[SI-LIST] Re: Common-mode return loss in Hspice

Hi TK,

There is a much easier and more effective way to do this.  HSPICE
supports extracting both common (beginning in 2003.09) and mixed mode
S-parameters (beginning in 2004.03) using the linear analysis command
(.LIN).  Unlike the .NET command, the .LIN command extracts noise and
linear transfer parameters for a general multi-port network, not just 1
or 2 ports.  The .LIN command is used in conjunction with the .AC
analysis command and automatically calculates a series of noise and
small-signal transfer parameters between the terminals identified using
port (P) elements.  The results can be output to a .sc* file, a
Touchstone file, or a CITIfile.

.OPTIONS  post

Xline1  vcm_in1  vcm_in2  vcm_out1  vcm_out2  0 trace1

* Define differential port elements.  Reference node is 3rd node.
P1 vcm_in1 vcm_in2 0 port=3D1  ac=3D1                    $ input port
element, default z0=3D50, AC magnitude=3D1
P2 vcm_out1 vcm_out2 0 port=3D2                         $ input port
element, default z0=3D50

* Define linear analysis.  Output common mode S-parameters
(mixedmode2port keyword) in Touchstone format.
.LIN  format=3Dtouchstone mixedmode2port=3Dcc
.AC     lin  1k  10meg  10000meg
.PROBE  scc11(db)

.SUBCKT trace1  in1     in2     out1    out2    Vss
Wline1          in1     in2     Vss     out1    out2     Vss
+ RLGCFILE=3D 'my_trace.rlc'    N=3D2 L=3D.049
.ENDS

.END

Please email me directly if you have any further questions about this.

Tracy Barclay
CAE
Synopsys

-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx]
On Behalf Of Jeon, Tae-Kwang
Sent: Friday, May 26, 2006 19:45
To: si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] Common-mode return loss in Hspice

Hello all,
=20

I'm trying to simulate common-mode return loss in hspice, and want to
double check my simulation with you because the result showed me was
somewhat different than what I expected over 100MHz ~ 10GHz.

First of all, below is my simple diagram implemented in the spice deck.

       =20

         Port1                                         Port2


            + -------[[[[[[[[[[[[[[[[[[[[[[[[[[[[[-------+

      +----+                 dif'l traces             +-------+

       |    +--------[[[[[[[[[[[[[[[[[[[[[[[[[[[[[-------+        |

    ((V))  common-mode                                /////

       |     input voltage source

     /////

=20

Since I assume that both source impedance and the load impedance are
50ohms, I put 25ohms of Zcm to Rin and Rout variable as shown in the
input file below. So, here are my questions to ask.

=20

1. Is my diagram is reasonable for scc11 measurement?

2. What impedance value should both Rin and Rout have in the .NET
statement. Is it Zo, Zeven or Zcm? If I set it to Zo(=3D50ohms), I have
6dB less loss than I expected. My W-elements model was based on dif'l
traces having roughly 70ohms of even mode impedance, which is Zcm =3D
Zeven/2 =3D 35ohms, although the odd mode impedance is ~53ohms.
Interestingly, If I set both Rin and Rout in .NET statement to
35ohms(=3DZcm of trace), then it resulted in exactly what I expected. So =
I
want to clarify what is the right setting.

3. Is it right to use Sij(db) rather than either Sij(m) or Sij(r) for
the simple math like scc11=3D(s11+s21+s12+s22)/2?

=20

*My spice deck

Vin vcm_in 0  AC=3D1

=20

Xline1  vcm_in  vcm_in  vcm_out  vcm_out  0 trace1

=20

Rdummy  vcm_out  0  1meg

=20

.OPTIONS  accurate post=3D2  probe

.NET    v(vcm_out) Vin Rin=3D25  Rout=3D25

.AC     lin  1k  10meg  10000meg

.PROBE  scc11=3Dpar('(s11(db)+s21(db)+s12(db)+s22(db))/2')

=20

.SUBCKT trace1  in1     in2     out1    out2    Vss

Wline1          in1     in2     Vss     out1    out2     Vss

+RLGCFILE=3D 'my_trace.rlc'    N=3D2 L=3D.049

.ENDS

.END

=20

Thanks,

TK

=20


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