[SI-LIST] Re: DC Resistance calculation in 2.5D solver
- From: Istvan Novak <istvan.novak@xxxxxxxxxxx>
- To: Tesla <emcesd@xxxxxxx>
- Date: Thu, 17 May 2012 08:59:07 -0400
Hi Tesla,
The answers to your questions depend on whether you want to simulate a
link with DC blocking capacitor or not. For a DC coupled network you can
do either 1) or 2) below as long as it is done correctly. This means for
1) you need to make sure the solver is set up correctly to give you an
accurate enough DC answer, and for 2) this means the lowest-frequency AC
data point has to be sufficiently low in frequency where the response
would not change further as you step from that frequency down to zero.
Not having a DC blocking capacitor and further assuming a typical
one-ounce copper thickness in your PCB, usually a megahertz or so lowest
frequency point is good enough.
If, however, this question came up because you want to simulate a link
with DC blocking capacitors, it is a different game. There are a few
ways around it, if you search the SI-List archives, you will find
several threads on this topic.
Regards,
Istvan Novak
Oracle
On 5/17/2012 1:54 AM, Tesla wrote:
> Hi,
> Thanks for your kindly advice.
> If i want to get the S-Parameter of DC to Fmax for time domain
> simulation from some 2.5 field solver. Could i use the
> 1. IR drop calculated value(DC) and FEM high frequecny(1M to 1GHz) to
> combine a DC to 1GHz S parameter.
> 2 Use the FEM high frequecny(1M to 1GHz) only, let the time-domain
> simulator do the extrapolation work.
> it may be a old and discussed many times topic.
> i do a little experiment in ADS of Agilent, It seems that ADS did not
> do very well in low frequency extrapolation for S-parameter(Maybe i
> miss something).
> I use the S-Parameter of a 0.1uF capacitor from vendor. Suppose it has
> 0.3MHz to 1GHz data of S-Parameter. Then i use the dataset of vendor
> to calculate S-Parameter of DC to 1GHz. The simulator simply give
> results that the value below 0.3MHz all equal to the value at 0.3MHz.
> obviously the result do not make sense.
> Are simulator not suitable for S-parameter extrapolation?
> Thanks.
>
>
>
> At 2012-05-16 20:40:41,"Istvan Novak"<istvan.novak@xxxxxxxxxxx> wrote:
> >Hi,
> >
> >I wont comment on the specific tools, but will give you some generic ideas.
> >
> >We many times dont realize that DC resistance calculations can be almost
> >as tricky as the high-frequency computations. We usually assume
> >(wrongly) that at DC the current density is uniform in the conductor
> >cross section, but except of a few hypothetical cases, it is not. This
> >is why, even at DC, the correct answer needs careful volume meshing, to
> >make sure that the different current density values are captured
> >properly throughout the conductor volume, including the end connections
> >leading to the observation points. Most tools have knobs for you to
> >turn on some of the key parameters (you may be surprised to see that
> >once you start turning those knobs, you get different answers from the
> >same tool to the same DUT).
> >
> >So when you compare results from different tools, you may want to check:
> >- how the meshing is done and get them as close to be similar/same as
> >possible
> >- how the connection is assumed
> >
> >For this second item, one hint: we can not use point connection, because
> >for zero cross section area the current density and the equivalent
> >resistance would be infinite: we have to use finite connecting cross
> >section area. So first you have to find out how the connections are
> >assumed in the two tools and then make sure that they are as
> >close/similar as possible. If these key elements are the same or close,
> >we can then expect similar results.
> >
> >Regards,
> >
> >Istvan Novak
> >Oracle
> >
> >
> >On 5/16/2012 7:52 AM, Tesla wrote:
> >> Hi, Experts
> >> In 2.5 field solver(eg: Sigrity or SIwave), if i want to get DC
> >> resistance of interconnect, i use the two method:
> >>
> >> 1 Use FEM to calcute from DC to Fmax Hz, use the DC s parameter to get
> >> the S parameter
> >>
> >> 2 Use IR drop in the analysis to get the DC resistance
> >>
> >> but the two method give two different DC resistance value, Which one i
> >> should trust?
> >>
> >> Thanks.
> >>
> >>
> >
> >
>
>
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