I am putting together a mixed high speed digital and low level analog
board. Everything I've read suggested putting an analog ground plane
on the top layer directly under the ADC. With a LCC/gull wing type
package, the 'ground plane on the top layer' method always ended up
with a small ground patch inside the pin pads, isolated from the rest of
the ground plane except for a few pad connections where the pads
happen to be for a ground pin. That just doesn't seem like a good
way to do low impedence ground. Wouldn't I be better off using a
solid analog ground plane one layer down and run vias to the ground
pads??
-Anthony