[SI-LIST] Re: Cap discontinuity
- From: Ray Anderson <Raymond.Anderson@xxxxxxx>
- To: si-list@xxxxxxxxxxxxx
- Date: Thu, 16 May 2002 11:05:10 -0700 (PDT)
>
> Thanks for your comments, Jian.
>
>However, I still don't know the answer - does the width of the pad versus the
trace matter. I know the cap will cause discontinuity, as you mentioned below.
Can we safely assume that the discontinuity from the pad is much less than the
the cap. I can't find a simple simulation to do to verify.
>
>Thanks
>
>
The answer to your question is : perhaps
To find out if it does or doesn't in your particular case
perhaps you could run two simulations:
1) One scenario would have a t-line and a set of capacitor pads
the same width as your proposed capacitor in series with
the t-line. Connect the pads together with a short section of
t-line (same Z as the input/output t-lines). Terminate the
output line.
__ __
============|__|=|__|==============
2) Scenario 2 would be the same as above EXCEPT, don't short
the pads together, but put your proposed capacitor there.
__ __
============|__|-|(-|__|==============
Run a freq. domain simulation on both of these and compare the
results. If the results of the two simulations are substantially
the same then the cap isn't contributing much more degradation
than the cap mounting pads are. On the other hand, it the simulation
with the cap in place is "worse" by your criteria, then you can
probably conclude the cap is contributing more of a discontinuity
that just the pads.
-Ray
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