Subject: IBIS modeling questions

From: [email-masked] (Greg Edlund)
Date: Thu, 9 Nov 95 13:01:50 -0600

Anybody care to take a stab at these?

1. I was discussing IBIS model support with one of
   our IC vendors, and they raised a concern about
   ESD diode SPICE models not being accurate at
   -5 V and + 10 V.  Any clues about how to get
   around this without setting up a test lab?  Why
   do you need such a wide range in the first place,
   since nobody operates out there?

2. When will s2ibis 2.0 be available on Windows?
   Actually, I'd be happy with DOS, but that's
   probably not in the plan...

3. Has anybody written a "theory of operations"
   paper on behavioral simulators?  For instance, if
   I have a simple behavioral driver model (no ESD
   diodes, no package) driving a 50 Ohm transmission
   line terminated at the far end into 50 Ohms, how
   do I calculate the current and voltage vs. time at
   the output of the driver?  At the far end?  This
   must be an easy problem to solve.  I'd like to
   write a little C program to do this so I can better
   understand IBIS and critically compare it to SPICE.
   (For the sake of accuracy in system design issues,
   not so I can write another simulator!)

4. Has anybody thought about organizing an IBIS
   users group and mailing list?

Thanks in advance,

--
Greg Edlund                +----+----+ 
Circuits and Modeling      |    |    |
Chen Systems Corp.        <     |     )
1414 W. Hamilton Ave.      >  -----   )
Eau Claire, WI 54701      <   -----   )
voice (715) 833-7067       >    |     )
FAX   (715) 833-7096       |    |    |
email [email-masked]    +----+----+

---

From: Arpad Muranyi <[email-masked]>
Date: Thu, 09 Nov 95 12:19:00 PST

Text item: 

Greg,

I will make an attempt to answer some of your questions.

1) To be more accurate, the requirement is -Vcc to +2*Vcc.  There are two 
reasons for this.

First, in an idealized situation, you can have a 100 % reflection at the 
unterminated end of a transmission line.  If you have a strong buffer driving it
(again in an ideal situation), it can switch a full swing (i.e. 5 volts to 0 
volts).  Under conditions like this it is possible to have a -5 volt undershoot 
at the unterminated end (receiver).  The amount of undershoot (or overshoot for 
a rising edge) at the receiver will greatly depend on the clamping 
characteristics of the input structure.

Second, different simulators extrapolate I-V curves differently (horizontally, 
vertically, linearly, or any other way).  The best way to ensure that the curve 
is "correct" in the required range (-Vcc to +2*Vcc) is to define it.

Now, we all know that not all real devices can be measured all the way in this 
range (even though I did succeed measuring some).  However, you can do your best
in the lab and then extrapolate the curve to the required limits.  Most often 
these curves become a straight line because the resistive properties of the 
diodes dominate their exponential nature beyond a certain voltaqe.  If you 
simulate this with a SPICE model, don't worry about hair splitting accuracy at 
the limits.  The point is to define something to the best of your knowledge that
otherwise might get messed up.  However, I would recommend that the curve be 
fairly accurate in the range of Vcc and GND +/- 1-2 volts, since most over and 
undershoots could have such magnitudes. 

On the other hand, if your SPICE model gives you kilo, Giga and Tera amp 
currents at -1 to -2 or +6 to +7 volts for a 5 V device, you better make sure 
that the resistive properties of the diodes and transistors are modeled 
correctly in the SPICE model.  If these are ignored, the defult number in SPICE 
is usually 0 for the resistance, and the pure junction and channel current 
equations can indeed yield currents in the kilo amp range already at -1 volts!  
Real life measurements would give around 5-10 amps around -5 volts (~ couple of 
Ohms slope).

For example the voltage in the exponential diode equation refers to the junction
voltage, which is not the same as the voltage at the terminals of the diode.  
The current has to go through a significant chunk of resistive material before 
it gets to the junctions where you are actually making you connection to the 
device.

2) I don't know the answer to this one.

3) You can do that by "programming" what Lattice diagrams or Bergeron diagrams 
do graphically.  As far as how to construct these, you could probably find text 
books or other literature (app notes in high speed logic data books) on the 
subject.  (I was born with this knowledge, so I am not sure where to find this 
info... :-)

4) It was discussed in some of the IBIS Open Forum meetings, but I don't remeber
what the outcome was.  Maybe someone else could answer that?

