Specifications

Intel

810E2 Chipset Platform

84 Design Guide

Figure 49. Trace Routing

45 degrees

Trace

degrees

Trace Geometry and Length

The key factors in controlling trace EMI radiation are the trace length and the ratio of trace width to trace

height above the ground plane. To minimize trace inductance, high-speed signals and signal layers close

to a ground or power plane should be as short and wide as practical. Ideally, this ratio of trace width to

height above the ground plane is between 1:1 and 3:1. To maintain trace impedance, the width of the

trace should be modified when changing from one board layer to another, if the two layers are not

equidistant from the power or ground plane. Differential trace impedances should be controlled to

~100 Ω. It is necessary to compensate for trace-to-trace edge coupling. This can lower the differential

impedance by 10 Ω when the traces within a pair are closer than 0.030” (edge-to-edge).

Traces between decoupling and I/O filter capacitors should be as short and wide as practical. Long-and-

thin traces are more inductive and would reduce the intended effect of the decoupling capacitors. For

similar reasons, traces to I/O signals and signal terminations should be as short as possible. Vias to the

decoupling capacitors should have diameters sufficiently large to decrease series inductance.

Additionally, the PLC should not be closer than one inch to the connector/magnetics/edge of the board.

Signal Isolation

Comply with the following rules for signal isolation:

• Separate and group signals by function on separate layers if possible. Maintain a gap of 100 mils

between all differential pairs (Phoneline and Ethernet) and other nets, but group associated

differential pairs together.

Note: Over the length of the trace run, each differential pair should be at least 0.3” away from any parallel

signal trace.

• Physically group together all components associated with one clock trace, to reduce trace length and

radiation.

• Isolate I/O signals from high-speed signals to minimize crosstalk, which can increase EMI emission

and susceptibility to EMI from other signals.

• Avoid routing high-speed LAN or Phoneline traces near other high-frequency signals associated

with a video controller, cache controller, processor or other similar device.