Incorrect Direct Rambus* Ground Plane Referencing; Direct Rambus Ground Plane Reference - Intel VC820 - Desktop Board Motherboard Design Manual

2.6.2.3 Direct Rambus* Ground Plane Reference
All RSL signals must be referenced to GND to provide an optimal current return path. The direct
Rambus ground plane reference must be continuous to the Vterm capacitors. The ground reference
island under the RSL signals must be continuous from the last RIMM to the back of the termination
capacitors. Choose the reference island shape such that power delivery to the components is not
compromised. The return current will flow through the Vterm capacitors into the ground island and
under the RSL traces. Any split in the ground island will provide a sub-optimal return path. In a 4
layer board, this will require the Vterm island to be on an outer layer. The Vterm island should
ALWAYS be placed on the top layer. Refer to
example of power plane splits.
Figure 2-15. Incorrect Direct Rambus* Ground Plane Referencing
Figure 2-16. Direct Rambus Ground Plane Reference
The ground reference island under the RSL signals MUST be connected to the ground pins on the
RIMM connector and the ground vias used to connect the ground isolation on the 1
®
Intel 820 Chipset Design Guide
MCH
1.8V Plane
MCH
GND Plane
GND Plane
Extend GND PLANE
Reference Island Beyond
Vterm Capacitors
Section 6.2, "Power Plane Splits" on page 6-7
Wrong
3.3V Plane
RIMM1
Wrong
RIMM2
Required
1.8V Plane 3.3V Plane
RIMM1
RIMM2
Vterm Resistors
Vterm Capacitors
Vterm Layer Not Shown
Layout/Routing Guidelines
for an
GND Plane
st th
and 4 layers.
2-13