Re: [SI-LIST] : About the AC analysis with HSPICE

Mike Degerstrom (
Thu, 2 Sep 1999 10:12:42 -0500


I saw Ray's post and will reiterate some of his thoughts. Also,
I'll try to explain s-parameters vs. AC sweep.

Please read on.


On Sep 2, 8:23am, Rachild Chen wrote:
> Subject: Re: [SI-LIST] : About the AC analysis with HSPICE
> All Sirs,
> Thanks for your advice.But I still have some questions.
> I use the .AC analysis to simulate the high frequency loss of
> transmission line.I use the .NET option of the .AC analysis.I mainly simulate
the S21 parameter.
> But I found that the loss DB between simulation and test (I test with HP
network analyer) is
> more and more different with frequency increasing.The loss DB of simulation
is less than that of

As Ray say's, its either launch (pad/via discontinuities) or some
other effect taking over in the transmission line loss not accounted
for in the w-element model (or combination of the two). We find
that we need a very good launch to do analysis of lossy line measuresurements
versus simulation.

> test.I want to know the reason.The .sp file is following:
> *******************************************************************
> .options probe post csdf
> Vac nd_pin1 gnd ac 1v
> Rrerm cpin1 gnd 100k
> .NET V(cpin1) vac ROUT=50 RIN=50
> .AC DEC 100.00 30k 2000MEG
> Ws1 gnd nd_pin1 nd_pin2 gnd gnd gnd cpin1 cpin2 gnd gnd
rlgcfile=hmbstrip42.rlgc n=4 l=14600mil
> .PRINT AC S11(DB) S21(DB)
> .END
> *************************************************************************
> The transmission line is from rlgcfile=hmbstrip42.rlgc which is extracted
through :
> Vin1 nd_pin1 gnd pulse( 0v 3v 0.0n 0.3n 0.3n 2.15n 4.9n)
> Vin2 nd_pin2 gnd pulse(3v 0v 0.0n 0.3n 0.3n 2.15n 4.9n)
> *Vin1 nd_pin1 gnd pulse(0v 3.3v 0.0n 0.3n 0.3n 0.1n 4.8n)
> *Vin2 nd_pin1 gnd pulse(3.3v 0v 0.0n 0.3n 0.3n 0.1n 4.8n)
> *Vin3 nd_pin2 gnd pulse(0v 3.3v 0.0n 0.3n 0.3n 2.15n 4.9n)
> *Vin0 nd_pin4 gnd pulse(3v 0v 0.0n 0.3n 0.3n 2.15n 4.9n)
> *.options brief = 0
> *.options probe post csd
> .options scale=1u
> Ws1 gnd nd_pin1 nd_pin2 gnd gnd gnd cpin1 cpin2 gnd gnd
> + Fsmodel=mother1 n=4 l=14600mil
> .material copper1 metal conductivity=5.96e+7 $inner
> .material copper2 metal conductivity=3.43e+7 $surface
> .material die_1 dielectric er=4.5 losstangent=1.7e-2
> .shape rect_1 rectangle width=10mil,height=1.38mil
> .layerstack stack_1 layer=(copper1, 1.38mil) layer=(die_1, 20mil )
layer=(die_1, 20.87mil ) layer=(copper1, 1.38mil)
> .Fsoptions wopt1 accuracy=high computegd=yes computers=yes
computego=yes computero=yes printdata=yes gridfactor=3
> .model mother1 w modeltype=FieldSolver,layerstack=stack_1,fsoptions=wopt1,
> + rlgcfile='hmbstrip42.rlgc'
> + conductor= (material =copper1, shape=rect_1,origin=(0mil, 21.38mil))
> + conductor= (material =copper1, shape=rect_1,origin=(22mil,21.38mil))
> + conductor= (material =copper1, shape=rect_1,origin=(39mil, 21.38mil))
> + conductor= (material =copper1, shape=rect_1,origin=(61mil,21.38mil))
> .TRAN 100p 20n
> .end
> ********************************************************************************
> I want to know how should i assign values to 'ROUT' and 'RIN' in the .NET
> of the .AC analysis of the HSPICE.I have seen that very different results can
be got
> with different values of 'ROUT' and 'RIN'.What's the theory of .NET analysis
to 'S21'
> in HSPICE?

Since your s-parameter meter has 50 ohm ports use ROUT=RIN=50. The .NET
statement mathematically produces s-parameters. I don't know exactly
how it works but I've recreated the s-parameter approach using a standard
small signal AC analysis and get the same results. Beyond this, you
will need to understand s-parameters to obtain a thorough understanding
of what you are trying to simulate.

> I also noticed that even i use different stimulus signals(100M,500M,1G or
2G) applying to transmission lines.There is no anything changed in the
parameter matrix Ro,Lo,Co,Go,Rs,Gd.Why?How can i deal with these matrixes in
> frequency ?Perhaps it concerns somehow to the results of the loss of
transmission line.

I'm not sure what you mean above. As I think Ray said some of the
w-element parameters are multiplied frequency to get your loss versus
frequency characterstics.


> Regards
> Rachild
> [ Attachment (text/x-vcard): "vcard.vcf" 252 bytes
> Character set: us-ascii
> Card for Rachild Chen ]
>-- End of excerpt from Rachild Chen

Mike Degerstrom         Email:	
Mayo Clinic 
200 1st Street SW 
Gugg. Bldg. RM 1042A                 Phone:    (507) 284-3292
Rochester, MN 55905                    FAX:    (507) 284-9171

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