[SI-LIST] Re: Effects of anti-pad diameter on SDD11 for differential vias

  • From: Mark Filipov <markfilipov81@xxxxxxxxx>
  • To: andersson.pehr@xxxxxxxxx
  • Date: Tue, 24 Apr 2012 20:20:55 +0200

I have also noticed that behavior, maybe this could mean that if you
are designing for lower data rates, it can be worse to have larger
anti-pad and thus higher impedance of the via!

BR /Mark

2012/4/23, Pehr Andersson <andersson.pehr@xxxxxxxxx>:
> Hello fellow SI engineers!
> I have noticed when running some simulation of vias, that by varying
> anti-pad diameter, but keeping other parameters intact, that the return
> loss for lower frequencies is higher then for case when the anti-pad is
> smaller.
> But for the higher frequencies there is an opposite effect, the return loss
> decreases with the increasing anti-pad diameter.
> I have included the picture that shows this effect.
>
> What is physical explanation for this effect?
>
> Why do RL increase for larger anti-pad compared to via with smaller
> anti-pad diameter, when the frequency is < 5GHz ?
>
> Also why do the return loss decreases for the via with larger anti-pad
> diameter compared to via with smaller anti-pad diameter, for f > 5GHz ?
>
>
> Best regards, Pehr
>
>
>
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