Length Tuning Equation Derivation - Intel Pentium M Processor Design Manual

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Intel Pentium M Processor and Intel
High-Speed Design Concerns
12.6.3

Length Tuning Equation Derivation

When routing a motherboard, only one piece of the equation is a variable: PCB trace length . For
example, when signals are tuned with respect to the strobe, the final equation used by a
motherboard designer is derived as follows. First, two equations are defined:
Total_Strobe
Total_Signal
Combining these equations yields:
Total_Strobe
Strobe
Solving for
Signal
Now substituting in velocities and trace lengths, we conclude with
Equation 3. Tuning for One Signal with Respect to One Strobe
Signal
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E7501 Chipset Platform
= Strobe
Flight Time
+ Strobe
= Signal
Flight Time
+ Signal
=
Total_Signal
Flight Time
+ Strobe
Component1 Flight Time
= Signal
Component1 Flight Time
+ Signal
Component2 Flight Time
Signal yields:
PCB Flight Time
= Strobe
PCB Flight Time
+ Strobe
Component2 Flight Time
– Signal
Component2 Flight Time
= ((Strobe
PCB Trace Length
+ (Strobe
+ (Strobe
– (Signal
– (Signal
* Signal
PCB Trace Velocity
+ Strobe
Component1 Flight Time
Component2 Flight Time
+ Signal
Component1 Flight Time
Component2 Flight Time
± Tolerance
Flight Time
+ Strobe
PCB Flight Time
+ Signal
± Tolerance
+ Strobe
Component1 Flight Time
– Signal
± Tolerance
/ Strobe
Component1 Trace Length
/ Strobe
PCB Trace Length PCB Trace Velocity
/ Strobe
Component2 Trace Length
/ Signal
Component1 Trace Length
/ Signal
Component2 Trace Length
± Tolerance
PCB Flight Time
PCB Flight Time
Component2 Flight Time
PCB Flight Time
PCB Flight Time
Component1 Flight Time
Equation 3.
Component1 Trace Velocity
)
Component2 Trace Velocity
Component1 Trace Velocity
Component2 Trace Velocity
Design Guide
)
)
)
) )