[IBIS] RE: Understanding IV-VT mismatch errors / warnings and their fix

From: <birendra.rana_at_.....>
Date: Wed Mar 04 2009 - 21:15:24 PST
Hi Bob,

Thanks for subscribing me to the IBIS reflector.

You are correct about the out of sync data in this mail and the IBIS
model that I had sent across the first time. The IV table indicated as
"ORIGINAL PULLUP TABLE" in my mail is different since it is generated
with different GMIN across corners. The first IBIS model had IV table
generated with a single GMIN value. I had indicated in my first mail
that using different GMIN, I was able to reduce the number of mismatch
errors/warnings. The remaining mismatch which could not be removed, was
removed by correcting the IV data. The IV table under "CORRECTED PULLUP
TABLE" is this latest one.

I just realise that in my mail I have wrongly mentioned the IV table as
Pullup table. It is actually the Pulldown table (as can be noticed in
the tables definition) which I had modified.

Your observation on the inconsistency between rising edge and falling
edge is correct. I guess this inconsistency can be attributed to the
buffer taking time to have all its internal nodes get to a stable
condition. So the PAD voltage at T=0 is not the correct one. This forces
me to capture the third rise / fall transition for the VT table. Now
doing this makes the rise and fall consistent. However, the IV tables
that get generated with DC simulations are consistent with buffer
condition at T=0. As described in my previous mail, trying different
GMIN, shifting to transient analysis and sweeping PAD with a slow PWL
after ramping up supplies was looked into but with different level of
success and failures. The method of varying GMIN across corners and
correcting the Pulldown table does help in resolving the mismatch. The
only concern after doing this is whether my IBIS model simulations will
correlate with the Spectre netlist simulations? This might be the next
problem to solve and take me back to where I started.

Best regards,

Birendra Rana

-----Original Message-----
From: Bob Ross [mailto:bob@teraspeed.com]
Sent: Thursday, March 05, 2009 1:17 AM
To: Birendra Rana (WT01 - Wipro NewLogic)
Cc: bob@terasoeed; cin
Subject: Re: Understanding IV-VT mismatch errors / warnings and their
fix

Hi Birendra:

The last message went out on the IBIS Users reflector, but bounced on
the IBIS reflector.  I subscribed you to the IBIS reflector.

I think we are out of sync. on the examples since the data (old) does
not match the data I used.

It is correct to get the proper I-V tables.  If that solved the
Error/Warning problems for V-T mismatches, then you did the correct
thing.  What I looked for in the data was possible double counting of
the I-V data with the clamp data, but the clamps looked clean
(negligible current) in the normal operation region.  Internal weak
on-die pullup terminators are often the source of V-T mismatch.

My main concern in the model that I looked at was the the V-T data
itself looked inconsistent.  The rising edge for one of the test loads
had different beginning/end points than the following edge.  For the
case I looked at, the typical falling edge had correct end points with
50 ohms to GND (.33 and 0) whareas the rising edge started at 0, but
only went to .31.  That was enough to produce a Warning.

So I think you may have a better updated model than the one I was
looking at.

Best Regards,
Bob

birendra.rana@wipro.com wrote:
> Hi Bob,
>
> Let me update you on what I did to get the mismatches removed. Instead

> of scaling the VT tables, I updated the pullup IV table. This removed
> all the mismatch warnings/errors. Found out that the pullup table
> generated has deficiency of 1.2mA current for min corner and 0.2mA for

