| Electronics > Projects, Designs, and Technical Stuff |
| Proper way to tie Analog Ground, Digital Ground, and Earth Ground together. |
| (1/2) > >> |
| SirDan:
Hello, I have been searching the net for answers on how to properly tie Analog Ground, Digital Ground, and Earth Ground together on our PCB. I found many ways to do this. Some use caps, some use resistors and caps, etc. I found a forum post on electronics.stackexchange.com and chose a variation of the method the top answer likes the best --- Quote ---Short them together directly via the mounting holes on the PCB --- End quote --- . The reference design that our project is based on shows the grounds tied together like the attached image, through a bead and a resistor: reference-design-grounds.jpg I marked L1 and R1 do not populate on the schematics so I have some options when EMC testing. What I have done is shown (attached) in layout.jpg Just looking for any opinions on this. What is the best way? Does the layout we have look OK? Regards, Dan |
| OM222O:
you need to use the star grounding technique. 0ohm resistors or inductors are used in order to allow the PCB design software to distinguish between the nets and to avoid ground loops. for prototyping on a breadboard or similar, just use 3 wires tied at one end to the common Earth/AGround/DGround and use each of the other ends for a seperate circuit. |
| DaJMasta:
Yep, star grounding is the right approach. Putting extra impedance between the local and common grounds means you can end up with different potentials on each side, much moreso than is generated by a nice large grounding trace or wire. If your grounds are at different potentials, that's where you run into trouble, so a low impedance path that meets at a primary point keeps the analog and digital grounds at similar potentials, while still keeping them somewhat separate, and prevents one of your eventually connected grounds from moving to something else and causing trouble. |
| T3sl4co1l:
If you don't know what you're doing, tie everything together, as often as possible, as widely as possible -- on a ground plane. When something is looking to need some ground isolation, don't try and hack it. Isolate it fully, and deal with signals and the common mode as you can. If management / customer balks, just remind them of what they are truly asking for. They may decide to relax the spec as a result, or they will proceed with a higher quality design than the compromise they had anticipated. It takes years of theoretical and practical knowledge, perhaps decades, to understand all the factors in play here. Even for all my experience, I don't have much confidence in pulling off anything fancier, and even then only in extreme cases that are worth the extra consideration. I cannot begin to answer your particular question from the information provided. To do that, I would require as inputs, what all the connecting cables are intended to be connected to, what they may (unintended) be connected to, what the enclosure and connectors look like, and what the complete circuit looks like, both in schematic and layout. (I don't necessarily need the whole circuit, but the kind of information that I'm looking for is again hard to describe. The circuit may not've been designed or laid out in the same format as the information I need, so it's most likely easier to read the design myself, and parse it into the format I need.) Finally, I need the EMC specs (if any) for the project. I hope that, by enumerating how much is required to make a judgement, that this gives some perspective on how in-depth this question really is. Tim |
| capt bullshot:
--- Quote from: T3sl4co1l on April 23, 2019, 05:47:05 pm ---If you don't know what you're doing, tie everything together, as often as possible, as widely as possible -- on a ground plane. --- End quote --- I'd expand that to "if you don't know or if you think you know what you're doing". Otherwise nothing to add. There's a lot of use cases that may require isolation here. Most of these cases require "real" isolation, like T3sl4co1l said. Only a few may work without, but most approaches I've seen to separate Earth and circuit GND without real isolation failed in some way. |
| Navigation |
| Message Index |
| Next page |