Post by thread:[EE] circular board and ground plane

I've got a square board, but with a circle routed out in the middle. Its about 200mm square, with a 100mm diameter circle. So, I'm thinking that its probably not a really good idea to have it be a solid ground plane, but for EMI purposes somwhere it should slice that plane so its not a complete loop and act as an antenna. Thoughts? --------------------------------- Never miss a thing. Make Yahoo your homepage.

See, when boys heard about holes, mucles. :) On 1/23/08, alan smith <spam_OUTmicro_eng2TakeThisOuTyahoo.com> wrote: > I've got a square board, but with a circle routed out in the middle. Its about 200mm square, with a 100mm diameter circle. > > So, I'm thinking that its probably not a really good idea to have it be a solid ground plane, but for EMI purposes somwhere it should slice that plane so its not a complete loop and act as an antenna. > > Thoughts? > > > --------------------------------- > Never miss a thing. Make Yahoo your homepage. > -

On Jan 23, 2008 10:54 AM, alan smith <micro_eng2KILLspamyahoo.com> wrote: > I've got a square board, but with a circle routed out in the middle. Its about 200mm square, with a 100mm diameter circle. > > So, I'm thinking that its probably not a really good idea to have it be a solid ground plane, but for EMI purposes somwhere it should slice that plane so its not a complete loop and act as an antenna. > > Thoughts? It depends.. (standard EMI answer :) If you have a lot of high speed current flowing, then it will go around the circle, but then again, the root problem would be that you don't have the source and return currents taking the same path, or as close to it as possible. If you do, then having the plane go all the way around should be fine, as you wouldn't have current using the plane to find it's way home.

A slice may cause it to look more like an antenna than a solid plane. It depends greatly on the types and locations of current flowing through the ground plane. Regardless, it's a large enough plane that if you have a matching power plane, place several decoupling capacitors around (perhaps as part of normal decoupling), and the entire circuit is fairly low speed then I'd be surprised if you had any issues due to the ground plane design. If you want to experiment and can afford a few extra resistors, place the slit in the plane and place pads for a few zero ohm resistors to bridge the gap. Then you can put nothing in, shorting resistors, and even inductors or capacitors for testing to see what the best policy is. Let us know how it turns out! -Adam On 1/23/08, alan smith <.....micro_eng2KILLspam.....yahoo.com> wrote: > I've got a square board, but with a circle routed out in the middle. Its about 200mm square, with a 100mm diameter circle. > > So, I'm thinking that its probably not a really good idea to have it be a solid ground plane, but for EMI purposes somwhere it should slice that plane so its not a complete loop and act as an antenna. > > Thoughts? > > > --------------------------------- > Never miss a thing. Make Yahoo your homepage. > -

Thats actually my plan, add a few 0603 pads for jumpers and give me options. Probably wont have the board for any EMI testing till fall sometime, but if I can get my hands on one of the early proto's when the software is up and running, might be fun to stick it in the chamber and sniff it out. Thanks all for the replies. "M. Adam Davis" <EraseMEstienmanspam_OUTTakeThisOuTgmail.com> wrote: A slice may cause it to look more like an antenna than a solid plane. It depends greatly on the types and locations of current flowing through the ground plane. Regardless, it's a large enough plane that if you have a matching power plane, place several decoupling capacitors around (perhaps as part of normal decoupling), and the entire circuit is fairly low speed then I'd be surprised if you had any issues due to the ground plane design. If you want to experiment and can afford a few extra resistors, place the slit in the plane and place pads for a few zero ohm resistors to bridge the gap. Then you can put nothing in, shorting resistors, and even inductors or capacitors for testing to see what the best policy is. Let us know how it turns out! -Adam On 1/23/08, alan smith wrote: > I've got a square board, but with a circle routed out in the middle. Its about 200mm square, with a 100mm diameter circle. > > So, I'm thinking that its probably not a really good idea to have it be a solid ground plane, but for EMI purposes somwhere it should slice that plane so its not a complete loop and act as an antenna. > > Thoughts? > > > --------------------------------- > Never miss a thing. Make Yahoo your homepage. > -