I hope I gave you some insight with this reply.

Arpad Muranyi
Intel Corporation
================================================================================
Anybody care to take a stab at these?

Thanks in advance,

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Subject: IBIS modeling questions
From: [email-masked] (Greg Edlund)
To: [email-masked]
Date: Thu, 9 Nov 95 13:01:50 -0600
)
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---

From: Fred Vance <[email-masked]>
Date: Thu, 9 Nov 95 12:44:34 -0800

Hi Greg,

>Anybody care to take a stab at these?

I'll give it a try.

>   since nobody operates out there?

I think that some simulators use the last couple of points to extrapolate out  
to infinity or some asymptotic value, so if your data is not available over the  
full range, you can probably do the same. Maybe it doesn't matter whether the  
full range is provided. It might depend on a simulator's interpretation of the  
IBIS specification. If I remember correctly, using the full range is optional  
in the latest IBIS revision. (Someone help me here.)

>   probably not in the plan...

I believe someone would be glad to make the source code available to you. Since  
you seem to have some experience with C compiling, you might be the right  
person to create the DOS/Windows executable and upload it to [email-masked].

>   not so I can write another simulator!)

Maybe, I can't really say.

I believe the way to approach this is to use piece-wise linear dependent  
functions to control a conductance to Vdd, simulating a pull-up switch and one  
to Gnd simulating a pull-down switch. The independent variable controlling the  
dependent conductance functions would be the voltage at the driver's output  
pad. Both conductance switches also need to be dependent on the pin's logic  
state and need to make a transition between states at a controlled rate using  
the dV/dt information in the IBIS. The state transition would have to occur  
based on some threshold value and the buffer's input level.

Sounds simple, only the details get in the way.

>   users group and mailing list?

This is it, I think. I would be happy to discuss the "theory of operations" of  
behavioral simulators in more detail.

I agree that for the "sake of accuracy in system design issues" it is good to  
know issues and limitations involved with behavioral model simulations. It may  
be difficult to discuss IBIS models independent of a specific simulator, but  
might be interesting to try.

Regards,

Fred Vance
FirePower Systems, Inc.
(415) 462-3055 Phone
(415) 462-3051 Fax

---

From: [email-masked] ( Bob Ross)
Date: Thu, 9 Nov 95 14:46 PST

Greg:

Here are some brief responses to your questions.

(1) Arpad covered that one well.

(2) We seem to be having a problem in compiling a Windows verion
of s2ibis2 which seems difficult to resolve, so I cannot give a date
or committment.

(3) I do not know of any theory of operation of behavioral models
(even from CAE vendors), but many vendors use IBIS models or 
translated versions for simulation with excellent results and
correlation with Spice Models.  So while vendors are not 
necessarily open about all the details of their internal 
algorithms, the fundamental IBIS architecture gives
enough detail for using IBIS models in simulation.  IBIS
models work well in tranmission line simulations.

(4) There was extensive discussion regarding an IBIS USERS group
last February and March.  There was agreement of the need, but
we got bogged down in what specific from it should take.  After
discussing this with Will Hobbs, I intend to set up a users mail
group reflector.  This may take several days or a week.  This
will be announced on the IBIS and SI reflectors, and people can join
at that time.  We can elaborate elsewhere on what the scope and
rules should be, but this is basically an unmoderated group
focused on user questions and applying IBIS models.  We will
archive all of the mail.

Bob Ross
Interconnectix, Inc.

> Status: R

---

From: Will Hobbs <[email-masked]>
Date: Thu, 09 Nov 95 16:27:00 PST

Text item: 

Fred, Greg,

Sorry to be a bearer of bad news, but the source code must be licensed, for a 
fee.  There are many companies who have licensed the code, and we are in the 
process of porting it to various O/S and platforms. When that work is done, the 
resulting object code will be made freely available on vhdl.org.  If you do want
to license the parser, here are the details:

There are three options for licensing the IBIS Golden Parser source code,
V2.1, depending on your membership status in the IBIS committee of EIA:

1) If you are a current member of the IBIS committee, you can license the
parser source for an additional $250.00
2) If you are not a member, but would like to be, you can join the committee
and license the parser source for a total of $750
3) If you are not a member, and do not wish to become a member, you can
license the source for $500.

