[SI-LIST] Re: What do you do when the manufacturer's model doesn't match the measurements?

$15K o $25K sounds high.  If you are paying that kind of money for your 
measurement based models, you should shop around more. 

Steve.

Katkoria, Deepak wrote:
> Hi Iain,
> Usually vendor don't gives a guarantee about the model..
>
> You need to check the file, if some reading are not according to device then 
> you can ask for circuit used for simulation.
>
> They will give you a RLC diagram..
> Otherwise you have to look for 3rd party, who can create a model for you..
> They charge from 15K to 25K depends upon time..
>
> I have faced similar problem in  past..
>
> You can even ask for spice model and create your own Ibis model..
> For ask for IO cell parameters(technology used) and based on that you can 
> create the Ibis model..
>
>
> Deepak
>
>
> -----Original Message-----
> From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx] On 
> Behalf Of Iain Waugh
> Sent: Friday, August 27, 2010 3:00 PM
> To: si-list@xxxxxxxxxxxxx
> Subject: [SI-LIST] What do you do when the manufacturer's model doesn't match 
> the measurements?
>
> Hi all, please can you advise!
>
> Our aim is to prove the vendors' IBIS models on a dev board so we can have 
> confidence that simulations of our own 400MHz DDR2 design (using the same 
> parts) will be accurate.  We're simulating with Hyperlynx 8.0 and have taken 
> the most up-to-date IBIS models from the vendors' websites.
>
> We've made a pretty good free-form schematic model of the dev board with the 
> target CPU and memories (plus 'scope probe at the receiver's pin).  The 
> initial simulations were horrible with a massively non-monotonic rising edge 
> crossing the Vil and Vih levels of the receiver twice.  We used a 6GHz LeCroy 
> 'scope with 1GHz probes to measure the actual dev board's signal integrity 
> and the edges were clean.
>
> In my mind, that proves that I can't trust the model.  The catch, however, is 
> that the vendor then told us to put the simulation probes at the die instead 
> of at the pin.  We re-simulated and the non-monotonic edges went away - they 
> actually looked like the measurement!
>
> Would you trust the results of a simulation when the measured case only 
> correlates with a simulation having probes in a different place?  Can we use 
> the wrong (but matching) model to guide us to the best routing topology?  I'm 
> tempted to just use standard good SI practises and ignore the simulations.
>
> Best regards,
>
> Iain Waugh
>
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-- 
Steve Weir
IPBLOX, LLC 
150 N. Center St. #211
Reno, NV  89501 
www.ipblox.com

(775) 299-4236 Business
(866) 675-4630 Toll-free
(707) 780-1951 Fax


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