EMI, Cross Talk, Ground Bounce
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Posted by samiam on April 23, 2007, 9:01 pm
Please log in for more thread options I am sure you all know the myriad of problems that can plague a digital circuit on a PCB, most through the fault of that phenomenon called INDUCTANCE!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! I am trying to change the way I lay out circuits on double sided PCB's that I build at home. I have reading up on signal integrity issues and learning that perhaps the way I have been doing things are flawed - ok TERRIBLY flawed. The question I have for the gurus on here is this?: assuming a situation where I dont go with the ideal layout method of seperate ground and power planes (a 3 - 4 layer board minimum) is there a way to get some of those sort of benefits on a two layer design? I can only build double sided boards at home, so any suggestions on optimal ways/methods of laying out signal/power/gnd tracks and vias to best defeat the voltage drops between traces and the noise and cross talk effects would be SINCERELY appreciated | ||||||||||||||||||||||
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Posted by Hal Murray on April 23, 2007, 9:55 pm
Please log in for more thread options I'd start by making the bottom layer a ground plane. That probably works OK for simple board. You have to find some way to get decent power distribution. You can get more "layers" by using wires, including helpers for the power. -- These are my opinions, not necessarily my employer's. I hate spam. | ||||||||||||||||||||||
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Posted by Fred Bartoli on April 24, 2007, 2:41 am
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samiam a écrit : > I am sure you all know the myriad of problems that can plague a digital
> circuit on a PCB, most through the fault of that phenomenon called > INDUCTANCE!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! > > I am trying to change the way I lay out circuits on double sided PCB's > that I build at home. > > I have reading up on signal integrity issues and learning that perhaps > the way I have been doing things are flawed - ok TERRIBLY flawed. > > The question I have for the gurus on here is this?: > assuming a situation where I dont go with the ideal layout method of > seperate ground and power planes (a 3 - 4 layer board minimum) is there > a way to get some of those sort of benefits on a two layer design? > > I can only build double sided boards at home, so any suggestions on > optimal ways/methods of laying out signal/power/gnd tracks and vias to > best defeat the voltage drops between traces and the noise and cross > talk effects would be SINCERELY appreciated Make your bottom layer a GND plane. Use SMDs as much as possible, and work hard on placing the components. Route the supplies with tracks and have a good bypass policy. If you have the possibility to place the bypass caps on bottom side (and for hobbyist boards you can) then do it. That should, for reasonable hobbyists project, leave few tracks to run on the bottom side and when you have to, do this on the shortest possible distance. If you have some difficult case, still for hobbyist use, you can easily live with a few additionnal jumpers, wires,... I've made some moderately complex (~400 SMDs) high volume boards that way and they were plain success. -- Thanks, Fred. | ||||||||||||||||||||||
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Posted by Joerg on April 26, 2007, 8:21 pm
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Fred Bartoli wrote: > samiam a écrit :
> >> I am sure you all know the myriad of problems that can plague a
>> digital circuit on a PCB, most through the fault of that phenomenon >> called >> INDUCTANCE!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! >> >> I am trying to change the way I lay out circuits on double sided PCB's >> that I build at home. >> >> I have reading up on signal integrity issues and learning that perhaps >> the way I have been doing things are flawed - ok TERRIBLY flawed. >> >> The question I have for the gurus on here is this?: >> assuming a situation where I dont go with the ideal layout method of >> seperate ground and power planes (a 3 - 4 layer board minimum) is >> there a way to get some of those sort of benefits on a two layer design? >> >> I can only build double sided boards at home, so any suggestions on >> optimal ways/methods of laying out signal/power/gnd tracks and vias to >> best defeat the voltage drops between traces and the noise and cross >> talk effects would be SINCERELY appreciated >
> > Make your bottom layer a GND plane. > Use SMDs as much as possible, and work hard on placing the components. > Route the supplies with tracks and have a good bypass policy. If you > have the possibility to place the bypass caps on bottom side (and for > hobbyist boards you can) then do it. > That should, for reasonable hobbyists project, leave few tracks to run > on the bottom side and when you have to, do this on the shortest > possible distance. If you have some difficult case, still for hobbyist > use, you can easily live with a few additionnal jumpers, wires,... > > I've made some moderately complex (~400 SMDs) high volume boards that > way and they were plain success. > In a pinch you can also buy jumpers in SMT. Often they are called "zero ohms resistors". They come in the popular SMT resistors sizes and probaby 1210 would be nice for hobby projects because that leaves a bit more space to route underneath. My layouter would close his eyes and tunnel a 0603 without breaking a sweat but don't do that for hobbyist boards. -- Regards, Joerg http://www.analogconsultants.com | ||||||||||||||||||||||
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Posted by Marra on May 5, 2007, 4:57 pm
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I would look for a decent PCB layout software that does autoplacing of components for shortest nets www.ckp-railways.talktalk.net/pcbcad21.htm | ||||||||||||||||||||||
>assuming a situation where I dont go with the ideal layout method of
>seperate ground and power planes (a 3 - 4 layer board minimum) is there
>a way to get some of those sort of benefits on a two layer design?