[sdiy] PCB layout rules

[Antti Huovilainen]

On Fri, 22 Dec 2006, John Luciani wrote:

> The cap is there for stability. It delivers surge currents through a low 
> impedance path to the IC. Without the capacitor you would have the 
> series inductance of a much longer trace which would result in voltage 
> dips and ringing at the Vcc pin of your IC.

Only if you had no cap there. I was speaking of the choice of cap between
V+ cap V- and V+ cap GND cap V-. The first cannot contaminate ground, yet 
should guarantee stability (an opamp after all does not actually use a 
ground for anything).

> The currents are probably not large enough in most sdiy applications to 
> require force and sense grounds.

Currents such as VCO cap discharge... Because nobody ever suffered from 
VCO soft sync ;)

> If you start chopping up your ground plane you may create ground loops 
> that will cause you more problems than the uV of accuracy you gain.

Of course you'd use tree/star ground then.

If you start using mixed signal circuitry (such as wavetable oscillators) 
then you're going to see a lot more noise and digital hash on the ground.

Antti

"No boom today. Boom tomorrow. There's always a boom tomorrow"
  -- Lt. Cmdr. Ivanova