[SI-LIST] Re: IBIS min, typ and max. values

From: "Muranyi, Arpad" <Arpad_Muranyi@xxxxxxxxxx>
To: <si-list@xxxxxxxxxxxxx>
Date: Thu, 27 May 2010 11:11:10 -0700
Answers to your question:

1)  Given that A > B > C you should put them in the model
this way:

typ = B
min = C
max = A

regardless of how the I-V curves turned out.

2)  Simulators should allow the user to have a say in what happens.
Ideally the user will check all possible combinations, meaning they
will try both min and max C_comp with the min and max I-V curves.

3)  This is probably up to the simulator vendor's implementation.
A certain vendor whose IBIS implementation I happen to be familiar
with will pick all min values when you tell it to do a "min" simulation,
all max values for a "max" simulation and it will pick min C_comp with
max I-V curves for "fast" simulation and max C_comp with min I-V
curves for "slow" simulations.  The user can have a choice between
these combinations.

4)  I do not know why this is only a warning in IBISCHK.  Maybe there
are cases when this convention doesn't apply and we didn't want to
invalidate those cases.

Arpad
========================================================================

-----Original Message-----
From: Lance Wang [mailto:lwang@xxxxxxxxxx] 
Sent: Thursday, May 27, 2010 12:44 PM
To: Muranyi, Arpad; si-list@xxxxxxxxxxxxx
Subject: RE: [SI-LIST] Re: IBIS min, typ and max. values

Arpad,
I guess that you disagree with me about put smaller C_comp value in the
Max
column. If not or not only that, please clarify. Thanks.

Here is a made-up example and few questions for you:
I have buffer spice netlists with TT, FF, SS corner libraries. When I
extract c_comp values from them, I got A, B and C. And A > B > C. I put
TT
iv/vt data in typ column, SS iv/vt data in max column and FF in min
according to the reference voltage and temperature settings. 
Questions:
1. what should I do with A, B and C in C-comp typ/min/max?
2. in your prediction, if I simulate it for slow and fast, which c-comp
values simulator will pick?
3. if I simulate for Min and Max (not fast and slow), which c-comp
values
simulator will pick?
4. if it is crucial, why does IBISCHK only give Warning messages not
Errors?


Thanks in advance.

BTW, I think modeling work is about how to represent a real device in an
accurate and reasonable way. Not about design the buffer self. Hope we
are
on the same page.

Best regards,

Lance Wang
978-764-2298
IO Methodology Inc.
 
 

-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx]
On
Behalf Of Muranyi, Arpad
Sent: Thursday, May 27, 2010 12:42 PM
To: si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] Re: IBIS min, typ and max. values

Lance,

Sorry, but I must disagree with you...

There are at least two reasons the IBIS specification says that the
small value of C_comp should be in the min place and the big value
in the max place.

One is that C-Comp doesn't always track with other effects.
For example, you can get a weak I-V curve by reducing the supply
voltage, but that will not change the value of the die capacitance.
And there are other process related effects which may not track
either.

The other is that it is very easy to get mixed up in the terminology.
People often associate worst case with slow, and best case with fast.
But think of an example where the buffer switches very fast, has 
very small capacitance.  In this case the transition will most likely
have some ringing, especially in reflective environments.  If the
ringing after the edge is large enough, it may enter the "forbidden
zone" where the receiver may switch.  For this reason the timing of
the system will have to wait for the ringing to settle, and from an
SI perspective the fast buffer may actually become the worst case.

Increasing the die capacitance may help in slowing down the buffer
and/or reducing the ringing.  This could result in much better SI
timings, even though the buffer is "slower".

These were the primary reasons for writing the IBIS specification
the way it is.  It is really the simulator tool's and its user's
responsibility to pick the correct combinations of the min and max
values from the IBIS model.  To cover all possible scenarios you may
need to do more combinations to find out what could cause systems
to fail.

Arpad
====================================================================

-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx]
On Behalf Of Lance Wang
Sent: Thursday, May 27, 2010 10:17 AM
To: si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] Re: IBIS min, typ and max. values

We might need to think differently for this. 

For simulators, how do they know which corner in IBIS is slow or fast or
nominal? They just use Max, Min and Typ corners. Easy! Do they know if
you
put the corners in the wrong places? Definitely not. What IBIS spec
suggested is to put slow in Max and fast in Min to have simulators pick
the
correct one for you since they might have default setting as min=fast
and
max=slow. Some simulation software even allow you changing the
relationships
as you needed. For an example, Cadence PCB SI.

For the buffer-self, when you have 3 spice netlists for each corners,
the
C_comp value is set since it is an extracted value as the same as its
IV/VT
data. Your c_comp needs to be with the other extracted data in the same
corner for sure to have correct simulation results. I have seen some
buffers' min c_comp values larger than max c_comp values. And min is
faster.
In this case, I would suggest you just have them as is. IBIS golden
parser
might give you warning messages. But it should not give Errors. 

