It looks like you have multiple problems with this buffer's model. This error is very common and means that the IV and VT tables do not agree with each other. First the IV tables are predicting a swing of 20mV (1.19V - 1.17V) or 40 mV (1.37V - 1.33V). I don't think these swings will work in any application. So I question your IV tables. Second, I'm not sure what you mean by pseudo LVDS but your termination voltage should be Vcommon_mode, not ground. The weak 4 mA or so LVDS pullup driver will never pull a 50 Ohm load to ground to over a Volt. LVDS is usually differentially terminated with something like 100 Ohms which is equivalent to a 50 Ohm resistor to the average output voltage from each output. Are you terminating both sides of the LVDS driver when you are doing your extractions, For the VT waveforms make sure you have a 50 Ohm load from both outputs tied to your termination voltage. In many cases in IV extraction we load the non-measured side with 50 Ohms so the buffer is working more like its typical application. We have seen funny IV tables when this is not done. Tom Dagostino Teraspeed(R) Labs 13610 SW Harness Lane Beaverton, OR 97008 503-430-1065 tom@teraspeed.com www.teraspeed.com Teraspeed Consulting Group LLC 121 North River Drive Narragansett, RI 02882 401-284-1827 -----Original Message----- From: owner-ibis-users@server.eda.org [mailto:owner-ibis-users@server.eda.org] On Behalf Of Marek Gebura Sent: Wednesday, March 07, 2007 5:09 PM To: ibis-users@server.eda.org Subject: [IBIS-Users] RE: an equivalent load applied to the model's I-V tables yields different voltages. Hi, I am trying to make a model for a pseudo LVDS pad, but I can't extract the proper IV tables from it. To extract the rise/fall waveforms I have to run the simulation at high frequency for a while (250ns) - before it gets to the proper voltage levels. But it looks like the IV curves yield different voltages. These errors are coming from my Hyperlynx session: ERROR - Model LVDSTX: The [Rising Waveform] with [R_fixture]=50 Ohms and [V_fixture]=0V has TYP column DC endpoints of 0.01V and 0.38v, but an equivalent load applied to the model's I-V tables yields different voltages ( 1.17V and 1.19V), a difference of 6615.72% and 4640.59%, respectively. ERROR - Model LVDSTX: The [Rising Waveform] with [R_fixture]=50 Ohms and [V_fixture]=1.29V has TYP column DC endpoints of 0.78V and 1.64v, but an equivalent load applied to the model's I-V tables yields different voltages ( 1.37V and 1.33V), a difference of 1712.86% and 916.29%, respectively. Has anyone seen such an Error & has an Idea on how should I extract the IV tables correctly? I made some simple IBIS models before - but I can't make one for this pad. I am not an expert in IBIS & any help is appreciated. Thanks Marek -- This message has been scanned for viruses and dangerous content by <http://www.mailscanner.info/> MailScanner, and is believed to be clean. -- This message has been scanned for viruses and dangerous content by <http://www.mailscanner.info/> MailScanner, 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 Wed Mar 7 17:59:45 2007
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