Flight Time Segment Analysis - Intel Pentium M Processor Design Manual

12.6.2

Flight Time Segment Analysis

Length matching often requires package compensation. Every time a signal changes innerconnect
or layer, there is an affect on flight time. The most effective way to calculate flight time is to break
up each signal into segments of constant flight time, analyze those segments, and then add the
segment together.
Flight time is directly proportional to trace length by a constant trace velocity.
Equation 1. Flight Time
To determine the total flight time, each segment with a constant trace velocity must be identified.
These segments are commonly defined at component interconnects. For example, a signal which
connects two different components through a PCB would be calculated as follows:
Total_Signal
Figure 158. Total Signal Length with Two Components
Using the segment lengths and velocities yields:
Equation 2. Total Flight Time
total_flight_time
Design Guide
®
Intel Pentium
flight_time
= Signal
Flight Time
+ Signal
component1_trace_length
component1_length
= --------------------------------------------------- -
component1_velocity
®
M Processor and Intel
High-Speed Design Concerns
trace_length
= ----------------------------------- -
trace_velocity
+ Signal
Componet1 Flight Time
Component2 Flight Time
PCB_trace_length
component2_trace_length
component
pins
PCB_length
+ -------------------------------- - +
PCB_veloctiy
®
E7501 Chipset Platform
PCB Flight Time
component2_length
--------------------------------------------------- -
component2_velocity
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