Hi All, Thanks Tom ,Todd Scott and Arpad for your valuable answers. Arpad, with your clear explanation i am able to solve all the problems i had in my modeling. One general question i have to the forum is , in the IBIS website is all the mails are stored in some central location. Because i was accessing IBIS forum mails from my other email id 3 months back. Now i am accessing from other email id. I think sometime back there was a question on analog pads IBIS model. Do i need to put a NC for these pads in pin mapping section ? Regards Sudarshan On 10/23/07, Todd Westerhoff <twesterh@sisoft.com> wrote: > > Oops, > > > > You're right: -VDDQ to 2*VDDQ. > > > > Todd. > > > > > Todd Westerhoff > VP, Software Products > SiSoft > 6 Clock Tower Place, Suite 250 > Maynard, MA 01754 > (978) 461-0449 x24 > twesterh@sisoft.com > www.sisoft.com > ------------------------------ > > *From:* owner-ibis@eda.org [mailto:owner-ibis@eda.org] *On Behalf Of *Muranyi, > Arpad > *Sent:* Monday, October 22, 2007 2:01 PM > *To:* ibis@eda.org; ibis-users@eda.org > *Subject:* RE: [IBIS-Users] RE: [IBIS] I-V and V-t curve mismatch > > > > While both Tom and Todd are suggesting the right thing, > > I think both need some correction, or clarification... > > > > Todd wrote "-2*VDD to 2*VDD" in which the first -2*VDD > > should have read -VDD. > > > > Tom's comment about using typical VDD is correct for the > > range calculation but you need to be careful an not > > apply that suggestion to the VDD of the power you > > apply to the device under test and the VDD-relative > > calculations (in case you don't measure it VDD relative > > directly). > > > > So to sum it up, my numbers in my first reply were > > calculated as follows: > > > > For the pulldown the sweep range is always: > > -VDD_typ to 2*VDD_typ = -3.3 to 6.6, > > regardless of which case you are generating, > > i.e. whether the supply voltage to the chip > > is typ=3.3, min=3.0, or max=3.6 volts (assuming > > that the chip's pulldown is connected to GND > > or 0 volts). > > > > For the pullup, which is swept VDD relative, > > the numbers for the sweep ranges in GND relative > > orientation will work out this way: > > > > -VDD_typ to 2*VDD_typ with respect to VDD_typ = 6.6 to -3.3 > > -VDD_typ to 2*VDD_typ with respect to VDD_min = 6.3 to -3.6 > > -VDD_typ to 2*VDD_typ with respect to VDD_max = 6.9 to -3.0 > > > > Note that this numbers are only this confusing because > > you are looking at the sweep ranges in a GND relative > > way, while you are really doing the same rule as above > > for the pulldown with respect to VDD. > > > > Of course the direction of the sweep is irrelevant, as > > long as the device doesn't act up. Some times devices > > can do funny things depending on which direction you > > do the sweep. Also, to help the simulator to find an > > operating point I suggest that you start the seep at > > the same rail voltage the device is driving to (i.e. > > VDD for logic high or GND for logic low) and then do > > the sweep you need for the IBIS model. There is a > > better chance to get the simulator converge that way... > > > > I hope this helps, > > > > Arpad > > =========================================================== > ------------------------------ > > *From:* owner-ibis-users@server.eda.org [mailto: > owner-ibis-users@server.eda.org] *On Behalf Of *Todd Westerhoff > *Sent:* Monday, October 22, 2007 10:09 AM > *To:* ibis@server.eda.org; ibis-users@server.eda.org > *Cc:* tom@teraspeed.com > *Subject:* [IBIS-Users] RE: [IBIS] I-V and V-t curve mismatch > > I agree with Tom. > > > > The choice of -2*VDD to 2*VDD is somewhat arbitrary … it's simply meant to > ensure that you have valid V/I data for any voltage that the part will be > exposed to. Thus, you don't need to adjust the voltage ranges based on the > MIN and MAX cases. For most technologies, if you have overshoot that's > equal to the supply voltage, you have bigger problems than model accuracy ! > > > > Todd. > > > > > Todd Westerhoff > VP, Software Products > SiSoft > 6 Clock Tower Place, Suite 250 > Maynard, MA 01754 > (978) 461-0449 x24 > twesterh@sisoft.com > www.sisoft.com > ------------------------------ > > *From:* owner-ibis@eda.org [mailto:owner-ibis@eda.org] *On Behalf Of *Tom > Dagostino > *Sent:* Monday, October 22, 2007 12:11 PM > *To:* 'Sudarshan H N'; 'Mirmak, Michael' > *Cc:* ibis@eda.org; ibis-users@eda.org > *Subject:* RE: [IBIS] I-V and V-t curve mismatch > > > > Model all three corners from –Vdd to 2*Vdd where Vdd is the typical > voltage. > > > > 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 > > *From:* owner-ibis@server.eda.org [mailto:owner-ibis@server.eda.org] *On > Behalf Of *Sudarshan H N > *Sent:* Monday, October 22, 2007 7:43 AM > *To:* Mirmak, Michael > *Cc:* ibis@server.eda.org; ibis-users@server.eda.org > *Subject:* Re: [IBIS] I-V and V-t curve mismatch > > > > Hi Michael & All, > > Can you people answer to my question regarding the voltage ranges in MIN > and MAX case as explained below. As Arpad mentioned in one of the earlier > mails the range for MIN and MAX case is > > typ: -3.3 to 6.6 > > min: -3.6 to 6.3 > > max: -3.0 to 6.9 > > How do we select this range for MIN and MAX case. Is there any document > which explains the selection criteria for these corners ? If there is no > logic , then how can we decide if the supply is 1.8 V supply or 2.5Vsupply? > > Let me know your answers. > > Regards > Sudarshan > > > > On 10/19/07, *Sudarshan H N* < hn.sudarshan@gmail.com> wrote: > > 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 <http://www.mailscanner.info/>*MailScanner, and is > believed to be clean. * > > * * > > * > > -- > 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 <http://www.mailscanner.info/>, and is > believed to be clean. > -- > 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* <http://www.mailscanner.info/>, and is > believed to be clean. > -- > 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 Tue Oct 23 10:06:59 2007
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