[SI-LIST] Re: Estimate ISI with S parameters -- Using TDR to do SDD21 correlation?

Funny - I was going to post something similar.  My additional comments
would be (referncing your numbering scheme):
3a) For simple differential structures, you might not only be able to
invoke symmetry about the horizontal axis, but also the vertical axis,
allowing injecting into a single port (never having to move the
stimulus).
4a, 5a) IConnect's TDA does this nicely. Error correction is a lot less
involved than in the frequency domain (this has intrigued me for a while
- why can we correct wonderfully with a single "thru" in the time
domain, but need several "lines" for a TRL in the frequency domain?).

Replies to your questions:
a) yep - it can be done
b & c) one of the challenges will be to make sure your 2 receiver
channels are aligned, else you might end up with bogus (non-passive)
results. One of the nice things about the time domain is that you can
look at your 4-port data and make sure it "makes sense" before going
through the exercise of converting to S-parameters, etc.   =20

For instance, does your T41 pulse occur before T21?  If so, you probably
induced an error somehow.  You'll especially want to compare T11 and T31
waveforms - these would give the clearest indication that you had
erroneous skew between your receiver channels.

P1   ------    P2
P3   ------    P4


Jeff Loyer

-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx]
On Behalf Of Chris Cheng
Sent: Tuesday, May 17, 2005 1:22 PM
To: si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] Re: Estimate ISI with S parameters -- Using TDR to do
SDD21 correlation?

I have to admit I've never try this before but I am about to give it a =
=3D
shot
myself so tell me I am crazy or worst trying.
1)      If you have a TDR head, you should be able to do single ended
TDR
and TDT.
2)      If you treat your differential lines as 4 ports, you can measure
TDRxy and TDTxy on sequential pairs of ports while terminating the =3D
other 2
ports with 50 ohm terminators.=3D20
3)      If you invoke symmetry on the lines you just need to measure the
upper or lower diagonal of the matrix.
4)      Do your FFT to transform the TDT/TDR to single ended Sxy
parameters
5)      Clean them up with your favorite SOLT error corrections methods
6)      Transform the Sxy matrix into mix mode Sddcc matrix.

My questions are :
a)      Can this be done ?
b)      How "clean" do I need on the SOLT error corrections ? Can it be
skipped ?
c)      Do I have to worry about passivity on these extracted parameters
?

-----Original Message-----
From: John@xxxxxxxxxxxx [mailto:John@xxxxxxxxxxxx]
Sent: Monday, May 16, 2005 7:13 PM
To: Scott McMorrow
Cc: steve weir; si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] Estimate ISI with S parameters -- Using TDR to do =3D
SDD21
correlation?


Hi Scott,
=3D20
Thank you for helps.
Yes, I can run circuit with s-parameter model.  Here, one question. =3D
Before,
I would like to  run random pattern for ISI.   Recently studying, show =
=3D
only
need to do pulse response to see
how the result waveform penetrates to next signal. It makes sense to me
=3D
and
also easier to run simulation.   Any comments on this method?
=3D20
Also, I don't have a 4 port VNA to measurement SDD21 for correlation.
However I have a TDR with only one differential module to measure trace
impedance (SDD11).=3D20
(I cannot use TDT functions since only one module installed)
=3D20
Is it reasonable to correlate SDD11 as a indicator for the correlation =
=3D
of
SDD21?  Do I miss something?
=3D20
Thanks,
John  =3D20
=3D20
=3D20
________________________________

From: Scott McMorrow [mailto:scott@xxxxxxxxxxxxx]=3D20
Sent: Monday, May 16, 2005 9:21 PM
To: John Lin (=3DAAL=3DB4=3DC2=3DB7=3DD7)
Cc: steve weir; si-list@xxxxxxxxxxxxx
Subject: Re: [SI-LIST] Re: Estimate ISI with S parameters?


John

If you have HSPICE available, you can set up a circuit with s-parameter
modeling to measure any pattern dependent ISI that you want.

scott


Scott McMorrow
Teraspeed Consulting Group LLC
121 North River Drive
Narragansett, RI 02882
(401) 284-1827 Business
(401) 284-1840 Fax

http://www.teraspeed.com

Teraspeed(r) is the registered service mark of
Teraspeed Consulting Group LLC


John Lin (=3DAAL=3DB4=3DC2=3DB7=3DD7) wrote:=3D20

        Hi Steve,
=3D09
        Thanks for your helps.
=3D09
        >From other response, it looks like, I need to transfer
channel's S
=3D3D
        parameters into time domain
         and do pulse repsonse to see how the curve at the falling edge
=3D3D
        penetrates to the period=3D3D20
        Of a next signal.
=3D09
        In your mail, ISI is relative to attenuation,SDD21.
=3D09
        I read SAS/SATA spec. There is a ISI compliant curve shown on a
SDD21 =3D3D
        chart.=3D3D20
        The ISI curve is steeper than SDD21 compliant curve.=3D3D20
=3D09
        How to generate a ISI curve at the frequency domain by
simulation to
=3D3D
        check if meet the requirement.?
=3D09
        Thanks,
        John
=3D09
=3D09
=3D09
=3D09
        -----Original Message-----
        From: steve weir [mailto:weirsi@xxxxxxxxxx]=3D3D20
        Sent: Saturday, May 14, 2005 1:34 AM
        To: John Lin (=3D3DAAL=3D3DB4=3D3DC2=3D3DB7=3D3DD7); =
si-list@xxxxxxxxxxxxx
        Cc: John Lin (=3D3DAAL=3D3DB4=3D3DC2=3D3DB7=3D3DD7)
        Subject: Re: [SI-LIST] Estimate ISI with S parameters?
=3D09
        John variable attenuation versus frequency within the symbol
frequency =3D3D
        band will give rise to ISI as the amplitude at any given point
will
=3D3D
        depend on the previous history of symbols, and hence the name
ISI.
=3D09
        Steve
        At 10:25 AM 5/13/2005 +0800,
=3D3D3D?big5?B?Sm9obiBMaW4gKKpMtMK31yk=3D3D3D?=3D3D3D =3D3D
        wrote:
         =3D20

                Dear all SI experts,
        =3D09
                Can some ones explain how to relate ISI (inter-symbol
interference) to=3D3D20
                S parameters?
        =3D09
                What can be observed from S -parameter for differential
4
parts=3D3D20
                simulation?  For example, crosstalk, attenuation,
reflection,....etc.
        =3D09
                Thanks,
                John
=3D09
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