Fwd: Re[6]: Non-Monotonic Drivers

-- [ From: Ron Christopher * EMC.Ver #2.10P ] --

Forwarding to the reflector.

Ron Christopher
------- FORWARD, Original message follows -------

> Date: Thursday, 24-Aug-95 11:31 AM
>
> From: Will Hobbs \ Internet:
> (will_hobbs@ccm2.jf.intel.com)
> To: Ron Christopher \ PRODIGY: (EGJJ77A)
>
> Subject: Re[6]: Non-Monotonic Drivers
>
> Text item:
>
> John,
>
> Thet V/T curves with reference load in IBIS 2.1 address the problem
of
> simulator accuracy by providing actual expected results under known
> conditions. Multiple such curve/load pairs can be included in the
model
> file and can be used by the end customer to check the simulator's
> handling of the data.
>
> Will
>
> Arpad,
>
> Yes, and that is exactly what we did... CMOS 4 SI tool was IBM ANDAP
(we
> already had the models done). Since we are ASIC library suppliers,
we
> actually let our customers decide which tool where practical.
>
> Ofcourse we could as a silicon vendor just put the IBIS data out
there
> and give the user enough rope to hang themselves(user beware), or put
the
> burden on the Simulation vendor to handle. Sounds like that's what
they
> are asking for by keeping it out of the spec. Generating IBIS data
is
> easy, making sure it simulates right is another story.
>
> Thanks,
> John
>
>
***********************************************************************
> John Brennan Internal: jbrennan@btv
> IBM Microelectronics Internet:
jbrennan@vnet.ibm.com
> G77V/862-1 Tel: 802-769-6982 (Tie-Line:
446)
> Burlington, VT Fax: 802-769-5882 (Tie-Line:
446)
>
***********************************************************************
>
> ------------------ Referenced E-Mail ----------------------------
>
> Date: Wed, 23 Aug 1995 14:54:11 PST
> cc: jbrennan@VNET.IBM.COM, EGJJ77A@prodigy.com, jonp@qdt.com,
> Will_Hobbs@ccm2.jf.intel.com
> From: Arpad Muranyi <Arpad_Muranyi@ccm.fm.intel.com>
> Subject: Re[4]: Non-Monotonic Drivers
> Message-Id: <950823145411_1@ccm.fm.intel.com>
>
> Text item:
>
> John,
>
> I see your point in suggesting a spec on how to handle the I-V
curves.
> However
> ,
> I am afraid that this will never happen. We had similar, or even
more
> importan
> t
> issues surface up in previous Open Forum meetings, yet these
discussions
> ended
> with the conclusion that the software tool vendor should not be told
how
> to do
> things. That is their specialty, and that is how they differentiate
on
> the
> market. Each one of them knows everything better than the other, so
they
> wouldn't listen anyway. :-)
>
> You, the user must decide which tool suits your needs the best.
>
> Arpad
>
=======================================================================
==
> =====
> Arpad,
>
> I agree 100% with your point #2. In fact non-monoticity was a non-
issue
> with our ASX simulator because we knew ahead of time that these
waveforms
> were non-standard. Our ASX analysis did not match up that well
because the
> Vout vs. Time waveforms were not symmetric about the center voltage,
the
> shape of the waveform assumed by the vendor tool was different from
> actual. IBIS has addressed this in ver 2.1.
>
> Thus we analyzed the VI cureves and did what you said in #2. The
problem
> is ofcourse that the standard does not tell one writing a simulation
> program how to handle these IV curves. Current programs that I looked
at
> changed the data to be monotonic, I beleive so they could calculate
> impedances. I would imagine different programs would do different
things.
> I suspect you have seen other non-monotonic drivers that are non-
monotonic
> for other reasons that may need to be treated different yet. A
challenge
> would be to write the spec to handle all of the known cases.
>
> We are not getting sufficient demand for CMOS 4 IBIS models to
justify any
> lengthy studies on how to model these drivers.
>
> John
>
>
***********************************************************************
> John Brennan Internal: jbrennan@btv
> IBM Microelectronics Internet:
jbrennan@vnet.ibm.com
> G77V/862-1 Tel: 802-769-6982 (Tie-Line:
446)
> Burlington, VT Fax: 802-769-5882 (Tie-Line:
446)
>
***********************************************************************
>
> ------------------ Referenced E-Mail ----------------------------
>
> Date: Wed, 23 Aug 1995 10:46:08 PST
> cc: jbrennan@VNET.IBM.COM, EGJJ77A@prodigy.com, jonp@qdt.com,
> Will_Hobbs@ccm2.jf.intel.com
> From: Arpad Muranyi <Arpad_Muranyi@ccm.fm.intel.com>
> Subject: Re[2]: Non-Monotonic Drivers
> Message-Id: <950823104608_4@ccm.fm.intel.com>
>
> Text item:
>
> John,
>
> Thanks again for your reply. I have mixed feelings about what to say
now.
>
> 1) This kind of a behavior is most likely caused by a feedback
circuit in
> the
> buffer. It is true, IBIS currently does not have provisions to
describe
> buffer
> s
> with feedback. However, we had discussions on this subject in the
open
> forum
> meetings before, and we could pick it up again if there is a real
need for
> modeling such buffers in IBIS.
>
> 2) On the other hand, I am not sure if IBIS is to blame for the
situation
> that
> you described, that simulators alter the curve this and that way. I
> imagined
> how I would use this data in my HSPICE behavioral (=IBIS) models. I
am
> using
> piecewise linear (PWL) sources for the I-V curves. If I make the
> voltage value
> s
> the independent variable, and current the dependent variable, it will
work
> no
> problem, because each voltage value is assigned only one current
value.
> (It
