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Subject: Modeling and Simulating Line-Interface IOs of Communications Chips

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anassar
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7/30/2007 4:27 AM
I have encountered a consistent practice by most vendors telecommunications chip vendors. They do not provide IBIS models for the line-interface IOs of their chips (e.g. Ethernet, E1/T1, etc.). These IOs are usually left non-connected (NC) in the IBISDevice models. However, these IOs must still be modeled and simulated to develop an understanding of the constraints governing its proper operation. Please let me know how such IOs can be *modeled* and simulated, or provide any information that may be of help in this situation.

Donald Telian
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8/10/2007 9:50 AM
When you work at a semiconductor company, how (even IF) IBIS models are constructed is largely a function of customer demand. If/when there's something you need in an IBIS model, you need to make that request to the IC manufacturer. If you work at a large company that buys lots of volume, the IC vendor will work quickly to satisfy your request - particularly if you make your request through your purchasing department. (They control the contracts on what needs to be delivered, and how and when. Adding delivery of a certain type of IBIS model can be included in this.) If you work at a smaller company that isn't buying a significant volume, I'd still encourage you to make your request. They may not act on it as fast, but when a number of similar requests come in they eventually get the message. That said, a successful SI engineer can't always wait on getting the model from a semi vendor. Be ready to make educated assumptions and approximations. Some data is better than none. Download the macromodel templates available at this site, and learn how to use them. Many IC vendors are not yet skilled at making good differential driver models, even thinking they can't be done in PCB simulators. But that isn't so, and there's a ton of info at cdnusers about how to model them. Many SI engineers don't care for making models, but it's part of the job. So work both paths in parallel: (1) make requests of the IC vendor, and (2) learn to make your own models. I did both things on a recent project, and the vendor's model arrived the day I finished the project. When I compared their model with mine, I actually liked mine better. (I didn't feel they did a good job of spanning min/typ/max. I suspect they were new at making models.) However, comparing the models further helped to confirm that my assumptions were correct. IO drivers are not a mystery and, with the exception of Gbit Rx EQ, the majority of IC vendors solutions are quite the same. Hope that helps, Donald

Donald Telian SI Consultant telian@sti.net 559-760-5793

anassar
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8/12/2007 2:22 AM
Thanks for this enlightening reply, although it added one more task to those already on my shoulder.

Donald Telian
Posts: 42
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8/20/2007 6:14 PM
Sorry about that. You had a lot of views on your post but no answers, which indicates there isn't a nice pain-free solution to the problem. Maybe others watching this thread can chime in with good ideas on how to motivate an IC company to offer the right models. Donald

Donald Telian SI Consultant telian@sti.net 559-760-5793

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Forums > Silicon-package-board > Signal Integrity and Modeling > Modeling and Simulating Line-Interface IOs of Communications Chips

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