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Can someone give me some pointers on using ibis models?

Hi,

I have been doing designs, digital and analog, for over 20 years, without making use of ibis data, but I think that is about to end.

I was doing a design with one of the newer Altera BGA's and could not find the ususal "rise time", "fall time" data, so I inquired to Altera. Altera told me that they provide ibis models for more cases than I could count but that the "old style" specifications were no longer applicable.

What I am trying to do is match the output of an Altera device to a transmission line. If I don't know the rise time and the output impedance then I have little chance of making a good match.

I tried using the freeware tool from Intusoft that can translate ibis models to spice models (I have used spice for a long, long time) but the translator would only translate models up to ibis version 3.0. The ibis models provided by Altera were based upon ibis 3.2 and there were errors in the translation.

The whole process of making use of ibis models must be easier than I am making it.

I would think that if I had an ibis simulator, then I could use the ibis models provided by manufacturers and then create ibis models of my own to simulate the transmission lines in my design.

1) Is that last assumption correct? 2) Are there freeware ibis simulators? 3) Can someone recommend an inexpensive ibis simulator? 4) What am I missing in all this that makes the process seem more complex than it probably is?

Thank You Tom

Reply to
Teece
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Tom,

What you are missing in all of this is:

support.

If you asked the same question of the Xilinx hotline, a Xilinx SI expert would reply to your "what if" simulation, and give you the output impedance of the driver type you had chosen.

If you were in a big company with premium support, you would get the answer quickly.

If you were a student, or a very very small customer, a webcase may take a few days to get you the answer.

If you posted the same question that you did but for Xilinx here on c.a.f., I would run the simulation myself, and post the results here (just to illustrate the tools I used, and the method for general education).

Austin

Reply to
Austin Lesea

Tom,

Further, just to show that I feel sorry for you in your plight, a SSTL driver for Stratix II was 23.7 ohms, and suggested using a 59 ohm series resistor to match 65 ohm t-line, and the same driver for V4 was 30.8 ohms, and suggested using a 45 ohm series resistor to match the 65 ohm line.

I use Mentor's Hyperlynx (not free), and it takes seconds to get the answer. How much is your time worth? How much is a re-spin of the pcb worth? You pay for the tool if you save just one re-spin.

Don't like Mentor? Cadence has a very nice tool set, and there are others, too.

Austin

Reply to
Austin Lesea

Hi Tom, Have a look at the contents of the ibis file with a text editor. Some sections of the file will show I vs V figures for the IO. So using V/I = R you can get an approximation for the output impedance of any drivers.

In my experience, not quite. For example, in hyperlynx you can use their GUI to enter parameters/geometry etc from your transmission line, and import the ibis model for the drivers/receivers. One doesn't "create" IBIS models for the transmission lines as such.

Reply to
Andrew FPGA

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