> doesn't matter whether the current values are repeated). If I turned
> it around
> ,
> however, to have current values as the independent variable and
voltage
> the dependent one, it would not work, because the simulator would
have to
> pick between two or more voltages for one current value. What I am
trying
> to say here is that this kind of a curve should work, as far as IBIS
is
> concerned (as it does in my HSPICE behavioral models). It depends on
what
> the simulator tool does with it.
>
> Arpad
>
=======================================================================
==
> ====
> Arpad,
>
> Each point on the curve is what you would get if you put a battery DC
> voltage at the output of the driver and measured the current through
the
> pad with all other operating conditions constant. The curves were
> generated with multiple DC analysis using ASX(the IBM SPICE program).
I do
> not think IBIS can handle this today. Specifically, simulation
programs
> will try to alter the DC curves, and there is nothing that tells them
how
> to do this(I believe the correct thing to do would be to not alter
the
> curve).
>
> Thanks,
> John
>
>
***********************************************************************
> John Brennan Internal: jbrennan@btv
> IBM Microelectronics Internet:
jbrennan@vnet.ibm.com
> G77V/862-1 Tel: 802-769-6982 (Tie-Line:
446)
> Burlington, VT Fax: 802-769-5882 (Tie-Line:
446)
>
***********************************************************************
>
> Text item:
>
> John,
>
> Thanks for the graphical response to my question. This is the kind
> of response
> I really wanted to get. I have a question, though. Is this I-V
curve a
> function of the voltage on the output pin, or time. I mean, is
> "translating
> between two Vgs curves" done with a feedback circuit by monitoring
the
> output
> voltage, or is it a function of time as slew rate controlled devices
> usually do
> it?
>
> If the answer is time, IBIS can definitely do it, but if it is
voltage (as
> in feedback), IBIS would not be able to help you at this time.
However,
> the open forum committee did consider this issue in meetings before,
and I
> don't think that it would be impossible to incorporate features that
can
> model it.
>
> Arpad
>
=======================================================================
==
> =====
>
>
> Arpad,
>
> The drivers Ron refers to have the following IV curve shape...
>
> Ids * *
> * *
> * *
> * *
> * ****************
> *
> *
> *
> * Vds
>
>
> Instead of the normal transistor curve shape like...
>
> Ids * ***********************
> *
> *
> *
> *
> *
> *
> *
> * Vds
>
>
> The top curve comes about because we are manipulating the gate
voltage to
> control di/dt noise in the maximum Vds region of the large output
device.
> Essentially we are translating between two Vgs curves for the output
> transistor. Hence the non-monotonicity is real and not noise related.
> Clamp diodes would add another bend in the curve and create 3 current
> values for 1 voltage value.
>
> The simulation tools we looked at would "correct" the data by making
the
> top curve look like the bottom. We saw some extreme differences in
> benchmark nets after this manipulation from the full transistor
> simulation. Since there is no standard on how to "correct" the above
> curve, we would not know how various simulation vendors would treat
the
> model.
>
> The above and the time schedule of IBIS 2.1 and CMOS 4 makes
supporting
> the IBIS modeling strategy unattractive for our CMOS 4 products.
>
> Thanks,
> John Brennan
>
>
***********************************************************************
> John Brennan Internal: jbrennan@btv
> IBM Microelectronics Internet:
jbrennan@vnet.ibm.com
> G77V/862-1 Tel: 802-769-6982 (Tie-Line:
446)
> Burlington, VT Fax: 802-769-5882 (Tie-Line:
446)
>
***********************************************************************
>
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> From: "John Brennan" <jbrennan@VNET.IBM.COM>
> Date: Tue, 22 Aug 1995 13:34:03 -0400
> Subject: Non-Monotonic Drivers
> To: EGJJ77A@prodigy.com, arpad_muranyi@ccm.fm.intel.com, jonp@qdt.com
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> From: "John Brennan" <jbrennan@VNET.IBM.COM>
> Date: Wed, 23 Aug 1995 09:01:18 -0400
> In-Reply-To: Your message of Tue, 22 Aug 1995 15:47:55 PST.
> <950822154755_9@ccm.fm.intel.com>
> Subject: Re: Non-Monotonic Drivers
> Cc: jbrennan@VNET.IBM.COM, EGJJ77A@prodigy.com, jonp@qdt.com,
> Will_Hobbs@ccm2.jf.intel.com
> To: Arpad Muranyi <Arpad_Muranyi@ccm.fm.intel.com>
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> From: "John Brennan" <jbrennan@VNET.IBM.COM>
> Date: Wed, 23 Aug 1995 16:22:17 -0400
> In-Reply-To: Your message of Wed, 23 Aug 1995 10:46:08 PST.
> <950823104608_4@ccm.fm.intel.com>
> Subject: Re: Re[2]: Non-Monotonic Drivers
> Cc: jbrennan@VNET.IBM.COM, EGJJ77A@prodigy.com, jonp@qdt.com,
> Will_Hobbs@ccm2.jf.intel.com
> To: Arpad Muranyi <Arpad_Muranyi@ccm.fm.intel.com>
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> From: "John Brennan" <jbrennan@VNET.IBM.COM>
> Date: Thu, 24 Aug 1995 09:47:13 -0400
> In-Reply-To: Your message of Wed, 23 Aug 1995 14:54:11 PST.
> <950823145411_1@ccm.fm.intel.com>
> Subject: Re: Re[4]: Non-Monotonic Drivers
> Cc: jbrennan@VNET.IBM.COM, EGJJ77A@prodigy.com, jonp@qdt.com,
> Will_Hobbs@ccm2.jf.intel.com
> To: Arpad Muranyi <Arpad_Muranyi@ccm.fm.intel.com>
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Received on Thu Aug 31 09:16:40 1995