Subject: Re: [IBIS-Users] pullup/pulldown range LVDS
From: Ingraham, Andrew (a.ingraham@ieee.org)
Date: Fri Aug 15 2003 - 10:32:10 PDT
MessageDr. Lynne Green gave this as an example:
> Example with 12mA end points in I-V data:
> -3.3V -12m | dummy end point
> 0.4V -12m | end point of actual operating region
> | normal data, up to 96 more lines
> 1.6V 12m | end point of actual operating region
> 6.6V 12m | dummy end point
Personally, and maybe this is just me, I hate it when the endpoints do not continue the slope of the measured (or simulated) data.
In the case above the regions <0.4V and >1.6V have zero slope. Is this realistic? Probably not. Only part of the reason for the dummy end points is to satisfy the IBIS Parser. But it is also there to tell the simulator SOMEthing about how your device really behaves, to get the simulator back on track when it wanders out into that region.
Personally I would prefer that you extrapolate the measured or simulated data points when picking the dummy end points. If the measured/simulated data has a positive slope, pick dummy end points that are on that slope, or close to it.
Accuracy is less important when you are that far out of the normal operating region, as is giving the simulator the right ballpark idea. If not, you might find that the circuit actually converges at 6V and then you'd be in trouble.
Regards,
Andy
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