RE: [IBIS-Users] Mixed-Signal Analog IO ?

Hello, Lars,

There is a known algorithmic bug in s2ibis2.  In  s2ibis2, the clamp
currents are "double-counted".  That is, these currents appear correctly in
the clamp current tables, but are not subtracted from the pullup and
pulldown tables.

This bug was fixed in s2ibis3, which is available on the IBIS web site, or
directly from NCSU at 
http://www.ece.ncsu.edu/erl/ibis/s2ibis3/s2ibis3.htm

Since a bandgap reference is (nominally) a DC output, I would assume you are
worried about crosstalk coupling onto that signal.  In that case, you could
probably model it as an Input.  You might want to check with Arpad about
whether clamp reference voltages should be set to Vcc/GND, or set to the
bandgap output voltage.

Best regards,
Lynne

-----Original Message-----
From: owner-ibis-users@eda.org [mailto:owner-ibis-users@eda.org] On Behalf
Of Lars Snith
Sent: Tuesday, August 16, 2005 11:51 PM
To: Muranyi, Arpad
Cc: ibis-users@eda.org
Subject: Re: [IBIS-Users] Mixed-Signal Analog IO ?

Hello Arpad,

Sorry for my vague description. I will try to do better below.
It is clear that every buffer type have clamp tables, and that I can model
analog IO using *-AMS langauges and External Circuit declarations. 
But since my tools fall back on s2ibis2 which conforms to IBIS v2.1
specification which (correct me if I'm wrong), does not include these
features, it would be an additional manual procedure to add it.
Hence my question how you did model analog IO (like for example the output
of a bandgap reference with sink & source capability) in "the good old days"
with only I,O,I/O,VDD,GND and NA to choose from.
If this is not possible/advisable I will of course have to take measures.

As I hope is clear from the above, I have no intention to add clamps tp
power pins (although ESD protection calls for snapbacks), that would not be
a good idea having multiple supplies.


Best regards,  Lars Snith


Muranyi, Arpad wrote:

> Lars,
> 
> I think you are asking the question in the right forum.  However, I 
> don't understand your question.
> To include a clamp, you don't have to make it an input, every buffer 
> type can have clamp tables.
> Especially if you do it using the *-AMS languages, you can do it any 
> whichever way you want.  So I am not sure what you are asking really, 
> or how to answer the question.  Please explain it better.
> 
> On the other hand, I wouldn't put clamp tables on power pins, it 
> doesn't make any sense...  Clamps are supposed to clamp overshoot on 
> signal pins.
> What would they do on power pins?
> 
> Arpad
> ==================================================
> 
> 
> -----Original Message-----
> From: owner-ibis-users@eda.org [mailto:owner-ibis-users@eda.org] On 
> Behalf Of Lars Snith
> Sent: Monday, August 15, 2005 11:22 PM
> To: ibis-users@eda.org
> Subject: [IBIS-Users] Mixed-Signal Analog IO ?
> 
> Hello,
> 
> I hope I am adressing the right forum with this. If not, please excuse 
> my intrusion.
> 
> I have been making a number of IBIS models for microcontrollers of 
> medium complexity, successfully as it looks.
> As I will soon take on more complex products, with purely analog 
> parts, I have been considering the "correct" way of modeling a truly 
> analog IO (if at all).
> Clearly, to include the power clamps I should treat it as an input. On 
> the other hand this might not be the correct procedure, maybe it would 
> be better to treat it as a power/ground pin? It would certainly mean 
> less work. A third option is to ignore it altogether (NA).
> 
> Any comment/feedback on this issue would be most welcome.
> 
> 
> Best regards,  Lars Snith

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