In any case, submit a request to:

     EIA
     2500 Wilson Blvd.
     Arlington, VA 22201
     (703) 907-7545 (phone)
     (703) 907-7501 (fax)
     
Enclose a check in the appropriate amount made out to EIA.  EIA will take
care of distributing the source.

Regards,

Will Hobbs,
Chair, EIA IBIS Committee
Intel Corp.

Hi Greg,

I'll give it a try.

I think that some simulators use the last couple of points to extrapolate out 
to infinity or some asymptotic value, so if your data is not available
over the
full range, you can probably do the same. Maybe it doesn't matter whether the 
full range is provided. It might depend on a simulator's interpretation
of the
IBIS specification. If I remember correctly, using the full range is optional 
in the latest IBIS revision. (Someone help me here.)

>   probably not in the plan...

I believe someone would be glad to make the source code available 
to you. Since
you seem to have some experience with C compiling, you might be the right 
person to create the DOS/Windows executable and upload it to [email-masked].

I believe the way to approach this is to use piece-wise linear dependent 
functions to control a conductance to Vdd, simulating a pull-up switch 
and one
to Gnd simulating a pull-down switch. The independent variable controlling 
the
dependent conductance functions would be the voltage at the driver's output 
pad. Both conductance switches also need to be dependent on the pin's logic 
state and need to make a transition between states at a controlled rate using 
the dV/dt information in the IBIS. The state transition would have to occur 
based on some threshold value and the buffer's input level.

>   users group and mailing list?

This is it, I think. I would be happy to discuss the "theory of operations" 
of
behavioral simulators in more detail.

I agree that for the "sake of accuracy in system design issues" it is good to 
know issues and limitations involved with behavioral model simulations.
It may
be difficult to discuss IBIS models independent of a specific simulator, but 
might be interesting to try.

Regards,

Fred Vance
FirePower Systems, Inc.
(415) 462-3055 Phone
(415) 462-3051 Fax

Cc: [email-masked]
Subject: Re: IBIS modeling questions
To: [email-masked] (Greg Edlund)
Date: Thu, 9 Nov 95 12:44:34 -0800
From: Fred Vance <[email-masked]>
4:36 -0800 (PST)
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---

From: Fred Vance <[email-masked]>
Date: Fri, 10 Nov 95 05:25:00 -0800

Will,

This is only a personal opinion, but for what it is worth, I think it would be  
equitable for someone to provide an executable on a platform for which you have  
none, in exchange for the license fee for the source code. (I'm not  
volunteering.) If you were concerned that you might not get the executable in a  
timely manner, you could at least offer to refund the license fee on recepit  
and approval of the executable.

Fred

Begin forwarded message:

Date: Thu, 09 Nov 95 16:27:00 PST
From: Will Hobbs <[email-masked]>
Message-ID: <Thu, 09 Nov 95 16:32:07 [email-masked]>
To: [email-masked], [email-masked]
cc: [email-masked]
Subject: Re[2]: IBIS modeling questions

Text item:
Fred, Greg,

Sorry to be a bearer of bad news, but the source code must be licensed, for  
afee.  There are many companies who have licensed the code, and we are in  
theprocess of porting it to various O/S and platforms. When that work is done,  
theresulting object code will be made freely available on vhdl.org.  If you do  
want
to license the parser, here are the details:

     EIA
     2500 Wilson Blvd.
     Arlington, VA 22201
     (703) 907-7545 (phone)
     (703) 907-7501 (fax)

Regards,

Will Hobbs,

Hi Greg,

You wrote:

>To: [email-masked]
>From: [email-masked] (Greg Edlund)>Subject: IBIS modeling questions
>
>Anybody care to take a stab at these?>

I'll give it a try.

>1. I was discussing IBIS model support with one of>   our IC vendors, and they  
raised a concern about>   ESD diode SPICE models not being accurate at
>   do you need such a wide range in the first place,>   since nobody operates  
out there?

