gap with a fast signal is a disaster.

author: ejeffrey
author_rank: Super Contributor
timestamp: February 22, 2023, 04:04:52 am
content: Quote from: wraper on February 18, 2023, 09:27:46 amThe case in the article was when a large DC return current is flowing past the analog circuitry. It's DC so it will fan out to cover the entire width of the ground plane and create a voltage gradient across the board due to the non zero resistance of the copper. This means that each device in the analog section sees a slightly different ground voltage and if you have ground reference signals they will see that offset.The ground slit has no traces over it but corrals the return current away from the analog circuits.It's not an ideal situation to be in but it does happen, particularly when building very high resolution low frequency analog circuits such as DMMs.

author: David Hess
author_rank: Super Contributor
timestamp: February 22, 2023, 02:36:11 pm
content: Quote from: Bud on February 17, 2023, 04:22:49 amThey can do that because their evaluation boards are much simpler than what most of their customers are doing. They only require the analog section and its digital interface. Those boards, and the specifications that come from them, represent the best case performance available from the part. Real world designs may never achieve that no matter how well they are laid out, like with multiple separate converters where a single point ground is impossible.Quote from: JohanH on February 18, 2023, 08:16:47 amBut he is not an expert in precision design. He even admits that the people he advise are not dealing with precision, like telecom companies. The difference can easily be a factor of 1000 when dealing with 16+ bit converters.Doing what he suggests will prevent getting full performance out of high resolution converters, and for many applications that is good enough. The RF guys get away with it because they are not combining baseband conversion and precision, and other factors like IP3 limit their ultimate performance anyway.