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2.2
Backward and Forward Coupling Coefficient Calculation
Some designs require a stackup build that is outside of the ranges provided. In this
case, compare the routing electrical characteristics versus the Intel recommendation.
Comparing the single-ended and differential impedances is important. However,
crosstalk level, which is governed by trace spacing, is not implied by the impedance
target. Calculating and comparing the backward coupling coefficient is recommended
to choose proper trace spacing in cases where the selected stackup varies from the
Intel recommendation. The coupling coefficient represents the source voltage
percentage that is coupled to victim lines. As shown in
backward coupling coefficient. For backward (near- end) crosstalk, inductive and
capacitive coupling are of the same polarity and the noise magnitude is not a function
of trace length. The backward coupling coefficient (Kb) values can be used to determine
trace spacing. For forward (far-end) crosstalk, Kf inductive and capacitive coupling are
of opposite polarity, and the crosstalk magnitude (Vfe) is proportional to both trace
length and edge rate. Kf is typically a very small value in most practical designs.
Therefore, Intel has not included the Kf values in the design guide. However, if the value
is desired, the equation for calculating Kf is provided in
Figure 6. Backward Coupling Coefficient
Figure 7. Forward Coupling Coefficient
Intel® Quark™ Microcontroller D2000
Platform Design Guide
14
System Assumptions
Figure
6, Kb is defined as the
Figure
7.
November 2016
Document Number: 333580-002EN
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