I think that some simulators use the last couple of points to extrapolate outto  
infinity or some asymptotic value, so if your data is not available
over the
full range, you can probably do the same. Maybe it doesn't matter whether  
thefull range is provided. It might depend on a simulator's interpretation
of the
IBIS specification. If I remember correctly, using the full range is optionalin  
the latest IBIS revision. (Someone help me here.)

>2. When will s2ibis 2.0 be available on Windows?>   Actually, I'd be happy  
with DOS, but that's
>   probably not in the plan...

I believe someone would be glad to make the source code availableto you. Since
you seem to have some experience with C compiling, you might be the rightperson  
to create the DOS/Windows executable and upload it to [email-masked].

>   paper on behavioral simulators?  For instance, if>   I have a simple  
behavioral driver model (no ESD
>   diodes, no package) driving a 50 Ohm transmission>   line terminated at the  
far end into 50 Ohms, how
>   do I calculate the current and voltage vs. time at>   the output of the  
driver?  At the far end?  This
>   write a little C program to do this so I can better>   understand IBIS and  
critically compare it to SPICE.>   (For the sake of accuracy in system design  
issues,>   not so I can write another simulator!)

I believe the way to approach this is to use piece-wise linear  
dependentfunctions to control a conductance to Vdd, simulating a pull-up  
switchand one
to Gnd simulating a pull-down switch. The independent variable controllingthe
dependent conductance functions would be the voltage at the driver's outputpad.  
Both conductance switches also need to be dependent on the pin's logicstate and  
need to make a transition between states at a controlled rate usingthe dV/dt  
information in the IBIS. The state transition would have to occurbased on some  
threshold value and the buffer's input level.

>4. Has anybody thought about organizing an IBIS>   users group and mailing  
list?

This is it, I think. I would be happy to discuss the "theory of operations"of
behavioral simulators in more detail.

I agree that for the "sake of accuracy in system design issues" it is good  
toknow issues and limitations involved with behavioral model simulations.
It may
be difficult to discuss IBIS models independent of a specific simulator,  
butmight be interesting to try.

Regards,

Fred Vance
FirePower Systems, Inc.
(415) 462-3055 Phone
(415) 462-3051 Fax

Cc: [email-masked]
Subject: Re: IBIS modeling questions
To: [email-masked] (Greg Edlund)
Date: Thu, 9 Nov 95 12:44:34 -0800
From: Fred Vance <[email-masked]>
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---

From: "Alan W. Glaser" <[email-masked]>
Date: Fri, 10 Nov 1995 11:27:28 -0500

Folks:

Just to make this clear, I believe Will is referring to the IBIS Golden
Parser.  Greg's question regarding source code was referring to s2ibis
v2.0, for which source code is freely available from ftp.vhdl.org and
the NCSU ERL software archive at
(http://www2.ncsu.edu/eos/project/erl_html/erl_home.html).

Note that s2ibis v2 is still officially in beta, and probably will be
until the end of the year.  Thanks to everyone who has reported any
lurking bugs and inconsistencies.  Please keep the comments coming.

Regards,

Alan

On Nov 9,  4:27pm, Will Hobbs wrote:
> Sorry to be a bearer of bad news, but the source code must be
> licensed, for a fee.  There are many companies who have licensed the
> code, and we are in the process of porting it to various O/S and
> platforms. When that work is done, the resulting object code will be
> made freely available on vhdl.org.  If you do want to license the
> parser, here are the details:
<snip>
>-- End of excerpt from Will Hobbs

-- 
Alan Glaser
ECE Dept.
North Carolina State University

---

From: Will Hobbs <[email-masked]>
Date: Fri, 10 Nov 95 16:02:00 PST

Text item: 

Mea culpa,

I responded too quickly.  Alan is exactly right-- I was thinking the question 
was about the golden parser. I should have re-read the message before I 
responded. Sorry for the confusion.

Will

Folks:

Regards,

Alan

<snip>

Cc: [email-masked]
Subject: Re: Re[2]: IBIS modeling questions
To: Will Hobbs <[email-masked]>
Date: Fri, 10 Nov 1995 11:27:28 -0500
From: "Alan W. Glaser" <[email-masked]>