Agilent Technologies 93000 SOC Series Training Manual page 538

Lesson 2 – DUT Board Design Considerations
Stubs
Branch (Stub)
In the above example, if the signal frequency is very high, these stubs
cause signal reflections at the points. Consequently, the trace should be
drawn without a stub.
Crosstalk
If two signal lines are traced in parallel on a PC board and if one carries a
small and precise signal and the other carries a high level signal, the large
signal may couple to the sensitive line and cause trouble (level change and
jitter). This is called "Crosstalk".
Signal Lines
To avoid the crosstalk in your test circuit, you must consider the following:
For traces that carry high frequency signals (such as clock), do not draw
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these traces in parallel.
(If possible) Use a coaxial cable to protect any sensitive signal from noise.
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Increase the distance between traces.
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Decrease the adjacent surfaces by bending the traces.
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Use a guard line between traces.
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