> max corner. This "correction" changes the IV end points and brings
> them closer to VT end points.
>
> I have one question on this method: is this a legal way to do it?
>
> FYI, I am yet to run a correlation check on the generated IBIS model
> sim against the spectre netlist simulation. So verification is
pending.
>
> Below are the IBIS pullup IV tables for your reference. The
> corrections are done for voltages from 0.6V to 2.34V.
>
> Apologies for sending you a direct mail to you. I am not sure if my
> mails have reached the group. Thanks once again for the previous
> response.
>
> Best regards,
>
> Birendra Rana
>
> _________________________________________________________
> Wipro Technologies
> Plot No 72, Keonics Electronics City, Hosur Main Road, Bangalore -
> 560100
> Mob: +91 80 9880340060 | Tel: +91 80 30295448
> Email: birendra.rana@wipro.com | Website: www.wipro.com
>
> ORIGINAL PULLUP TABLE
> --------------------------------
> [Temperature Range]   25.0000           0.1250k             -40.0000
> [Voltage Range]        1.8000V           1.6500V             1.9500V
> [Pulldown]
> |Voltage   I(typ)              I(min)              I(max)
> |
>   -1.8000   -0.5584mA         -0.3486mA           -0.6344mA
>   -1.7400   -0.6003mA         -0.3735mA           -0.6834mA
>   -1.6800   -0.6489mA         -0.4022mA           -0.7406mA
>   -1.6200   -0.7059mA         -0.4355mA           -0.8081mA
>   -1.5600   -0.7735mA         -0.4747mA           -0.8887mA
>   -1.5000   -0.8551mA         -0.5212mA           -0.9869mA
>   -1.4400   -0.9554mA         -0.5776mA           -1.1088mA
>   -1.3800   -1.0812mA         -0.6469mA           -1.2641mA
>   -1.3200   -1.2437mA         -0.7342mA           -1.4681mA
>   -1.2600   -1.4606mA         -0.8471mA           -1.7473mA
>   -1.2000   -1.7632mA         -0.9980mA           -2.1501mA
>   -1.1400   -2.2106mA         -1.2081mA           -2.7758mA
>   -1.0800   -2.9258mA         -1.5165mA           -3.8553mA
>   -1.0200   -4.2139mA         -1.9996mA           -6.0823mA
>   -0.9600   -6.8113mA         -2.8219mA           -11.5493mA
>   -0.9000   -11.9362mA        -4.2583mA           -21.6409mA
>   -0.8400   -16.6401mA        -6.3737mA           -25.1748mA
>   -0.7800   -17.6857mA        -8.0105mA           -24.8418mA
>   -0.7200   -17.2472mA        -8.5735mA           -23.9135mA
>   -0.6600   -16.3772mA        -8.7003mA           -22.7636mA
>   -0.6000   -15.2791mA        -8.3475mA           -21.3760mA
>   -0.5400   -13.9840mA        -7.6882mA           -19.6898mA
>   -0.4800   -12.4838mA        -6.8675mA           -17.6476mA
>   -0.4200   -10.8035mA        -5.9456mA           -15.3009mA
>   -0.3600   -9.0504mA         -4.9630mA           -12.8798mA
>   -0.3000   -7.3321mA         -3.9775mA           -10.5093mA
>   -0.2400   -5.6846mA         -3.0357mA           -8.2118mA
>   -0.1800   -4.1192mA         -2.1602mA           -5.9989mA
>   -0.1200   -2.6443mA         -1.3594mA           -3.8830mA
>   -0.0600   -1.2683mA         -0.6380mA           -1.8782mA
>   0.0000   13.4705fA         0.9549pA            8.7393pA
>   0.0600   1.1519mA          0.5511mA            1.7338mA
>   0.1200   2.1780mA          1.0120mA            3.3023mA
>   0.1800   3.0687mA          1.3798mA            4.6793mA
>   0.2400   3.8125mA          1.6513mA            5.8299mA
>   0.3000   4.3968mA          1.8277mA            6.7118mA
>   0.3600   4.8145mA          1.9249mA            7.2995mA
>   0.4200   5.0789mA          1.9736mA            7.6319mA
>   0.4800   5.2302mA          1.9987mA            7.8038mA
>   0.5400   5.3145mA          2.0127mA            7.8958mA
>   0.6000   5.3627mA          2.0211mA            7.9500mA
>   0.6600   5.3914mA          2.0262mA            7.9851mA
>   0.7200   5.4084mA          2.0289mA            8.0092mA
>   0.7800   5.4178mA          2.0302mA            8.0259mA
>   0.8400   5.4222mA          2.0310mA            8.0369mA
>   0.9000   5.4256mA          2.0313mA            8.0434mA
>   0.9600   5.4268mA          2.0315mA            8.0509mA
>   1.0200   5.4275mA          2.0316mA            8.0526mA
>   1.0800   5.4279mA          2.0316mA            8.0535mA
>   1.1400   5.4282mA          2.0317mA            8.0540mA
>   1.2000   5.4285mA          2.0318mA            8.0544mA
>   1.2600   5.4287mA          2.0318mA            8.0546mA