Hope this clears a bit.

Best regards,


Lance Wang
978-764-2298
IO Methodology Inc.
www.iometh.com

 
 

-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx]
On
Behalf Of Muranyi, Arpad
Sent: Thursday, May 27, 2010 9:50 AM
To: Sudhanshu SINGH; si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] Re: IBIS min, typ and max. values

Follow the suggestion in the spec, put the big values
in the max location and the small values in the min
location...   The simulator will pick and choose for
you.  For example, if you read the HSPICE manual, you
will find a table in there which explains what values
it will pick from the IBIS file for typ min max fast slow
simulation settings in the B-element...

Arpad
==========================================================

-----Original Message-----
From: Sudhanshu SINGH [mailto:sudhanshu.singh@xxxxxx] 
Sent: Thursday, May 27, 2010 8:10 AM
To: si-list@xxxxxxxxxxxxx; Muranyi, Arpad
Subject: RE: [SI-LIST] Re: IBIS min, typ and max. values

Hello All,

In my case I have seen that spice Vs IBIS correlation is better if the
c_comp values are put in typ/min/max tables exactly as they are
extracted.

Even if the magnitude wise order is not strictly followed as in the IBIS
spec.

What is then the best approach to put c_comp values in IBIS tables?

Thanks in advance,

Best Regards,
Sudhanshu


-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx]
On
Behalf Of Muranyi, Arpad
Sent: Thursday, May 27, 2010 5:00 AM
To: si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] Re: IBIS min, typ and max. values

Hermann,

I am not sure where you got the idea from that the IBIS spec
says "one can place the largest value in the min Column in
order to have the worst slow case covered".  If you look in
Section 9 of the specification, you will find the following:

| The "min" and "max" columns for all remaining keywords and
subparameters
| will contain the smallest and largest magnitude values. This applies
to the
| [Model] subparameter C_comp as well even if the correlation to the
voltage,
| temperature, and process variations are known because information
about such
| correlation is not available in all cases.

Thanks,

Arpad
==============================================================

-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx]
On Behalf Of Hermann Ruckerbauer
Sent: Wednesday, May 26, 2010 10:29 AM
To: si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] Re: IBIS min, typ and max. values

Hello Sudhanshu,
that's interesting.
In this case the spec and the IBIS cookbook mention it differently ...
The cookbook mentiones to use the same order (smallest value in the min
column) and let the tool decide, while the Spec mentiones, that one can
place the largest value in the min Column in order to have the worst
slow case covered ...

Any feedback from the tool vendors how they implemented this selection ?

Thanks and Regards

Hermann

EKH - EyeKnowHow
Hermann Ruckerbauer
www.EyeKnowHow.de
Hermann.Ruckerbauer@xxxxxxxxxxxxx
Veilchenstrasse 1
94554 Moos
Tel.:   +49 (0)9938 / 902 083
Mobile: +49 (0)176  / 787 787 77
Fax:    +49 (0)3212 / 121 9008


