[SI-LIST] Re: SI Simulation of GHz signals
- From: "Ken Willis" <kwillis@xxxxxxxxxxx>
- To: <clifford@xxxxxxxxxxxxx>, <si-list@xxxxxxxxxxxxx>
- Date: Tue, 27 Jul 2004 08:50:49 -0700
Hi Clifford,
While it is true that you can use the HSPICE simulator with
SPECCTRAQuest (SQ),
it is not mandatory for multi-gigaHertz (MGH) signals. SQ has a very
robust behavioral MacroModeling capability that is well-suited for
effects like pre-emphasis, receiver equalization, and the like. Using
these types of models with the native simulator in SQ has allowed users
to overlay with transistor-level models, with performance speed-ups of
up to 400x.
While I agree that creating MacroModels from scratch is not for
everybody, we have started to put in place a library of model templates
for a number of common types of MGH drivers and receivers. With a
working template to start from, it is no longer a huge stretch for users
to create models, especially if they are familiar with SPICE (the SQ
circuit simulator is a SPICE-based engine). You can find a white paper
on this topic and downloadable model templates at
http://www.allegrosi.com/. We have had some good customer success using
this approach.
On the simulation front, I agree that MGH signals are pushing beyond the
scope of traditional circuit simulation. We are seeing that to get a
stable eye pattern, you may need to simulate a far larger bit stream
than what has been feasible in the past. We are addressing this need
with new "Channel Analysis" functionality, which includes a channel
simulator capable of simulating bit streams of 1 million bits or more in
very reasonable time frames. We are typically seeing performance on the
order of 1000 bits/sec, (not including characterization, which can take
a couple of minutes).
There was a detailed webinar given recently on this topic that describes
all of this in some detail. If you are interested, you can take a look
at the webinar archives at
http://www.cadence.com/webinars/webinars.aspx?xml=3Dchannel_analysis. =
The
archives for this particular webinar should be posted there within the
next week. Also, you can contact your local Cadence AE if you are
interested in taking a closer look at this new technology.=20
thanks,
Ken Willis
Cadence Design Systems
-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx]
On Behalf Of Clifford van Dyk
Sent: Monday, July 26, 2004 1:32 PM
To: si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] SI Simulation of GHz signals
Hello
I would like to perform reliable simulation of GHz signals (up to
3.125GHz), specifically Xilinx RocketIO. I would like to include in the
simulation the effects of the following:
Driver->PCB trace (incl. vias)->connector->cable->connector->PCB
trace(incl. vias)->Receiver
The models that I have obtained from the various vendors are HSPICE=20
models. I have evaluated two of the most recommended S.I. toolchains:=20
Mentor G. HyperLynx and Cadence Spectraquest. Both tools use HSPICE as=20
the simulation engine, and essentially act as a front-end gui to HSPICE,
as well as extracting the PCB trace/via models. My experiences thusfar=20
with both tools have not been good. Anything but the most simplistic of=20
traces causes the tools to either crash or take rediculous time to=20
process (of the order of hours for even a simple net). A further issue=20
is that both of these tool vendors claim that the HSPICE simulator is=20
not necessary, and that the simulation can be performed without it, but=20
practically this is not the case, due to a lack of availability of=20
reliable models in anything other than HSPICE format. The conversion=20
from HSPICE to any of the custom modelling types is also, in my opinion,
non-trivial and potentially an extremely tedious manual process.
I believe that S-Parameter based simulation provides much faster=20
simulation, but again there is a lack of availability of S-Parameter
models.
Can anyone recommend a method for simulating the above signals that is=20
simple, robust and reliable, or is the simulation of such signals still=20
premature? Coming from a HW design background, I am fairly new to S.I.,=20
but it seems surprising that there is no industry-standard modelling=20
type (equivalent of IBIS) that cable/connector vendors will provide, but
maybe this level of simulation is in its infancy, and S-Parameter models
will emerge as the standard?
Is the simulation of such signals entirely necessary? I am dubious about
the reliability of the results of such simulations, and I am wondering=20
whether it is not more practical to just take all the precautions=20
possible and hope for the best!
Please let me know if you have any advise, or a good solution to my
dilemma!
Kind regards,
Clifford
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