>   1.3200   5.4290mA          2.0319mA            8.0549mA
>   1.3800   5.4291mA          2.0319mA            8.0551mA
>   1.4400   5.4293mA          2.0319mA            8.0552mA
>   1.5000   5.4295mA          2.0320mA            8.0554mA
>   1.5600   5.4296mA          2.0320mA            8.0556mA
>   1.6200   5.4298mA          2.0321mA            8.0557mA
>   1.6800   5.4299mA          2.0321mA            8.0558mA
>   1.7400   5.4300mA          2.0321mA            8.0560mA
>   1.8000   5.4302mA          2.0323mA            8.0561mA
>   1.8600   5.4303mA          2.0332mA            8.0562mA
>   1.9200   5.4304mA          2.0377mA            8.0563mA
>   1.9800   5.4305mA          2.0596mA            8.0565mA
>   2.0400   5.4308mA          2.1260mA            8.0566mA
>   2.1000   5.4319mA          2.2658mA            8.0567mA
>   2.1600   5.4421mA          2.4934mA            8.0567mA
>   2.2200   5.5048mA          2.8120mA            8.0569mA
>   2.2800   5.6991mA          3.2150mA            8.0576mA
>   2.3400   6.0690mA          3.6918mA            8.0673mA
>   2.4000   6.6199mA          4.2243mA            8.1655mA
>   2.4600   7.3386mA          4.7298mA            8.5126mA
>   2.5200   8.2052mA          5.0516mA            9.1705mA
>   2.5800   9.1922mA          5.3079mA            10.1258mA
>   2.6400   10.1981mA         5.5241mA            11.3425mA
>   2.7000   10.8061mA         5.7470mA            12.7798mA
>   2.7600   11.1784mA         6.0130mA            14.3806mA
>   2.8200   11.4924mA         6.3168mA            15.8396mA
>   2.8800   11.7180mA         6.6517mA            16.4096mA
>   2.9400   11.6296mA         7.0121mA            16.6678mA
>   3.0000   11.5414mA         7.3945mA            16.7924mA
>   3.0600   11.6634mA         7.7959mA            16.7979mA
>   3.1200   11.8881mA         8.2132mA            16.6454mA
>   3.1800   12.1672mA         8.6432mA            15.7287mA
>   3.2400   12.4834mA         9.0822mA            13.8846mA
>   3.3000   12.8266mA         9.5270mA            13.3560mA
>   3.3600   13.1923mA         9.9746mA            13.0529mA
>   3.4200   13.5774mA         10.4217mA           12.8283mA
>   3.4800   13.9791mA         10.8657mA           12.6493mA
>   3.5400   14.3931mA         11.3041mA           12.5008mA
>   3.6000   14.8132mA         11.7350mA           12.3783mA
>
> CORRECTED PULLUP TABLE
> -----------------------------------
> [Temperature Range]   25.0000           0.1250k             -40.0000
> [Voltage Range]        1.8000V           1.6500V             1.9500V
> [Pulldown]
> |Voltage   I(typ)              I(min)              I(max)
> |
>   -1.8000   -0.5584mA         -0.3486mA           -0.6344mA
>   -1.7400   -0.6003mA         -0.3735mA           -0.6834mA
>   -1.6800   -0.6489mA         -0.4022mA           -0.7406mA
>   -1.6200   -0.7059mA         -0.4355mA           -0.8081mA
>   -1.5600   -0.7735mA         -0.4747mA           -0.8887mA
>   -1.5000   -0.8551mA         -0.5212mA           -0.9869mA
>   -1.4400   -0.9554mA         -0.5776mA           -1.1088mA
>   -1.3800   -1.0812mA         -0.6469mA           -1.2641mA
>   -1.3200   -1.2437mA         -0.7342mA           -1.4681mA
>   -1.2600   -1.4606mA         -0.8471mA           -1.7473mA
>   -1.2000   -1.7632mA         -0.9980mA           -2.1501mA
>   -1.1400   -2.2106mA         -1.2081mA           -2.7758mA
>   -1.0800   -2.9258mA         -1.5165mA           -3.8553mA
>   -1.0200   -4.2139mA         -1.9996mA           -6.0823mA
>   -0.9600   -6.8113mA         -2.8219mA           -11.5493mA
>   -0.9000   -11.9362mA        -4.2583mA           -21.6409mA
>   -0.8400   -16.6401mA        -6.3737mA           -25.1748mA
>   -0.7800   -17.6857mA        -8.0105mA           -24.8418mA
>   -0.7200   -17.2472mA        -8.5735mA           -23.9135mA
>   -0.6600   -16.3772mA        -8.7003mA           -22.7636mA
>   -0.6000   -15.2791mA        -8.3475mA           -21.3760mA
>   -0.5400   -13.9840mA        -7.6882mA           -19.6898mA
>   -0.4800   -12.4838mA        -6.8675mA           -17.6476mA
>   -0.4200   -10.8035mA        -5.9456mA           -15.3009mA
>   -0.3600   -9.0504mA         -4.9630mA           -12.8798mA
>   -0.3000   -7.3321mA         -3.9775mA           -10.5093mA
>   -0.2400   -5.6846mA         -3.0357mA           -8.2118mA
>   -0.1800   -4.1192mA         -2.1602mA           -5.9989mA
