Subject: FAQ #6 and #7 revised....

From: [email-masked] (Syed Huq)
Date: Mon, 21 Aug 95 15:27:09 PDT

IBISfans,

As mentioned in the last IBIS Minutes (Aug11th'95), the last two
FAQ that need to be re-worded were #6 and #7.

I am attaching the revised answers based on some inputs I received.

Pls post your comment/changes/suggestions on the reflector and we
shall vote on this on the Aug25th meeting.

Regards,
Syed.
National Semiconductor.

--------------------------------------------------------------------------
6.0 Can IBIS model SSO(Simultaneous Switching Output) ?  

IBIS as a model, has all the parameters required to model an SSO event. These
are mainly the package inductance parameters and other associated parasitics.
IBIS specifies R, L and C in matrix format and the use of a matrix for the 
inductance accounts for the "loop"inductance i.e. the mutuals between the 
pins. Specifying the mutual inductance is necessary to account for SSO event 
simulation. Modeling an SSO event is more of a simulator issue than IBIS.

7.0 Why do we need to sweep -Vcc to 2Vcc ?

Simulation accuracy is greatly enhanced by the "beyond-the-rail" data.  
Overshoot and undershoot generally fall within this range, and the range 
encompasses the forward-biased regions of protection diodes often used on 
buffers. Also, reflections caused by improper terminations can produce    
voltages at the driver/receiver terminals from -Vcc to 2Vcc. The drivers
and receivers, therefore, need to be modeled over this entire range. 

Since measurement of diodes over the entire range is often not possible,
measurement over a reasonable range and extrapolation of data to the 
end-point values is permitted to produce IBIS models.

Most non-SPICE based simulators will do their own extrapolation to get to 
the end point. Most Spice simulators truncate data to the table 
end-points.  

The -Vcc to 2Vcc range ensures consistent performance for both types of 
simulators.
-----------------------------------------------------------------------------

---

From: [email-masked]
Date: Mon, 21 Aug 95 17:12:36 MST

Syed,

I have been thinking about the possibility of IBIS model
providing any SSO noise estimation. I was trying to set it aside
until I have an alternative suggestion. However, I decide it is 
better to issue the problem before we spread a propaganda.
I am afraid that SSO noise prediction might not be possible with 
present IBIS format.
The reason is that the present format doesn't have rise/fall
time informations at the input of output buffers.
Generally, the SSO noise is determined by the input transition
time and the maximum current of output driver (not the output
transition time).
An I/V characteristic of output buffers may provide the maximum
current. But the input transition time is still missing.
Also the on-chip decoupling capacitor would make the noise characteristics
different, which is not yet included in the format. 
In conclusion, I am suggesting we might drop out this QA until
we have better understanding/solution to it.

Regards,

Sung Oh
VLSI Technology, Inc.

 >>From [email-masked] Mon Aug 21 15:43 MST 1995
 >>Date: Mon, 21 Aug 95 15:27:09 PDT
 >>From: [email-masked] (Syed Huq)
 >>To: [email-masked]
 >>Subject: FAQ #6 and #7 revised....
 >>Content-Type >>:  >>text >>
 >>Content-Length: 1937
 >>X-Lines: 44
 >>
 >>IBISfans,
 >>

---

From: Arpad Muranyi <[email-masked]>
Date: Mon, 21 Aug 95 17:08:00 PDT

Text item: 

Syed,

I would combine the very last two paragraphs into one (in #7).

Regarding #6, I was expecting to read something about the [Pin Mapping] keyword.
To be able to do good GND bounce simulations one must know how many buffers are 
getting their supply current through the same power and GND pins.  Your answer 
does not address this side of the issue, only the L,R,C part.  Could you add 
this to it?

Arpad
===============================================================================
IBISfans,

Regards,
Syed.
National Semiconductor.

Text item: External Message Header

The following mail header is for administrative use
and may be ignored unless there are problems.

***IF THERE ARE PROBLEMS SAVE THESE HEADERS***.

Subject: FAQ #6 and #7 revised....
To: [email-masked]
From: [email-masked] (Syed Huq)
Date: Mon, 21 Aug 95 15:27:09 PDT
:27:03 -0700
Received: from hermes.intel.com by relay.jf.intel.com with smtp
     (Smail3.1.28.1 #2) id m0skfae-000txEC; Mon, 21 Aug 95 15:45 PDT