How to calculate the track length of a signal?

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kishore21

Joined: 27 Jun 2007
Posts: 1

25 Jul 2007 7:08 How to calculate the track length of a signal?

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

kiddy

Joined: 19 Jul 2007
Posts: 16
Helped: 1

25 Jul 2007 11:04 How to calculate the track length of a signal?

You can see in specifications

Siliconray

Joined: 17 Jul 2007
Posts: 4

27 Jul 2007 14:02 Re: How to calculate the track length of a signal?

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

Rame

Joined: 23 Dec 2005
Posts: 369
Helped: 40
Location: BANGALORE

28 Jul 2007 3:44 Re: How to calculate the track length of a signal?

Hi,

Check this site out,

http://64.70.157.146/archive/old_archive/980415.html

http://www.industrienet.de/objekte/epp/heft/text4.htm

Regards

Ramesh