Ground planes?

[Scarr]

Hi,

I have been doing a project from quite some time now but have hit a interference problem, the project consists of GSM+GPS+MCU usual tracker thing.

I placed one large ground plane on both sides using a polygon pour after routing but I think this has caused a problem whereby I get interference on the 3.3v from the 3.8v supply to the GSM (in metal can), all IC's have decoupling caps and the GSM has smoothing as per manufacturers spec.

My question is, what it the best general rule for ground planes in a mixed deign like mine?

1) One ground place on both sides with more smoothing
2) two/three ground planes, power circuit, GSM, MCU
3) Run a track around outer edge on both sides

Hope someone can help, I know it's a large subject but just some guidance as to the best approach.

Thx

 

[hjames]

I'm not sure if this is going to be terribly helpful for this particular problem, but in the vein of "here's the 'FM', read it when you get a chance":

**broken link removed**

All you wanted to know about signal integrity issues.

How many layers is this board?

 

[Analog]

I've used many ground planes, and power planes for that matter. Generally, I embed them in the internals of a multi-layer design so they're not visible from either side. The problem is, that ground planes are basically large capacitive plates, and can hinder high frequency circuits, so you have to be careful, as they may introduce unwanted parasitics.

I use them in primarily mixed signal analog and digital designs. I usually have a ground plane in sensitive amplifying and signal conditioning circuitry. I usually split the ground plane into a digital and analog ground, keeping digital and analog circuits separate on the board. The A/D is usually where they meet. HTH.

 

[Styx]

not only that but if you make the GND and power planes oo big they are a real pain to solder things downto, unless thermal relief vias a used