[IBIS] RE: [IBIS-Users] hspice vs IBIS model correlation at different capacitive loads

Venu,
 
From your first waveforms it appears that the timestep could be an
issue. It is less apparent from your second set of waveforms, though.
Unfortunately, you can't specify a fixed timestep in Hspice, that I know
of, but you can set a maximum timestep. I don't remember the option off
the top of my head, but I'm sure you can find it in the manual. Set this
to something small enough that both simulations are forced to use nearly
the same timestep and see if the correlation gets a little better.
 
There are other issues that other experts here have already identified
that are worth looking in to.
 
Regards,
Weston
 

________________________________

From: owner-ibis-users@eda.org [mailto:owner-ibis-users@eda.org] On
Behalf Of Ummalaneni, Venu Babu (Venu)
Sent: Tuesday, December 13, 2005 4:49 AM
To: Todd Westerhoff (twesterh); ibis-users@eda.org; ibis@eda.org
Subject: RE: [IBIS-Users] hspice vs IBIS model correlation at different
capacitive loads



Todd,

 

Thanks for your inputs. 

 

I have verified the programming options of driver and it's fine. Here, I
am attaching the correlation waveforms of the simulations by using a 0.1
ohm resistor instead of transmission line in both load (5pF & 30pF)
cases. Still, I am seeing a bad correlation in 30pF case.

 

Please ignore my previously attached *.PDF.

 

Once again thanks for your response.

 

Best Reagrds,

Venu

 

 

-----Original Message-----
From: Todd Westerhoff (twesterh) [mailto:twesterh@cisco.com] 
Sent: Tuesday, December 13, 2005 5:43 PM
To: Ummalaneni, Venu Babu (Venu); ibis-users@eda.org; ibis@eda.org
Subject: RE: [IBIS-Users] hspice vs IBIS model correlation at different
capacitive loads

 

Venu,

 

How long is the transmission line you're using ... about 1ns?

 

Your IBIS driver in the 30pf case seems to be taking several round-trips
to charge the load where the HSpice driver doesn't - if this is a
programmable driver, is it possible the driver settings for the two
plots are different?  In the top plot for the 30pf case, the IBIS driver
looks like a much weaker output with a faster slew rate to me ...

 

Todd.


Todd Westerhoff
High Speed Design Group Manager
Cisco Systems
1414 Massachusetts Ave
Boxboro, MA 01719
email:twesterh@cisco.com
ph: 978-936-2149
____________________________________________
"Always do right.
 This will gratify some people and astonish the rest."

 

- Mark Twain

 

 

________________________________

From: owner-ibis-users@eda.org [mailto:owner-ibis-users@eda.org] On
Behalf Of Ummalaneni, Venu Babu (Venu)
Sent: Tuesday, December 13, 2005 5:38 AM
To: ibis-users@eda.org; ibis@eda.org
Subject: [IBIS-Users] hspice vs IBIS model correlation at different
capacitive loads

Hi Gurus,

I have an ATA* IBIS model and it is correlating well with hspice model
when I am using a 5pF load followed by a transmission line. If I replace
the 5pF load with 30pF correlation is bad (particularly in 2nd page
waveform of attached PDF). 

Could some one comment on this, where it is going wrong?

Your comments/inputs are highly appreciated.

Attachments: ata4nik_5pf.pdf - hspice and IBIS model waveforms captured
using 5pF load

                    ata4nik_30pf.pdf - hspice and IBIS model waveforms
captured using 30pF load

Thanks & Best Regards,

Venu

<<ata4n1k_30pf.pdf>> <<ata4n1k_5pf.pdf>> 


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