[SI-LIST] Re: why do I need mixed mode S parameters?
- From: <vince_cavanna@xxxxxxxxxxx>
- To: <cclewell@xxxxxxxxx>, <vince_cavanna@xxxxxxxxxxx>
- Date: Thu, 16 Sep 2004 12:42:59 -0600
Thanks for the many helpful replies. I got exactly the information I was =
searching for.=20
Basically I got confirmation of my belief that the value of mixed mode S =
parameters is mainly in interpretation of the characteristics of the =
differential device that they represent. But I also learned that there =
may be more value than I thought in using a mixed mode model. I note =
some specifics below.
Jim Nadolny and Bill Beale made me realize another application of mixed =
mode S parameters. When we only know the response of the n-port to =
differential stimulus, and thus don't have enough information to convert =
back to standard s parameters to get a complete model, we can still =
model just the differential response using a mixed mode S parameter =
model - basically we have reduced the 4 port to a 2 port model.=20
This seems to have practical implications beyond that of turning a 4 =
port into a 2 port device. In fact it seems that, if a true mixed mode =
VNA were available and could apply true differential stimulus, then the =
response to a differential stimulus could be measured without connecting =
the gnd of the VNA to the GND of the DUT (which may not be accessible). =
I suppose the same could be done in the time domain using a TDR/TDT and =
those instruments do seem to be available with true differential drive. =
What do you think?
Gary Otonari made me realize about the challenges of de-embedding a 4 =
port device versus a 2 port when we are only interested in differntial =
response.
I agree with Brad Cole that mixed mode S parameters are not restricted =
to lossless devices. Like the standard S parameters they depend on the =
linearity of the n-port that they represent.
Thanks again to all who replied. Looks like I asked the right group.
Vince
> -----Original Message-----
> From: Craig Clewell [mailto:cclewell@xxxxxxxxx]
> Sent: Thursday, September 16, 2004 6:12 AM
> To: vince_cavanna@xxxxxxxxxxx
> Cc: si-list@xxxxxxxxxxxxx
> Subject: RE: [SI-LIST] why do I need mixed mode S parameters?
>=20
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> Vince,=20
>=20
> I've embedded my responses to your questions below
>=20
> .
> Q. What I am trying to understand is why I would ever want to=20
> use mixed
> =3D
> mode S parameters in a time-domain or frequency domain=20
> simulation, and =3D
> how to use them. =20
>=20
> A. As I believe Bill alluded to the mixed mode S parameters will allow
> you to see if there is any asymmetry in the coupling. If=20
> there is than
> you will have a larger cross mode coupling in one direction vs. the
> other direction, meaning that you're differential to common=20
> mode will be
> different in both directions. You may want to know this=20
> information for
> a read/write line, or any other bi-directional line. This information
> may be useful when you look at the affects of even and odd mode
> switching on your system.
>=20
>=20
> Q. I am also interested to learn what simulators support =3D
> mixed mode S parameters directly, as using them in a=20
> simulator such as =3D
> Hspice seems cumbersome. My approach today is to simply use=20
> standard S =3D
> parameters directly.
>=20
> A. As my friend and ex-compatriot Jim Nadolny pointed out you may only
> have a model of the differential response. I am not aware of any
> simulator that will allow you to import the mixed mode S parameters
> directly other than HFSS? I always use the natural S parameters and
> then post process if I need to see the other terms as you have pointed
> out in your e-mail.
>=20
> Regards,=20
>=20
> Craig
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>=20
>=20
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>=20
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