Intel Quark SoC X1000 Design Manual page 172

before transitioning to a different layer. At any via transition the n/p mismatch for
the entire route preceding the via cannot exceed 15mils.
• When trace length matching occurs, the matching should be made as close as
possible to the point where the length variation occurs, as shown in
the discontinuity won't propagate across the channel. For example, length
matching in a chipset breakout area or connector pin field should occur within the
first 125 mils (3.175 mm) of the structure that causes the length mismatch.
• Serpentine layout introduces discontinuity to the channel and should be minimized
so as to make it transparent to the signal. This is done by making its electrical
length shorter than the signal rise time. In general, keeping serpentine routing
length <100 mils is adequate. Trace spacing should not become greater than two
times the original spacing. See
• In determining the overall length of a given signal in a differential-pair, use pad or
pin edge-to-edge distances rather than the total etch present, unless the amount of
trace routing inside each pad is identical. The amount of etch within a given pad is
electrically part of the pad itself. In other words, only the etch outside of the pad
edge is relevant to the overall length of a differential-pair. For example:
— If the P signal of the differential-pair has an extra 5 mils (0.127 mm) of etch
length compared to the N signal, and the extra 5 mils (0.127 mm) occurs due
to extra etch extending into a component pad, the two signals should be
considered identical length.
— Similarly, trying to length match signals by adding etch inside a pad boundary
(such as extra bends inside the pad itself) does not produce the intended
length matching effect on the interconnection (see
Figure A-1. Length Matching Example
Figure A-2. Serpentining Example
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Intel Quark™ SoC X1000
PDG
172
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Intel Quark™ SoC X1000—General Differential Signals Design Guidelines
Figure
< 100 m ils
F
A B
E
Intra-pair diffe re ntial ske w com pe nsation.
Re com m e nde d dim e nsions: A =B=C=D,
E=F=G=3W (W =trace w idth) and S2<2S1
A-2.
Figure
S2
C D
G
Order Number: 330258-002US
Figure A-1, so
A-3).
S 1
June 2014