Emerson COM Express Carrier Design Manual page 73

 Do not completely isolate the analog/audio ground plane from the rest of the carrier board ground
plane. Provide a single point (0.25 in to 0.5 in wide) where the analog/isolated ground plane
connects to the main ground plane. The split between the planes must be a minimum of 0.05 in
wide.
 Any signals entering or leaving the analog area must cross the ground split in the area where the
analog ground is attached to the main carrier board ground. This means that no signal should cross
the split/gap between the ground planes because this would cause a ground loop, which in turn
would greatly increase EMI emissions and degrade the analog and digital signal quality.
COM Express Carrier Type 2
Design Guide
Page 73 of 103