[SI-LIST] Re: AC Analysis in Hspice
- From: "Michael J. Degerstrom" <degers@xxxxxxxxxxxxxxxxxxxx>
- To: jeff.loyer@xxxxxxxxx,"Signal Integrity Mailing List" <si-list@xxxxxxxxxxxxx>
- Date: Fri, 1 Nov 2002 15:41:17 -0600
Jeff,
I didn't read your entire post but perhaps you are having the same problem
that I had. If so, then you need to set up another source of the same
magnitude and phase as your driving source. Then S11 is port1 minus the
voltage at this second source. You just can't subtract '1' from the port 1
node since you leave out the phase. S21 should be OK as you've indicated.
I assume your original ckt used 2Volt sources with 50 ohm source resistance
and 50 ohms at port 2.
Mike
On Friday 01 November 2002 03:29 pm, Loyer, Jeff wrote:
> > I came upon a problem and wondered if any of you have seen something =
>
> similar (and hopefully know of a fix).
>
> >=20
> > I normally use the ".NET" statement in Hspice to easily extract my S* =
>
> parameters from simulations. As an exercise to further my =
> understanding, I decided to do the same thing manually. I was able to =
> do this for S21, but I can't get it to work for S11. I've checked my =
> theory with co-workers, and we can't find anything. I suspect there's =
> some quirk with Hspice's AC analysis (or some option I'm not setting =
> right).
>
> >=20
> > In the spice deck below, I set up 3 circuits. =20
> > The first (nodes have "net" in them) uses Hspice's ".NET" statement to =
>
> print the S* parameters.
>
> > The second (nodes have "dir" in them) should give me the same results, =
>
> by comparing the resultant voltage to the input voltage.
>
> > The third (nodes have "ref" in them) is a reference circuit that I use =
>
> to determine my input voltages for the second circuit.
>
> >=20
> > It doesn't work. A plot of S11 magnitude (from the ".PRINT AC S11(m)" =
>
> statement) doesn't agree with a plot of the parameter "s11m" (supposed =
> to be the same thing, derived manually).
>
> >=20
> > It does work for S21 magnitude and phase.
> >=20
> > The spice deck is:
> >=20
> > * Experiment to derive S parameters directly
> >=20
> > .AC Lin 800 30K 6G
> > .PRINT AC S11(m)
> > .NET V(N_nettrm) V_netsrc ROUT=3D50 RIN=3D50
> > *.PRINT AC S21(db) S21(p) S11(db) s11(p)
> >=20
> > V_netsrc N_netvs 0 ac=3D1 dc=3D0
> > T_net1 N_netvs 0 N_nettrm 0 td=3D100pS Z0=3D35
> > R_nettrm N_nettrm 0 R=3D50Meg
> >=20
> > V_dirsrc N_dirvs 0 ac=3D1 dc=3D0
> > R_dirin N_dirvs N_dirsrc r=3D50
> > T_dir1 N_dirsrc 0 N_dirtrm 0 td=3D100pS Z0=3D35
> > R_dirtrm N_dirtrm 0 R=3D50
> >=20
> > V_refsrc N_refvs 0 ac=3D1 dc=3D0
> > R_refin N_refvs N_reftrm R=3D50
> > R_reftrm N_reftrm 0 R=3D50
> >=20
> > .print s11m=3Dpar('(v(N_dirsrc)-v(N_reftrm))/v(N_reftrm)')
> > *.print s21m=3Dpar('v(N_dirtrm)/v(N_reftrm)')
> >=20
> > *.print s11db=3Dpar('20*log10((v(N_dirsrc)/v(N_vrefsrc)))')
> > *.print s11p=3Dpar('(vp(N_dirsrc)-vp(N_vrefsrc))')
> > *.print s21db=3Dpar('20*log10((v(N_dirtrm)/v(N_reftrm)))')
> > *.print s21p=3Dpar('(vp(N_dirtrm)-vp(N_vreftrm))')
> >=20
> > .END
> >=20
> > Jeff Loyer
> >=20
>
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