Backward Coupling Coefficient; Forward Coupling Coefficient - Intel Quark SoC X1000 Design Manual

Stack-Up and PCB Considerations—Intel
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 backward coupling coefficients is recommended to
choose proper trace spacing in cases where the selected stack-up varies from the Intel
recommendation.
The coupling coefficients represent the source voltage percentage that is coupled to
victim lines. As shown in
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 (K
For forward (far-end) crosstalk, K
polarity and the crosstalk magnitude (Vfe) is proportional to both trace length and edge
rate. K is typically a very small value in most practical designs. Therefore, Intel has not
f
included the K
provided in
K values for all interfaces for all routing layers can be found in
b
They were calculated assuming a nominal or typical stack-up configuration based on
the values in
crosstalk seen between each typical spacing. For typical spacing differential interfaces,
the K values reflect the crosstalk seen between each differential pair based on the
b
typical pair-to-pair spacing.
Figure 4.

Backward Coupling Coefficient

Figure 5.

Forward Coupling Coefficient

June 2014
Order Number: 330258-002US
®
Quark™ SoC X1000
Figure 4, K
) values can be used to decide trace spacing.
b
f
values in the Design Guide. However, the equation for calculating K
f
Figure 5 if the value is desired.
Table 1 to Table 4. For single-ended interfaces, the K
1

K
b
4

V
NE

C
1


K

f
2
C

ii
 
V K Length
FE f
is defined as the backward coupling coefficient.
b
inductive and capacitive coupling are of opposite

C L

ij ij


C C L L

ii jj ii jj

K V
b 0

L


ij ij

L C L

ii ii
C L L

jj ii jj
dV
*
dt
Table 3 and Table
values reflect the
b


,



1 4 /
C
jj jj
®
Intel Quark™ SoC X1000
is
f
4.
PDG
21