[SI-LIST] Re: DC Resistance calculation in 2.5D solver
- From: Cristian Gozzi <cristian.gozzi@xxxxxxxxx>
- To: Tesla <emcesd@xxxxxxx>
- Date: Thu, 17 May 2012 09:01:33 +0200
Hi Tesla
with SIwave you can create multiple concatenated frequency sweeps.
Since AC solver is not optimized for DC extraction, as I told you it
extrapolates DC value
to let this extrapolation works well, I suggest to create first sweep with
dense step points close to DC (let me say, for instance from 0 Hz to 1 MHz,
with 100 points for decade, log sweep)
than use another sweep from 1MHz to Fmax
NOTE: you can also try to compare DC value extracted from S-parameter with
this such sweep with same port setup and IR simulation in SIwave and get
the worth of its accuracy!
Be aware that usually this kind of non uniform frequency sweep could be
difficult for spice time domain solver, since it use convolution method and
usually is better to have dense and uniform step frequency sweep
I'm not an expert of ADS, last time I used it was to many years ago, so I
cannot help you so much on that...
I'm using Nexxim, within Ansys DesignerSI, and there are different
options/algorithms to extrapolate DC point from an S-parameters model that
start from 1MHz
One suggestion, I understood that the purpose of SI -list is to drive users
on specific SI & PI application challenges that it may involve simulators,
measurement or both
but if you want to talk deeply inside specific software feature, setup and
tricks I strongly recommend you to contact your local reference AE from
Ansys, Sigrity and Agilent
all of them have a great AE team to support and assist you on all these
topics
if you need more info, you can contact me off-line
Regards
Cristian
SI & PI Specialist
Technoprobe
2012/5/17 Tesla <emcesd@xxxxxxx>
> 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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