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How to calculate the track length of a signal?

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kishore21

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Hello Gurus,

I have a question regarding the relationship between the frequency of the signal and the track length on the PCB. I thought of posting here hoping that I could get some light from any corners, as there are many experts in this group.

Does the length of the track depends on the frequency (or rise time) of the signal? If this is true, then how is the track length calculated for high speed signals?
For example, what could be the track lengths for signals operating at 250Mhz, 500MHz?

Thanks in advance for any of your help.

Regards,
Kishore
 

You can see in specifications
 

Hi,

this is copied from AP0107 Impedance-Controlled Routing.pdf from Altium

The speed at which the electrical energy can travel along the route it known as the propagation velocity, where
VP = speed of light / √dielectric constant

Using
Time = 1/3 * rise time
εR = 4.7 (approximation for FR4)
C = 11.811 in/nSec (speed of light, in inches per nanosecond)
To find the length of route above which the integrity of the signal could become a problem:
LR = Time * VP
= Time * C / √ εR
LR = .33 * 11.811 / 2
= 1.95 in

but also depends where do you route track(microstrip,stripline) and width also depends on impedance.

r,S
 

Hi,


Check this site out,

**broken link removed**

**broken link removed**



Regards

Ramesh
 

if you are using CAD package, you should be able to get the report of the track length you have routed
 

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