FSB Design Guidelines
R
34
Intel
®
855PM Chipset Platform Design Guide
Figure 3. Trace Spacing vs. Trace to Reference Plane Example
Reference Plane (VSS)
Trace
Trace
X
2X
4.1.1.2.
Trace Space to Trace Width Ratio
Figure 4 illustrates the recommended relationship between the edge-to-edge trace spacing versus trace
width ratio for the best signal quality results. In general, a 3:1 trace space to trace width ratio is preferred
and highly recommended. In case of routing difficulties on the motherboard, using a 2:1 ratio would be
acceptable
only
if additional simulations conclude that it is possible, and this may include some changes
to the stack-up or routing assumptions. In the case of the FSB signals, routing recommendations for a
2:1 trace spacing to trace width ratio can be found in Topology 2 for the source synchronous signals (see
Table 5).
Figure 4. Trace Spacing vs. Trace Width Example
v
Trace
Trace
3X
v
X
4.1.1.3.
Recommended Stack-up Calculated Coupling Model
The importance of maintaining an adequate trace space to trace width ratio is to achieve the best signal
quality possible given routing constraints. The simulations performed that resulted in the recommended
3:1 trace space to trace width ratio is to keep the coupling between adjacent traces below a maximum
value. For the recommended stack-up, the constants shown in Figure 5 are assumed to be constant for a
typical
stack-up. This means the mutual to self-coupling relationship given below does not take into
account the normal tolerances that are allowed for in the recommended board stack-up’s parameters. For
the recommended stack-up shown in Figure 2, the calculated capacitive coupling maximum value is
represented by the following relationship:
( C
MUTUAL
/ C
SELF
) x 100 = 8.15%
As shown in Figure 5, the coupling values are calculated based on a three-line model, represented by
Trace 1, Trace 2, and Trace 3. Based on the capacitive coupling model shown, the aforementioned
parameters are:
C
MUTUAL
= C21 + C23
Содержание 855PM
Страница 18: ...R 18 Intel 855PM Chipset Platform Design Guide This page intentionally left blank...
Страница 22: ...Introduction R 22 Intel 855PM Chipset Platform Design Guide This page intentionally left blank...
Страница 32: ...General Design Considerations R 32 Intel 855PM Chipset Platform Design Guide This page intentionally left blank...
Страница 124: ...Platform Power Requirements R 124 Intel 855PM Chipset Platform Design Guide This page intentionally left blank...
Страница 182: ...Hub Interface R 182 Intel 855PM Chipset Platform Design Guide This page intentionally left blank...
Страница 228: ...I O Subsystem R 228 Intel 855PM Chipset Platform Design Guide This page intentionally left blank...
Страница 328: ...Platform Design Checklist R 328 Intel 855PM Chipset Platform Design Guide This page intentionally left blank...