schrieb Sudhanshu SINGH:
> Hello All,
>
> Reagrding c_comp as put previously in this mail, I have a query that,
> why c_comp values extracted in typ, min or max conditions are not put
> respectively in same typ, min or max columns in IBIS.
>
>
> As Section 5.1.3.1 of cookbook ver4 says:
>
> Note that when constructing the IBIS file the numerically largest
value of
> C_comp is listed as the "max" value while the numerically smallest
value of
> C_comp is listed as the "min" value. C_comp min and max values do not
> necessarily correlate with the min and max conditions under which the
I-V
> and switching data was gathered. The actual association of C_comp
corner
> values with simulation corners is performed at the tool level.
>
>
> Thanks and Regards,
> Sudhanshu
>
> -----Original Message-----
> From: si-list-bounce@xxxxxxxxxxxxx
[mailto:si-list-bounce@xxxxxxxxxxxxx] On
> Behalf Of Hermann Ruckerbauer
> Sent: Wednesday, May 26, 2010 2:23 PM
> To: Lynne D. Green
> Cc: si-list@xxxxxxxxxxxxx
> Subject: [SI-LIST] Re: IBIS min, typ and max. values
>
> Thanks to all who replied (that fast).
> I just love the List and everybody sharing his knowhnow there !!!!
>
> BTW: Happy Birthday!!!!
>
> Hermann
>
> EKH - EyeKnowHow
> Hermann Ruckerbauer
> www.EyeKnowHow.de
> Hermann.Ruckerbauer@xxxxxxxxxxxxx
> Veilchenstrasse 1
> 94554 Moos
> Tel.: +49 (0)9938 / 902 083
> Mobile:       +49 (0)176  / 787 787 77
> Fax:  +49 (0)3212 / 121 9008
>
>
> schrieb Lynne D. Green:
>   
>> Hello, Hermann,
>>
>> Note that the "SPICE"  temperature is JUNCTION temperature, not
>> ambient. IBIS [Temperature] is also junction temperature. The
junction
>> is hotter than ambient.
>>
>> Since the TYP temperature is only 25C, it is likely that ambient was
>> used instead of junction when creating the model. Generally,
>> increasing TYP and HOT temperatures by 25C is used to account for
self
>> heating when simulating to create I/O models for IBIS.  COLD
>> temperature is not adjusted.
>>
>> Note the Max [Temperature] is higher in bipolar I/O and lower in CMOS
>> I/O.
>>
>> Hope this helps.
>>
>> Lynne Green
>> Chair, IBIS Model Committee
>>
>>
>>
>> Hermann Ruckerbauer wrote:
>>     
>>> Hello *,
>>>
>>> I hope somebody can help me with interpreting some things in an IBIS
>>> file
>>> I'm just working with an IBIS file where the min, typ, max values
are
>>> arranged in the following way:
>>>
>>>                                        typ               
>>> min                 max
>>>
>>> C_comp                       0.284pF             0.409pF            
>>> 0.264pF
>>> [Voltage Range]              1.200V              1.100V             
>>> 1.300V
>>> [Temperature Range]          25                  125
125
>>>
>>> The C_comp min is the largest value and the Temperature is in there
>>> twice with 125C.
>>> The same order is used for RAC and CAC for a terminator (largest
value
>>> in the min column)
>>>
>>>
>>> e. g. in a Micron IBIS file is even some comment on having 0C as
max.
>>> temperature :
>>>
>>> | Junction Temperature (Ambient temp is 25C typ, 85C min, 0C max)
>>> |                                       typ                
>>> min                   max     
>>> [Temperature Range]        40.0               100.0
0.0
>>>
>>> Regarding C_comp the Micron model lists it in the different order:
>>> |                                    typ                  
>>> min                    
>>> max                                                        
>>> C_comp                      2.466pF             2.316pF            
>>> 2.616pF
>>>
>>> In the IBIS spec I found the comment that C_comp is independent of
>>> fabrication process and therefore to generate worst case it can make
>>> sense to use the largest C_comp for slow process ==> in the min
column.
>>> Basically this makes sense to me, but does it then make sense to use
the
>>> smalles C_comp value in the min column  ?
>>>
>>> So my questions would be:
>>> Is there any common usage of the min column regarding parameters
like
>>> C_Comp, RAC, CAC (and maybe ohters) ?
>>> Usually I would expect low temperature for fast devices, so having
0C in
>>> the max column make sense, but does it make sense to have 125C in
min
>>> and max column ?
>>>
>>> Any feedback is highly appreciated!
>>>
>>> Thanks and regards
>>>
>>> Hermann
>>>
>>> EKH - EyeKnowHow
>>> Hermann Ruckerbauer
>>> www.EyeKnowHow.de
>>> Hermann.Ruckerbauer@xxxxxxxxxxxxx
>>> Veilchenstrasse 1
>>> 94554 Moos
>>> Tel.:    +49 (0)9938 / 902 083
>>> Mobile:    +49 (0)176  / 787 787 77
>>> Fax:    +49 (0)3212 / 121 9008
>>>
>>>
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Follow-Ups:
- [SI-LIST] Re: IBIS min, typ and max. values
  - From: Lance Wang
References:
- [SI-LIST] SI opening at NetLogic Microsystems
  - From: Margaret Wang
- [SI-LIST] IBIS min, typ and max. values
  - From: Hermann Ruckerbauer
- [SI-LIST] Re: IBIS min, typ and max. values
  - From: Lynne D. Green
- [SI-LIST] Re: IBIS min, typ and max. values
  - From: Hermann Ruckerbauer
- [SI-LIST] Re: IBIS min, typ and max. values
  - From: Sudhanshu SINGH
- [SI-LIST] Re: IBIS min, typ and max. values
  - From: Hermann Ruckerbauer
- [SI-LIST] Re: IBIS min, typ and max. values
  - From: Muranyi, Arpad
- [SI-LIST] Re: IBIS min, typ and max. values
  - From: Sudhanshu SINGH
- [SI-LIST] Re: IBIS min, typ and max. values
  - From: Muranyi, Arpad
- [SI-LIST] Re: IBIS min, typ and max. values
  - From: Lance Wang
- [SI-LIST] Re: IBIS min, typ and max. values
  - From: Muranyi, Arpad
- [SI-LIST] Re: IBIS min, typ and max. values
  - From: Lance Wang
[SI-LIST] Re: IBIS min, typ and max. values

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