Hi Michael, Thanks for your detailed reponse. I made a small mistake in putting the voltage ranges as you mentioned. As i was writing a new tool , at this point of time i didnt give much attention to printing correct voltage range , and i was only worried about the correct extraction of V-t and I-V tables. I have considered the formula you have mentioned for calculating Vcc-relative Pullup and Powerclamp tables. I changed the voltage range to ( 3.3, 3.0 and 3.6 which is the actual case) and now i am able to get rid of all these errors. But still i have one query regarding the values for I-V curves when it is in the Min or MAX corner. I asked about this in my previous mail. Lynne and Arpad gave some answers but that didnt solve my problem. The problem with MIN and MAX corner is , what is the voltage range we need to consider for MIN and MAX case . For example if we consider 3.3 V supply, the typical range would be -3.3 to 6.6 and this is the voltage range in the IBIS file for all 3 corners. As per the cookbook we need to consider voltage range -Vcc to +2Vcc and hence for the MIN case the range will be -3.0 to +6.0. So in that case what current values we need to put for the voltage range -3.3 to -3.0 and +6.0 to +6.6 whose values will be missing in MIN corner simulations. I hope i have explained the problem correctly and let me know your answers. Thanks & Regards Sudarshan On 10/18/07, Mirmak, Michael <michael.mirmak@intel.com> wrote: > > Sudarshan, > > Thanks for the message. The major issue appears to be problems in > generating the Vcc-relative information, but some general supply issues are > cropping up too. Assuming this is just a regular I/O buffer without > internal terminations... > > 1) I would expect the Pullup I-V tables to pass through the zero V, zero I > axis intercept. Yet they do not, with the max and min data shifted by ~0.3 > V above and below 0 V, respectively. This suggests that the math used to > generate the tables may be incorrect. Remember that, if the data at Vout is > collected ground-relative, you can make the power clamp and pullup table > data in Vcc-relative by the formula (Vtable_corner = Vcc_corner - > Vout_corner), where xxx_corner refers to a value collected for typ, min or > max. For example, if Vcc_min is 4.5 V, data collected ground-relative for > 0.0 at the output would be entered in the table for the 4.5 V row. > > The supply voltages and the Pullup I-V axis intercepts (when plotted > ground-relative) don't agree, which implies a problem with the supply > listed for the [Voltage Range] keyword not matching either the real circuit > or the values used to generate the Vcc-relative tables. > > 2) The voltage for the buffer is 5 V +/- 0.5, but the V-t fixture is 3.3 V > +/- 0.3 V. This complicates the math (it gets very hard for me to > calculate the intercepts if they don't match, at least before my first cup > of coffee), but it also suggests that the buffer V-t and I-V data sets were > collected using different settings or otherwise using different conditions. > I would recommend checking the actual fixtures used for the V-t extraction; > matching the fixture voltages to the voltage supply would make checking > easier. > > Calculating the right I-V intercepts vs. V-t levels will be easier once > these issues are addressed. > > - Michael Mirmak > Intel Corp. > Chair, EIA IBIS Open Forum > > ------------------------------ > *From:* owner-ibis@server.eda.org [mailto:owner-ibis@server.eda.org] *On > Behalf Of *Sudarshan H N > *Sent:* Thursday, October 18, 2007 2:16 AM > *To:* ibis@server.eda.org; ibis-users@server.eda.org > *Subject:* [IBIS] I-V and V-t curve mismatch > > Hello Experts, > > I am finding problem with one of my IBIS model in I-V and V-t curve > mismatch. Please find the attached model for the refernence. > > ERROR - Model dummy: The [Rising Waveform] > with [R_fixture]=80 Ohms and [V_fixture]=0V > has TYP column DC endpoints of 0.01V and 2.66v, but > an equivalent load applied to the model's I-V tables yields > different voltages (-0.00V and 3.90V), > a difference of 0.25% and 31.85%, respectively. > > I wrote a new tool to generate IBIS models and i am not able to make out > where it is going wrong. > I actually tried to manually calculate the currents at the points , that > it has reported in the above error. > > As it is a rising waveform having a R_fixture to ground the current at > 2.66v (steady state) would be 2.66v/50 = 33.25mA. > > I looked at the voltage corresponding to 33.25mA in pullup table and i > found it is coming around 0.66v. There is a mismatch in the way i am > caluculating also. But i observed a different voltage of 0.66v compared to > what ibischk4 has reported i.e, 3.9v. > > Let me know is the way i am cross checking is correct or not ? If not let > me know the exact procedure. > > Also let me know what might have been gone wrong in the curves. From the > shape of the curves i am not seeing any problem with the way i have > generated. > > Please let me know your answers as soon as possible. > > Note : Please dont consider any other values apart from the curves like > Ramp , C_comp etc as i have dummy values for these place holders. > > Thanks & Regards > Sudarshan > > > > -- > 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 Thu Oct 18 22:32:38 2007
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