Ibis validation

Your question requires a long answer.

First, is your measurement set up using the appropriate bandwidth to be able to properly see the waveform? We have had cases where overshoots and undershoots are missed due to insufficient bandwidth.

Do you have a low inductance ground path for the scope probe? Are you using a high impedance probe or making a coaxial measurement?

Is the board file correctly set up for simulation? Have you checked that the IBIS file has a reasonable package model? Does the ibis file pass the ibis parser and what kind of warnings do you get? Can the ibis buffer drive into the reference load at the max specified frequency? Does the ibis buffer have I-V and v-t curves or only I-V?

My experience is that for most cases, the simulation and measurement do agree reasonably well. Generally it is the typical case but there have been times when either the slow or fast case agrees better.

Hi, thank you for the reply, yes, the BW of the scope is enough, i used an active probe and the setup of the simulation is done (post layout). i suspect the ibis but don't know how to run serie of tests to check it. thank you, Doron.

Go to SigXP and drive the buffer into the reference load at the maximum interface rate. Do the waveforms look OK? If the model fails this test, it is no good. This test does not necessarily mean the model is accurate though.

what do you mean by reference load?
i did that i think by driving R // C to GND and put a dummy prob.
the waves were OK at 200MHz

The data sheet should have timing reference fixture. It should be the same in the ibis file but is often not. Use a dummy probe with the timing reference fixture and see if it works at the max frequency.