
51
Tsi572 Hardware Manual
May 18, 2012
Integrated Device Technology
www.idt.com
Figure 23: Serpentine Signal Routing
Figure 26
describes the guidelines for length matching a differential pair. If it is necessary to
serpentine a trace, follow these guidelines:
•
Make the minimum spacing between parallel sections of the serpentine trace (see “S” in
Figure 23
) at least 3 to 4 times the distance between the signal conductor and the reference
ground plane.
•
Minimize the total length (see “Lp” in
Figure 23
) of the serpentine section in order to
minimize the amount of coupling.
•
Use an embedded microstrip or stripline layout instead of a microstrip layout.
3.3.2
Crosstalk Considerations
The Serial RapidIO signals easily capacitively couple to adjacent signals due to their high
frequency. It is therefore recommended that adequate space be used between different
differential pairs, and that channel transmit and receive be routed on different layers. Cross
coupling of differential signals results in an effect called Inter-Symbol Interference (ISI). This
coupling causes pattern dependent errors on the receptor, and can substantially increase the bit
error rate of the channel.
To maximize the signal integrity, clock lines should not be serpentine.
Ti
p
For a detailed discussion about serpentine layouts, refer to Section 12.8.5 of
“High-Speed Signal Propagation, Advanced Black Magic”
by Howard Johnson and
Martin Graham.
Lp
S
DRIVER
RECIEVER
crosstalk path
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