Digital Signal Processing Reference
In-Depth Information
Figure 14.11
A pair of vias forming a differential pair passing through two planes. Ground stitching
vias are visible on either side. The rectangular tabs coming from the vias tops are microstrip traces.
(Figure generated by the Simbeor 3D solver [18].)
used by metal screws to secure the circuit board) not be placed close to either of the
vias forming the pair.
14.6 Main Points
Mitered corners can be used on traces to remove the excess capacitance and
inductance caused by bends.
•
The degree of chamfering usually is not critical.
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Chamfering is important when signaling at high-speeds.
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Routing traces near the board's edge changes its electrical characteristics and
can increase EMI.
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Crosstalk must be minimized when using serpentine traces to adjust timing.
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It is better to use a few long serpentine elements than many short ones.
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The via and antipad sizes strongly determine the vias electrical characteristics.
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Nonfunctional pads help secure the vias in a stackup, but are not visible in
the artwork and can be removed on high-speed nets.
•
References
[1]
Silvester, P., and P. Benedek, “Microstrip Discontinuity Capacitances for Right-Angle
Bends, T Junctions, and Crossings,”
IEEE Transactions on Microwave Theory and Tech-
niques
, Vol. MTT-21, No. 5, May 1973, pp. 341-346.
[2]
Silvester, P., and P. Benedek, “Corrections to Microstrip Discontinuity Capacitances for
Right-Angle Bends, T Junctions, and Crossings,”
IEEE Transactions on Microwave Theory
and Techniques
, Vol. MTT-23, No. 5, May 1975, p. 456.
