Intel VC820 - Desktop Board Motherboard Design Manual page 109

3.2.3.3 Monte Carlo Analysis
Perform a Monte Carlo analysis to refine the passing solution space region. A Monte Carlo analysis
involves randomly varying parameters (independent of one another) over their tolerance range.
This analysis intends to ensure that no regions of failing flight time and signal quality exists
between the extreme corner cases run in pre-layout simulations. For the example topology, vary the
following parameters during Monte Carlo simulations:
•
Lengths L1 through L3
•
Termination resistance R
•
Termination resistance R
•
Z of traces on processor cartridge #1
0
•
Z of traces on processor cartridge #2
0
•
S of traces on processor cartridge #1
0
•
S of traces on processor cartridge #2
0
•
Z of traces on baseboard
0
•
S of traces on baseboard
0
•
Fast and slow corner processor I/O buffer models for cartridge #1
•
Fast and slow corner processor I/O buffer models for cartridge #2
•
Fast and slow package models for processor cartridge #1
•
Fast and slow package models for processor cartridge #2
•
Fast and slow corner 82820 MCH I/O buffer models
•
Fast and slow 82820 MCH package models
3.2.3.4 Simulation Criteria
Accurate simulations require that the actual range of parameters be used in the simulations. Intel
has consistently measured the cross-sectional resistivity of the PCB copper to be approximately
1 Ω*mil 2
material. Using the 1 Ω*mil
Positioning drivers with faster edges closer to the middle of the network typically results in more
noise than positioning them towards the ends. However, Intel has shown that drivers located in all
positions (given appropriate variations in the other network parameters) can generate the worst-
case noise margin. Therefore, Intel recommends simulating the networks from all driver locations,
and analyzing each receiver for each possible driver.
Analysis has shown that both fast and slow corner conditions must be run for both rising and
falling edge transitions. The fast corner is needed because the fast edge rate creates the most noise.
The slow corner is needed because the buffer's drive capability will be a minimum, causing the V
to shift up, which may cause the noise from the slower edge to exceed the available budget. Slow
corner models may produce minimum flight time violations on rising edges if the transition starts
from a higher V
violations with both the fast and slow corner models. The fast and slow corner I/O buffer models
are contained in the processor and Intel 820 chipset electronic models provided by Intel.
The transmission line package models must be inserted between the output of the buffer and the net
it is driving. Likewise, the package model must also be placed between a net and the input of a
receiver model. Editing the simulator's net description or topology file generally does this.
®
Intel 820 Chipset Design Guide
on the processor cartridge #1
TT
on the processor cartridge #2
TT
/inch, not the 0.662 Ω*mil
2
/inch value may increase the accuracy of lossy simulations.
. So, Intel highly recommends checking for minimum and maximum flight time
OL
2
/inch value for annealed copper that is published in reference
Advanced System Bus Design
OL
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