>   -0.1200   -2.6443mA         -1.3594mA           -3.8830mA
>   -0.0600   -1.2683mA         -0.6380mA           -1.8782mA
>   0.0000   13.4705fA         0.9549pA            8.7393pA
>   0.0600   1.1519mA          1.5511mA            1.7338mA
>   0.1200   2.1780mA          2.0120mA            3.3023mA
>   0.1800   3.0687mA          2.3798mA            4.6793mA
>   0.2400   3.8125mA          2.6513mA            5.8299mA
>   0.3000   4.3968mA          2.8277mA            6.7118mA
>   0.3600   4.8145mA          2.9249mA            7.2995mA
>   0.4200   5.0789mA          2.9736mA            7.6319mA
>   0.4800   5.4302mA          2.9987mA            7.8038mA
>   0.5400   5.5145mA          3.2827mA            7.8958mA
>   0.6000   5.5627mA          3.2811mA            7.9500mA
>   0.6600   5.5914mA          3.2862mA            7.9851mA
>   0.7200   5.6084mA          3.2889mA            8.0092mA
>   0.7800   5.6178mA          3.2802mA            8.0259mA
>   0.8400   5.6222mA          3.2810mA            8.0369mA
>   0.9000   5.6256mA          3.2813mA            8.0434mA
>   0.9600   5.6268mA          3.2815mA            8.0509mA
>   1.0200   5.6275mA          3.2816mA            8.0526mA
>   1.0800   5.6279mA          3.2816mA            8.0535mA
>   1.1400   5.6282mA          3.2817mA            8.0540mA
>   1.2000   5.6285mA          3.2818mA            8.0544mA
>   1.2600   5.6287mA          3.2818mA            8.0546mA
>   1.3200   5.6290mA          3.2819mA            8.0549mA
>   1.3800   5.6291mA          3.2819mA            8.0551mA
>   1.4400   5.6293mA          3.2819mA            8.0552mA
>   1.5000   5.6295mA          3.2820mA            8.0554mA
>   1.5600   5.6296mA          3.2820mA            8.0556mA
>   1.6200   5.6298mA          3.2821mA            8.0557mA
>   1.6800   5.6299mA          3.2821mA            8.0558mA
>   1.7400   5.6300mA          3.2821mA            8.0560mA
>   1.8000   5.6302mA          3.2823mA            8.0561mA
>   1.8600   5.6303mA          3.2832mA            8.0562mA
>   1.9200   5.6304mA          3.2877mA            8.0563mA
>   1.9800   5.6305mA          3.2896mA            8.0565mA
>   2.0400   5.6308mA          3.2860mA            8.0566mA
>   2.1000   5.6319mA          3.2858mA            8.0567mA
>   2.1600   5.6421mA          3.4934mA            8.0567mA
>   2.2200   5.6048mA          3.8120mA            8.0569mA
>   2.2800   5.6991mA          3.8150mA            8.0576mA
>   2.3400   6.0690mA          3.9918mA            8.0673mA
>   2.4000   6.6199mA          4.2243mA            8.1655mA
>   2.4600   7.3386mA          4.7298mA            8.5126mA
>   2.5200   8.2052mA          5.0516mA            9.1705mA
>   2.5800   9.1922mA          5.3079mA            10.1258mA
>   2.6400   10.1981mA         5.5241mA            11.3425mA
>   2.7000   10.8061mA         5.7470mA            12.7798mA
>   2.7600   11.1784mA         6.0130mA            14.3806mA
>   2.8200   11.4924mA         6.3168mA            15.8396mA
>   2.8800   11.7180mA         6.6517mA            16.4096mA
>   2.9400   11.6296mA         7.0121mA            16.6678mA
>   3.0000   11.5414mA         7.3945mA            16.7924mA
>   3.0600   11.6634mA         7.7959mA            16.7979mA
>   3.1200   11.8881mA         8.2132mA            16.6454mA
>   3.1800   12.1672mA         8.6432mA            15.7287mA
>   3.2400   12.4834mA         9.0822mA            13.8846mA
>   3.3000   12.8266mA         9.5270mA            13.3560mA
>   3.3600   13.1923mA         9.9746mA            13.0529mA
>   3.4200   13.5774mA         10.4217mA           12.8283mA
>   3.4800   13.9791mA         10.8657mA           12.6493mA
>   3.5400   14.3931mA         11.3041mA           12.5008mA
>   3.6000   14.8132mA         11.7350mA           12.3783mA
>
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>


--
Bob Ross
Teraspeed Consulting Group LLC     Teraspeed Labs
121 North River Drive              13610 SW Harness Lane
Narragansett, RI 02882             Beaverton, OR 97008
401-284-1827                       503-430-1065
http://www.teraspeed.com           503-246-8048 Direct
bob@teraspeed.com

Teraspeed is a registered service mark of Teraspeed Consulting Group LLC


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Received on Wed Mar 4 21:16:28 2009

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