Sorry to bother you again. But I am not sure that I understood all. Especially the next sentence: "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." I am using DDR buffer with internal termination of 50 ohm. So when the voltage range is between 0 to VCC, I do not have a zero current. Is that current should be treated as a leakage current? If the power clamp and gnd clamp are overlapped (in the range 0 - vcc). I will get the same current results for this range in the power and gnd clamp. And I will have double counting. Should I write the current results for this range only in one of the clamps (gnd or power), And in the second writing zeroes? Thanks. Kobi. -----Original Message----- From: Lynne D. Green [mailto:lgreen22@mindspring.com] Sent: Monday, August 03, 2009 1:25 AM To: ibis-users@eda; Kobi Pinhas Subject: Re: [IBIS-Users] Quetion about the power clamp ranges. The IBIS Quality Checklist strongly recommends both clamp tables cover -Vcc to +2Vcc. Having several points between 0 and Vcc, even if they are all zero, could also help. Another recommendation is to have at least 10 (preferably more) points in the transition region of the V-t data table. This improves simulation accuracy. This is because the IBIS specification does not specify a method for INTERPOLATION (calculating intermediate points) or for EXTRAPOLATION beyond either end of a table. So different tools are free to interpolate/extrapolate differently. If points are placed closely in table regions where the slope is changing, the tool's choice of method has less effect on the simulation results. A quick graphical check of the model data is good for identifying these, as well as the double-counting Andrew mentioned. Regards, Lynne "IBIS training when you need it, where you need it." Dr. Lynne Green Green Streak Programs http://www.greenstreakprograms.com 425-788-0412 lgreen22@mindspring.com Andrew Ingraham wrote: > 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* <http://www.mailscanner.info/>, and is > believed to be clean. -- 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 Mon Aug 3 12:35:43 2009
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