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What about Polygon VIA shielding ?
xddarko , 05-07-2020, 07:34 AM
Hello guys,
I use 3 big polygon islands for GND to separate DGND, AGND, and PGND. All these copper pours are in the second layer (I use 4 layer board)
I was reading about via shielding lately which is used in shielding RF signals mostly and I thought to myself would it be good practice to use this technique to isolate GND planes from each other? Maybe power planes too??
I did not find anything talking about this topic, so I hope you share your thoughts.
Thank you.
I use 3 big polygon islands for GND to separate DGND, AGND, and PGND. All these copper pours are in the second layer (I use 4 layer board)
I was reading about via shielding lately which is used in shielding RF signals mostly and I thought to myself would it be good practice to use this technique to isolate GND planes from each other? Maybe power planes too??
I did not find anything talking about this topic, so I hope you share your thoughts.
Thank you.
beamray , 05-09-2020, 08:10 AM
May I ask why on Earth you split your ground? Most time it is not a good. You should do it only (!) it is critical, when you got your digital world close to analog. Power ground is only expectable for switching power supplies or for isolated power supplies ( supply divides input and output ground. You can say, it filters GND). U can do that but need to do star topology for your grounds. Also powers and signals should not switch GND planes.
I use isolated GNDs for well isolated signals^ power supply inputs, relay outputs, transformers coupled signals (Ethernet as example) and safety and chassis grounds.
You should shield signal with it's own ground (now ground overlapping, no signals changing GNDs).
I recommend you to look closely on your design. May be you do not need separating GND, may be a cut out will be fine, or may be just shielding vias.
I will leave here terry Fox's video (hope he is alive) https://www.youtube.com/watch?v=FLUHIzRbm1U
Also I'll share the story of subordinate of mine. Where was a nightmare analog-digital PCB with actual audio channel. But it was was so tiny. We made in rigit-flex big and small rigid parts. so what did we make: on the both sides of small part was digital circuits and in the big rigid part bottom was all digital, but top was analog.we put analog in enclosure and we separated PCBs stackup horizontally in the middle of in all was a 3 GNDs' sandwich (top to bottom) AGND-Chassis GND-DGND and we chose a point near the outer connector where we made 0Ohm resistors pads to connect theme. also we had to decouple GNDs using 1uF cap, 1MOhm Res and ferrite bid. and it works nicely, but now i can tell it was a nightmare.
I use isolated GNDs for well isolated signals^ power supply inputs, relay outputs, transformers coupled signals (Ethernet as example) and safety and chassis grounds.
You should shield signal with it's own ground (now ground overlapping, no signals changing GNDs).
I recommend you to look closely on your design. May be you do not need separating GND, may be a cut out will be fine, or may be just shielding vias.
I will leave here terry Fox's video (hope he is alive) https://www.youtube.com/watch?v=FLUHIzRbm1U
Also I'll share the story of subordinate of mine. Where was a nightmare analog-digital PCB with actual audio channel. But it was was so tiny. We made in rigit-flex big and small rigid parts. so what did we make: on the both sides of small part was digital circuits and in the big rigid part bottom was all digital, but top was analog.we put analog in enclosure and we separated PCBs stackup horizontally in the middle of in all was a 3 GNDs' sandwich (top to bottom) AGND-Chassis GND-DGND and we chose a point near the outer connector where we made 0Ohm resistors pads to connect theme. also we had to decouple GNDs using 1uF cap, 1MOhm Res and ferrite bid. and it works nicely, but now i can tell it was a nightmare.
mir0mik , 05-09-2020, 04:20 PM
Hello guys,
I use 3 big polygon islands for GND to separate DGND, AGND, and PGND. All these copper pours are in the second layer (I use 4 layer board)
I was reading about via shielding lately which is used in shielding RF signals mostly and I thought to myself would it be good practice to use this technique to isolate GND planes from each other? Maybe power planes too??
I did not find anything talking about this topic, so I hope you share your thoughts.
Thank you.
I use 3 big polygon islands for GND to separate DGND, AGND, and PGND. All these copper pours are in the second layer (I use 4 layer board)
I was reading about via shielding lately which is used in shielding RF signals mostly and I thought to myself would it be good practice to use this technique to isolate GND planes from each other? Maybe power planes too??
I did not find anything talking about this topic, so I hope you share your thoughts.
Thank you.
You probably don't deal with such wave lengths that via shield wold help you...@beamray - it depends on what he is doing, most of the "tutorials" on the internet are for high speed, where homogeneous ground (and ideally power planes too) are the way to go... But in SMPS is totally different world...
xddarko , 05-09-2020, 07:47 PM
@beamray Well, I use separate grounds because I use two switching DC DC buck converters (24V-12V and 12V-5V) , so I would like to keep its ground separated from the other digital/analog system, which are indeed near each other. They are connected via star topology so that way I insure there is no loop as mentioned in the video
Now I may not need via shielding normally, but I am asking about this because in my board, my usb connector happens to be near the edge of the DGND and close to the power GND which is a return path for a high current therefore can be very noisy, so I thought maybe some vias between the two planes would be good for the sake of good precaution? I mean would it harm?
All this apart, is this technique used for polygons or not?
Now I may not need via shielding normally, but I am asking about this because in my board, my usb connector happens to be near the edge of the DGND and close to the power GND which is a return path for a high current therefore can be very noisy, so I thought maybe some vias between the two planes would be good for the sake of good precaution? I mean would it harm?
All this apart, is this technique used for polygons or not?
mir0mik , 05-10-2020, 02:34 AM
It shouldn't do any harm - if you have free space for the vias...
robertferanec , 05-11-2020, 02:52 AM
I use separate grounds because I use two switching DC DC buck converters (24V-12V and 12V-5V)
Watch this, GND on server board: https://youtu.be/rdlEm2xjCsc?t=631
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