[SI-LIST] Re: AC Analysis in Hspice
- From: "Loyer, Jeff" <jeff.loyer@xxxxxxxxx>
- To: "Signal Integrity Mailing List" <si-list@xxxxxxxxxxxxx>
- Date: Mon, 4 Nov 2002 09:51:46 -0800
Oops - 2 things.
1) the explantion of ACOUT below was straight from the Hspice manual. I =
don't want to plagiarize.
2) Wierd characters got into the explanation. It should read (if THIS =
doesn't get garbled):
The default value, ACOUT=3D1, selects the Star-Hspice method, which =
calculates the difference of the magnitudes of the values. The SPICE =
method, ACOUT=3D0, calculates the magnitude of the differences.
Jeff Loyer
-----Original Message-----
From: Loyer, Jeff=20
Sent: Monday, November 04, 2002 9:34 AM
To: Signal Integrity Mailing List
Cc: Ye, Xiaoning
Subject: [SI-LIST] Re: AC Analysis in Hspice
Xiaoning was exactly right. Thanks to him, I was able to set ACOUT
correctly, and modify the derivation of "s11m". All agrees now. The
correction is below.
The default value, ACOUT=3D3D1, selects the Star-Hspice method, which
calculates the difference of the magnitudes of the values. The SPICE
method, ACOUT=3D3D0, calculates the magnitude of the differences.
* Experiment to derive S parameters directly
.option probe $ reduce unwanted output
.option ACOUT=3D3D0
.AC Lin 800 30K 6G=3D20
.PRINT AC S11(m)
.NET V(N_nettrm) V_netsrc ROUT=3D3D50 RIN=3D3D50
*.PRINT AC S21(db) S21(p) S11(db) s11(p)
V_netsrc N_netvs 0 ac=3D3D1 dc=3D3D0
T_net1 N_netvs 0 N_nettrm 0 td=3D3D100pS Z0=3D3D35
R_nettrm N_nettrm 0 R=3D3D50Meg
V_dirsrc N_dirvs 0 ac=3D3D1 dc=3D3D0
R_dirin N_dirvs N_dirsrc r=3D3D50
T_dir1 N_dirsrc 0 N_dirtrm 0 td=3D3D100pS Z0=3D3D35
R_dirtrm N_dirtrm 0 R=3D3D50
V_refsrc N_refvs 0 ac=3D3D1 dc=3D3D0
R_refin N_refvs N_reftrm R=3D3D50
R_reftrm N_reftrm 0 R=3D3D50
.print s11m=3D3Dpar('(vm(N_dirsrc,N_reftrm)/vm(N_reftrm))')
*.print news11m=3D3Dpar('(vm(N_dirsrc)-vm(N_reftrm))/vm(N_reftrm)')
*.print s21m=3D3Dpar('v(N_dirtrm)/v(N_reftrm)')
*.print s11db=3D3Dpar('20*log10((v(N_dirsrc)/v(N_vrefsrc)))')
*.print s11p=3D3Dpar('(vp(N_dirsrc)-vp(N_vrefsrc))')
*.print s21db=3D3Dpar('20*log10((v(N_dirtrm)/v(N_reftrm)))')
*.print s21p=3D3Dpar('(vp(N_dirtrm)-vp(N_vreftrm))')
.END
Jeff Loyer
-----Original Message-----
From: Ye, Xiaoning=3D20
Sent: Sunday, November 03, 2002 12:50 PM
To: Loyer, Jeff; Signal Integrity Mailing List
Subject: RE: [SI-LIST] AC Analysis in Hspice
Jeff,
I think this line in your deck is the troublemaker:
.print s11m=3D3Dpar('(v(N_dirsrc)-v(N_reftrm))/v(N_reftrm)')
It uses the magnitude to do the substraction instead of complex number.
In other words, mag(A-B) is not equal to mag(A)-mag(B)
I use the following calculation:
S11=3D3D(zin-50)/(zin+50),
where zin is the input impedance (complex number)
The results agree very well with the .net analysis.
