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Date: 01/10/03 at 3:48 AM
Posted by: Roberto
E-mail: roberto.perez@sainco.abengoa.com

In Reply to: Re: how calculate rise time from driver to receiver posted by Randy Jackson on 01/08/03 at 12:18 PM:

These are some of information I consider but I have many doubts.

The rise time of my driver is for instance 70 ns. Therefore the operating frequency is approximately F=0.35/rise_time.
The wavelength in the free space is
lambda= c/F.
Reduced wavelength is
lambdar= lambda/sqrt(E’r)
For a surface microstrip E’r = 0.475Er+0.67.
Generalizing for internal traces and FR4 material, we get: lambdar = 857*rise_time/sqrt (Er).
For external traces and FR4 material lambdar = 857*rise_time/sqrt (0.457*Er+0.67)

These are some formulas for estimating critical conductor length in order to avoid transmission line effect depending on the path is either digital or analog

On the other hand the driver output signal is 6 MHz bandwidth centered in 40 MHz. Should I consider these data in order to determine whether there is transmission line or not, and how should I do it? Should I apply again the formula rise_time = 0.35/F, and compare the result with the one obtained earlier, and choose the worst case?

Beside, I suppose the driver load (capacitive termination, input capacitive of the receiver) have some effect on delay time. How can I include it in my calculation?

Thanks

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