[SI-LIST] Re: Group Delay of FR4 Trace
- From: "Dmitriev-Zdorov, Vladimir" <vladimir_dmitriev-zdorov@xxxxxxxxxx>
- To: <si-list@xxxxxxxxxxxxx>
- Date: Wed, 3 Jun 2009 09:50:18 -0600
Hi Neo,
Here is a simple technical trick.
If you expect that your line has nearly ideal termination, and if your
S-parameters are normalized accordingly (you mentioned that you analyze
Sdd21) then, yes, this component should be close to the line's
propagation function. It is true that relative contribution from skin
and dielectric losses is not very prominent: log(G(s)) = sqrt((sL +
sqrt(s)*Rs)*(sC + G(s))), therefore as you see it is dominated by
s*sqrt(L*C). Try to exclude this component by multiplying the
propagation function on an "inverse" or negative delay operator:
Exp(+s*sqrt(L0*C0)). Select the parameters L0 and C0 conservatively, so
as not to exceed group delay with losses. Typically, you should select
L0, C0 a few percent smaller than you would expect in the loss-less
mode. The result of multiplication should therefore remain causal. You
will find the effect of group delay variation more visible then, after
you remove the largest portion of the delay.
Vladimir
Neo neoflash2008@xxxxxxxxx wrote:
Subject: [SI-LIST] Re: Group Delay of FR4 Trace
HI,
I realized that with the large delay from channel transmission line, the
group delay distortion is not very visible since the distortion is at ps
level while the trace delay is on the order of ns.
I should figure out a way to split them to get a better view.
Regards,
Neo
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