[SI-LIST] Re: DC Resistance calculation in 2.5D solver
- From: "Brad Brim" <bradb@xxxxxxxxxxx>
- To: "'Tesla'" <emcesd@xxxxxxx>
- Date: Fri, 25 May 2012 07:57:16 -0700
hi Tesla,
Yes, PowerSI adds the correct DC value automatically during a swept
frequency analysis. A separate DC [IR Drop] solver is applied to get the
correct zero-frequency point. The trick is to properly blend the DC and AC
solutions. To avoid an inappropriate product-specific discussion on SI-LIST
I will contact you offline for any further discussion/details.
cheers,
-Brad
_____
From: Tesla [mailto:emcesd@xxxxxxx]
Sent: Friday, May 25, 2012 2:30 AM
To: bradb@xxxxxxxxxxx
Cc: si-list@xxxxxxxxxxxxx; Istvan Novak; cristian.gozzi@xxxxxxxxx
Subject: Re:RE: [SI-LIST] Re: DC Resistance calculation in 2.5D solver
Hi, Brad
Thanks for all your patient precious advice.
You said PowerSI "This capability is available in PowerSI". Does this mean
PowerSI can automatically add the correct DC value(the Value like IR Drop
one) in the frequency sweep process? Do you have any document and examples
about this capability?
How this can be done. i know PowerSI is base FEM method. it should also be
ill-conditioned in low frequency? Please correct me if i miss anything.
Hi, Istvan
My aim is to see the transient response of PDN, so i think the S_Parameter
of DC and low frequency is also important for a good simulated data. i know
you are guru in PI, could you provide me some documents on such kind of
simulation.
Best Regards.
Tesla
At 2012-05-18 02:25:55,"Brad Brim" <bradb@xxxxxxxxxxx> wrote:
>hello all,
>
>Life is easier if the EM solver natively includes both AC and DC solutions
>and applies the DC as an "anchor" for the frequency-swept results. This
>capability is available in PowerSI.
>
>AC solvers consider the full set of coupled Maxwell's equations for both RL
>and GC effects, where in the DC case Maxwell's equations decouple into two
>independent set of equations. To solve for RL you apply only the
>magnetostatic equations. The DC solution is much easier and better
>conditioned numerically. Typical AC solver formulations can not solve at
>exactly DC and are ill conditioned numerically at "low" frequency. Consider
>that in an AC solver you are simultaneously dealing with numerical values
>proportional to (j*omega*L) and 1/(j*omega*C), or the inverse of each. As
>you approach DC the numerics become ill conditioned as 1/(omega*omega). The
>frequency at which the numerical instability becomes significant varies and
>can be controlled to some extent by formulation and matrix solvers. This
>lower frequency of stability is also dependent on the design being
>simulated, the mesh size/quality and a few other factors not often under
>user control. If you are not careful, then your low frequency results may
>have significant error due to this instability. This behavior defines
>conflicting goals. You want to simulate as low in frequency as possible to
>enable better extrapolation to DC by a circuit simulator later, but you
want
>to stop at a high enough frequency to maintain accuracy in the AC
>formulation. For each design the low frequency stability point can vary;
and
>it can vary with the mesh applied. For some simulators the low frequency
>bound can be as high as 100MHz, for others 1kHz or even less.
>
>A related but somewhat independent issue is the current distribution within
>metals at low frequencies - as mentioned earlier in this thread. This can
be
>addressed in various solvers, but in all cases it implies a larger and more
>complex solution. For 3D solvers it can be addressed with volumetric
meshing
>of metals - a pursuit for the brave of heart who have large compute
>resources available. For planar (2.5D) solvers it is often accomplished by
>considering independent currents on the top/bottom of a metal. For parallel
>plate (2D) solvers it is often addressed by considering field penetration
>through metals. All of these improve accuracy at low frequency, some waste
>effort at high frequency, and some can even cause issues at high
>frequencies. For example, in a 3D solver volumetric meshing is only
required
>for metals thinner than about 3 skin depths, so the current distribution
>doesn't vary rapidly and a coarse mesh is often adequate. However, at high
>frequencies the coarse mesh is not adequate to represent the rapid decay of
>current in the metal. Therefore, it is often not adequate to use the same
>mesh over a frequency range spanning bulk to skin current flow regions.
>
>For capacitors (especially blocking caps) I would simulate the design with
>extra port(s) and then insert the cap model in the subsequent circuit
>simulation. It is likely your circuit simulator has more options to control
>the frequency extrapolation for your cap model. To extrapolate cap vendor
>S-parameters to low frequency you might want to use the special knowledge
>you have - that it's a capacitor. A fairly simple RLC equivalent circuit
>fitted to the data may work very well for you. Some people insist on using
>S-parameters, assuming they are inherently more accurate than a lumped
>model. However, you should consider the manufacturing variations that
*will*
>occur prior to adopting this assumption too firmly. If your cap
S-parameters
>are showing higher order resonances you may also want to ask yourself how
>much variation these will experience when the device is applied in your
>design vs the test board and mounting structure applied for the
measurement.
>
>best regards,
> -Brad
> Sigrity
>
>
>> -----Original Message-----
>> From: si-list-bounce@xxxxxxxxxxxxx
>> [mailto:si-list-bounce@xxxxxxxxxxxxx] On Behalf Of Cristian Gozzi
>> Sent: Thursday, May 17, 2012 12:02 AM
>> To: Tesla
>> Cc: Istvan Novak; long.0.yang@xxxxxxxxx; weirsi@xxxxxxxxxx;
>> rtatikola@xxxxxxxxx; si-list@xxxxxxxxxxxxx
>> Subject: [SI-LIST] Re: DC Resistance calculation in 2.5D solver
>>
>> 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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