Looking at your plots, and knowing that you are concerned about average levels, the first thing I would try is slowing down the clock, to give the waveforms time to stabilize. That would tell you something about whether the problem is due to the transient response (or perhaps overclocking the model beyond its intended capabilities), or something else. The IBIS spec says the power clamp should cover from Vcc to 2Vcc, but there is nothing that says it must not go beyond that. The reason it says Vcc to 2Vcc and not more, is that most power clamps don't do anything below Vcc, so the current data would be zero there, and it SHOULD make no difference if those zeros are omitted from the tables. Check to see if your clamp current drops to zero near Vcc, or if it seemed truncated. But the most important thing, that everyone must do when creating IBIS files, is to make sure that all device currents are properly accounted for. This means that not only is nothing left out, but also that nothing is counted twice. Never blindly create models without thinking and checking that everything is there and that everything adds up. In the end, the only currents that you ought to leave out, are the ones well beyond the range of normal operation (i.e., below -Vcc and above +2Vcc). If your device has a lot of leakage current, or continuous pulldown or pullup current when the output is "inactive," then those currents go in the clamp tables. You need to decide whether and how much to put it in the gnd clamp or the power clamp tables. The same current should not go in both places (which is why the gnd clamp normally ends at Vcc and the power clamp normally begins there). Take a close look at the data you added in by extending your power clamp data. Is it meaningful? Is it something already accounted for anywhere else, such as the gnd clamp? If the data you added in were zeros, maybe what you need are more data points right at the knee of the clamp curve, to tell the simulator more about the shape of the curve. It might be extrapolating poorly based on too few data points. Regards, Andy -- This message has been scanned for viruses and dangerous content by MailScanner, and is believed to be clean. -------------------------------------------------------------------- |For help or to subscribe/unsubscribe, e-mail majordomo@eda-stds.org |with the appropriate command message(s) in the body: | | help | subscribe ibis <optional e-mail address, if different> | subscribe ibis-users <optional e-mail address, if different> | unsubscribe ibis <optional e-mail address, if different> | unsubscribe ibis-users <optional e-mail address, if different> | |or e-mail a request to ibis-request@eda-stds.org. | |IBIS reflector archives exist under: | | http://www.eda-stds.org/pub/ibis/email_archive/ Recent | http://www.eda-stds.org/pub/ibis/users_archive/ Recent | http://www.eda-stds.org/pub/ibis/email/ E-mail since 1993Received on Sun Aug 2 08:25:13 2009
This archive was generated by hypermail 2.1.8 : Sun Aug 02 2009 - 08:27:15 PDT