[SI-LIST] Re: Simulating frequency dependent s-parameters in HSPICE
- From: Ray Anderson <ray.anderson@xxxxxxxxxx>
- To: Krishna Chaitanya <krishna1abc@xxxxxxxxx>
- Date: Tue, 13 Mar 2012 11:00:33 -0700
Krishna-
As with most SI issue, "it depends" when determining how high the
interconnect should be characterized to.
In general you should characterize your interconnect up to at least 3X
the frequency of maximum spectral content (which would be 3 X 10 GHz or
30 GHz for a signal with a NRZ data rate of20 GB/s) or 3 times the
frequency of the maximum spectral content as determined from the
risetime (a commonly used approximation is .35/Rt or .35/10ps = 35GHz
for your case) which would be 3 X 35 GHz (105GHz). The factor of 3X is
kind of arbitrary (some people suggest 5x) but the object is to have a
bandwidth that most (say 90+ %) of the signal significant spectral
energy of your exciting signal fits in. If you wanted to cover 100% of
the spectral energy you would need "DC to Daylight" bandwidth.....
In this case the frequency determined by the risetime criteria will be
the determining factor (105GHz > 30 GHz).
10psec RT is quite fast, but seeing as you are concerned with on die
signals, it is possible. Accurately characterizing the interconnect up
to the 100 GHz region may be challenging. Even though it is easy to tell
your extractor to run up to 100GHz you need to make sure that your
modeling assumptions are accurate at those frequencies. If your modeling
assumptions aren't good at very high frequencies, the s-parameters
generated at those frequencies may be highly suspect.
-Ray
Xilinx Inc.
From: Krishna Chaitanya [mailto:krishna1abc@xxxxxxxxx]
Sent: Monday, March 12, 2012 4:50 PM
To: Sinha, Snehamay; Ray Anderson
Cc: Ihsan Erdin; si-list@xxxxxxxxxxxxx
Subject: Re: [SI-LIST] Simulating frequency dependent s-parameters in
HSPICE
Thanks Snehamay, Ray and all others for helping me understand how
s-parameters are simulated in HSPICE.
Thanks for the set of guidelines Ray. I think Q3D has the adaptive
sweep.
One quick question regarding the frequency range for s-parameter
extraction using Q3D. When you say the highest frequency of interest,
should I consider maximum data rate I am targeting or the bandwidth from
the rise/fall time?
If I am looking for a 20 Gbps with rise/fall times of 10ps, should I
consider the frequency sweep from DC to 100GHz (corresponding to 10ps
rise/fall) or to 10 GHz (corresponding to 20Gbps)?
I am planning to use adaptive sweep so that the step size can be
determined by the solver as mentioned earlier.
Thanks,
Krishna
.
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