[SI-LIST] Re: time domain simulation of s-parameter

I'd like to add the following question to this thread of discussion:

Why does a transient simulation run in HSpice using an S-parameter model
of a network predict a lower resonant frequency for that network than
any of the following?
- AC sweep of the S-parameter model
- AC sweep of the original network, in netlist format
- transient analysis of original network, in netlist format

All 3 bulleted items, above, agree in their prediction of the resonant
frequency of the network. Why does the S-parameter transient analysis
differ?

I can make it match by performing the HSpice ".LIN" extraction over a
bandwidth of 500 GHz, but who's got a tool that can give me an accurate
package extraction out to that limit?! As soon as I limit the upper
frequency to something that is reasonable for the current generation of
extractors (say, 10 GHz), I lose the match. Why? (The resonance is down
near 300 MHz.)

Here's the HSpice deck for doing the S-parameter extraction
(pdn_xtrct.sp):

.TITLE Extraction of netlist S-parameter model

.include 'pdn_xtrct_netlist.main'=20
P1      pwrbga    0         DC=3D0V  AC=3D0V  Z0=3D50  port=3D1
P2      pwrdie    0         DC=3D0V  AC=3D0V  Z0=3D50  port=3D2
P3      pwrdcap   0         DC=3D0V  AC=3D0V  Z0=3D50  port=3D3

.AC LIN   10000  0  10e9  $ 0 - 10 GHz w/ 1 MHz resolution
.OPTIONS  post list
.LIN format=3Dtouchstone

.END

And here's the deck for running the comparisons:

.TITLE Test of extracted S-parameter model

.MODEL pdn_xtrct S
+N=3D3
+TSTONEFILE=3D'pdn_xtrct.s3p'

.param use_mod =3D 0

* Vcco supply
Vcco    vcco      0         1.8V AC 1
Lpwr    vcco      lout      10nh
Ccco    lout      0         200uf  $IC=3D1.8           $ PCB decoupling
cap.
Lpwr2   lout      pwrbga    1nH
Rpwr2   lout      pwrbga    10MEG

* Package PDN
.IF (use_mod)
** Extracted model
Smod pwrbga pwrdie pwrdcap 0 mname=3Dpdn_xtrct fmax=3D10e9
+interpolation=3Dlinear highpass=3D3
.ELSE
** Netlist
.include 'pdn_xtrct_netlist.main'
.ENDIF
** Package decoupling
Rdcap   pwrdcap   10        .05
Ldcap   10        11        60pH
Rdcap2  10        0         10MEG
Cdcap   11        0         1uF  $IC=3D1.8

* Die Model
** Die capacitance
Rdie    pwrdie    dievcco   0.05
Cdie    dievcco   0         1000pf  $IC=3D1.799 $ induced perturbance at
time 0
Rdie2   dievcco   20        .05
Istep   20        0         PWL(0ns 0 10ns 0 11ns 1mA 50ns 1mA)  $ Note
the very long rise time!

.TRAN     0.01ns  50ns $UIC
.AC dec 10 1MEG 1G
.OPTIONS  post
.OPTIONS accurate=3D1
$.OPTIONS method=3Dgear
$.OPTIONS relq=3D.005 $lvltim=3D3 dvdt=3D4 maxord=3D2 $delmax=3D.001ns=20

.ALTER
.param use_mod =3D 1

.END

And here's the contents of "pdn_xtrct_netlist.main":

Cpkg1   pwrbga    0         1pF
Lpkg1   pwrbga    1         L=3D100pH R=3D.01
Rpkg1   pwrbga    1         10MEG
Cpkg2   pwrdie    0         1pF
Lpkg2   pwrdie    1         L=3D100pH R=3D.01
Rpkg2   pwrdie    1         10MEG
Cpkg3   pwrdcap   0         1pF
Lpkg3   pwrdcap   1         L=3D100pH R=3D.01
Rpkg3   pwrdcap   1         10MEG
Cpkg4   1         0         1pF

Thanks,
-db


> -----Original Message-----
> From: si-list-bounce@xxxxxxxxxxxxx
[mailto:si-list-bounce@xxxxxxxxxxxxx]
> On Behalf Of Lynne D. Green
> Sent: Thursday, November 29, 2007 12:16 PM
> To: saoer.sinaga@xxxxxxxxx; si-list@xxxxxxxxxxxxx
> Subject: [SI-LIST] Re: time domain simulation of s-parameter
>=20
> Interesting thread so far.
>=20
> There are tools that can convert the S-params to an equivalent passive
> circuit, which automatically insures passive/causal.  Other tools can
> "adjust" the S-params to guarantee passivity and causality (such as a
> pole/zero format), to account for noise in the data.
>=20
> The usual caveat applies: the modified model could result in slower
> simulation.  For example, slower simulation with added "nodes" is a
known
> issue in SPICE.    Some tools let you select the number of RLC stages
to
> use, so you can trade off accuracy against SPICE simulation time.
>=20
> - Lynne
>=20
>=20
> "IBIS training when you need it, where you need it."
>=20
> Dr. Lynne Green
> Green Streak Programs
> http://www.greenstreakprograms.com
> 425-788-0412
> lgreen22@xxxxxxxxxxxxxx
>=20
>=20
>=20
> -----Original Message-----
> From: si-list-bounce@xxxxxxxxxxxxx
[mailto:si-list-bounce@xxxxxxxxxxxxx]
> On
> Behalf Of Saoer Sinaga
> Sent: Thursday, November 29, 2007 11:02 AM
> To: si-list@xxxxxxxxxxxxx
> Subject: [SI-LIST] Re: time domain simulation of s-parameter
>=20
> That's not always the case. When you don't have DC data in your S-par,
not
> to mention the S-par is not passive guaranteed, your transient
simulation
> will not converge.
> saoer
>=20
>=20
>=20
> On 11/29/07, sanjeev_gupta@xxxxxxxxxxx <sanjeev_gupta@xxxxxxxxxxx>
wrote:
> >
> > Hi SKGUPTA,
> >
> > Kindly contact ADS online Tech support! ADS provide the most robust
=3D
> > convergence on S-parameters.
> >
> > Sanjeev
> > Agilent EEsof
> >
> > -----Original Message-----
> > From: si-list-bounce@xxxxxxxxxxxxx
> > [mailto:si-list-bounce@xxxxxxxxxxxxx] =3D On Behalf Of Sanjeev Gupta
> > Sent: Tuesday, November 27, 2007 6:49 AM
> > To: si-list@xxxxxxxxxxxxx
> > Subject: [SI-LIST] time domain simulation of s-parameter
> >
> > Hello All
> > I am trying to do time domain simulation using Agilent ADS after =3D
> > extracting s-parameter model from Power SI.
> > But, i am getting lot of convergence issue. Simulation gets
terminated
> > immediately.  I do not get any time domain waveform.
> > kindly suggest a solution.. which tool can solve such problem very
> > efficiently?
> > Thanks in advanve
> > Sanjeev
> >
> >
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>=20
>=20
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