[SI-LIST] Re: SI Simulation of GHz signals

What a great question Clifford!  When you have hardware that needs to be
designed, it can be hard justifying weeks getting simulations running,
either using spice models or s-parameters when you could be getting your
schematics, placement and routing done.

To be honest, at 3.125Gb/s there are enough systems running and resultant
knowledge available that you probably don't need to get the simulations
perfect.  Unless of course, you're working with a tighter than usual jitter
specification or a very long link with more loss than usual.

I would opt for taking all the precautions possible, assuming that doing so
doesn't drive cost through the roof, and move on with your actual design.
Maybe you pay an SI consultant or work with a very knowledgable company to
get you started with the list of all the precautions.

Regards,
Chris

**********************
Chris Heard
Teradyne
Email: christopher.heard@xxxxxxxxxxxx



                                                                                
                                                        
                      Clifford van Dyk                                          
                                                        
                      <clifford@blackho         To:      si-list@xxxxxxxxxxxxx  
                                                        
                      le.net>                   cc:                             
                                                        
                      Sent by:                  Subject: [SI-LIST] SI 
Simulation of GHz signals                                         
                      si-list-bounce@fr                                         
                                                        
                      eelists.org                                               
                                                        
                                                                                
                                                        
                                                                                
                                                        
                      07/26/2004 01:31                                          
                                                        
                      PM                                                        
                                                        
                      Please respond to                                         
                                                        
                      clifford                                                  
                                                        
                                                                                
                                                        
                                                                                
                                                        




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
models. I have evaluated two of the most recommended S.I. toolchains:
Mentor G. HyperLynx and Cadence Spectraquest. Both tools use HSPICE as
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
with both tools have not been good. Anything but the most simplistic of
traces causes the tools to either crash or take rediculous time to
process (of the order of hours for even a simple net). A further issue
is that both of these tool vendors claim that the HSPICE simulator is
not necessary, and that the simulation can be performed without it, but
practically this is not the case, due to a lack of availability of
reliable models in anything other than HSPICE format. The conversion
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
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
simple, robust and reliable, or is the simulation of such signals still
premature? Coming from a HW design background, I am fairly new to S.I.,
but it seems surprising that  there is no industry-standard modelling
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
whether it is not more practical to just take all the precautions
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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