Hope this helps,
Xiaoning Ye
-----Original Message-----
From: Loyer, Jeff [mailto:jeff.loyer@xxxxxxxxx]=3D20
Sent: Friday, November 01, 2002 1:30 PM
To: Signal Integrity Mailing List
Subject: [SI-LIST] AC Analysis in Hspice
> I came upon a problem and wondered if any of you have seen something =
=3D
=3D3D
similar (and hopefully know of a fix).
>=3D3D20
> I normally use the ".NET" statement in Hspice to easily extract my S*
=3D3D
parameters from simulations. As an exercise to further my =3D3D
understanding, I decided to do the same thing manually. I was able to =
=3D
=3D3D
do this for S21, but I can't get it to work for S11. I've checked my =
=3D
=3D3D
theory with co-workers, and we can't find anything. I suspect there's =
=3D
=3D3D
some quirk with Hspice's AC analysis (or some option I'm not setting =
=3D3D
right).
>=3D3D20
> In the spice deck below, I set up 3 circuits. =3D3D20
> The first (nodes have "net" in them) uses Hspice's ".NET" statement to
=3D3D
print the S* parameters.
> The second (nodes have "dir" in them) should give me the same results,
=3D3D
by comparing the resultant voltage to the input voltage.
> The third (nodes have "ref" in them) is a reference circuit that I use
=3D3D
to determine my input voltages for the second circuit.
>=3D3D20
> It doesn't work. A plot of S11 magnitude (from the ".PRINT AC S11(m)"
=3D3D
statement) doesn't agree with a plot of the parameter "s11m" (supposed =
=3D
=3D3D
to be the same thing, derived manually).
>=3D3D20
> It does work for S21 magnitude and phase.
>=3D3D20
> The spice deck is:
>=3D3D20
> * Experiment to derive S parameters directly
>=3D3D20
> .AC Lin 800 30K 6G
> .PRINT AC S11(m)
> .NET V(N_nettrm) V_netsrc ROUT=3D3D3D50 RIN=3D3D3D50
> *.PRINT AC S21(db) S21(p) S11(db) s11(p)
>=3D3D20
> V_netsrc N_netvs 0 ac=3D3D3D1 dc=3D3D3D0
> T_net1 N_netvs 0 N_nettrm 0 td=3D3D3D100pS Z0=3D3D3D35
> R_nettrm N_nettrm 0 R=3D3D3D50Meg
>=3D3D20
> V_dirsrc N_dirvs 0 ac=3D3D3D1 dc=3D3D3D0
> R_dirin N_dirvs N_dirsrc r=3D3D3D50
> T_dir1 N_dirsrc 0 N_dirtrm 0 td=3D3D3D100pS Z0=3D3D3D35
> R_dirtrm N_dirtrm 0 R=3D3D3D50
>=3D3D20
> V_refsrc N_refvs 0 ac=3D3D3D1 dc=3D3D3D0
> R_refin N_refvs N_reftrm R=3D3D3D50
> R_reftrm N_reftrm 0 R=3D3D3D50
>=3D3D20
> .print s11m=3D3D3Dpar('(v(N_dirsrc)-v(N_reftrm))/v(N_reftrm)')
> *.print s21m=3D3D3Dpar('v(N_dirtrm)/v(N_reftrm)')
>=3D3D20
> *.print s11db=3D3D3Dpar('20*log10((v(N_dirsrc)/v(N_vrefsrc)))')
> *.print s11p=3D3D3Dpar('(vp(N_dirsrc)-vp(N_vrefsrc))')
> *.print s21db=3D3D3Dpar('20*log10((v(N_dirtrm)/v(N_reftrm)))')
> *.print s21p=3D3D3Dpar('(vp(N_dirtrm)-vp(N_vreftrm))')
>=3D3D20
> .END
>=3D3D20
> Jeff Loyer
>=3D3D20
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