RE: [IBIS-Users] IBIS model for a slow slew rate output driver question

Anshul,

Don't mess with Vfixture and Rfixture.  They
are not going to make a difference in this
situation.  Unfortunately your attachment
didn't make it through (these email servers
are set up to strip attachments).  Could you 
describe it in words what the discrepancy
looks like (or send the attachment to me
directly)?

Thanks,

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

-----Original Message-----
From: owner-ibis-users@server.eda.org [mailto:owner-ibis-users@server.eda.org] On Behalf Of Anshul Bansal
Sent: Wednesday, October 15, 2008 8:47 AM
To: ibis-users@server.eda.org
Subject: [IBIS-Users] IBIS model for a slow slew rate output driver question

Hello All,

My name is Anshul Bansal and I am trying to create an IBIS model for an 
output driver that has the same drive strength but some config bits that 
can select different output slew rate settings. The fast setting for 
output driver has a slew rate in order of 5ns whereas the slow setting 
has a slew rate of 30-50ns.

I have been able to successfully generate the IBIS model using the 
conventional method for rising and falling waveforms i.e. 50ohm 
termination resistor to ground and vcc_io. However when I try to run 
some co-relation simulations on the IBIS model and compare the results 
with the actual circuit, I can get very good co-relation (within 5-10% 
of actual circuit) for the fast setting of the output driver (waveform 
attached in fast.pdf). However the co-relation for slow setting of 
output driver is about 40-50% off as compared to actual circuit 
simulations (waveform attached in slow.pdf).

I was wondering if there are other techniques that I should be using to 
model this slow setting for the output driver in the IBIS model, instead 
of the conventional settings like changing the Vfixture or Rfixture. Can 
anyone tell me how are such models captured by other engineers?

Any response to these questions are highly welcome.

Thanks,

Anshul

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